Building new countertop question


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Old 12-31-06, 07:04 AM
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Building new countertop question

I'm installing a countertop and have a problem with the plywood. I'm using 2 sheets of 3/4" plywood and the top sheet has a gap by 1/4" from the bottom sheet. This sheet is in between two columns and might be too long and hence the bowing. I can push it down to close the gap and screw it together but i'm concened that this may not hold long term. Otherwise, i'll have to take apart the columns to fix it.

I had someone else put the columns up and they didnt realize the plywood wasnt screwed together yet....

A second question about this project...the two layers of plywood are not perfectly aligned and the edge isnt lined up flat by 1/4 in or so. does this need to be flat for the backer material?
Thanks!
 
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Old 12-31-06, 09:23 AM
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Expansion gap should have been left on ends between plywood and columns to accommodate any expansion in wood. Plywood pieces should have been cut the same size and even on all edges.
 
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Old 01-01-07, 04:22 AM
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IMHO(and those in the business), plywood is not a good substrate for a countertop, industrial grade particle board is a better choice. Plywood expands/contracts and warps considerably more the particle board.
 
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Old 01-01-07, 06:15 AM
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I agree 100% with Just Bill, that industrial (particle) board is the material to use for countertops. And yes, the front edge of the countertop should be perfectly flush.
 
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Old 01-01-07, 12:14 PM
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Sounds like I need to start over! Didnt think about the expansion part. One idea i thought of is to slice the board down the middle, which would add the width of the kerf, but this probably wouldnt be enough.

As far as particle board, doesnt that swell if it gets wet? I'm using exterior grade plywood.
 
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Old 01-01-07, 12:16 PM
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forgot to mention...this would be for granite tile countertop, not laminate.
 
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Old 01-02-07, 02:04 PM
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Plywood is the way to go if you'll be using granite tile. Particle board should not be used in a tile installation. Remove the second sheet of plywood and trim it to the proper size. You'll want the counter top to be as solid as possible, as any movement could result in failure. Screw the two sheets of plywood together every 8" in the field and every 6" around the edges. Use deck screws for this. Use 1/4" cement backer board over the plywood, bedded in unmodified thinset and screwed to the plywood (same screw pattern as the plywood). Use a 1/4" notched trowel for the thinset.
 
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Old 01-02-07, 08:30 PM
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Wow...you answered many of my questions i never got around to asking! thanks!
 
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Old 01-03-07, 04:00 AM
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What johnny said is good, and make sure there is support at each cabinet wall. Hardibacker is better than duroc in this case. It will stop any water that might get thru the grout joints, duroc is pourous. Particle board is the substrate of choice for laminates, and yes it does have problems when it gets wet. That is why proper caulking around sinks is critical.
 
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Old 01-03-07, 09:28 AM
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Neither Hardibacker, nor durock are waterproof, they will both absorb and allow water to pass through them. If you want to waterproof the substrate, there are other ways to do that, but its not at all necessary.
 
 

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