I’m building a post and beam house with radiant floor heat. We’re using pex embedded in colored colored/polished concrete finish floor over 1 1/8″ plywood and 2 x12’s on 1′ centers. Can I get away with a 2″ slab thickness? Appreciate any advice /anecdotes.
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Replies
no
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It doesn't matter who he is, just so long as he says something "we" like. RJW 1/07
Yes , check the american wood council joist span chart for a rough idea.Depends on the span but I have done this many times including my own home.
You forgot to post the clear span, proposed mix and even the expected loads, for starters.
I pour a few meters of concrete every once in a while and I wouldn't consider your plan.
Gabe
Thanks for all the feedback! The clear span is 15'. The specs in the plans called for 2" of concrete, but my specialty concrete sub says he won't guarantee good results with any less than 3" pea gravel/six sack mud with plasticizer and 6x6 re-wire. I'm the carpenter, and got t-boned by the architect and engineer on this one...I've poured floors with pex, done colored concrete work, used warmboard, but haven't done polished colored concrete floor with pex over wood frame. We were planning on 4' grid control joints. Until we found the engineer had done the calcs for gypcrete and the architect hadn't talked to any concrete subs about slab on wood framing. The first floor deck is already framed, double rim joists, 4x10 and 6x12 headers over basement doors and windows, an awesome stout frame. But not stout enough for 36#/sf concrete load, apparently. My mud man suggested we try to find a volcanic lightweight aggregate, he used it years back and tho difficult to finish it might cut the weight sufficiently. My client is bummed. Me too. A pox on white collar professionals! Anyone heard of lightweight finish grade concrete in a floor?
Add fiber mesh to your mix.
The clear span is 15'. (You would need to ensure that the max. distance center to center for your bridging or blocking doesn't exceed 4 ft.) The specs in the plans called for 2" of concrete, (The mix is more important than the thickness.) but my specialty concrete sub says he won't guarantee good results with any less than 3" pea gravel/six sack mud with plasticizer and 6x6 re-wire. (He won't be able to guarantee any more than if he were to use a half inch of concrete or 10 inches.)I'm the carpenter, and got t-boned by the architect and engineer on this one...I've poured floors with pex, done colored concrete work, used warmboard, but haven't done polished colored concrete floor with pex over wood frame. We were planning on 4' grid control joints. (You may want to reduce the size of the grid to a 3 ft. pattern) Until we found the engineer had done the calcs for gypcrete and the architect hadn't talked to any concrete subs about slab on wood framing. The first floor deck is already framed, double rim joists, 4x10 and 6x12 headers over basement doors and windows, an awesome stout frame. But not stout enough for 36#/sf concrete load, apparently. My mud man suggested we try to find a volcanic lightweight aggregate, he used it years back and tho difficult to finish it might cut the weight sufficiently. (Don't try any DIY experiments, go with a engineered mix, you have enough problems.) My client is bummed. Me too. A pox on white collar professionals! Anyone heard of lightweight finish grade concrete in a floor?
Use a structural poly fibre mix, do not waste your time with any 6 x 6 wire mesh. Talk to your local ready mix agent and get his or her input.
Gabe
Read Gabes advice twice, then send it back to the architect and let him PlAY with the engineer.SamT
Guys that don't do things correctly the first time.....then argue that they did nothing wrong.....if made to agree to fix the problem, rarely put the time and effort into truely doing it properly. they'll just look for the quickest fix to appease you and get their money. JDRHI <!----><!----> 84310.51
<<Read Gabes advice twice, then send it back to the architect and let him PlAY with the engineer.>>Agreed.The only thing I would add is I would talk with whoever is installing the radiant heat and see what they want in terms of coverage over the tubing and how they intend to fasten the tubing. Thin spots in the concrete can be trouble.
Catskinner's cut right to the heart of the matter. The most likely location for a crack in a 2" heated floor is the thin concrete at the curvilinear pattern the pex tubing makes embedded in the thin slab. I make it a fat inch thick over the pex. That's with the pex fastened directly to the 1 1/8" ply subfloor. The 6x6 re-wire is preferable because fiber reinforced concrete finishes out fuzzy. The wire mesh protects the pex and is a real sweet way to lay out the system grid, which resembles some kind of labrynth, and often is divided into several discrete zones with designated tubing lengths.The information I need is whether anyone has poured a 2" finished- concrete heated floor with embedded pex over a wood-framed substrate? Sorry to sound like a broken record. TIA
Just a comment on the 6-6-10-10 wire mesh .
