I need to do a slab for a carport (mine) 18x20x3″. I’m going to use a mixer and do it myself……..(something I always subbed out when I was building)
My thought is to mix it, wheelbarrow it, spread it smooth and finish it as best as possible after it sets. Probably take at least a week.
I got the time, but I will be putting fresh against dry and semi-dry and am not too sure what problems I’ll be creating for myself. Any ideas?
I already know it will be a bit rough, but as to cracking later, etc.?
Replies
why not ready mix?
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
Could you divide the slab into quadrants and do one fourth each day. Set dowels between the quads and put in redwood strips or expansion matl as well. Basically creating four slabs pinned together.
OR save you back and order the truck. :)
That's what I was thinking, but then I didn't know if that was necessary..............(the expansion joints)i'd love to order a truck, but I'm an old man/one man band and I'd probably end up with a big pile of hard cement to drive over
its going cost you double and crack like crazy. three inches is not deep enough
Each place you stop and begin again the next day will be a "cold" joint that will not stay together. The slab will come apart.
Your only choice would be to do the perimeter all in one pour, and then do the interior slab as a series of independent squares with movement joints between them.
Who knows the price difference between buying sakrete and ready mix?
I am guessing the ready mix will be cheaper enough to hire a temp for the pour and rent a power trowel.
JJ, I would say 4" minimum thickness for your slab, and be certain to put some steel in there.
18x20? Thats 4.44 yards (figure on 5, unless your REAL accurate with the rake) Thats right around $500 in concrete in my area for a 6 bag mix.
What is your sakrete estimate? Could you do something for pay in the 4 days you would have off to make the $$ back?
Or just do it by hand and save on the gym membership.
it takes 37 sacks to make a yard, @ $4 a sack plus hauling. 10,000 lbs
$651.00 and you havent started yet. plus all that mixing, and wheel barrowing, and water, then finishing.
> Who knows the price difference between buying sakrete and ready mix?Quikcrete runs about $4.60 plus tax for a sack that makes 2/3 cubic foot around here. Last time I checked, calling the truck in was about $85 a cubic yard, but it's probably higher now. It's been quite a while. It can also be hard to get them to come by with a small order.George Patterson, Patterson Handyman Service
The price of ready mix concrete is very reagional. Right now, here in Raleigh NC the price is about $103 a yard, depending on who is buying it.
It can also be hard to get them to come by with a small order
Yeah, it seems small, but did you catch (I think) bb's ciphering? It's 4-5 yards, or a half truck-full. My local redimix joints usually (usual being the key word) have a 3 yard minimum. But, as long as you reassure them that you don't expect them to show up with a finishing crew, they'd deliver 4-5 yards mostly happily.Occupational hazard of my occupation not being around (sorry Bubba)
Nope, didn't catch that. Four or five yards should be no problem.George Patterson, Patterson Handyman Service
jj,
While I don't want to advocate for what you want to do if that is what you want to do then I would suggest metal "keykold" (sp.?)
Use it to divide the slab into workable areas, , it will act as both a temporary form and build a "keyway " into the edge of your slab so the next pour will lock into it.
Should be able to find some version of it thru a lumber yard or mason supply place .
Price out ready mix concrete from a local ready mix company and also price it out by the bag. Get back to us and tell us what you found out.
You will need ~4.5 yards to place a slab the size you specified that is 4" thick. Order 5 yards to be safe.
If you do it by 80# bags it will be at least 180 bags, and probably more like 190 for that same 18'x20'x4".
Edited 4/4/2007 9:13 pm ET by Matt
I did what you suggest once.
Inside the basement, into another closed room where I had dug out the crawlspace by hand. Had to under pin the footings, run a stemwall for the differences found in the footing height, and wheelbarrow 10 yds of 60/40 into the basement itself (up a 10 ft hill, around the house, back down and into the basement to build the gravel pile.
Then I brought my mixer downstairs (1/3 bag) and set it up in the doorway. Had two kids work as fast as they could loading that mixer with cement, gravel, and water. Then tipped it over into the room, pouring it into another barrow to wheel it in place.
Was able to finish one level one day, the second the next. Had to do that to keep from making the aforementioned cold joint.
