Hi all:
I’m ready to pour my basement ICFs tomorrow- wish me luck! The fellow who is helping me out has done a couple hundred ICF homes, so he should know what he’s doing. It’s all true- it went together like Lego, and was up and braced in a weekend. So as long as we don’t blow it out, I’ll be a pretty happy guy for choosing this method!
It has me thinking on to the next step, which is the garage foundation. The garage is supported on piers and grade beams, which I think I’ve got figured out. But the garage slab is troubling me a bit. The soil is heavy clay. The topsoil has been removed (probably more than the tree people would like, but it’s all over and done with), but it’s by no means down to “undisturbed soil”. It’s been well rolled over by the bobcat, but no compaction has been attempted yet.
The slab will be on 6 mil poly on 2″ of heavy EPS on 4″ of crushed stone on soil, with expansion joints at all edges. The slab will have welded wire mesh and PEX tubing for heating (the garage will be my shop). Forget about making the slab bear on the foundation- the piers are dug and my plans are approved so I’m not going back to have this thing re-engineered.
I guess I could just dump a load of crushed stone on top of this crappy clay fill and let the inevitable happen: expect the soil to dry out and settle under the slab over time, leaving pockets under my slab and inevitably leading to cracks. I could compact the stone on top of the clay, probably driving half of the stone into the clay. Somehow doesn’t seem satisfactory!
I was reading that landscape fabric is a way to stabilize shallow stuff like driveways on top of fill. Does my application sound like a good one for landscape fabric? If so, any suggestions on the type? The only stuff I’ve found around here is the stuff which is used as walkway/garden weed barrier. Should I attempt to compact the clay base first, then put down the fabric? Or should I put it down and then dump stone on top and compact the stone?
Replies
Sounds like your clay soil is soggy wet. I would recommend dumping few loads of sand or, better yet, stone dust. I'd spread this out evenly, then I'd dump in the gravel... but I'd put down the gravel in lifts of a few inches at a time, and then run a compactor machine over each lift before adding another.
I probably would not use the landscape fabric...but if I was inclined to use it, then the fabric would go down right after the sand so that the gravel would hopefully not be swallowed up by the clay.
I think the sand and/or stone dust will help to dry out your soil, and thus should firm it up some.
Although you say you don't plan to re-engineer your slab, if you remain worried about how the integrity of the slab will hold up over the long haul, then you might want to consider substituting 1/2 inch diameter rebar in place of using the planned 6X6 welded, wire mesh.
Wire mesh's primary purpose is to help keep the concrete form falling apart when it cracks. Rebar's role is to give the slab strength, both in compression and tension. The rebar acts as a bridge over troubled soil areas like you are encountering. The rebar should be laid 12 inch OC and another layer should be laid on top, perpendicular to the first layer. The layers are tied together with wire ties and this rebar "mat" needs to be held off the ground so that it will be engulfed in the bottom third of the poured slab's overall proposed thickness. This can be accomplished by using prefabbed "chairs" that are sold at masonry supply stores. The first layer of rebar lays on top of these chairs, and then the second layer lays on top of the first rebar layer. The finished mat resembles a big, checker board. You only need to tie every other square to hold the rebar in place. First layer gets tied to the chairs...2nd layer gets tied to the 1st rebar layer.
Rebar is not that expensive, but will make your slab dramatically stronger. I've been involved in many floating slab pours of various thickness's and we always used rebar. WWM was only ever used for sidewalks, and other low impact areas.
Good luck with your project.
Davo
Have you ever used 6/6x6/6 ww mesh?
That is highway grade 6x6" squares made with # 6 wire each way. I have used it on two driveways over questionably compacted bases. I also used a geotextile fabric beneath the crushed stone. As far as I know both jobs are still holding up after 8 and nine years.
Maybe Gabe will pop in and offer his advice on this one. I am interested b/c I have a floating floor pour coming up, and although it will never have vehicles on it, it will have RFH.
