To all who work with concrete.
What does concrete weight per cubic foot?
Does concrete tend to stick to forms?
I would like to design and pour a couple of garden benches out of concrete. So, naturally I don’t want to pour a six hundred pound bench. And I would like to use framing materials for forms (plywood and 2x4s). So will the concrete stick to my forms and thus the concrete will chip out when I remove teh forms? Can I spray the forms with something like WD40, Silicon, wrap them in wax paper?
Replies
spray/wipe down the forms with oil to keep the concrete from sticking.
concrete wighs approximately 2500 lbs/cubic yard (i'm sure some one will be along to correct that)
are you mixing your own or using pre-mixed in a bag?
bobl Volo, non valeo
Baloney detecter WFR
"But when you're a kibbutzer and have no responsibility to decide the facts and apply the law, you can reach any conclusion you want because it doesn't matter." SHG
Thanks bobl, and everyone.
You and others say use oil. What kind of oil? Crankcase drainings? new motor oil?
And, I guess I was thinking about using premixed bag stuff. For benches I would not want stone in the mix. I suppose I could buy sand and cement and mix that up, but for this small amount I just figured I would buy premixed.
My ideas here are to:
First not get too crazy, detailed, or carried away.
Second it is kind of an experiment. If I come up with a product that is "pretty ok" I may refine it. Perhaps even carve some leaves/vines, etc. into the forms for interest. But I am looking for a first pass, and don't want a major screw up or mess.
figure closer to 150 lb. / CF
almost any kind of oil will do.... old crankcase oil used to be the norm, but people were worried about poluting water sources , so they use some more benign mix now
and you need the stone for strength.. a straight sand/cement mix will not be strong enough
also, for a bench , you will need some kind of reinforcing steelMike Smith Rhode Island : Design / Build / Repair / Restore
I was planning on the steel but did not see the use in stone. Really, stone is for strength? I thought it was to save money, as the strength is in the chemical reaction of the lime and . . . whatever else is in cement.
Yes, I am working on the steel component. I need to have steel running the length of the seat and then bend it down into the legs (just one leg per end). My problem is figuring out a way to bend it. I am sure I don't need steel as thick as for a foundation and HD sells the stuff in two and three foot lengths. But I need to be able to bend a few 90 degree pieces. The bends would not need to be very tight so I am not sure I can't just rig-up up some kind of big clamp and hit it with a sledge. Pretty chessey perhaps, but like I said I am not in this for a business.
A rebar bender bends nice 90 degree angles - ~$15/day at the rental place - it will cut the rebar nicely too - 3/8" is nice to work with, and probably enough for a bench, but 1/2" is probably what you'll find at the Depot.
I'd put wire mesh in the top too. Veggie oil works as a form release, we used to mix diesel with motor oil and spray with a garden sprayer, whatever you want...
If you are mixing from bags of sakrete, you'll have a pretty good idea what you are getting into by the weight of the bags.
Treat every person you meet like you will know them the rest of your life - you just might!
"you'll have a pretty good idea what you are getting into by the weight of the bags."That neglects to consider the weight of the water. Crete does not cure by drying and releasing the water, tho some of it will evaporate. making concrete is a chemical reaction, producing heat as a by-product, and incorporating the water as a part of the whole, so its weight must be added to that of the dry mix.
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"you'll have a pretty good idea what you are getting into by the weight of the bags."
yup, what I said.
so add 20%...
Treat every person you meet like you will know them the rest of your life - you just might!
Sorry if I misunderstood or missed a vague implication, but underscoring by 20% is not what I'd call pretty good.
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To bend rebar you can use a vice and a piece of steel pipe, 2 pieces of pipe, or if it is fairly long and you don want tight bends you can bend #4s with your foot and your muskles. :-) #4 means 4 eights of an inch. #5 is 5/8, etc. There are actually rebar benders, but I don't think you really need one.
My concrete guy sprays his forms with diesel. He sometimes mixes some oil in with it. I wouldn't use used oil - it will get your project all nasty dirty.
I'll go with the 145# per cu ft. Things made out of concrete get real heavy real quick...
DoRight,Cover your form boards with visqueen(poly) and the concrete won't stick and will be very slick. Any wrinkle will show! We always try to make some stepping stone boxes when we pour a slab. Add a thick leaf or two on the bottom of the box and you won't have to carve. Iris leaves make a good impression.KK
Edited 12/6/2006 9:15 pm by coonass
http://www.cement.org/tech/faq_unit_weights.asp
I have been thinking about the leaves. I was looking for some Devil's Club leaves. They are very large, think, and interesting looking. It is now winter so I am not sure what I can fine. I was not sure if leaves would leave a good enough impression. But, like I said, this is an experiment.