But the quality of mix due to variation in water (not to mention the kid's measuring errors) resulted in not the type of slab one dreams of.
That was when I was young and poor. But I saved by getting the 60/40 via my trailer and hand shoveling it off.
But in retrospect, I would have saved more if I had gotten redimix and an inline pump.
Please don't take offense but................you're not serious ?
Many little batches mixed by hand are ususally inferior due to the slowness of mixing, and inconsistancy of batching. Most people add way too much water.
Do yourself a big favor and find a pro and buy ready mix product.
And don't forget to re-inforce the slab with 6 guage wire mesh throughout, and rebar around the perimeter.
Save your energy for the carpentry. Cheers.
Edited 4/4/2007 10:44 pm ET by ericicf
<Please don't take offense but................you're not serious ?>:-)........yeah, I really am...... I have thirty some years as a carpenter/builder.....and a couple days doing cement. My expertise involves calling my cement guy .....(but I did do a garage floor in Alaska one time by myself) and since this is for myself if I get it to a decent trowl I'll be satisfied.....I'm just looking for the easiest way and thought the sectioning it into four individual parts sounded pretty good. I could handle that (about a yard at a time) Buying bags of redi-mix is a bad deal unless you're doing deck footers IMO.......so I get a mixer, some sand, some gravel......lay the whole thing out (a good gravel base) and pour 1/4 each day........anything wrong with that?
You have your 2 options:
by hand:
- more expensive
- terrible job impossible to float smooth with many cold joints
- 'will take a week'
- will be full of cracks
vs.
by ready-mix:
- cheaper
- faster (with two people you could have it placed/floated in 2 hours)
- much better job
PS - having done this *nearly* by myself (4 yard pour) I can tell you that you will have a very difficult time trying to place and screed this by yourself before it sets up, especially if it is warm out. You can float and jitterbug it by yourself, but trying to place and screed it fast enough is almost impossible.
PPS - 6" compacted crushed stone, 4" x F'c = 3,500 psi / thicken edges to 6" minimum, rebar in leading edge, 6x6 wire mesh + fiber (best combination for no cracks), contraction joints at 10' spacing saw-cut after 24-hour set
Jeff
Edited 4/5/2007 1:55 am ET by Jeff_Clarke
If I were stuck, doing this job by myself, I'd do it in four lateral pours. I would form the perimeter, then stake a pre-drilled 2X4, four and a half feet in from the 18' edge. Lay in the wire and stick one foot pieces of rebar in the holes drilled in the 2X4. Support the outside ends of the rebar with scrap lumber to keep them level. This will allow you to pull the drilled 2X off easily.
Then pour it, finishing one lateral at a time and repeating each step. You should be able to screed four and a half feet OK by yourself, with concrete of the right consistency. As you will be screeding off the edge of the previous pour, try to make that area smooth.
If the weather is cool and cloudy, you may even have time to trowel. If not, I'd suggest a broom finish and an edging trowel around the perimeter.
if i was doing it myself, i order a 4000 pea gravel. throw a lot of super p in it. add alot of water, get it about a ten inch slump. pour it wet and be done in thirty minutes. it stll be better than the sack crete, and about $200 cheaper
4000 pea gravel. throw a lot of super p in it. add alot of water, get it about a ten inch slump
Semi-technical question, would you be inclined to bump the fly ash content too? Not for the final strength, but for how "sharp" the fly ash can make a high slump pour finish to.Occupational hazard of my occupation not being around (sorry Bubba)
I love fly ash. I usually use at much as 20% flyash
I love fly ash
I like how the finishers love it, and it takes steel troweling oh so well.Occupational hazard of my occupation not being around (sorry Bubba)
super P?.....10 inch slump? I'm presuming that super p is some sort of an additive
10" slump is a thick/thin definition and 10" slump would be pretty wet?So you'd put up firm perimeter, wire it and pour the concrete wet enough to practically level itself? Will the super p make it strong enough?
>> super P?.....10 inch slump?
I'm presuming that super p is some sort of an additive10" slump is a thick/thin definition and 10" slump would be pretty wet?