Dave
Definitely thinking about going with rebar. I can buy 10M (1/2") cheap enough here. But I'm going to be so sick of rebar by the end of this thing I tell ya! Rebar for the ICFs, rebar for the piers and grade beams- geez, $300 worth of steel to reinforce $1000 worth of concrete seems like it's a bit out of proportion somehow. Dragging home those 20'ers is a royal PITA and anybody who delivers charges a fortune for the material- but not quite enough to pay for me to rent a truck. We agree it'll make a far stronger slab, and since this is my own place and I intend to stay a while, maybe it's worth the bother and $$$
As to the landscape fabric, I saw what was in the FHB article and just wondered where the heck I could get it- and if anybody could make sense of a selection for my particular application. I still wasn't sure after reading it myself. As I said, the only stuff I've ever seen around here is the weed barrier material- probably better than nothing, but not ideal for my situation I'm sure.
Definitely thinking about going with rebar.
Having seen set, and having set & finished myself, more concrete than I care to remember--I'd rather #3 @ 12" OC than even 6x6x6 WWM (that's 6 wire gauge--not AWG, either--not 6/8" bar). Even if the WWM is "enough" for the slab--unless you can get nice flat sheets, it's curling like the devil the whole time you try to work it. And, without some sort of proper stirrup support, the folk finishing the concrete really jsut mash it down to the bottom (mostly, 'sept where it's curling out <grrr>).
Probably not a good time for me to rant about the difference between steel rebar and ferrous oxide WWM (with its lovely bright orange scale coat, too).
As to the landscape fabric,
Uhm, when you ask, ask for geotex or geotextile fabric. I know around here, there's a Darrel (or his other brother Darryl) who would try to set you up with weed-control fabric instead of the geotex you want.Occupational hazard of my occupation not being around (sorry Bubba)
Have you ever used the ww mats for slab?
My steel suppliers has 6/6 x 6/6 and 6/6 x 10/10 mats that are 5' x 12'. I am thinking of using them for a RFH slab in a studio/kennel building I am building. The roll ww mesh is a PITA for a couple of experienced men. Even flipping the pieces over and back rolling the ends isn't enough to keep it in the slab sometimes, and forget the concrete crew, they'll walk it to the bottom almost 100% of the time.
I am thinking, that with the mats and chairs to hold it up, I might be able to keep it at least in the lower 1/3 of the pour, inspite of the subs best efforts to walk it down.
I have never used them before, so if you or anyone has, tell what you think.
Dave
I have never used them before, so if you or anyone has, tell what you think.
No problem here. But I was out in the mud with everybody else. Don't know about chairs, doesn't sound so good unless you have a forest of them. We simply hooked the ww with a rake. When the mud was dumped, lifted. Worked fine. Even rolled ww, which is much more difficult. The rake guy(s) needs to be careful. Walking on the ww after it's in the mud was OK. Didn't appreciatively move. We pour stiff. I get complaints about that, and good slabs.PAHS Designer/Builder- Bury it!
I have poured thousnds of sq. ft. of flat work with ww mesh in rolls with an experienced crew with no problems. Like you , we just hook the wire with the come-a-long and hold it up as the concrete is poured. Everyone on the crew knew how, what, and when to do things, but that was all commercial construction years ago.
I have watched a few residential guys in the last few years, and I haven't seen one in eight that has a clue. Unfortunately, I can't raise a crew of experienced people to do this myself. I'll have to draw from the best for the $$ residential guys in this area. All I want them to do is place and finish. I'll do all the prep work to assure myself of quality control right up to the pour.
If there is a way to bulletproof any part of that (especially the ww placement) I want to use it. With PEX in the slab for RHF, I don't want to take any chances on having it screwed up. Still looking for a sub that has done a RFH slab, but haven't found one yet. A lot of them want to "try it" on my dime. That is scarey.
Appreciate your post.
