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crash525 04-08-2013 10:15 PM

subfloor for tiling a kitchen
I plan on tiling my kitchen here shortly. Ive never done it before but im pretty confident in getting it done properly. My problem is that I have carpet with about 3/8in board under it then old hardwood floor then the original subfloor. I plan on tearing up all but the subfloor. How thick of board do I need to lay under the backer board to prevent the floors from flexing?

oh'mike 04-09-2013 05:44 AM

Usually 3/4" BC plywood---as little as 1/2" might be acceptable----

Of more concern is the floor joists---if you will let us know the size and unsupported length and spacing --someone will run a deflection chart for you.

crash525 04-09-2013 09:57 AM

My joist are 13-15 inches apart. The kitchen os 110'x166'. The sub floor looks to be about an inch thick and 7 1/4 wide going at a 45 degree angle across the joists. Ibwas thinking about doing 3/4 board over the subfloor for extra strenght. Im not sure if I would need anymore than that.

wkearney99 04-09-2013 05:54 PM

3/4 over the subfloor would likely be sufficient. But the question about deflection needs to know the size of the joists. What size lumber are they and how far do they span? Because if they're not large enough lumber and/or they're spanning too great a distance then the added weight of the tile could be a problem.

crash525 04-10-2013 11:01 AM

The joists are 7 1/2 x 1 1/2. They span a length of 110'' and are spaced every 14" or so inches through 160''. They seem sturdy to support the weight.

wkearney99 04-10-2013 01:18 PM

Right, so it's 2x8's of regular lumber on 14" centers. The John Brown Tile forums (a GREAT resource for tiling info) has a calculator for this sort of thing:

Which, according to the numbers you present, allows for ceramic tile, but perhaps not for heavier natural stone.

You might want to bring up the ideas in their forum for more info.

crash525 04-10-2013 02:07 PM

Thank you for using the John Bridge Forums Deflect-O-Lator :-)For joists that are SYP or Douglas Fir, in good condition, 7.25 inches tall, 1.5 inches wide, 14 inches on center, and 9 feet long between supports, the deflection calculated is 0.152 inches.This translates to a deflection of L / 709.Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Ceramic tile, Congratulations!

This is what I got. What does deflection of .152 inches mean and the deflection ratings for tile and stone. I was thinking about using sandstone for the tile but we were up in the air with it. Would ceramic be best or porcelain , slate, or some typer of other stone?

Goodyear 04-12-2013 12:12 PM

I have removed tile from my kitchen and i need to know how to get the remaining concrete off of the wood subfloor if possible for a smooth clean surface?

oh'mike 04-12-2013 05:13 PM


Originally Posted by Goodyear (Post 1157712)
I have removed tile from my kitchen and i need to know how to get the remaining concrete off of the wood subfloor if possible for a smooth clean surface?

Welcome to the forum--Please start a new thread in 'Flooring'--Mike---

crash525 04-12-2013 06:06 PM

Does adding thicker floor boards change the deflection rating or is it just based on the joists.

wkearney99 04-13-2013 06:33 AM

It's the joists, mainly. If you want more support it's common to attach another joist to the side of the exist ones, aka 'sistering' them. The idea being the new joist is glued and screwed to the old one and this improves the deflection. Bearing in mind you generally need to run the new ones the same span as the existing ones, supported on each end. This can be a non-trivial job if there's a lot of electrical or plumbing running through there. If it's not going to be simple to get new ones in there then you'd very likely want to contact a local structural engineer and get advice on how to best proceed.

crash525 04-13-2013 11:13 AM

Thanks for the help. I have a lot of plumbing, wires, and ducts running between then and through them.

wkearney99 04-13-2013 11:27 AM

Ok, so if you either have to deal with improving the floor deflection (by sistering the joists) or use a material that won't exceed it's deflection. You've got enough for ceramic. Was there a particular stone you were considering leading you to continue the thought process?

crash525 04-13-2013 11:55 AM

Thought about slate or sandstone but I dont want the upkeep of sealing it. Im going to look into putting sister joist in. I cant put a support beam in because itll be right in the middle of my basement. What would be the ideal deflection rating for ceramic tile because from what I understand im kind of close to the limit for tile.

crash525 04-13-2013 12:45 PM

I want to prevent the floor from sagging later on down the road if im going to do any tile.

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