Thanks for helping in the idea collection stage.
folks have said a lot along the way.IIRC the 90 degree bend has a minimum radius so just clamping it and wacking it tain't good. also overlapping pieces of rebar (IIRC) has to have an overlap of 20 times the diameter. find a local yard that sells rebar, it comes in 20 foot lengths. depending on the yard they may have a bender and cutter you can use there. hack saw works for cutting.
bobl Volo, non valeo
Baloney detecter WFR
"But when you're a kibbutzer and have no responsibility to decide the facts and apply the law, you can reach any conclusion you want because it doesn't matter." SHG
I believe that the lap or splice for reinforcing bar is 30 diameters minimum. (15" for a 1/2" bar).
Plus if someone is going to hand bend the bar they need to get Grade 40 not Grade 60.
For all of this discussion I still think Piffen had it right, the OP should spend time looking at sites that discuss the concrete counters.
Good finish on CIP is always a function of the forming details and materials, and casting benches is not the same as pouring a basement wall.
Also, countertops are made with light weight concrete, IIRC. Weight being relative.
"I cut this piece four times and it's still too short."
for a project like this, I think I would be using #3 but doing it to excess instead of fighting with #4 for small spaces
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Yep, I was just using the #4 as an example for the length of splice. It had been posted that 20 x diameter was a splice length .
If I was building it in two pours (legs and top), I would just epoxy the top to the legs using dowels and holes precast into the legs.
Rebar in the center of any pour may as well be left out , it doesn't do anything for tensile strength, although it does work to tie say a stem wall to a footing against uplift.
Location of the rebar for CIP concrete is a studied science.
All true, which is why I suggested studying books and articles, because to refine a design like this, he has to understand a lot more than is likely to be covered in this thread
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It's a bench for goodness sakes, not a bridge. As a boss once told me, we are not saving lives here. It's a bench. A weekend project. I don't think I need a masters degree to build a bench. Yes, knowledge is power and I clearly appreciate all the great advice, thoughts, ideas, and sources of information offered here. This is a fantasitic site with some great people, and it is obviously a lot of fun for everyone involved. I am sure that if I were attempting to build a bench as a clear span to seat twenty people a bit more work would be required. As it is a failed bench built for two would be cause for nothing more than a coffee break. ANd then prehaps some more homework.
Ever see that joke about dogs? It circulates in emails often. It shows some twenty different dogs and their response to a light bulb burning out. The Poodles says I will bat my lashes and someone will change it for me. The German Shepard, coincedintally named Piffin, say " I wll change it but, first I will makes sure everyone is all right, check the other rooms for damages, and then patrol the area to insure that no one is taking advantage of the situation, and then ...."
" As it is a failed bench built for two would be cause for nothing more than a coffee break."
Of course another scenario is that the guest who happened to be sitting on the bench when it failed is married to a good lawyer...
Or the injuries incurred when the guest hit the ground will prevent them from ever walking again....(Wrong rebar details, connection from legs to bench seat inadequate )
Or the child who happened to be crawling under then bench when it collapsed died of a crushed skull...( Bench slab not thick enough to bridge the span, inadequate rebar detail, voids in concrete, pour not allowed to reach strength before being disturbed)
Or maybe the guest's nice white wedding dress gets ruined from using that old used motor oil on the forms... (Bad advice from those who don't care about the environment, look, smell and feel of the final project)
Any of these Might be more than just a reason for a coffee break.
And yes you can pour concrete when the temp. is below 32 deg.F., Read up on it and you will learn how.
dove, I see you are "patroling the area" as well. Get a life! GeeWisss
Newsflash! One rebar in the seat will prevent any catosphic failure. No crushed children. Then agian. Just to be sure we could all never get out of bed unless we are patroling the area, never ride in a car, build benchs a full 3 feet square and only 12 inches high ( no risk of topling), we could hire not one, not two, but three engineers to design teh 3 x 3 x 1 monolithe, and insist on unanomious design consensus from those engineers. And then immedicately retire to our beds again . . . of course after patroling the perimeter and posting warning signs around the bench.
Me , I would just go down to the garden shop and buy one.
Before or after you checked for other potential dangers, barred all doors and windows, patroled teh perimeter, check the doors a second time, called teh neighbors to see if they were in any need for assistance, ....
I reread my earlier posts, as far as I can tell I gave solid advice to you. Form oil suppliers and care in building your forms as the final pour will be mirror image of what you build. The encouragement to follow Piffens advice had to do with forming techniques as far as I was concerned.
As in many threads there were digressions and bad advice, I know that others may use the information given in threads for other projects , citing that it was posted here. Hence my input about rebar lap lengths and again appropriate form oil.
