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vbtalent 01-24-2020 06:05 AM

Tiling over dimensional lumber..
I'm doing a home renovation in my kitchen and the floor has dimensional lumber with a top layer of 1/4" plywood with a linoleum on that.

We are going to lay Large Format Tiles and I'd like to know what the suggestion would be for prepping the floor?? I do have some floor height restrictions so keeping it as low as possible would be ideal...

Can I use some Schluter DITRA on the linoleum, or should I pull the linoleum and the 1/4" floor and replace with 1/2" ply on top of the dimensional lumber, Schluter it and go??

Any input is welcome.



ss3964spd 01-24-2020 07:02 AM

Welcome, VB.


Originally Posted by vb
or should I pull the linoleum and the 1/4" floor and replace with 1/2" ply on top of the dimensional lumber, Schluter it and go??


But first you really ought to determine if your floor framing is strong enough to support a tile floor. Joist width, depth, on-center spacing, free span. Our handy-dandy Deflecto tool, located in the darker blue bar above, might tell you what you want to know once you enter your data points.

cx 01-24-2020 10:16 AM

Welcome back, VB. :)

What Dan said. And if you actually have dimension wood for a subfloor, it might help to add a geographic location to your User Profile so we know where on the Left Coast you might be.

vbtalent 01-24-2020 12:30 PM

2 x 10 joist 16" centers.. so weight isn't an issue.

Can I cheat using 1/4" ply and the Schluter in order to keep the height down?

cx 01-24-2020 12:34 PM

What is the unsupported span of those joists, VB? Weight is not the most important factor in the joist structure for a ceramic tile or stone installation, it's deflection you're concerned with.

And do we understand that you actually have dimension lumber as a subfloor over those 2x10 joists? Or perhaps you have boards instead?

vbtalent 01-24-2020 01:48 PM

1 x 8 decking on top of the 2x10's with 1/4" ply then lenolium.

Span is appx. 14'


speed51133 01-24-2020 01:57 PM

unsupported span is NOT the room size. It is the distance UNDER the room between joist supports. This MAY be the same distance as the room width, but often is not.

You can also bet that 1/4in plywood is not going to be recommended or useful for anything at all.

vbtalent 01-24-2020 02:22 PM

yup, 14' is the span...

speed51133 01-24-2020 02:28 PM

Thank you for using the John Bridge Forums Deflect-O-Lator :-)

For joists that are Unknown wood, but in good condition, 9.25 inches tall, 1.5 inches wide, 16 inches on center, and 14 feet long between supports, the deflection calculated is 0.578 inches.

This translates to a deflection of L / 290.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Sheet Vinyl or wood.

Doesn't look good. If I switch it to douglas fir (instead of unknown wood), it comes in at JUST enough for ceramic tile, but right on the cusp.Still no good for stone.

Not sure if you care, but I would not recommend tiling without beefing up the support. NO, more plywood will do nothing for deflection. You can add a pole/post and LVL header/beam in the middle of the 14ft span.

vbtalent 01-24-2020 02:34 PM

So that says there is too much deflection in 14' span with 2x10? Is that irrelevant of decking material, meaning if it was sheeted with 3/4" ply I assume that would change??

speed51133 01-24-2020 02:37 PM

Does not matter how much or how thick the plywood is.

Can you access your actual joists? Can you throw a ruler on them to verify the ACTUAL size? Maybe it is actually thicker than 2x10 nominal?? Look for any stamps of the wood as well. ALSO, look to see if ANY of the joists are cut for plumbing/hvac/electrical.

vbtalent 01-24-2020 04:14 PM

1 Attachment(s)
Looks a little different here unless I'm missing something?

ss3964spd 01-24-2020 04:59 PM

You have Alaska Cedar, VB?

RichVT 01-24-2020 05:00 PM

I've never seen or heard of cedar being used for floor joists. More likely to be Douglas Fir or Spruce/Pine/Fir.

vbtalent 01-24-2020 05:04 PM

Well... no but the result is about the same 460L @ 14' which is suitable for tile, no?


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