1/2 subfloor + 1/4 plywood underlayment + ditra?

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Old 01-06-14, 08:46 PM
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1/2 subfloor + 1/4 plywood underlayment + ditra?

Hi there,

I'm new to this site, and have been reading up on subfloors for the past few days.

I tore out tile over 1/4 ply, over stick down vinyl, over sheet vinyl, over MDF.
I 'm now down to the subfloor which is 1/2 ply.

I want to install 12" porcelain tile with ditra on our foyer. The problem is I only have enough room to install 1/4 ply over the existing subfloor.

The floor is 16 oc with a joist span of approx 65" with about half of it resting on the foundation. The joists are 2x6.

Do you think I'd be ok with screwing down the existing subfloor into the joists with deck screws (it was nailed down in 1973), then screw down 1/4 BC plywood over the subfloor (not into the joists though)?

The measurement I have from the top of the joist to the top of the hardwood transition is only 1-1/4, so I'm thinking 3/4 is the max thickness I can have down before the thinset/ditra/thinset/tile.

I was thinking of tearing out the subfloor and installing 3/4 advantech, (instead of having 1/4 ply over 40 year old 1/2 ply subfloor) but removing certain areas of the subfloor is going to be tricky since there is a baseboard heater installed. The entry door and front wall sit on the subfloor. This will be the biggest diy job I've ever done.

I was thinking it would be good to use 2" deck screws to screw into the joists and maybe 1.5" deck screws to screw the underlayment ply to the 1/2" subfloor.

Thanks for any info!
 
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Old 01-07-14, 04:08 AM
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Welcome to the forums!

A little out of my area of expertise but I'm not sure those joists and span will adequately support a tile floor. The guys that know for sure should be along later
 
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Old 01-07-14, 04:41 AM
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Welcome. The 1/2" alone won't be enough for tile. I know you are worried about a transition, but it will be inevitable. I would not jeopardize a good tile job on too flexible a subflooring.

You have been reading well, as all your techniques are textbook. You will need to add a minimum of 1/2" ply to your subflooring. 1/4" is not sufficient.
 
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Old 01-07-14, 07:17 AM
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Thanks a lot for the responses. I was afraid the 1/4 underlayment would not be enough.

If I go with 1/2 over the 1/2 subfloor I will have to make some more cuts in the tile to fit it around the base of the staircase and around the stair stringer trim. I've never done tile before so it should be interesting I'm very particular, so I will try my best at it.

Should I try and find tongue and groove 1/2 ply, or will square cut be ok?

Would you recommend ripping out the original 1/2 and going with a 3/4 advantech subfloor? I'm guessing no? It seems like 3/4 advantech might be stronger than the old subfloor + 1/2 ply. That would be more work I guess though.

installing 1/2 ply over the original 1/2 subfloor would be easier, as far as not having to cut out the old subfloor. I'm not sure how I'd be able to get at the areas closest to the walls with a circular saw.

I look forward to getting the subfloor all set this weekend.
 
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Old 01-07-14, 07:51 AM
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You would use a Toe Kick saw to cut out the floors near the walls and a sawsall to finish out the corners where the Toe Saw can not reach.
If it was my floor I'd just go over the whole floor with 3/4 T & G Advantech making sure the seams do not line up with the seams below.
I've seen 1/2 over 1/2 still flex and cause squeaks.
 
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Old 01-07-14, 08:17 AM
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So Joecaption1, when you say you'd use 3/4 advantech, would you go over the old 1/2 or rip it out?

There is only one area of the subfloor I would have to cut with a circular saw, the rest I can pry up and remove since nothing is sitting on them. This is a foyer to a split foyer ranch (aka raised ranch).

Thanks!
 
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Old 01-09-14, 07:46 PM
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Originally Posted by 70sfixer
So Joecaption1, when you say you'd use 3/4 advantech, would you go over the old 1/2 or rip it out?
Please read Joe's answer again.

Originally Posted by Joe
If it was my floor I'd just go over the whole floor with 3/4 T & G Advantech making sure the seams do not line up with the seams below.
When your house was built the subfloor system was 1/2" ply with 5/8" (probably) over it. The two layers together made up the subfloor. A single 1/2" alone isn't good enough regardless of the finish flooring you choose, with the exception of hardwood. BTW, 1/2 + 1/4" does NOT equal 3/4", strength wise.

How your floor was probably built: 1/2" + 3/4" hardwood =1 1/4". The adjoining rooms without hardwood: 1/2" + 5/8" underlayment + resilient flooring = 1 1/4".

But now you wanna install ceramic, so...... You need min. 5/8" ply over the 1/2", then either Ditra or 1/4" CBU, then the tiles. Ditra and standard tiles will add about 1/2", 1/4" CBU and tiles will add 3/4".

If in good condition and installed correctly the 2x6 joists should be fine.

Jaz
 
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Old 01-17-14, 12:23 PM
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Thank you for the information Jaz!
I mis-read Joe's answer the first time around.
 
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Old 01-17-14, 03:43 PM
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I will have to make some more cuts in the tile to fit it around the base of the staircase and around the stair stringer trim.
The easiest way to install tile is to under cut the moldings at door openings, as well as the door jambs themselves. That way you can slide the tile under the wood for a nice finished look. Those areas that you can not undercut get covered with shoe molding to hide your cuts. Odd cuts can be made with an angle grinder and a diamond blade, although that creates a lot of dust.
 
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