Dave
Dave, you have immensely more experience than I do. Slabs are a real problem for me too. I'm not all that good and don't have a crew. The one time I wanted a really flat slab, here in the house, which was intended to by my future furniture shop, I hired the best in the area.
He came with his rake guy, screeded all by himself. I couldn't wait to see. Turns out if you water the hell out of it, mud self-levels. The added salt made it set up fast enough to finish. You know the rest, cracks everywhere. So much for the "best". He ain't coming back.
What I get with whatever labor I can scrounge isn't as flat, but has minimal or no cracks. I have acquired vibratory screeds to eliminate a lot of the labor. That's for the next slab, which I'm not looking forward to, but haven't found anybody here I want to hire. My client house required 2 slabs. Fortunately I was responsible for neither.
I'm better than the guy who did them, but that ain't saying much. I can direct the pour, do some of the work, usually screeding, and at the same time make sure that the other parts are done as well as the labor talent permits. Any rake guy on my pour will do the right thing, even if he doesn't have experience. It's too important to screw up. Attitude is the main thing, then direction.
You have a problem. How about foregoing ww and hoping for the best with fiber? I don't deal with radiant heat, makes no sense with passive annual heat storage. So I'm thinking for you, pour a slab, however flat, and top it with your applied tubes and a small stone mix which would be easier to ensure flatness. Sounds convoluted to do 2 pours, but it'll work. A friend had machine problems placing the concrete in his shop, leaving it rough. A top coat solved that. I'm not sure what it was, but your readymix plant would know.
Wish I could be more help. Louisville isn't exactly around the corner. And as I said, I'm not that great. Got a vibratory screed you can borrow, long as you don't want delivery. <G> I've also got a pallet of 5' wide chairs, I think originally for bridge work, that'd probably do you, but it's here.
Good luck. PAHS Designer/Builder- Bury it!
Have you ever used the ww mats for slab
I never have, but I've used concrete subs who have. It has typically been a difficult experience. Usually, the consulting engineer got to be the "bad guy," what with requiring rust & scale removal, and good chairs.
The best results I've seen have been in floor slabs over corrogated metal deck--commercial work, in other words. The best jobs included extensive control joints, too; but commercial work is usually 100% covered too. Out of sight = out of mind.
Was almost funny, I was pulling out city codes for a town south of here, and their minimum was either 6x6 6/6 (rust & scale-free) or #3 at 18" O.C.E.W.Occupational hazard of my occupation not being around (sorry Bubba)
Moltenmetal, I used to live on a lake and had to put a driveway in. The drive was going over some very soggy black dirt. I was advised to dig out the black dirt at least 12'' deep but i didn't want to because I was afraid that I'd kill too many tree roots. We were going right through some very mature trees. The stone guy advised me to use a swamp mat. I agreed and he put the mat down and then a layer of stone. It held up very well, despite the fact that we were sometimes under water on the drive.
I don't know what the name of the product was but any road builder would know what I'm talking about.
blue
Swamp mat, eh? Hmm- any road builders out there? My clay's not quite as nasty as Blue's black dirt, and there's no standing water, but it's still pretty soggy.
May I suggest you look in the latest FHB magazine (Apr/May), page 110 (+/-), as I recall. Types of geo-textiles was one of the subjects covered in the "What's the difference?" section. There are three choices listed, with the first two being a woven and a non-woven fabric. The third was a 1" rigid grid formed of some type of plastic. If I remember correctly, the text stated that the grid dug in like golf cleats and would turn a muddy area into a very stable base, on which a patio could be constructed. Good luck! -Rick
Last year I completed the foundation and floor slab for my building in Central Ontario. Canada. ICF frost walls, 7" reinforced concrete floor slab with an 800 ft2 area of RFH.