The photos that were posted on the bridges (which I enjoyed), my own posting on the project I did were clearly digressions from bench building.
I for one learned much from the other posters and the sites given about concrete, the way it works and it's strength and weight.
My reply while entirely sarcastic was a reaction , and not a well thought out one, to your post to Piffen. My apologies.
The truth is that many serious accidents do happen and often can be traced to seemingly innocuous events often starting out with a "how big a deal can this be" or "what difference can it make really" attitude.
For example you may want to look up the thread on the floor sander fire here at breaktime, I am sure the floor finishers thought .. "hey , no sweat , how big a deal can it be"
I do hope that your bench turns out well.
I know that I for one have spent a good deal of time "unlearning " what I was told and taught early in my career by well meaning but ignorant teachers. Ignorant is defined as uneducated .. and has nothing to do with mental capacity.
dove, thanks.
There is a difference between diversions and other posters inane purely argumentative crp.
Is sand just a very tiny rock? And should I beat the tar out of you over the issue? Particularly when the inane posters attacks and arguements are clear from a positon where he knews dammmm well that the other post was not attempting to argue that sand was not an agragate. Come on man! That is just BS.
Then there is the fake fane that "he was just interested in the original post". Oh really? Teh original post was about form release and the weight of concrete. And yet the scope of the know-it-all-belittling-one went to the inane obserd. And yet he was only interested in teh original post. A piece of work in my book.
And again the expansion of the thread was AWESOME, fun and useful. Thanks to everyone without the additude.
"Is sand just a very tiny rock? And should I beat the tar out of you over the issue? Particularly when the inane posters attacks and arguements are clear from a positon where he knews dammmm well that the other post was not attempting to argue that sand was not an agragate. Come on man! That is just BS."IIRC I'm the poster who made the comment about cement and sand.I was not beat upsand is an aggregate.and there are different kinds of sand, in concrete and mortar, the type sand you use effects the results you get, particularly in mortar, where it is the only aggregate.
bobl Volo, non valeo
Baloney detecter WFR
"But when you're a kibbutzer and have no responsibility to decide the facts and apply the law, you can reach any conclusion you want because it doesn't matter." SHG
Yes, and when the poster pointed out to you that you were an idot for not knowing that sand is an aggregate he really already knew that you knew that, but that did not spare you the and the rest of us the inane spanking.
Nuff said.
nope.I've met Piffen, and you are wrong.the breath of experience and knowledge on this site runs the whole gammet. insuring that everyone understands is not "inane spanking".
bobl Volo, non valeo
Baloney detecter WFR
"But when you're a kibbutzer and have no responsibility to decide the facts and apply the law, you can reach any conclusion you want because it doesn't matter." SHG
Well, his grasp of the obvious is very impressive. Sand is aggragate. I am in awe.
just in case Doright is right and I missed something -
Did you feel beat up by me?
I thought we were just discussing and clarifying about the properties of concrete. If I owe YOU an apology, You got it
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I may have said it obtusely before, but I didn't feel beat up at all. No apology necessary to me.
bobl Volo, non valeo
Baloney detecter WFR
"But when you're a kibbutzer and have no responsibility to decide the facts and apply the law, you can reach any conclusion you want because it doesn't matter." SHG
Be well.Yours is one of those faces I recall from Rhodefest and wishing later there had been more time to visit.
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http://www.blueridgeparkway.org/linncove.htm
tells the story of the Linn Cove precast viaduct bridge. Pre-cast segments, post-tensioned, each dropped in place from the previous one. An amazing structure.
This is a commercial project , doesn't rightly belong here in FHB. But just some concrete work pics.
Job I oversaw 2 yrs ago.
CIP walls, pre-cast planks.
Edited 12/8/2006 3:02 am ET by dovetail97128
That's how they are building the replacement for the SF Bay Bridge. Last of the pre-cast sections went in yesterday. Cool pics:
http://www.sfgate.com/cgi-bin/object/article?f=/c/a/2006/12/08/BAG9IMS10H1.DTL&o=4
very cool.
bobl, thanks for the warning. I did not intend to wack the stuff for a sharp 90 degree bend. If strength is a concern of yours, well this is a garden bench not a skyscrapper. LOL. Did I miss your point? Thanks again.
