Replies

1. 
   mike_guertin | Oct 24, 2004 03:43pm | #1

   Do you know what preparation was done beneath the slab before it was placed? If you don't know it may be worth cutting out a hole to see. Good practices for radiant slab prep is foam insulation board and plastic sheet. If the plastic sheet is there then you need no vapor retarder on top. If there isn't plastic but just foam with crushed stone or well drained gravel beneath then I'd skip the vapor retarder too and just apply a coat of latex sealer (not waterproofer but sealer). The sealer looks like skim milk and drys shiny. It has a perm rating and does allow moisture vapor to migrate through it but it slows the rate.

   Now the owners know that when the wood is applied above the slab that they are minimizing the efficiency of the radiant heat? The wood acts as an insulating layer. This changes the radient curve (flow/temp/output) and may require some adjustments at the manifold/injection mixing valve to raise the circulation tempreture so enough heat is emmited through the wood.

   If it were my house, I'd use Advantec OSB rather than plywood. 3/4" T&G. It lays flatter than plywood and holds nails well. The trick will be determining the nail penetration. You could also use DriCore panels. I've used them frequently in the past year when finishing basements - however I've not used them over radient floors. They may isolate the flooring further from the slab due to the dimple-mat backing. They are great for installing hardwoods to though. The interlocking panels float nice and flat on the slab and take nails well. I'll be installing a laminate floor over one in a week or two myself.

   For the best heat transmission - stain the concrete and call it a day. The radient will keep the floor nice and warm. Tile is good too. Make sure the slab is at least a month old and turn on the radient to dry the slab out (if it is new). Don't want to put the flooring over a green slab and then turn on the heat - that will drive the moisture out and wreak havoc with the flooring.

   Good luck,

   MG

1. 
   darius | Oct 24, 2004 04:08pm | #2

   Mike,

   Thanks for your reply.

   We poured the slab yesterday. We put about 3 inches of crushed 3/4 "stone, then Insul-tarp (which is closed cell foam and an aluminum reflective material with a protective poly coating all within three thin layers). I didn't put any foam insulation.

   Is it better to glue or not the OSB or CDX to the concrete?

   I called the tech support from DriCore and they do not recomend to use the panels over radiant heat.

   darius

1. 
   mike_guertin | Oct 25, 2004 09:48am | #3

   Interesting on the drycore reply from the company.

   I don't know if the glue would work long term. I suppose it depends on the adhesive. Ordinary construction adhesive probably wouldn't last but a trowel applied adhesive intended to bond materials to concrete probably would help with heat transfer.