I have only done one hydronic floor with PEX and it was not on wood but on a sand/gravel base on grade. The 6-6-10-10 mesh was placed under the PEX and used to tie the PEX into place. It would have virtually no impact on the concrete's ability to resist cracking in that location.
The piping will promote cracking because of several reasons. If it's on the bottom, it's the same as sawcutting lines throughout your floor. If it's in the middle of a thin slab, the difference in density/mass as the slab cures will cause hairline cracks over the tubing. As a slab cures it also shrinks, pulling inward.
What you will experience with your slab over wood framing is deflection, more than anything else. When the concrete is wet, the loads are more localized towards the center of any spans. Once the concrete is cured and hard, the dead loads are better distributed. Add the live loads (you walking on the freshly cured concrete and furniture being placed or moved over the spans) and the areas with the least support will crack first.
This also occurs in steel mezzanine floors. We always sawcut over the beams to control the cracking. The beams have much less deflection than the steel joists and typically snap over the beam from the increased deflection in the middle of the joists areas on both sides.
Fibres in concrete can be a problem to inexperienced finishers and stubborn "this is the way we always finish our concrete" ones as well. The trick is to set the power trowels blades at zero pitch to start so that you drive the fibers down before adding pitch and finishing the floor.
Gabe
<<The trick is to set the power trowels blades at zero pitch to start so that you drive the fibers down before adding pitch and finishing the floor.>>I'm still waiting on that book my older and wiser friend. <G>
Hi David,
A friend of mine recently sold his spray foam insulation company to a group that specializes in coatings for heavy equipment. So they not only bought the nuts and bolts but they also had to buy the employees to maintain the same degree of quality for the many clients serviced by this company.
The oldest and most experienced applicator was asked to help them prepare a proceedures manual. They gave him a small recording device to carry with him as he worked so that he could simply talk into it and they in turn would write down his method of applying insulation.
Three days later, he still hadn't spoken a word in it. He couldn't think of anything worthwhile to say that would be of any help to anyone else.
To him, everything he did was out of experience, feel and touch as he had done for years and years before. He figure anyone in the business would already know this stuff.
I know what I would do in any given situation, I just have trouble giving it enough value to put it to print.
Gabe
Great story.I think that happens to people who are genuinely accomplished -- it's second nature. I know I have to really think through teaching someone how to ride a motorcycle.OK, maybe I can come up with a list of questions. Might take me a while to make that many mistakes, though. <G>
I haven't been able to determine if all of the cheerleaders who are encouraging you to do this have actually ever done it with heat tubes in the floor!!??
I do this type of work frequently, although we use lightweight concrete. I can guarantee you that it will crack randomly as will regular concrete. The fact that you have heating and cooling cycles, tubes running in all directions in the concrete, and a wood subfloor make this a risky job. Your only hope for a pour like this is to break it down into smaller squares and hope that it works.
Would you cut joints into the floor?? That would be taking quite a chance.
Regular concrete will give you a dead load of close to 25#/ sq. ft. Add the furniture and people using the space and those 2x12s are going to get springy!
If you live in a bigger city, I'd talk with the concrete company and see if they know of anyone who has done this. This could possibly turn out to be a mess and you don't want to be the pioneer who is left holding the bag.
Yes, and it's a big no no. Lightweight concrete is not a finish floor surface that you can depend on. I tried an acid stain on one a while back and it was the first time that I almost got sued. The lady swore that it was normal concrete but that it got blanched during finishing. The slab took the color but was too soft to keep from scracthing and spalling during normal use. I asked her for records on the mix and sure enough it was a lightweight mix. You can tile over or put carpet on a lightweight slab but you can't use it as a finish surface.
You're talking about lightweight concrete/gypcrete over a heavy subfloor system, set on top of a slab? I'm not familiar with this system and wonder why you chose it?