You refer to a standard parallel splice in reinforcement as twenty times the diameter of the bar in use. This is a good rule where linear loading of the reinforcement is required. In seismic code the required lap is 30 X.However, where the stress loading is lateral ( such as occurs at a 90 degree junction, or column head) this 20/30 X rule ceases to be applicable. Code requires a 90 degree bend engaging a similar sized bar, which, in turn, engages the vertical bars in the continuous structural member.Throughout this thread a lot of helpful people have posted information which suggests that they know parts of the technology very well. I do not claim to have engineering qualifications, so I am careful to limit my comments to experience-based detail.It wasn't till this week that I even heard about "concrete creep"This response is not intended to offend anyone, God forbid! I want to see guys like Doright get it right without being frightened of what he is trying to achieve. It may sound trite, but I wish I could drop over and give him a hand. But by the time I got there, the benches could be in use for a "Fest" of some sort. LOL.Lapun.
Lapun, thanks for your thoughts. This forum is great, even if you can get much more than you bargained for (not happen to this thread yet, perhpas a bit off topic on occasion). Well, not sure when the research will end or the bench built, as I really do need to patrol the area and insure that no one is trying to steel my ideas before I even have one.
stone for strength ?
in concrete ?
i would agree that it helps provide some structure to the hardened mass but that the primary use is in cost reduction of the product as a filler material.
rebar is the key.
our local precast suppliers often use no aggregate in their castings with great results.
i think their concrete is 6500 to 7500 psi compressive.
carpenter in transition
stone doesn't , by itself , reduce or increase the strength. but it does increase the workability
the most important factor in the ultimate strength is the water and the amount of hydration
if i were casting park benches, i'd be using a pea-stone mix, not a sand mix
here's a quick explanation fo the different factors:
<<<
Strength of Concrete
The strength of concrete is very much dependent upon the hydration reaction just discussed. Water plays a critical role, particularly the amount used. The strength of concrete increases when less water is used to make concrete. The hydration reaction itself consumes a specific amount of water. Concrete is actually mixed with more water than is needed for the hydration reactions. This extra water is added to give concrete sufficient workability. Flowing concrete is desired to achieve proper filling and composition of the forms. The water not consumed in the hydration reaction will remain in the microstructure pore space. These pores make the concrete weaker due to the lack of strength-forming calcium silicate hydrate bonds. Some pores will remain no matter how well the concrete has been compacted.
View Image
Figure 5: Schematic drawings to demonstrate the relationship between the water/cement ratio and porosity.
The empty space (porosity) is determined by the water to cement ratio. The relationship between the water to cement ratio and strength is shown in the graph that follows.
View Image
Figure 6: A plot of concrete strength as a function of the water to cement ratio.
Low water to cement ratio leads to high strength but low workability. High water to cement ratio leads to low strength, but good workability.
The physical characteristics of aggregates are shape, texture, and size. These can indirectly affect strength because they affect the workability of the concrete. If the aggregate makes the concrete unworkable, the contractor is likely to add more water which will weaken the concrete by increasing the water to cement mass ratio.
Time is also an important factor in determining concrete strength. Concrete hardens as time passes. Why? Remember the hydration reactions get slower and slower as the tricalcium silicate hydrate forms. It takes a great deal of time (even years!) for all of the bonds to form which determine concrete's strength. It is common to use a 28-day test to determine the relative strength of concrete.
Concrete's strength may also be affected by the addition of admixtures. Admixtures are substances other than the key ingredients or reinforcements which are added during the mixing process. Some admixtures add fluidity to concrete while requiring less water to be used. An example of an admixture which affects strength is superplasticizer. This makes concrete more workable or fluid without adding excess water. A list of some other admixtures and their functions is given below. Note that not all admixtures increase concrete strength. The selection and use of an admixture are based on the need of the concrete user.
SOME ADMIXTURES AND FUNCTIONS
TYPE
FUNCTION
AIR ENTRAINING
improves durability, workability, reduces bleeding, reduces freezing/thawing problems (e.g. special detergents)
SUPERPLASTICIZERS
increase strength by decreasing water needed for workable concrete (e.g. special polymers)
RETARDING
delays setting time, more long term strength, offsets adverse high temp. weather (e.g. sugar )
ACCELERATING
speeds setting time, more early strength, offsets adverse low temp. weather (e.g. calcium chloride)
MINERAL ADMIXTURES
improves workability, plasticity, strength (e.g. fly ash)
PIGMENT
adds color (e.g. metal oxides)
Table 3: A table of admixtures and their functions.
Durability is a very important concern in using concrete for a given application. Concrete provides good performance through the service life of the structure when concrete is mixed properly and care is taken in curing it. Good concrete can have an infinite life span under the right conditions. Water, although important for concrete hydration and hardening, can also play a role in decreased durability once the structure is built. This is because water can transport harmful chemicals to the interior of the concrete leading to various forms of deterioration. Such deterioration ultimately adds costs due to maintenance and repair of the concrete structure. The contractor should be able to account for environmental factors and produce a durable concrete structure if these factors are considered when building concrete structures.
