Plywood and backerbord sub-base


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Old 05-01-05, 05:13 AM
ShaunB
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Plywood and backerbord sub-base

I am building a 3/4" plywood and 1/2" backerboard sub-base for 16" x 16" countertop tiles. I have read in places to "re-enforce" with 4" wide strips of 3/4" plywood under the first layer of plywood.

Is this really necassary? I have clearance problems under a window and if I do this, it would make the countertop over 2" thick (2 Ply + 1/2" backerboard + thinset) Then more thinset and a 5/16" tile. For about 2.75" from top of cabinets to top of tile.

Any help? Thanks

Shaun
 
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Old 05-01-05, 07:12 AM
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One layer of 3/4" ply wont supply enough support under the tile if something heavy is [ploaced on the countertop. Dont look for the 1/2" cement board to offer any structural strength because it doesn't, its there to give a proper bond of the tile to the subsurface. You still need the cement board, its what is under it that needs to be beefed up. How about going with two layers of 1/2" BC grade ply, then a 1/4" cement board on top then the tile?
 
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Old 05-01-05, 04:07 PM
ShaunB
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Thanks for the info.

I think I am going to recess a piece of 3/4" ply inside the cabinet at the long un-supported runs, and then mount a piece on top of that flush at the top of the cabinets.

I get the 2 sheet durability with only 3/4" above cabinets that way.
 
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Old 05-02-05, 03:37 AM
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No you don't.
 
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Old 05-02-05, 05:44 AM
ShaunB
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I just need a little help understanding this, so on TOP of the cabinets, (1) full layer of 3/4" ply re-enforced with 3 to 4" wide strips of 3/4" ply. for a total of 1.5" above countertops. Correct? Then the backerboard then the tile?

By doing this it will raise my countertop height 2" from where it is now so I just want to fully understand this.
 
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Old 05-02-05, 06:50 AM
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I just don't see how the narrow strips are going to do anything but create extra work. The strips will flex considerably in my thinking. If you want to pursue this technique then use soild (hardwood) wood strips. I think you may be trying to re-invent the wheel here Shaun.

The reason for doubling the plywood is to provide some structural stability that isn't there with only one layer of ply. You could "cleate" 3/4" down inside the cabinets then drop-in a full piece of ply there. After that then add the top (full) layer of ply to that. The problem is, the open areas (cabinet frames/bases) that you are bridging with the plywood is far outside of tolerances that are used when manufacturing the plywood.
 
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Old 05-02-05, 10:13 AM
ShaunB
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Red face

Thanks for the info.

I just didn't realize the countertops would be close to 3" thick when done.

I will have to figure something out on the window.....
 
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Old 05-02-05, 11:44 AM
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Shaun if you do it like most would recommend doing it the finished countertops will be about two inches thick.
 
 

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