New install question

[rugman8]

I am planning on putting a new tile floor in the kitchen. I do grout cleaning and repair but this will be my first complete install. My house is an older pre-fab (1961). The floor was 3/4" chip board - ripped it up (boy that was fun!). Underneath that was the sub floor - only1/2" plywood. It butts up against 3/4 wood flooring. I want to have the tile even with the wood but it seems to me that I won't be able to get the floor stiff enough. Seems like I would have to use 1/4" underlay - Ditra - thinset and tile to equal the 3/4 " wood floor. That would leave too much bounce in the floor. Any ideas?
Also - I heard that you shouldn't use Haribacker with Ditra - true?

[cx]

Welcome back, rugman8. Please put a first name in a permanent signature line for us to use.

First thing you need to do is evaluate your joist structure to see if that needs some help, too. Use the Deflecto in the dark blue bar above to get you started on that.

Regardless your joist spacing the half-inch plywood is really useless as a subfloor. I'd recommend you remove it if you're serious about trying to keep your finished tile installation as low as possible.

My opinion; worth price charged.

[rugman8]

Thanks - updated my name - didn't realize it was not there. So if I rip up the sub - insrtall 3/4 ply I should be OK? Then I guess I could go ahead and and use 1/4" backer board - or would 1/4" ply and Ditra be better? Gotta keep it low budget as I have to also replace cabinets/elec also!

[rugman8]

I posted below about my 1/2" subfloor - I am trying to avoid removing it and repalcing with 3/4. Would it be a good idea to screw/glue sheets of 1/2" ply on top ofthe exsiting plywood to remove the bounce in the floor so I can install tiles? I am trying to avoid the floor being much higher than the adjacent wood floor. I plugged in and the deflection was OK with my joists.

[Brian in San Diego]

Please ask all your project questions on the same thread.

You can't count on 1/2" subfloor for much of anything. There isn't really enough thickness for screws to grab to add a second layer. I think it'd come out if it were in my house.

[bbcamp]

While I agee that 1/2" plywood isn't much to screw into, you can do it, but you must take a number of steps to assure the screws don't strip out.

1) Pre-drill and countersink all the necessary holes in each piece of new plywood. Considering the lack of bite, add more than the minimum number of screws. Spacing them on 6" centers is not excessive.

2) Clean off the splinters on the back side of the new piece. You want nothing to interfere with the glue.

3) Clean the old subfloor, then spread an even coat of a waterproof carpenter's glue. Titebond II is good. Use a squeege or a very small notched trowel.

4) Set the new piece in place and immediately start driving the fasteners. Start from the middle and work your way out in a spiral pattern. This forces any excess glue to the perimeter where you can clean it up. Since you predrilled and countersunk the holes, you don't need to over drive the screws, just get them snug.

[rugman8]

Looks like I will go ahead and add another 1/2" sheet of plywood with glue. How should I run the joints over the other sheets?

[Brian in San Diego]

Bob,

Read this article. Pretty much sums it all up.

Brian

[Bruce Johnson]

I deally you would run plywood past each joint to the second joist beyond, thereby positioning the joints equal distant from one another. If not possible at least stagger the the joint to the next joist. Never lay joints on top, this will telegraph the displacement directly to the tile. Even luan is laid ( yeah i use it for vinyl) staggered.

[Brian in San Diego]

Originally Posted by Bruce

Ideally you would run plywood past each joint to the second joist beyond, thereby positioning the joints equal distant from one another.

Gonna have to disagree with you on that point, Bruce. You do not want the edge of the underlayment landing on top of a joist. You want the edge of the top layer to be somewhere close to 1/4 of the span between joists which for 16" OC joists amounts to about four inches. It's all explained in the article I linked in my previous post.

Brian

[Bruce Johnson]

I'll stick with mine thank you.

[cx]

Bruce, it's desirable in tile applications that the second layer of subflooring not be attached with mechanical fasteners into the floor joists. While it's possible to almost comply with that by selecting fasteners of a perfect length that will fully penetrate the first subfloor layer but not much penetrate the joist, it's far easier - and more effective - to use the method described in the article BSD linked. Helps reduce tile installtion problems directly over the joists, a most common area of failure.


While perhaps not entirely intuitive, some of these industry standard procedures have been pretty well thought out and tested. That's why we like to recommend them to our visitors.