Why not put the PEX in Warmboard (/Infloorboard) over a crawlspace and forget the concrete finish floor? Avoids cement floor issues (moisture, cracking,weight). Allows you to use all sorts of finish flooring (hardwood, tile, carpet) now & in the future. If you're building a stem wall anyway, I would think it saves you money because you're eliminating that slab and don't need such a robust joist system (2x12s 1' oc, wow). Plus, for a home, that floor system sounds like it will be awfully stiff and hard under foot. For dogs, maybe good; for babies, not so good.
For my own timberframe workshop, I plan to put PEX in a 4" slab on grade and make that the finished floor (low cost, strong under machinery, simple, lotta thermal mass). I'm leaning toward a 4'8" precast stemwall around the slab. The posts will be set on the stem wall. In some environments, avoiding the stem wall and setting posts right on the slab could work (but I wanna raise them off the ground more and contain the radiant slab). Disadvantages of this system: also hard under foot, no subfloor access for wiring runs.
>Why not put the PEX in Warmboard (/Infloorboard) over a crawlspace and forget the concrete finish floor?1) Doesn't work as well as a mud bed for tranferring heat.2) It's at LEAST twice the cost.3) You can stick any flooring over slab, too. You just have to do a sleeper system with wood.Aren't there special specs for doing a mud bed for radiant? I thought it was supposed to be 3" thick with wire mesh reinforcement.
I have never seen a floor as you describe not crack randomly. Usually it doesn't matter because you are just using it for a big radiator and covering it with something else. In your case, you want to see it.
I can't imagine this working no matter how you do it. You have a lot of things working against you. The concrete will expand and contract from the heat/cooling cycle and the 2x12s will move with the seasons.
I don't even see how you could add enough joints to control random cracking.
the floor going crack like crazy.It doesn't matter who he is, just so long as he says something "we" like. RJW 1/07
Cracks in stained concrete floors add character. ; ^ ) Mike
Trust in God, but row away from the rocks.
cracks in stain concrete floor shows poor workmanship.It doesn't matter who he is, just so long as he says something "we" like. RJW 1/07
2x 12's 1' o.c. spanning ____ ?
If you want concrete, why not use the standard bar joists, vpan and a standard reinforced slab?
w/ 2x12s I am guessing you are not going for the finished look below, so staple-up would work for radiant with a standard floor.
Go for it!
I've done a coupe with 1.5 " of mud as a finished floor, one had a couple small hairline cracks after 3 years( sold that place), with cut control joints that looked like 3 foot tiles. One slab cracked with in hours of pouring on a hot day with a bad mix? from the plant. (living in that one) Poured another 3.5 inches thick and that one looks good too. Poured one the other day 3 inches thick and it looks great! Get a good finisher and engineer the floor to hold the weight you don't want the floor to sag when pouring it. Concrete will crack! The goal is to get it to crack in the control joints and to keep the cracks small.
Get a good mix and an experienced crew and it'll be a great floor
Rob
Depends on just two things; your concrete man and your wallet.
I can do it. I'll even ballpark the cost of doing it right now; get three estimates from most any concrete sub, take the highest and multiply it by 5 - 10 times.
I'll garuntee a finely polished concrete surface, ready for staining, that will be significantly crack free for ten years.
SamT
So much of the success of a company is not determined by degrees but temperature. gb93433 83537.46
Our floor is a 1.5 inch slab poured on a plywood deck with pex radiant tubing.
Joists beefed up for the weight. We stained the concrete. Did all the work but the pour ourselves.
We love it. Warm floors on cold mornings, easy to clean. We did not do control joints and did get cracks and even some quite wide ones. I filled them with flexible concrete crack filler and then painted them to match the floor. I know where they are but most people will not notice. Would do it again!
Jill
You can do it, Lots of good advise on this thread. Three things I would make sure happen though. #1 put temp support under floor to cut down on initial flex. #2 use a good mesh system in the slab and get high strength 3500 concete with small aggragate. #3 use controll joints 3 ft sq. get a nice tight finish and cover with wet burlap for a week.
I've pour concrete over wood floors... alot... in old buildings it gives me 1 a level floor, 2 fire rating between floors, heck of a sound deadner ( deadner a word? if not i claim it) 3. i finish & stain it as the finished floor... and i pour it around 2" all the time... in top of 3lb felt with 4mil poly on top of that and fiber and # 10 6x6 wire (sheets not rolls...) lightweight 4000lb mix...
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