So you'd put up firm perimeter, wire it and pour the concrete wet enough to practically level itself? Will the super p make it strong enough?<<
Super P (Superplasticizer) doesn't make the concrete stronger. Super P is a liquid admixture that makes the concrete more flowable, meaning higher slump concrete without appreciably reducing the cured strength of the concrete. It's something you add to the concrete rather than water. Super P is used in comercial concrete placing more than in residential.
Regarding slump, yes, a 10" slump is pretty darn runny. Here is a quick description of slump testing: A 12" tall metal cone with open ends is placed on a hard surface with the small end up. The cone is filled with the concrete to be tested in layers and tamped until the cone is full. Then the cone is removed. The number of inches that the remaining concrete falls down or "slumps" is the measurement. So a 10" slump would be very watery. A 4" slump is usually a good starting point, depending on what the project is. Much thicker than that, say a 3" slump", and it will hardly come down the chute on the back of the truck.
Did you get the $ numbers on the bag and ready mix concrete?
if you get a five inch slump , which is still a good mix, and pour a 4000 instead of a 3000, extra insurance, Then use pea gravel. they like to roll around easlier. By adding the super P to a five inch slump you will get a ten to tweleve inch slump but at the strength of a five. add some fly ash to the mix and you have a self leveling slab that will break 3500.But what do I know, I have never done a CEMENT slab
add some fly ash to the mix
What is the point of adding fly ash? It wil just weaken the mix - no point in going to 4000 psi if you are going to add fly ash.
Around here, only the shysters use fly ash.
fly ash has the same property as portland cement, it used as a filler in the portland paticles. so fly ash increase strength because it increase the cement content. it also has the ability to cool a mix so you dont get the hard flash. Mainly flyash particle are rounded and smooth so you get a more flowable mix without adding water.
http://www.toolbase.org/Technology-Inventory/Foundations/fly-ash-concrete
Fly ash is an inexpensive replacement for portland cement used in concrete, while it actually improves strength, segregation, and ease of pumping of the concrete. Fly ash is also used as an ingredient in brick, block, paving, and structural fills.
Fly ash concrete was first used in the U.S. in 1929 for the Hoover Dam, where engineers found that it allowed for less total cement. It is now
http://www.greenbuilder.com/sourcebook/Flyash.html
Although flyash offers environmental advantages, it also improves the performance and quality of concrete. Flyash affects the plastic properties of concrete by improving workability, reducing water demand, reducing segregation and bleeding, and lowering heat of hydration. Flyash increases strength, reduces permeability, reduces corrosion of reinforcing steel, increases sulphate resistance, and reduces alkali-aggregate reaction. used across the country.
http://www.flyash.com/flyashenvironment.asp
That makes concrete containing fly ash stronger over time than concrete made only with cement.SamT
There are three kinds of people: Predaters, Prey, and Paladins. For the life of me, I can't see why Prey feels safer from predators by disarming and emasculating Paladins.
A lot of posters have dumped on the sack redi-mix claiming it isn't as strong as batch plant even if mixed to according to the instructions. So has anyone ever had a test cylinder or two checked or is it just "Common Knowledge"
I have, I got 1800 in 28 days.
brownie,
Thanks for the reply. 1800... well that doesn't quite cut it ! Think I will still keep adding a 1/4 shovel of cement to it just like I was told to years ago..
Which brand? I'm assuming that it may vary a bit.
cant think of the name, yellow bag, quikcrete something like that.
That is a good part of the problem. The bagged concrete products aren't consistent. You get several bags of the same stuff, one has 2x as much gravel as the next... Add in the difficulty of mixing it consistently, thoroughly, and fast enough, and this whole thing about placing slabs or anything else of a significant size out of bagged concrete single handedly is just hack stuff. The guy want's something to drive cars on. I guess it's OK if your standards are low enough. I've done dovetail's thing about adding some cement to the mix of each bag, and it's not impossible to make work, but I just think this is another case where someone had an idea in his head and was just looking for someone to validate it. I mean this is the internet :-) I can validate anything using this tool :-). BTW - I'd like to build a house out of used tires. I have source where I can get them cheap. Got any tips? :-)
Not to belabor the point but the OP never intended to use bagged mix. He said he'd be mixing portland cement with sand and gravel. That's the least expensive way, which is one of his main aims.
