"Don't you love DIY'ers!

They jump us for saving them a ton of money, because it isn't what they want to hear."

Who did I jump? I asked a lot of relevent questions, maybe you're not use to that from a "DIYer"
I have laid probably 25,000 sq ft of oak and refinished another 75,000, never ONE call back. I have receipts so far this year totaling $700,000 in General Contracting and if I ever put tar mastic down on an interior space I would be laughed/run right out of this town.....probably have to go work in Texas.

And this is the one that is going to bite you!!! You need to go to Vegas with the odds your rolling.


Get out your NWFA or NOFMA Manual and reread the section about subfloors
and especially the part about sleepers. Then when you get laughed at, you can show them the specification, and laugh back at them for their lack of knowledge on the subject.

what's your advice then? You think tear up the ply and plastic would work? I have no problem going backwards at this point. It would REALLY suck later.

What did you know about the garage slab? It might be fine, but that is not the sort of thing i would want to leave to blind faith.

Here is the deal. If there is any appreciable moisture content in that slab, the radiant heat is going to make things happen. The main thing is that moisture will be driven to the friendliest place it can find while that system is running. That means the water above will be driven up and the water below will be driven down. Water goes to cold, not to hot.(that is why water condenses on your milkshake cup) While the floor is hot, your problem will be a lack of water instead on an abundace thereof.

Here is the cool part; as soon as you crank up the AC, that whole dynamic stays in place, but the factors are reversed. What does cold air do? It falls. This means that a head high thermostat reading 76 will make a floor that is much colder than 76. If that floor reaches a temp lower than the slab, water will react accordingly. Now if you have plastic draped over all those sleepers, the phenom will still happen, but the relative humidity under that plastic will reach an equillibrium with the slab at some point. As soon as that happens, vapor transmission is over. The whole engine simply shuts down. Without that plastic,however, the water always has a place to go and the phenom continues until the slab, the sleepers, the plywood and the bamboo is good and bone dry. That may happen someday, but your bamboo will be screwed long before it does.

I really dig this subject. Lets keep talking.

now that's the physics I was looking for!!! awesome explanation. The slab was poured 19 years ago. I am turning this old garage into a family room and I built a new 3 car garage about twenty feet away. All the moisture from the roof is collected in gutters and then into rain barrells and grade slopes away around the perimeter.

I did nothing to the slab whatsoever. I redheaded/liquid nails 2x4s flat and then shot rippers down to the 2x4s, then glued/screwed 3/4 t&g. Top of CDX is level with existing slab which has ceramic tile throughout the rest of the house; therefore top of my flooring will come real close to top of tile.

thanks bro.....

I just noticed that no one has mentioned the fact that solid over radiant is a really bad idea.

what about venting the space I created?

I would not bother. It will let in as much as it lets out.(if you are lucky) heehee I am speaking of passive excange, of course. Forced ventilation can be great, but damifiknow how you could do it at this point. You have created a series of independent airspaces. Add to this the the fact that any venting will naturally lead to a huge BTU loss, and it becomes worse than doing nothing.

that's what I figured....so I guess it's pull off the CDX and plastic it?

what moisture content is OK on the concrete for the gluedown?
what moisture content reading is ok on the ply? and the bamboo should be acclimated for a week or so?

Not only that but a bamboo. The more I reread the posts, I realised this had/has failure written all over it.

I can get engineered.

what are all the other issues you see as failures floorguy?

If you drape the sleepers with 10 mil, it does not matter what the VE(vapor emission) rate of the slab is. It becomes a moot issue. You still have the topside stuff to consider, though. Solid product sitting atop 90 degree coils is gonna shrink like the dickens. Wood does not make decisions. It simply responds to environmental conditions. There is a good reason everyone in the wood biz says you can't do solid over radiant. Radiant heat is like a friggen kiln, man. It will drive every bit of moisture out of solid product.

Then again, there is the plasticizer migration deal to worry about. Polyethelene is bad to break down in the presence of a heat source. Or was that UV? I forget. hoho

The supreme bitch in all this is that you know nothing about that slab. For all you know it is bone dry. Considering it is 20 years old, it is a pretty safe bet that there is no vapor barrier under the garage slab. I think it is also safe to say it was not poured over sand. I wish you and I could have had this discussion when it was just a garage. This Sherlock Holmes crap would have never been necessary.

I have a small section of glue down on the old slab, that's what I was referring to with the moisture reading

I have a friend here who installed a whole house with engineered bamboo over radiant a year and a half ago and it looks fine. His actually rests on the kitec. This will be 2"-4" above.

ok so 8 man hours later, 352 sq.ft. of T&G CDX has been removed from the rippers; thank god we screwed it! As it was glued the CDX was wasted, but the rippers were installed BOMBER so they are good to go. The rippers have been scraped clean of glue and I have a 20'x100' roll of 6 mil plastic that will cover the floor with no laps. 11 brand new sheets of CDX wait in the drive way to be installed manana. Any other advice before I cover the slab again?

Thanks to my bros Chuck and Tex for potentially SAVING MY ASS here.....if our paths ever cross I will be buying the rounds, all night long.