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Keith Carlson Ceramic 01-25-2009 12:51 PM

Portland based self leveling underlayment under travertine floors
I installed a Traverline floor over 3/4" plywood with United Self Leveling owned by Ash Groveas an underlayment. The sub-floor is in excess of L/720 and the directions for the installation of the leveling agent were followed. I am having random spider web cracks in a number of the 18x18 rhyme or reason in location of the 1400 s/f floor. The thin set we used was also made by united and the reason for this is a supposed lifetime warranty United offered. When I chopped out a couple tiles the self leveling split. All tiles were back burned and the thin set stuck to them . It looks like a thin area of the self leveling stuck to the thin set but broke away clean from the self leveling attached to the floor. We were carefull when installing the self leveling to make sure non of the polimers ( I probablly mispelled that) floated to the surface. We took a stone to the top of the floor, cleaned it and let it cure for a week. Is it suppose to split like that...Is that the reason some of the tiles are cracking. All other times when I chop of something I've installed it is a pain because it stuck so well. I am just trying to figure out what is wrong with the floor if anything. Are the spider web cracks in certain tiles just inherant in travertine and there is nothing that can be done to prevent it. Remember, if you tell me to use anti fracture membrane it only works for horizontal movement and not vertical...Keith

JazMan 01-25-2009 01:24 PM


I'm not so sure your "subfloor system" exceeds L720, how do you know? Let's start with the joists' type and size, spacing, species and grade if you know, and unsupported span. The tell us the subfloor sheet (s) etc. Does this SLC require a primer?


Keith Carlson Ceramic 01-25-2009 02:14 PM

I brought a stuctual engineer out with a set of the plans.

Keith Carlson Ceramic 01-25-2009 02:19 PM

I also used the primer made by USL and followed all installation instructions.

Bud Cline 01-25-2009 02:28 PM


I brought a stuctual engineer out with a set of the plans.

Are you saying this engineer has confirmed the deflection surpasses the minimum requirement?

I'll tell you what it sounds like to me. It sounds like a cohesive failure of the Self Levelling product. Was the SLC well within its expiration date when you installed it? All of those products have a shelf life. I have had issues with some of them being out of date and causing problems.

Without more details my guess is the SLC has failed internally and separated within its own thickness. Internal tensions have cause the product to assume a void-within, and that void is providing the deflection needed to cause the stone to fracture. The stone is still adequately bonded to the SLC but when walked on it is flexing enough to cause fissures in the stone without the stone literally coming apart.:)

The void would be a minimal gap but that's all that is required to fracture the stone tile.

The "spider-webbing" is the result of the natural makeup of the stone and is occurring at the weakest points within the stone.

Just a guess.:yes:

JazMan 01-25-2009 02:49 PM

I still wanna hear about the subfloor system, that is step #1. I agree with Bud that the SLC may have failed, but that is hard to tell from a distance.


Bud Cline 01-25-2009 03:47 PM


It's always a surprise to me when a general contractor of fine homes or an architect or a structural engineer doesn't consider the deflection requirements of a floor structure.

Just last year I had a guy that has been designing floor trusses (for builders) for years tell me he had never heard of the 1/720 requirement as it relates to stone floor tiles. He told me in all his years that this had never been an issue or a consideration. They never seem to ask about floor coverings.

So my point is...just because a "structural engineer" has "looked at" the job doesn't mean he knows anything about what is happening.:) The plans are of little use without the documented structural criteria. Anyone (almost) can look at a set of plans and agree that the structure "as-built" is in compliance with the plans - and it doesn't mean a thing.:)

mike costello 01-25-2009 03:58 PM

Did you use a primer before the self leveller ?

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