Tile substrate problem

Old 08-22-16, 08:05 AM
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Join Date: Aug 2016
Location: Canada
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Tile substrate problem

I have a small mudroom in a rear addition to the house, it is approximately 10x12', which I want to tile using 6x6 or 8x8 terracotta style tiles.

I've stripped off the existing flooring and the structure is 2x8" (edit: 16" o.c.) spruce joists with an unsupported span of 8'8", with cross-bracing along the centre-line.
The subfloor is 3/4" spruce ply, it appears to be tongue and groove. Unfortunately this was laid incorrectly, parallel to the joists. However it was evidently fastened with glue and screws.
The floor is level for the most part with some 'peaking' along one of seams of the subfloor of about 3/16" that appears as though it could be sanded down if necessary.

From what I've read, my thinking is to install is to layer 1/2" ply on top of the existing floor surface, obviously perpendicular to the joists. This would be glued and stapled to the existing subfloor. Ditra on top of that.

I would be interested to hear if you all think this would work or if there are any better ideas.

Old 08-22-16, 09:47 AM
Join Date: May 2007
Location: USA
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Hi Roveet,

I agree with most of your plan, with the exception of the idea of glueing the new underlayment to the subfloor. Don't do that.

Of course you'll need to fix the subfloor before you install anything. The floor does NOT need to be level, but it must be flat. If the 3/16 is all "peak" and the floor is otherwise flat, you may be able to fix it. 3/16" is a lot to sand off, but if it's over a joist I think it'll be fine. Have you checked the floor for "flatness" yet? Use a long straight edge and let us know.

Once the floor is flat within specs, I think Ditra is the way to go.


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