Want To Install Ceramic/Porcelain And Insulate Basement Slab - Building & Construction - DIY Chatroom Home Improvement Forum

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Old 08-15-2012, 11:42 AM   #1
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Want to Install Ceramic/Porcelain and Insulate Basement Slab


I have scoured the internet up and down and I keep finding different answers to the question. This will be the first time I actually pose the question myself.

I am looking to re-finish my basement bathroom (house built in 1979). It is a raised bungalow, so only the lower 4ft of the basement is below grade. I live in Quebec, so I'm looking to protect the feet against the cold winters.

The bathroom is not used often enough to justify heated floors so I don't want to go that route.

So far I don't see any moisture problems on the slab I have exposed. The flooring I ripped out was 2x3 sleepers under ply under tile. None of the tiles and grout were in bad shape.

Obviously insulating below the slab is not an option at this point.

Now I have a couple of comments/questions

A) I was looking at DriCore tiles and I looked at the manufacturers website and it seems they don't recommend them for use below ceramic. I noticed on another thread that the company said that using the system is possible if you overlay cement board on the tile prior to tiling. Is this acceptable?

B) I like the idea that the DriCore tiles still provide an airspace for drainage/breathing, should moisture problems arise. I looked at a system like Delta FL, and again they make no mention of using it below ceramic tiles.

C) If I lay XPS directly on the slab would I need to pour self leveling concrete first? If moisture problems do arise, is the fact that there are no drainage channels in the XPS a cause for concern?

D) I read on another site that someone had issues with plywood laid over XPS. The tiles were cracking along the grout lines. It was later discovered that the cracks were due to the plywood joints sagging on the XPS. They had 2" XPS over a concrete slab floor, 3/4" plywood with screws going through the plywood into the slab, 1/4" Duroc, then 12" tile. If XPS on the slab is the route to take how should I avoid this? XPS+OSB+perpendicular OSB + thinset + concrete board? Is the second layer of OSB unnecessary? In the problem example above it was recommended that sleepers should have been used below the ply joints on top of the XPS. Besides the increase in height, wouldn't the usage of sleepers cause a PSI overload on the XPS given the reduced load bearing surface area and thereby introduce the possibility of more XPS flex?

E) Is Ditra really necessary in this situation? I know some of the TV guys are big on it (then again Ditra are sponsors) , but the stuff is pricey and will put a major dent on the budget.

F) Would my 2x4 partition walls sit on top of the subfloor, or should they be attached directly to the slab. I've gathered they should be on top of the subfloor, but I just want to confirm.

G) Should the XPS i have glued on my foundation wall sit on top of the sub floor XPS or should the wall XPS go down all the way to the slab. Again a drainage concern here.... Logic tells me that the wall XPS sits atop the slab XPS, but I can see how it would work the other way too.

I've spent hours researching and bought a couple of different books and I'm still not sure how to approach this seemingly simple dilemma. Thanks for your help.


illusion8055 is offline   Reply With Quote
Old 08-15-2012, 12:43 PM   #2
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If you go to the top of this page and do a key word search on these topics there has to be at least 1000 post on all these exact same questions.


joecaption is offline   Reply With Quote
Old 08-15-2012, 01:19 PM   #3
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Thanks for your input Joe. In my 28+ years of computer usage I've never realized there was a search button.....

That being said, there are pretty specific issues that I have mentioned for which I would appreciate useful feedback.

Last edited by illusion8055; 08-21-2012 at 08:21 AM.
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