Go to the quarry or batch plant and they'll dump a bucketfull of sand into your pickup. Go home, shovel it out next to your form and go back for the gravel. Most quarries are happy to sell a half ton of sand or gravel like that. It's not much but they're paying a guy to run their machines so your little load pays for an hour of his daily wage. Those with scales can tell you the price to a penny.
This is the way that concrete was mixed and poured on the job before redimix trucks came along. In many parts of the world, it's still done this way. I've watched some very efficient crews mix on site with a 1/2 bag machine and pour columns and floors for small buildings. Using 5 gallon buckets and a rope-pulley hoist, they lift the mixed concrete by hand, one bucket at a time. It's great to see the skill and teamwork which goes into this rapidly paced work.
When I worked at a cement plant here in Va. we would have concrete pouring parties,usually we had about 20 guys show up to form ,place and pour driveways and slabs we would all get free Portland 15 bags at a time,or if the company had some off color stuff all ready on the pallets we would pick that up and have it ready for sat.or sun. morning have a couple of mixers going usually a skidsteer / Georgia buggy was available or beuceu wheelbarrows.we did so often that everybody just kind of got in to a rhythm and knew what to do ,of course it could have been the abundance of party materials but we turned out a few dozen jobs back then that were quite noteworthy-- we also shingled roofs the same way,but sometimes that didn't turn out so well.Had fun though.
Edited for sp.
Edited 4/14/2007 3:28 pm ET by dedubya
So..are you saying essentially to do four pours.....each side by side @18x5....rebar sits 6" into pour and hangs out 6" awaiting to join the next pour? The rebar would act to hold the two separate pours together?.....and so on......Never thought of a broom finish....sounds good to me. thanks
That's right JJ, you've got the picure. Except I'd probably opt for 4 sections, 4 1/2' X 20', just to make them 6" narrower and a little easier to screed. If you keep the concrete fairly stiff and use plenty of portland, you should be able to get a decent float, just by working your screed board with some energy.
You know you're going to be mixing about one yard for each section but using this method you should have pretty good control of strength and appearance. The broom finish provides traction but is harder to keep clean. Of course it's very quick and easy to get that effect which is why it's often the best when finishing time is limited. If you're going to use a broom finish, don't wait too long to start. The surface needs to be a bit soft to do it. A stiff bristled push broom is the best but keep hosing it off, each time you lay it down so that it won't dry out and clog up. An edging trowel around the perimeter will give your slab a professional look. That can and should be done shortly after brooming.
PS: It's important to use 6x6 wire in a slab like this. It comes in 4' rolls so, using my suggested spacing and laying rebar around the perimeter, you won't have to do much cutting.
Edited 4/5/2007 2:31 pm ET by Hudson Valley Carpenter
Ok...I can do that......thanks for the help.
Happy to be of service, JJ.
Please shoot a few photos so you can show us all how it's done.
BTW, if you feel ambitious you could do two sections in a single day. For that to work well, you'd need to pour the first one next to a perimeter, then skip one space and pour the other one between two empty spaces. That's the way that many large floors are poured. Of course it would require two additional, drilled 2X4s.
If it was me, working on my own place, and I had the time I'd stick to one section per day.
At 64 years old ....one a day will do me just fine...thanks:-)
No wonder we're on the same page. I'm sixty-four too. :-)
Then you know........my once rather large muscle mass has atrophied, especially since the bypass ....and NO amount of excercise will bring it back.........and the aches and the pain....God how I love it!I'm alive! (at least until the pour)
<<I'm alive! (at least until the pour)>>
JJ, I think that you'll enjoy this job. I'd try to start early and take it easy, finish by lunch time each day.
By the way, I notice that many of those who are replying don't seem to understand that concrete can be mixed from it's basic ingredients, on the job site. I guess that comes from growing up with everything pre-packaged in single portions, huh? ;-)
"concrete can be mixed from it's basic ingredients, on the job site."
Sure can. But by the time you get into the mixing what you've poured has already set up. Therefore you have lots of cold joints = cracks.
'Round here there are one or two plants with 4-yard 'mini' mixers. Costs a little more but less than a 'short load'
Jeff
<<Sure can. But by the time you get into the mixing what you've poured has already set up. Therefore you have lots of cold joints = cracks.>>
I guess we'll just have to wait and hear how it goes, huh?
