Preparing sub floor for tiles

Franky · 01-19-2009, 09:47 AM

Hi,

I am installing 1/2" porcelan tiles in my kitchen. The current sub floor consists of wood slats. The home is 40 yrs old (+/-). The slats are 3/4" x 8" and the are nailed to 2" x 8" joists. I have screwed them down to the joists as added security with 2" floor screws.

I have added a 5/8" plywood on top, screwed down at every 6" directly into the joists. I also added PL glue between the 5/8" and slats.

Do you think this is strong enough to receive the tiles or should I add another layer of ply (perhaps 1/4")?

Thanks in advance.

jaros bros. · 01-19-2009, 10:08 AM

You failed to give enough information. How far is the spacing between joists? How long is the span of the joists? I'm trying to figure out how much deflection you have.
I would also recommend using Ditra as a backer for your tile. It allows movement of the subfloor and is very easy to install, in fact you can tile over it immediately after installation.

Josh Jaros (Jaros Bros. Construction)

angus242 · 01-19-2009, 10:30 AM

Quote:

Originally Posted by Franky

Hi,

I am installing 1/2" porcelan tiles in my kitchen. The current sub floor consists of wood slats. The home is 40 yrs old (+/-). The slats are 3/4" x 8" and the are nailed to 2" x 8" joists. I have screwed them down to the joists as added security with 2" floor screws.

I have added a 5/8" plywood on top, screwed down at every 6" directly into the joists. I also added PL glue between the 5/8" and slats.

Do you think this is strong enough to receive the tiles or should I add another layer of ply (perhaps 1/4")?

Thanks in advance.

There are a few issues.
1) You were not supposed to screw the 5/8" plywood into the joists, just the planks.
2) You shouldn't have used the PL glue under the plywood. I assume the PL was a construction type adhesive?

While the subfloor seems to be a strong enough choice, you haven't supplied us with enough info about the joists to see if they are within an acceptable deflection ration. We need to know how far they are spaced (16 OC?) and what their longest unsupported span is. Also, if you can see them, do they look in good condition? I mean, someone didn't decided to turn them into swiss cheese running plumbing through them or anything, right?

That said, I'd recommend using Ditra at this point. FYI, 1/4 ply is too thin to use for this application.

Franky · 01-19-2009, 10:54 AM

More Info:

The joists are 12" apart. Yes the PL is construction adhesive. Why not screw the 5/8" into joists? The longest span is 10'. They are 2" x 8" wood joists.

thanks,

angus242 · 01-19-2009, 11:03 AM

Quote:

Originally Posted by Franky

More Info:

The joists are 12" apart. Yes the PL is construction adhesive. Why not screw the 5/8" into joists? The longest span is 10'. They are 2" x 8" wood joists.

thanks,

Based off the supplied joist info, that is acceptable for ceramic/porcelain tile.

You shouldn't screw the 5/8" ply to the joists because of expansion/contraction. The 2 different levels of wood will expand or contract and not always together. Also, using a construction adhesive under the 5/8" can create small voids which you don't want. Unless you completely laminate the 5/8" to the planks, screwing alone is the way to go.

Because of your situation, I definitely recommend Ditra as your tile underlayment.

Franky · 01-19-2009, 11:41 AM

Thanks again for the info. Just one more?? - Should I remove the 5/8" and apply 5/8" ditra instead? I only put one sheet in so far. I don't want to go too high and put ditra after the 5/8"; this would give me quite a lip from one room to the next.

All suggestions are very much appreciated - The wife has a Tupper Ware party on the 30th, and putting the screws to me (so to speak) to get the tiles in ASAP.

Frank

angus242 · 01-19-2009, 12:01 PM

Quote:

Originally Posted by Franky

Thanks again for the info. Just one more?? - Should I remove the 5/8" and apply 5/8" ditra instead? I only put one sheet in so far. I don't want to go too high and put ditra after the 5/8"; this would give me quite a lip from one room to the next.

All suggestions are very much appreciated - The wife has a Tupper Ware party on the 30th, and putting the screws to me (so to speak) to get the tiles in ASAP.

Frank

Since you've only done 1 sheet, I'd consider ripping it out, scraping the construction adhesive off and screw back down properly. I'd keep 5/8" ply (which should be exterior grade). Ditra is only 1/8" thick. You're other option if not using Ditra would be to use 1/4" cement backer board. So actually, using the Ditra is keeping overall floor height lower.

JazMan · 01-19-2009, 11:39 PM

Frank,

You posted this project this morning (the 19th), at another forum and the details are different from this thread.

In the newer post you say the tiles are natural stone, not porcelain. The span is 8 ft. not 10 ft. like here. No mention of gluing the underlayment. Which is correct? Please follow up with the correct info.

Jaz

Franky · 01-20-2009, 12:52 PM

Hi Jaz

I re-measured and the correct span is 10'. the 5/8" was glued, which I unlglued last night. luckily only one sheet. Originally I was told natural and procelain were the same - not sure bout this, but the tile is 1/2" natural stone - I checked again last night.

angus242 · 01-20-2009, 01:32 PM

Based off the info given, your joists do not meet the minimum required deflection ration for installing natural stone.

JazMan · 01-20-2009, 03:22 PM

Frank,

Do you know the grade and species of those joists? Did you measure the span from face-to-face of the two supports? Just to confirm, the joists' spacing is 12" from center to center right? How flat is the floor?

This is what I now assume. 2x8 joists of unknown grade and species. Spaced 12" o.c. Max. unsupported span is 10'. Subfloor is 3/4" x 8" planks with 5/8" underlayment fastened to the subfloor every 8" in the field and 6" at edges. Tile is a thicker than average porcelain tile of unknown size.

Jaz

Franky · 01-20-2009, 04:15 PM

OK,

I'm actually home now and have checked all the above info (PS Thanx for your patience). The kitchen is 12' wide with joists running in the width direction. Underneath is the bsmnt. The support wall (in the bsmnt) is 6 feet span, then at the next 6' is an I beam support. So the first 6' is supported by a 2" x 4" wall in the basment and this wall is made of vertical 2 x 4 supports at 16" oc.

I don't know the grade of the joists but they are exactly 1 5/8" x 7 5/8" which I have been told is 2x8? They appear to be a solid piece of wood. They are exactly 12" oc from face to face. The tile is 1/2" travertine.

I just got the Ditra and will finish the 5/8" instalation 2-nite. Man this stuff is $$$. I got the instructional video and the full-flex cement for the ditra. The only thing I am unsure of is this:

The video says to tile right over once the dirta is down and no need to let it cure b-4 tiling. The tile place I bought it from says to trowel a cote of thin set into the cavities of the top layer of ditra and then lay tiles?

Frank

JazMan · 01-20-2009, 05:16 PM

OK, The joists system should be stiff enough if this info is correct.

Be sure to gap the plywood sheets 1/8" and leave a good space around the perimeter. Tec's FullFlex is a good modified thinset for installing your Ditra. What will you be using to install the travertine? What size trowel do you have?

You spread the thinset with the flat side of the trowel to fill the squares and to get a good mechanical bond, then go back and trowel with the notched side to get the ridges. Be sure to apply more than enough thinset at this stage. Make the final stroke so the ridges go from left to right.

Jaz

Franky · 01-20-2009, 09:16 PM

OK, so there is no need to fill the cavities with thin set, let it dry, and then trowel for the tiles. I can do it all at one time?

JazMan · 01-20-2009, 11:28 PM

They told you to fill the squares only and let it dry? Yikes, they don't know what they're saying.

It's done in one step.

Jaz