Made concrete cubes 2.5" on an edge with an embedded wire to tie my 10m rebar to. Used 9" OC for spacing of rebar. Set cubes on a 10 mil. poly slip sheet over 2" of Dow Corning HI 60 Extruded polystyrene insulation. Used no aggregate fill, only existing sand base damp compacted with a 24" X 36" Diesel Plate compactor in 6" lifts. Requested site added water reducer (super plasticizer) added to 6% air entrained type 1 4500PSI concrete with 3/4" limestone. Aside from some plastic shrinkage cracking I am quite pleased with the result. Cubes were placed approx. 24" OC and allowed concrete placing crew to walk on rebar without trampling it below its intended depth.(My depth was set to give me 2.5" of rebar cover)
Some notes on what I would do to improve my next effort:1. Demand better vibration in the ICF frost walls. (I've heard that a cheap Recip. saw with no blade installed can vibrate the outside of forms gently enough to consolidate without segregating, might be worth a try!) 2. Cut contraction joints ASAP in floor to 1/4 depth of slab EXCEPT over the radiant tubing. Try for square panels no more than 10ft on a side. I would use a preformed plastic joint to form joints within the tubing field to be sure not to cut into tubing with the diamond saw. (I poured in 32C windy weather in July and saw cut within 4 hrs of set and still had some errant shrinkage cracks despite 60 days of ponded wet curing.) 3. use canned urethane foam to seal ICF to footing, any loss of cement paste causes stone to be left dry and causes honeycombing within frost wall.
A suggestion for your design: since you are isolating your floor slab from foundation, use a urethane rubber caulking compound NO MORE THAN 1/4" deep to seal the top of your isolation joints (place a foamed type of backer rod to provide correct caulking depth.) Cyclical, seasonal opening and closing of an unsealead joint can allow dirt entry and joint ratcheting to spread your foundation walls away from your floor slab a suprising amount in not too many years. (How bad does 1.5" over a 10 yr. time span sound? I've seen it in my present attached garage house!) The caulking bead must be quite thin so it can stretch without tearing; go too deep, the caulking bead gets too strong and separates from the concrete. I pressure washed inside my contraction joints to insure good bond with the sealant.
I wanted an extremely flat floor and so I had my concrete finisher use a Laser guided screed and a heavy drive-on type power trowel. Finish as late as you can in the setting process to avoid sucking fines to the surface and resist adding water which increases water to cement ratio and degrades concrete strength. Consider painting with a 2 part epoxy over an acid etched surface damp cured at least 28 days and then allowed to dry out so that a 2 ft square of clear poly duct taped to the floor shows no sign of condensation after being down for 1 week. (Any moisture left in the concrete causes a vapor pressure that will lift any coating in time, do it right, do it once, do it to last for ever!)
I didn't improve my soil bearing with gravel thinking that wheeled traffic would eventually drive the stone into the sand anyway. On clay such as yours,wetting and drying of the subase are probably unavoidable with changing seasons. Accept that your floor will rise and fall, try to make it strong enough so that when cracks happen, they can't open, (small dia., closely spaced rebar is better than large dia. more widely spaced here) and can't differentially settle on either side of the crack. (All the cracks I've got are less than 0.01" wide and the floor is smooth to roll over.) You might want to detail your door thresholds with an embedded steel angle to provide edge strength to your concrete at the point where any wheel loads initially contact the floor, I placed mine down on a 2% slope from the top floor surface to prevent water from freezing my overhead doors to the floor when the weather gets nasty! By the way, I used rebar AND ww fabric for my reinforcement, the rebar seems easier for me to keep flat and doesn't bend under the feet of the placing crew. I also considered synthetic fiber reinforcement added to the mix but believe steel to be better for ultimate strength, the fiber is supposed to help with plastic shrinkage cracking only, little use after the concrete is cured.
Edited 5/26/2005 11:10 am ET by STAINLESS
Thank you for a most informative post. I've decided on 10M bar 12" on centre. Might buy the plastic chairs, might make concrete ones like yours- haven't decided yet. Good advice on the caulking- think you have the physics worked out pretty well.
Wish me luck!