Tiling over hardwood flooring

[alebrewer]

Hello

I am looking to tile my kitchen. It has 1926 Oak hardwood flooring which was covered with linoleum at some point. I have removed the linoleum and steamed and scraped 95% of the black mastic off the wood.

I would like to know if there is an acceptable way to tile over the hardwood flooring without removing it.

I have 2 ideas:

1) to secure flooring by screwing into joists and/or subfloor to minimize motion, coat with tile primer to cover black mastic, install uncoupling membrane and tile.

2) Secure flooring, install plywood floor over hardwood floor, install uncoupling membrane, and tile. I am ok with added height this will cause.

I have read that the accepted method is to remove the hardwood flooring and install plywood over subfloor. I would like to know if this can be avoided without high probability of failure. I have used the Deflecto Tool and floor structure is suitable for ceramic tile.

Thanks for any and all advice,

Alex

[cx]

Welcome, Alex.

No, there is no industry accepted method of tiling over what you've got.

If your subflooring is adequate, you could remove the hardwood, install a minimum of nominal half-inch plywood with no face of grade lower than C, then the tile substrate of choice and ceramic tile.

You may, of course, tile over anything you want in your house, eh? We can only tell you what the ceramic tile industry standards require and where the smart money will be betting.

My opinion; worth price charged.

[Kman]

What is the subfloor under the hardwood flooring?

[John Bridge]

In 1926 it's a safe bet the subfloor used was "ship lap" . . . one inch softwood boards.

I understand that removing the hardwood is a PITA, but it's really the way to go.

[jadnashua]

This is what Schluter says in their Ditra information sheet from Europe:
"Hardwood floors
In principle, ceramic coverings can be directly installed on sufficiently weight bearing, screw-fastened hardwood floors with tongue and groove connections. The wooden substrate should have balanced moisture levels before DITRA can be installed. It has proven beneficial to install an additional layer of chipboard or compressed wood panels. Uneven floor surfaces should be levelled with suitable measures beforehand."

While removing the hardwood is probably your best bet, prepping it per those instructions would mean installing LOTS of screws, which would be a major pain through oak, as would adding a layer more compatible on top. And, lots of oak floors didn't have T&G, so would be out.

[ss3964spd]

Interesting, Jim, that no mention is made of any water or oil based stains and protective top coats, which I'd guess could cause bonding issues.

[jadnashua]

Maybe the understated item about adding another layer on top is an implied...don't do it. The best alternative is to remove the hardwood for both stability and bond strength, though. The house I grew up in had oak floors, the original stuff was not T&G, while the newer stuff was, but in neither case were they well attached to the subflooring, and wouldn't have been a candidate for tile without removal, which is probably the OP's case, too.

[Dan Marvin]

I ran it by technical service and they don't recommend using Ditra directly over hardwood. Ideally you should remove the hardwood. If that is not doable, you can install 1/2" plywood or OSB over it and then use Ditra. Refer to page 7 in our Ditra Handbook, method D-SP-TS.

They also gave this disclaimer: Hardwood is very unstable and difficult to bond to, making it a poor substrate for tile. It will be very important, and perhaps challenging, to make sure that the plywood or OSB underlayment is properly fastened given the thickness of the assembly and nature of hardwood in general. If the plywood/OSB isn't fastened properly, there will be potential for vertical movement between the layers under load, which could lead to cracked grout and/or tiles.

[cx]

Dan, I believe y'all's method D-SP-TS indicates use over a sawn board subfloor, be it hardwood or softwood, whereas the OP here has hardwood flooring as a second layer over a board subfloor. I know Schluter has no published method for that application. You are officially sanctioning that installation method?

[Dan Marvin]

I'm officially sanctioning removing the hardwood. I'm offering an 'if you simply can't remove it, here's what you can try but no guarantees' to the added layer of plywood, lots of fasteners, a layer of Ditra, and a belief in the Almighty method.