question about deflectolator, subfloor thickness, joist reinforcement

[m&m]

Hi,

I used the Deflectolator and got a result of L/473 - ceramic OK, stone NOT OK. My parameters were: unknown wood, good condition, 2x10 (nominal), 16 in. O.C. and 11.5 ft. span.

Does the deflectolator assume there's any additional support such as cross bracing (sorry, I don't know the technical term) between the joists? All I have is 1x6 strips nailed into the bottom of the joists, running in a perpendicular direction to the joists).

I want to install porcelain tile in my entryway. I got the following advice for subfloor: 2 layers of 5/8 plywood. Is this good advice? I want to avoid the situation where I've added unnecessary thickness and my tile still cracks because of joist deflection. Beefing up my joists would make me feel good but I've read about many techniques and I don't know how to pick one.

Thank you for the Deflectolator.

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[Brian in San Diego]

M&M,

Welcome to the forum! Ceramic and porcelain are considered the same in terms of deflection. Your deflection would indicate that your joist structure is fine for a porcelain tile installation. You don't have to have two layers of 5/8" plywood for a ceramic installation, but it wouldn't hurt if you have the room. What is there presently? You will need some type of underlayment either a membrane or a backerboard over the plywood to install the tile on.

Brian

[m&m]

Hi,

Thank you for the welcome and your reply.

What is there presently is nothing - just joists. What was there was 5/8 board running diagonally to the joists (no tongue and groove or no lapped joint) - then 1/2" hardwood floor. Incidentally, this is what the tile installation is going to meet in the living room so I would like to avoid any unnecessary height.

I was going to tile on the top layer of the 5/8 plywood. I've no experience with underlayment.

[Brian in San Diego]

You can't just lay tile on plywood...that's from one DIYer to another. It can be done, but it has to be done exactly right or it'll fail. I think I would install 3/4" plwood subfloor and a membrane like Ditra over the plywood. Then install your tile. On 16" o.c. joists Schluter says you can use 5/8" plywood (CC or better, Exposure 1) but that is the minimum. I would go with at least 23/32" (3/4" nominal).

Is m&m what you prefer to be called? If not go to the UserCP tab in the dark blue toolbar and edit your signature so that it appears at the bottom of every post.

Brian

[m&m]

Hi,

I like that plan. I'm going to comb through Schluter's website. I didn't come across their recommendation of 5/8 for 16 in O.C. I'm curious though about tiling over plywood now.

I appreciate your help.

Maria

[Brian in San Diego]

Maria,

I wouldn't get too curious...unless it's just for the reading. Here are a couple of the guidelines in the TCNA 2007 Handbook...F149-07, F150-07 and F155-07. My advice...Do not attempt this at home!

Brian