Mike Smith Rhode Island : Design / Build / Repair / Restore
"This is because water can transport harmful chemicals to the interior of the concrete leading to various forms of deterioration"
Would an example of this be throwing salt on a sidewalk? Also, how about rain/surface water entering a cinder block or concrete block foundation? Thanks.
"use no aggregate "You must have mis-spokenI don't even think it is possibhle to have concrete with no aggregate. There are different sizes of aggregate, from fist sized stone to finely sized sand particles or silica dust, but each of these is an aggregate..You must have meant no stone lartger than such and such in the aggregate mix
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"don't even think it is possibhle to have concrete with no aggregate."limeless mortar?
bobl Volo, non valeo
Baloney detecter WFR
"But when you're a kibbutzer and have no responsibility to decide the facts and apply the law, you can reach any conclusion you want because it doesn't matter." SHG
but the sand in the mortar is an aggregate
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Always a pair willing to slice hairs and or intentionally goad someone on over a pimple. LOL!
Stone is more for compressive strength. What he needs in this is tensile strength, which comes from the portland and the steel
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Read Piffens reply he is right on the money.
I was off the money on the weight, but not intentionally. I was amazed when I opennned this to see that I had written a hundred when I was thinking 150# while I was writing that. my brain apparantly wasn't connecticated to my fingers
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I am actually curious about the final dry weight . Call it intellectual curiosity
I won't disagree on the weight as 145-150 # when poured, as the posts from marc and mike smith documented (# 82503.13 & # 82503.16).
Now what I remember is that if I buy an 80# sack of sackmix concrete, the directions are to add 1 gal. of water (+/-) to make .66 cu. ft. concrete. 80 lbs + 8.3 lbs = 88.3 lbs. for 2/3 of of a cu. ft.of concrete, that make 132 lbs. cu. ft.(WET)
I read in mike smiths post where the excess water (beyond what is needed for hydration) is held in the microscopic pores of the concrete. Having poured more than a few slabs in my day I can attest to the fact that a lot of water leaves the wet concrete really fast if the wind is blowing hard across the concrete so I wonder just how much of the 1 gal. is water is trapped and how much evaporates out of the wet mud as it sets.
I guess some day when I am doing another pour I will build a cu. ft box and pour it full and weigh it after full minimum cure time.
I tacked a rubber snake on the form for a bridge abutment and glued a large leaf and crescent moon out of plywood. Client loved it. Taper the edges of plywood or what ever you are using. Tile makes a nice mosaic surface.
Form oil, do not use diesel oil because it stains. You could line the forms with plastic sheeting,visqueen,polyethelene etc.Instead of carving decorate shapes, apply them with a brad nailer.The shapes will stand out and release easier.Form release oil is best for what you want to do. You can spray it on with a $15.00 garden pump sprayer, or brush or roller.
165 lbs wet, 140lbs dry.I would put 1/2" rebar in .Two or three depending on the width of the bench. You can buy "chairs" for either two bars or three.They hold the rebar off the bottom of the form.Cut the steel four inches short of the length.Teo inches short of the ends on each side.
mike
Thanks Mike. Nice summary of much of what has been said here.
I like the carved idea as it would show as a relief on the sides of the legs, although a recessed carve out which you suggest would look nice as well.
Masonry supply houses have "form oil " and release agents for just that pupose, yes it will stick with out using something to keep it from bonding. Make your forms out of as smooth a surface as possible unless you want to see the mirror image of the form works defects/grains in the final product.
Concrete has a nominal weight of 145 pounds per cubic foot. Use oil on your forms.
weight varies according to mix and aggregate, but figure about a hundred and fifty pounds per cu ft.
For this project, seek the threads and articles, books or video on building concrete countertops. There is a lot in there that will educate you and skills and techniques that can apply to this project. Also, read up on ferrocrete
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Edited 12/7/2006 8:00 pm ET by Piffin
The original post doesn't indicate how many benches he wishes to build.If he proposes to use 2 X 4 for forming, selective bottom edge bevelling will give him all the taper he needs for quick release and reuse.Strips of 2 inch X 2 inch arc mesh will do the reo, with slightly radiused corners and 6 inch lapped junctions. Strong enough and good economy too.A good project to learn a lot.Lukim Yu.
Lapun, Thank you very much for your thoughts. I think I would like to build at least two for my wife's garden. She has a large family and they all love this artsy fartsy stuff, so several more could be in the making. I also an a bit of an artist and therefore could be drawn into things if I get some interesting results without a pile of fuss.
Now for the questions:
You say "Strips of 2 inch X 2 inch arc mesh will do the reo..." What is reo? Are you saying to use a mesh of some kind rather than rebar for strenght?