By the way, I notice that many of those who are replying don't seem to understand that concrete can be mixed from it's basic ingredients, on the job site. I guess that comes from growing up with everything pre-packaged in single portions, huh? ;-)
I did this years ago (the old 3-2-1 etc) - thats why I am recommending ready mix!
Treat every person you meet like you will know them the rest of your life - you just might!
jj,
I have been following Hudsons advice and he is on track if you want to pour it yourself.
I might add that with the 2 x 4 you can add either a half round of 1 1/2 stock or make a bevelled "key" that you nail to the side of the 2 x 4 , this will also jhelp keep your pours locked in interms of verticle movement. I am not that much younger than you and I wouldn't be afraid of the task. You can eat an elephant one bite at a time! Planning saves the body ...Leave the sand gravel mix in the truck, saves lifting the shovels, mark a bucket for water level, always use the same amount of everything in each batch. Start early before the days warm up, keep it good and damp for a few weeks after you finish .
<I am not that much younger than you and I wouldn't be afraid of the task.>I'm going with Hudson and I need to sweat a little. I built this whole compound myself.....and tore a 60' trailer apart with a sawzall to get to the only flat spot there is......BRAG :-)and.....and.....when it get's time to empty the septic? why be a sissy and call the cement truck
I don't ever want to get that old !!!
<<and.....and.....when it get's time to empty the septic?>>
Holy sheet! I wouldn't even want to be taking that photo...much less holding the bucket! You may qualify for someone's DIYer of the year but don't expect them to invite you to dinner. ;-)
You'd be surprised to the lengths some people go to save a buck.........
JJ, I only know one guy who is tighter with a buck than I am but even he would call the pumper truck.
It occurs to me that you may now qualify to be known as The Most Northern Red Neck in the whole USA. Send that photo to Jeff Foxworthy...see if he agrees! ;-)
dont drink the water
How did it price out?
Yea, use the bagged material for the slab, and then use dismanteled pallets for the framing lumber.
Bagged concrete, low cement content, too small agg, its garbage. Order RM and get some help.
By the way , it's concrete, not cement.
Mike
Edited 4/5/2007 12:45 pm ET by Junkman001
Uhh Junkmouth,
He said he's using sand, gravel and portland, not bagged mix, a product with which you seem to be well acquainted. I'll have to give you credit too, thinking of using pallet oak for your finer cabinetry. Do you stack 'em in your back yard, give 'em time to season? Would you like us to save 'em for ya?
Geez, never heard of tounge in cheek humor? Save those pallets, I'll let you know whin to bring 'em by.
MikeInsert initially amusing but ultimately annoying catch phrase here.
<<Geez, never heard of tounge in cheek humor?>>
Sure but your post reads like unmitigated sarcasm to me.
Tongue in cheek would be like saying that because Hillary Clinton has spent so much time in the White House she should run for President. Logical but painfully ironic (to me anyway).
PS: I see by your profile that you enjoy things that fly. Is that a tongue in cheek reference or do you aviate?
Edited 4/5/2007 2:20 pm ET by Hudson Valley Carpenter
Non current VFR as well as Airframe & powerplant mech.
MikeInsert initially amusing but ultimately annoying catch phrase here.
PPSEL VFR Maule MX7-180A
I strongly suggest you save yourself a LOT of grief and sub this out like the old days. Your sack mix plan will yield a terrible job and sack mix really isn't that cheap compared to readymix. Your back will be shot. Get a crew of finishers in there. They can lay it all down and bullfloat it in about 20 minutes, then leave one guy to trowel and broom it.
Wanted to join the chorus for having a truck delivering concrete. I had a small conecting room to build 8' x 14'. I didn't want to pay for the less than minimum charge. Borrowed a cement mixer. I consider myself fairly fit ( I work out once a week) Once you start humping 50 - 70 lb bags you'll feel it the next day.
I needed something like 1.75 yards for each wall and 2 yards for the slab. Did three pours.
I don't know if I'd do it that way again.
Also my trailer has a limit of 3000 lbs. Thats only 60 fifty pound bags. So its fifty on and fifty off.
You'll need 7 yards. Thats alot of cement bags. A truck can dump that in 20 minuets
good luck