Red oak flooring over radiant in concrete. Actual experiences, not theories?

[Delawhere Jack]

I've got a milling client who is building an Appalachian style log home. The first floor is concrete slab with radiant pex tubing. He has a number of very nice red oak trees onsite that he would like to have milled for flooring.

I searched the forum and found a couple relevant threads, but most of it seemed to be theory and not practical experience. What I did gather seemed to confirm what I suspected, create a floating floor joined with mortise and floating tenons or T&G. Keep the boards narrow, and make sure that the flooring and the slab are properly dried before installation.

I'm wondering if anyone has actual first hand knowledge, and suggestions for installing hardwood flooring over radiant in concrete?

Thank you in advance.

JC

[POSTON WIDEHEAD]

This is a good thread Jack. I have always heard it takes a long time for concrete to fully cure. Whether this will have any bearing on the Oak floor...I don't know.
Should get a lot of info here.

[beenthere]

I don't have first hand knowledge of it being successful, but do have knowledge of a failure or two from concrete not being dried out.
At best, it is a risky practice and a gamble that everything will stay right over the long haul.

Being as the floor is heated, then likely less of a moisture problem from being too damp.
Good vapor barrier under the poured floor will likely be important. Then constant heat in the floor will help maintain low moisture content year in and year out.

[Delawhere Jack]

I don't have first hand knowledge of it being successful, but do have knowledge of a failure or two from concrete not being dried out.
At best, it is a risky practice and a gamble that everything will stay right over the long haul.

Being as the floor is heated, then likely less of a moisture problem from being too damp.
Good vapor barrier under the poured floor will likely be important. Then constant heat in the floor will help maintain low moisture content year in and year out.

One reference I found suggested running the heating system for an extended period to insure the concrete is dry. Maybe tape down a 2' x 2' piece of 20 mil poly on the concrete and check for condensation under it?

I will confirm that they placed a vapor barrier beneath the slab. The client is already aware that he will need one on top of the slab.

[Delawhere Jack]

This is a good thread Jack. I have always heard it takes a long time for concrete to fully cure. Whether this will have any bearing on the Oak floor...I don't know.
Should get a lot of info here.

Curing concrete should not give off much water. The water used in the concrete mix actually becomes part of the concrete, rather than evaporating. I imagine that some portion of the water remains unbound and dries out. It seems to me that this rather small portion of the water may cause a lot of problems if not accounted for.

[RavensWood]

I am not an expert and have not installed wood over concrete radiant but I have installed a few concrete radiant floors.
The concrete will probably take several months to dry fully - firing up the radiant heat at a low setting will help with the drying but it must be absolutely dry before laying the wood floor. I presume that you are in a fairly cold climate. If the slab is designed properly (6" coarse stone, vapour barrier and fully insulated under slab) then I can see no reason to put poly on top of the slab; but I would consult with an expert on that one. In general laminated/engineered wood flooring seems to be a better choice for radiant floors. For guidelines (both wood and engineered floors) refer to pages 207-210 of the following manual (UPONOR Complete Design Assistance Manual):
http://viewer.zmags.com/publication/9c73a879#/9c73a879/210
BTW, this is a great manual for all aspects of hydronic heat design. Hope this helps.

[Larry]

We kicked around the idea of radiant heat for a long time before deciding against it.  The biggest reason was the big temperature swings our climate has in winter.  With radiant heat under hardwood they recommend a slow temperature rise, low maximum temperature, and keeping it on all winter.

We did put in about 1,800 foot of hardwood on concrete.  Put poly down first than the concrete.  Gave it a few months to cure than 12" squares of poly taped down on the floor in each room to check for moisture.  I left the squares down for a couple of weeks.

I contracted out the flooring job to a couple of semi-retired installers.  They put down 6 mill poly on the concrete and covered with ¾" plywood.  They then shot about a zillion studs through the plywood and poly into the concrete.  Covered the plywood with tarpaper and laid standard T&G strip flooring.  Just a FYI they shot the studs with an air compressor that puts out 2,000 PSI and a special gun.

To lay the floor they brought it in and let acclimate for 6 weeks before laying it.  After laying it they insisted leaving it alone for two more months before sanding and finishing.  All of this was done with normal climate control on (AC as it was summer).  Finish was filler than two coats of gloss varnish followed by one coat of semi-gloss.

After two years this is the best hardwood floor we have ever had.  Absolutely no cracks anyplace, even in front of the wood stove.  I expect that may change as I haven't really run the stove hard.