You say "... with slightly radiused corners and 6 inch lapped junctions . . ." What radiused corners? Corners of bend mesh or corners on teh benches themselves?
I hope this will not become some kind of lecture. Since you are an artist, you will be able to imagine my thoughts. One largish reinforcement bar is not appropriate for your purposes, so a group of smaller bars would be better. But how to control separate rods in a small(cross)section becomes the limiting factor.The trick is to imagine two quarter inch bars side by side throughout the shape of the concrete frame. By using strips cut from an arc mesh sheet between the second and third strand, then the fourth and fifth strand, you will have two long strips with cross bars each two inches.It is easy to bend the strip to lie generally in the middle of your mold. But the bends should not be too sharp, as this weakens the way the concrete reacts to stress when the unit is loaded. A radius bend, such as would be created by bending around a half-inch stud, would do a great job. The cross bars also serve to support the concrete towards the outer edges of the section.By starting at the top of the rear leg and progressing across the bottom, up the front leg, then across the 'seat', you come to the point where the 'seat' reo meets the back leg reo. Here a short length is bent to overlap the steel in the back leg. Tie this overlap at the junction point and end, and you are done.When pouring (filling the mold) keep the ends of the cross bars off the bottom of the mold, or rust will destroy all your hard work.I hope this will satisfy your questions, but if not, get on the keyboard again.Lukim Yu.
"A good project to learn a lot."It was a similar project that got me to studying concrete.In the pursuit of that information, I learned that there are some fine concrete canoes and boats on the water
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Think Liberty Ships!
What do you want the top to look like? The pea stone idea is a good one if you want exposed aggregate. In California and other warmer places, they often cast rock salt over the top and work it in. When the concrete has cured, they wash out the salt and it leaves an interesting (to some) surface.
I have seen laundry detergent used as a form release, too.
If you don't want the benches to weigh 600 #, look at precast to get ideas about making a form that will displace some of the volume of concrete but leave a thick enough rim and top surface. Mesh should work for this.
If the form is smooth, the bench will be, too. Make sure you get rid of any air bubbles, too.
highfigh,
No I don't want a 600 pound bench. Just so you have a picture. I am thinking about a small one or two person (tight and romantic, LOL) bench, no back, and pretty low. The other issue is how thick must the seat be. I have mentioned using 2 x4, but I think 3 1/2 " is too thick, so I would likely rip them down to 2 1/2 inches.
What do you mean, "look at precast"?
Surface texture? My original thoughts were to lay large leaves in the forms. I like the idea of Devil's Club leaves. They are large, high in texture, heavy veins, etc. . Beyond that, even a heavy plywood texture might not be bad either. Well, perhaps a bit industrial looking.
When I said to look at precast, I meant that you should go into some public buildings and look at the ceilings, which are the underside of the floors. Large schools are a good place, too. You'll probably notice that the bottom of the precast floors frequently have what amounts to a grid system to make them strong with the least material. The vertical ribs act as joists and add a lot of strength. Look at a concrete block- it's very strong but it's also mostly air. You can also minimize the strength requirements by placing the supports directly under where the people will be sitting. That way, there won't be any bending to cause it to crack. Just for grins- google 'concrete canoe' and you may find some ideas on how to lighten the bench. Engineering schools all over have canoe races with concrete canoes every year. They may post some of their techniques.
"I cut this piece four times and it's still too short."
I googled: concrete bench design and got back
http://ewb.rice.edu/infodata/education/<!---->ceve499/ConcreteReport.doc
which has some interesting information.
I would look at using sidewalk reinforcement (wire reinforcement mesh) in lieu of fighting with rebar.... we are talking a bench after all :)
You can build the bench in a single lift as long as you use a fairly stiff mix.
Have fun,
Marc
Got it. Precast ribs.
Good idea, however, I have seen benches without such ribs. Just flat slabs. I just can't picture how think they were.
Go to the public library and get a copy of Leo D. Maldon's book "How to Build with Stone, Brick, Concrete & Tile". Or any other pubs. that catch your attn. The more you research the better you'll be prepared to go to battle with the gray stuff.
DoRight,
Sometime around 12 - 18 months back I seem to recall The Family Handyman having a good article on casting a cement bench. Provided a good form design that drafted to avoid locking the parts in and having to destroy the molds. Can't find it online right now, I'll look when I get home and try to post a link to the issue.
kgregor4, Thanks. I may see if I can find a copy.
As for forms, I figured I could screw them togather and reuse them. My design idea is pretty simple. I figured I could pour the seat, upside down naturally, with rebar protruding where the legs (just two) would go. I would also have some kind of "key" worked in where the legs would go. On the second pour I would form up the legs. Even thought hte legs would not bond to teh seat due to separate pours the rebar would be teh strength and no one would ever see a small crack that might develop where the legs join the seat.
