My next job involves setting Travertine stone (18x18in, 9/16†thick) over a radiant floor heating system in new construction. The floor is a sandwich slab design consisting of a monolithic concrete slab covered with 5†thick insulation sheets (Owens Corning Formular¯ 250, 3 Layers: 2 x 2†topped with a 1†thick sheet). The Pex tubing is attached to the insulation sheets and covered with 3†of concrete (NOT Gypsum based). The top concrete layer is not a continuous layer; slab size is limited by interior walls and/or construction joints to 16’ square or less. The design temperature of the circulating fluid is 104 º F maximum.
I am planning to use a thinset mortar (3/8“ notch). What, if any, special precautions/preparations should I make? Do I need a decoupling membrane or will the top concrete layer be stable enough?
Any help is greatly appreciated!
<!—-><!—-> Thanks,<!—->
<!—->Bernhard <!—->
Replies
Greetings Bernd,
As a first time poster, Welcome to Breaktime
This post, in response to your question, will bump the thread through the 'recent discussion' listing again.
Perhaps it will catch someones attention that can help you with advice.
Cheers
'Nemo me impune lacesset'
No one will provoke me with impunity
With that much insulation below the heated slab, a full thickness slab to even out the heat, and water temperatures that low I wouldn't hesitate to simply thinset the travertine.
You mentioned that the heated slab is not continuous. Does that mean there are joints in the slab? I'd want a caulk joint in the tile over any joints in the concrete to prevent possible slab movement from cracking the tile or grout.
Cheers,
Don
Don,
Thanks for the 'heads up'.
I did have construction joints installed to divide the slab into 16' squares with the exception of the great room which has 12x16 squares.
Regards,
Bernhard
Hi Bernd,
First, is your slab sealed? Not is a good thing, as the thinset needs to bond to the concrete. I use Ditra as my upcoupling membrane. http://WWW.Schluter.com for info on the product. Be sure and turn the heat either off or very low, as the heat will dry out or "flash" the thinset and it won't work for you. I follow Schluter's recomendations and have not had any problems since using it. About 9+ yrs. They have a handbook you can download from their site also. Also they have a 800 number and a "real live person with a head full of knowledge" Hope this helps.
Jim
Jim, Why do you think an uncoupling membrane is needed for a simple heated slab? Hydronic heat is very popular in the colder climates of the rocky mountain region and I have yet to see a tile installation with an uncoupling membrane. On a heated slab I've also yet to see a tile failure using nothing more than a good quality thinset.
Don
Don,
Great question! Let me start with the fact that you are trying to "marry" or bond 3 different items to act as one. Concrete, thin or medium bed thinset, and of course tile or stone. Remember that everything in this world expands and contracts, and at different rates from each other. This said the volume of the mass or in this case concrete has a lot to due with the rate. Rule of thumb is concrete expands at approx. 1/16" per 10'. Control joint intervals and placements are specified by ANSI, ACI, and TCNA. The new placement specs. by TCNA states 20' to 25' interior. Interior tile work exposed to direct sunlight or moisture is 8' to 12' in each direction. So when a 20' section of slab dived by control joints will expand 1/4". ANSI 118.4 for latex-portland cement mortar has to meet a minimum shear strength in 48 HRS is 100 PSI. Thats not much needed to break the bond. 12 week test is 300 PSI. Antifracture and uncoupling membranes are designed to absorb the latteral movement, therby reliving the stress imposed by the concrete to the tile. All of the above specs. are the minimum recommendations for a particular installation. TCNA has the minimums recommended for radiant heat. The only ones not showing a uncoupling or crack isolation requirement is for electric. Don't know why other than it is intended for "comfort" on bare feet and not for main source of heat. temp is usually lower. I still use a membrane over elec. Check out the article in FHB Sept 2005 issue by Tom Meehan.
Hope this answers your question, and I appoligize for being long winded.
Jim
I'm still not sold on the requirement for a membrane on a concrete slab.
Tile in direct sunlight gains heat, but the concrete slab acts as a heatsink and greatly reduces any heat differential between the tile and slab.
Still, based on dozens of tile installations I've inspected or helped place, consisting of ceramic or stone tile over radiant heat I have yet to see broken tiles or even damaged grout from expansion differential between concrete slabs and the tile. The other tile setters that I've known also haven't seen problems or used a membrane over a full thickness slab.
To me, in this particular application, it seems like an unneccesary extra cost without a real benefit.
Cheers,
Don
Jim,
Thank you for the info!!
I did read the article in FHB and was considering using a membrane.
I like to ask you another question: The greatt room measures 24 x 36 and the entrance hall measures 16 x 46'. The remaining rooms are all about 16 x 16. Do you think it acceptable to use the membrane on the two large areas only and tile the rooms w/o membrane?
Also, any recommondations on sealers to use on this stone? I like to tile a walk-in shower with it also.
Thanks in advance,
Bernhard
Bernd,
I'll try and give you as direct an answer as I can without beating around the bush and using political double talk. Ready for the answer? It's----No. Sorry about that, It's a moment of weakness caused by lack of medication. I promise to take my meds just as soon as I remember to do it. Seriously, why take a chance on those two rooms when you are doing the others. Also, if they connect at doorways, there could be a height problem caused by the membrane not being there. I noticed the size of your stone, be sure and use a medium bed mortar. It designed for larger tiles like yours.
As far as the sealers go, I have been using 511 Impregnator from Miracle Sealants. Also Aquamix. Both are very reputable outfits. and thats all they due are sealants. At the present time I'm looking into Sure Seal Sealants and Dry Treat Sealants. Both were developed in Australia. Sure Seal came to the U.S. in '95'. Not sure about Drytreat. Drytreat is mainly for stone. Sure Seal sent me some samples of their grout & tile Sealer to try. I'll let you know how is performs.(along with the National sales Guru)
Either way, remember to do you research on the subject, and buy from manufactures that that is all they do!! I try and stay away from companies that do it all. "I don't make an appointment with my family doctor when my eyes need fixin." we need smilies on here!! Be prepared for sticker shock, as these sealers will cost in the vicinity of 170.00 to 180.00 per gal. There are $7.00 per quart sealers on the market, don't bother to read the label. The stuff is no good.
Take care
Jim
Jim,
Forgot to mention that the slab is not sealed.
Bernhard