question about mortar and hardibacker

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  #1  
Old 02-15-08, 07:25 AM
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question about mortar and hardibacker

I am all ready to put my backerboard down and have a few questions....maybe dumb questions...but questions none the less.

Ok...I put down the mortar and level it with my 1/4" groove trowel. Then i place the backerboard in the mortar. Do I just press it down with my hands or what? How do I ensure it is going to be flat when I am done?

When do I put the fasteners in? Do I do it right away or let the mortar set first?

How long should I wait before putting down the ceramic tile?

When all is said and done I am going to have a small gap..probably 1/8" between the backerboard and my corner shower base. Should I fill in the gap with something now or put grout in it when I am done with the tile?
 
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Old 02-15-08, 10:21 AM
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Screw the backerboard before the mortar sets. Wait 24 hours before laying tile. Don't use grout to seal between the backerboard and the shower pan. Use a quality silicone caulk.

Your backerboard should extend over the shower base flange as should the tile. Set the tile so that it is just above the base and then caulk that joint.
 
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Old 02-17-08, 12:55 PM
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Originally Posted by cwbuff View Post
Screw the backerboard before the mortar sets. Wait 24 hours before laying tile. Don't use grout to seal between the backerboard and the shower pan. Use a quality silicone caulk.

Your backerboard should extend over the shower base flange as should the tile. Set the tile so that it is just above the base and then caulk that joint.
thanks for responding but it really doesn't answer my main question.

My shower base is mortared to the floor and the subfloor and backer board run right up to the shower base. The base and wall unit was installed by a plumber (friend). I really need to know how to press down the backerboard so it will be flat. If i put too much pressure on it I assume it will move the mortar and take the shape of the subfloor which is not perfectly flat in a few spots.
 
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Old 02-17-08, 04:45 PM
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DC,

What made you think that installing backer board, or any sheet of anything was going to make your old subfloor flat? It will not. You need to fix the floor either first or after the backer is installed, depending on how much work it needs.

As for the fastening, you either use roofing nails or the proper backer screws made for the brand you have. You simply follow the directions from the board manufacturer.

Jaz
 
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Old 02-18-08, 07:29 AM
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Originally Posted by JazMan View Post
DC,

What made you think that installing backer board, or any sheet of anything was going to make your old subfloor flat? It will not. You need to fix the floor either first or after the backer is installed, depending on how much work it needs.

As for the fastening, you either use roofing nails or the proper backer screws made for the brand you have. You simply follow the directions from the board manufacturer.

Jaz
I was under the impression that the mortar was used to fill in slight imperfections in the subfloor for stability purposes.
 
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Old 02-18-08, 09:32 AM
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The cement board is mechanically fastened to the plywood subfloor with nails or screws that draw it down to the subfloor. It will contour to the original subfloor. The thinset under the board is merely there to fill any voids between the subfloor and the cement board. You can do any minor leveling/flattening required on top of the cement board using a cement based patching compound.
 
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Old 02-18-08, 10:46 AM
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Originally Posted by HeresJohnny View Post
The cement board is mechanically fastened to the plywood subfloor with nails or screws that draw it down to the subfloor. It will contour to the original subfloor. The thinset under the board is merely there to fill any voids between the subfloor and the cement board. You can do any minor leveling/flattening required on top of the cement board using a cement based patching compound.
Thanks for the reply.

I have two spots where the floor is not flat. I am talking maybe a 1/16" over a 8" span....nothing major at all. Can this just be taken care of when I place the tile in those spots?
 
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Old 02-18-08, 11:30 AM
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1/16" over 8' thats nothing.

You shouldnt even notice that after your done. Thats pretty darn flat.
 
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Old 02-18-08, 11:40 AM
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Thanks for your help.

I just want to make sure i don't mess this up

One more thing...roofing nails or screws? Pros or cons to either? Just seems like the nails would be easier to get flush w/o cracking the board.
 
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Old 02-18-08, 12:05 PM
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I like screws, but thats just my personal preference. Either or is fine. I think the screws hold better. If you are concerned about getting the heads flush with the boards, use the square drive screws. Sometime you have to back em out about and then sink em again but square drives wont strip out. Without rereading the whole thread, they make special screws for cement board. You'll find them in the big box stores by the cement board. Get the square drives.
 
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Old 02-18-08, 01:54 PM
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Originally Posted by HeresJohnny View Post
I like screws, but thats just my personal preference. Either or is fine. I think the screws hold better. If you are concerned about getting the heads flush with the boards, use the square drive screws. Sometime you have to back em out about and then sink em again but square drives wont strip out. Without rereading the whole thread, they make special screws for cement board. You'll find them in the big box stores by the cement board. Get the square drives.
I actually have those screws. I just wasn't sure about them that's all.....

Thanks again
 
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Old 02-18-08, 03:24 PM
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Alkali resistant coating, hi/lo double threaded, square drive, self-setting nibs, and you weren't sure about them??? Why's that?
 
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