To slightly reduce teh weight of the legs and to add stablity to the bench, I would press an arc into the bottom of the legs when poured. Thsi would also make the bench appear to have four legs and make it more elegant, if a concrete bench can be elegant.
Found it. The Family Handyman - "Great Spring Projects" March 2006. Page 54. I'd saved this issue specifically to maybe one day build the bench. It's that nice, and a good project for a beginning cement project that I figured I could tackle.
Cool! the library has a copy. So, perhaps after Christmas I will get around to it.
Conrete pours in sub-32 degree weather? ? ? ?
Vegatable Oil works great for forms. It is cheap and non toxic.
Yep, something healthy that does not darken the concrete is a good idea. The OP should stay away from motor oil, diesel, etc.
Obviously a good point. Particlularly if I every build one using those concrete coloration powder stuff. That's technical gargon.
Works for me... Like I said , just curiosity. It sounds as if the sack mix to get up to the weights of 145 lbs. would have to have about 2 gallons of water added. Whew, pretty weak mix.
Edited 12/7/2006 9:04 pm ET by dovetail97128
Not just added water, but more portland, which fills the cavies between fines, and more stone aggregate. Stone is denser than sand so it weighs more for same volumn
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thats how they make money. the sack mix will barely hit 2500 psi.
If you stick with the name brands and keep a 5" or less slump mix, the bag mixes will test out aroun 3500 psi for Quickrete and Sakrete. If you are having trouble with the sack mixes, the most likely cause is excessive water in the mix.
Around here, most of the redi-mix places mix rich - so if you order 5 bag 3500 psi, you are really getting 6 bag. Leads some folks to think the bag mixes are weak, but it's really that the redi-mix is heavy.
In case you are curious, yes, we have tested the bag mixes and pretty consistently get 3500 psi minimum - assuming not too much water was added and it was cured properly.
I,m sorry, I will not post no more, and I will go back and delete all my threads
Weight is only a problem for moving and installing the benches. You might be able to make that easier using a very old British technique. Make your benches in three pieces. Secure the seat to the two legs with loose mortise and tenon joints, with gravity keeping it in place:
http://www.science-explorer.de/bilder/stonehenge003.JPG
If you start with pure portland cement and design your own mix with aggregates, one thing to watch out for is dirt in the aggregate. It weakens the concrete. Fill a bottle about half way with aggregate, and then the rest of the way with water. Agitate it well and let it sit. If a layer of mud settles out on top of the aggregate, it's too dirty, and needs to be washed before you can use it.
For grins once I tried to see how strong I could make a home brew mix. I used 3 parts by volume portland cement to 4 of sand and 4 of 3/4" gravel, all very well washed, and just enough water to be barely workable. The 29 day cylinder tested at 6390 PSI.
Another thing you may need to do is store portland cement between bench building sessions. I've had excellent results by double bagging it in those nylon bags you get from the termite fumigators. Just over the weekend I did a little patch using cement that had been double bagged for over four years. Take great care as you work with it to keep your powder dry.
BTW, per the 1948 Machinery's Handbook, concrete weighs 137 pounds per cubic foot.
-- J.S.
I didn't say anything before but I think it should be pre-stressed. Or, since there will be more weight at the back, a framework with catenary cables would double as a backrest. Q: What time is it?A: Well, you start with the bezel and make a movement that will fit inside......
"I cut this piece four times and it's still too short."
Ok, I need you to clear up something.
I went back to re-read your original question to see if I had misunderstood. I don't think I did.
Youwant to know how to build a more or less lightweight, serviceable bench and need tips on how to do it.
Then when you get that kind of pointers, you claim you don't want that much help and compare your advisors to dogs.
You post questions showing you know very little about forming and using concrete and then claim that only one rebar will be enough to prevent catastrophic failure.
You want to know how to do it with lightweight techniques but you aren't interested in learning how to visit the edges of possibilities with concrete.
before your halfassed insult, I was actually enjoying the exchange of information and the intellectual stimulation of this thread. now all I feel like doing is lifting my leg on your bench
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Piffin, I am very sorry but this is all too typical of you. You find a chink and grind it and grind it and grind. You appear to be a very lonely fellow. You find a guy who wishes to argue with you about whether or not dust or grains of sand are indeed aggregate. Ok, knock yourself out, but atleast admit your silliness and pointless of this arguement for any thing remotely related to the discussion.
As for my project. What can I say! I thank dozens of people for great information. I am sure that I have thanked you as well. And then nut jobs, start running off about killing small children and caved in skulls. And ramble on about structural strength, etal of project the size of a bridge. Well, structural strengths and all are very fasinating until know-it-all start belittling people, comparing benches to the effil tower or the San Fransico Bridge.
