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-   -   Do I need to glue my backerboard down? (http://www.diychatroom.com/f5/do-i-need-glue-my-backerboard-down-29637/)

skipjack 10-09-2008 09:45 AM

Do I need to glue my backerboard down?
 
I'm getting to the point where I'm thinking about my kitchen tile job (just got some drywalling to do.. oh.. and electrical... and maybe some plumbing... okay.. maybe I'm not that close.)

I tore up the old vinyl and linoleum flooring to find some sort of black felt adhered to the plywood subfloor. My plan was to just screw down cement board over the top, tape the joints and be done. But, after perusing the internet.. I see people either doing this or using thinset or adhesive to stick the board down to the subfloor.

Is glue/thinset really necessary?

Termite 10-09-2008 10:09 AM

Yes, you must use thinset (not glue) to bed the backerboard down. You also immediately screw it down.

JazMan 10-09-2008 10:28 AM

Jack,

As the termite said, there is no choice, you MUST apply thinset under all CBU's and then fasten per directions.

Before you start though, how about describing how the entire subfloor system is built? Start with the joists' type, size, grade and species spacing and their unsupported span. Then tell us about the subfloor sheets etc.

Jaz

Tileworks 10-09-2008 01:33 PM

Yes, thinset is a requirement. Avoid using glue however.

The purpose is not to "stick" the backerboard down. A good non-modified dryset mortar will suffice for underlayment (which does not stick, but it is the screws that fasten the board down). The point is to fill any voids beneath the board so that it will no flex or delfect when walked on.

If you do not thinset your backer board, your tile shall likely crack.

- Bob

skipjack 10-09-2008 09:36 PM

Quote:

Before you start though, how about describing how the entire subfloor system is built? Start with the joists' type, size, grade and species spacing and their unsupported span. Then tell us about the subfloor sheets etc.
I was working on plumbing today and just gave the floor a cursory glance... but it seem to be 1/2" plywood on top of 1/2" sub flooring (planks, perhaps... I'll have to check the basement to be sure). The span is only about 8' 6" and the joists appear 16" on center.

The floor is quite flat and sturdy as it stands.

Right now, there's this felt underlayment stuff adhered to it and also a bajillion little tack type nails that were used to hold the linoleum seams in place. The linoleum was that multi-colored stuff.. it looked like Walt Disney threw up in my kitchen. I should really get a picture of it before it goes in the dumpster. lol

Anyway.. today, I was considering just removing the top layer of plywood and replacing it with 1/2" of backerboard... or would it be better to lay 1/4" plywood and then 1/4" backerboard?

Not that you guys don't know what you're talking about.. but, I was thumbing through a tiling book at my local warehouse home improvement store the other day and there wasn't mention of concrete board anywhere. They merely said to insure the subfloor was level and sturdy and then they said to seal the plywood with some sort of rolled-on sealant and then tile right over that. (!?!?)

JazMan 10-09-2008 10:32 PM

Check all that info closer, none of it sounds right. Remember the span of the joists, is not the size of the room, it is the span from one support to the other and of course measured from under the floor.

I won't go into detail until I know what you've got. I do know that you should NOT install and 1/4" plywood anywhere in a tile installation.

Jaz

Termite 10-09-2008 11:28 PM

Trust me, this isn't opinion, it is accepted industry practice. You have every right to doubt us because you don't know us, so I'd suggest spending half an hour on the John Bridge tile forum. The information you find there will confirm what you're being told here. :yes:

I'd also suggest going to an actual tile shop that specializes in tile. There are professional tile folks at that type of place that have the experience that the box store folks typically lack, and you can get good advice from them.


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