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Unread 03-12-2012, 09:01 PM   #1
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Owner changes from pavers to tile on concrete, how to build up concrete surface?

I've got a dilemma with one of my customers. The situation is like this: I am building a pool house with an area of 475 s.f .under roof for a dining area. Originally this area was going to be done in brick pavers that were 1-1/2" thick. Around the perimeter of the foundation I installed rowlock bricks and poured a concrete pad inside the rowlocks about 1-3/4" offset below the rowlocks, to allow for 1/4' mortar and the pavers. The concrete finish was screeded and not smooth.

Now the homeowner has changed his mind and wants a high end porcelain tile instead. I have to raise this concrete surface up now (affordably) to within 1/2" of the top surface of the rowlocks. This is forcing me to place mortar or some other material over the concrete slab (poured two months ago, so hydration is not an issue) to a thickness of about 1" or a little more. My tile installer said he can use a different notched trowel and back butter the tiles to achieve a little more thickness in the adhesive but he absolutely could not use flexbond or any other latex-based mortar and achieve what I need .

I talked to my mason and he recommended the following: using type S mortar with a high sand/low water ratio and screeding it to the desired level and let it cure for at least a week; shrinkage should be almost eliminated with this mix and the highest, strongest bond should be achieved with the type S mortar. He is confident that this will work, but I am still worried about spalling and general adhesion problems.

I talked to my tile sales rep (also did installs for 20+ years) and he said it should work providing I use flexbond (which I always do anyway) and use RedGard over the mortar.

What do you people think here......will this work, will the mortar bed of 1" work over time and not crack or spall, and should I use RedGard over the mortar or would I be best using the flexbond directly on the mortar bed. I am concerned about the bonding/durability of the mortar base and the adhesion of the tile thinset on the mortar (esp. with the mortar being placed so close to the install) and moisture getting under the tile in the future and causing problems. I want no worries from the homeowner in the future and want to guarantee a good strong install that will last for years. TIA for your advice!
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Unread 03-12-2012, 09:18 PM   #2
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Look up deck mud in the Libbery. The recommended mix is regular portland (not type S) and sharp sand. the brickies just want to use type S for everything, but it's difficult to build a smooth bed with it. The mortar bed can be bonded to the concrete slab using a thin layer of modified thinset. Most tile guys worth the hire should be able to do this for you.
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Unread 03-12-2012, 09:24 PM   #3
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Welcome, Sam.

1. I don't see any indication in your User Profile of your geographic location.

2. Is this to be conditioned space, or an exterior installation?

3. Is this concrete you poured an actual structural SOG, or just a thin, un-reinforced place to set your pavers?

If all you can get for depth is one inch, and if your slab is structural in nature, I'd recommend a bonded deck mud (not Type S Mortar) bed as your most reasonable option.

Need answers to some of the questions before we can comment much further.

My opinion; worth price charged.

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