Now perhaps you wish to contnue your rant about sand and dust and pea gravel or whatever.
Hey, I like Piffen, ask him about metal roofs, or how to hang cabinets with the very popular patented piffen screws. Ask him about his trip to scotland and the barney stone. Ask him about all that grey hair. Or even ask him about how cold it gets in Maine. Ask him.... i like piffen.I know, try this... ask him about concrete.........
I thought the stone was in Ireland.. I must be missing something here.
as in Blarney
why dont we ask Piffen
Why not ask piffin what country the Blarney stone is in? Well, first we would have to establish that you are an idot. Then we would have to have him ask us forty-seven questions like, well first we need to know if the stone is sedimentary or igneous. And where teh stone had always been in that country or had only been recently transported there. Then we would have to establish what the meaning of recently is. Then where the stone was a military weapon or purely a ceremonial or religous icon. Now what was teh question again? LOL
two "I" in idiot
82503.88 in reply to 82503.87
Of course it does, I just thought Idiot was a naught word on the site and might appear as #####, you ######## #####. LOL!
So, how about posting a photo of your bench when it is completed? It is great when somebody has a question, they get answers, then do the project and follow through with a report. It completes the circle very nicely.Bill
That would be the plan.
However, with some additudes it is a risky proposition. Not that that applies in my case as I am hardly detoured by small people with additudes.
Just out of curiosity , what is your field of expertise? What is it you do as a career?
How classic.
Not a trick question, you just don't have any info posted on your profile .. so curiosity.
I have always found it easier to relate with people if I knew the line of work or trade they are in, easier to find analogies that are understood.
To all it may concern. I apologize for the OT posts.
Dove, I have been down this road so very many times. Curiousity? Ok, if you say so.
At any rate what is it you are wishing to address with an appropriate analogy?
The weight of concrete? The need for a releasing agent on forms? These were my questions.
So it is I who is curious.
Since you already have my answers to those specific questions I guess I will quit trying to be of any assistance to you. Enjoy your project.
I was just wondering if you could buy a concrete bench cheaper than you could make it yourself
If it's made in china or taiwan. Ya know what I'm sayin?^^^^^^
S N A F U (Situation Normal: All Fouled Up)
Actually, mrfixitusa, I was just in a concrete works store at the mall. And then did have benches. They were priced from $80 to $380. But then that is really not the point of any artistic endever.
Then again, this forum haas taught me that by the time I hire six engineers, four of which must be safety engineers, you might have a point.
dove, assist away. I am just curious (snicker snicker) what analogies you wished to share.
82503.101 in reply to 82503.98
dove, assist away. I am just curious (snicker snicker) what analogies you wished to share.That would depend entirely upon what problems you run into and what questions you might have arise as you work on the bench.But given the tone of your posts I think I will offer these. I guess it is the one about the dog that bites the hand that tries to feed it.
Or maybe the one about trying to befriend the junk yard dog.. I can't decide.
Now if you will excuse me I have an ignore box to go build.
Edited 12/12/2006 10:57 pm ET by dovetail97128
"I have been down this road so very many times."I think I understand now
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Gee, BB, you like me so much and now I have to correct you?Minor mistake - I've never set foot in Scotland. The Blarney Stone is in the Blarney Castle in Ireland. The teenagers in the area go sneak in at night to pee on the stone, knowing that tourists will be kissing it the next day.I kept my lips to my selffor a change;)
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But it is cold in Maine
I don't recall ranting in the least about. I was just clarifying for everyone's proper understanding that mineral filler in a concrete mix is called aggregate, regardless of what size it is.If you are at all interested in doing unique concrete projects, you need some rudimentary understanding of the makeup and the chemistry ionvolved.I don't see the guy whose information I clarified complaining about it.
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Pif,Since you have demonstrated your language skills previously, I share this observation with you:"Disela man, i gat wankine sik, ol i callim
bikhet. Time i tok, mi harim mauswara tasol. Mobeta yu lusim tingting
longen".I'll be thinking of you at Christmas, when we sit down to dinner on our deck in 97 degree temp with clothes and fans to match. You have a good one.Lapun whitegrass.
Perhaps he is a George type. He obviously respects you and what do you do in return, state the most elementary of obvious, your forte, as if he were ignorant of the obvious. Ok, if he is ok by that fine. But that does not change what is underlying.
And of course you don't recall. People don't take notice of what comes naturally to them.
Art of War
Sun TsuFirst, know thyself
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So what is your excuse?
I'm just me and you are you.I'm happy with that arrangement!
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