quartz/stone counter undelayment thickness?

14 years ago

I was talking to the kitchen countertop shop owner, not the fabricator. They told me to put 5/8" plywood as the underlayment to install 2cm quartze on top, doubled up for the edge. I always thought plywood is instlled by the fabricator, but apparently not?

I do more thinking, 2CM is 0.7874 inches. So it's actually over 3/4" a little.

next, I think lowe's 3/4" plywood is actually a little less than 3/4", so I think you would never see the plywood even if 3/4" ply is used as the underlayment..

5/8" plywood might have the stone rubbing my drawer doors.

I am asking because I bought my 3/4" ply long ago thinking that is the thickness I need, can I still use that plywood?

Featured Answer

azstoneconsulting

14 years ago

use 5/8" ACX grade

You could use the 3/4" you have IF you were not using any glue to
hold the stone down..

Usually - Some kind of glue is used to attach the stone to the subtop:

like this........

The glue will take up about 1/8 of an inch of space - RAISING the counters up
so that IF you were to use the 3/4" stuff - it would stick out on the bottom
and show from underneath when you looked at the bottom of the lamination:

like this........

Make sense????

Use the 5/8" ACX grade - been do'in it that way for the last 25 years - never a problem......

hth

kevin

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Comments (6)

PoorOwner
Original Author
14 years ago
I see, forgot about the glue.
You are clearly a company/fabricator..
Can you tell me if it is my responsibility (DIY install cabinet) to provide and fabricate the plywood? I wouldn't even know how deep to to cut the plywood front to back.
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azstoneconsulting
14 years ago
If you are having your countertops fabricated - just request that your
contractor include it in his bid - BUT - IF YOU are installing the cabinets -
they'd better be level - as in TOTALLY FLAT - using a 6 or 8 foot straight edge level to check 'em - otherwise
most guys will not do the install unless they are - either YOU fix 'em - or
I will - and that will cost you - regardless of who's doing it....

IF you are putting in your own subtops - use 5/8" ACX grade plywood -
screwed to the cabinet frames - cut flush with the face of the cabinet -
covering everything back to the walls.....

hth

kevin
julie94062
14 years ago
Our GC put the plywood on and I remember seeing 5/8" stamped on it. As Kevin said, ours was cut flush to the frame and screwed into the cabinets. We have full overlay drawers, so the granite ended up a bit past the drawers.

Not our granite, but this is how our edge looked, with the extra piece laminated underneath. You can see how it would sit on the plywood and extend over the edge. I don't know if this is the standard way it's done. We did have some plywood showing under the overhang where the barstools are. We stained it the same as the cabinets to blend in.
azstoneconsulting
14 years ago
Nice looking edge there Julie - Here in AZ - we call that a "Crescent" edge...

One thing to make sure of too - when the stone is installed over the subtops -
the wood should NEVER be cut tight to the stone.

THERE SHOULD BE A 1/4" GAP between the edge of the plywood and the
back edge of the lamination. No gap and you'll be sure to have fracturing
all along that line. I had to go look at a BEAUTIFUL kitchen project that
was all fractured up - because the plywood was too tight up against
the back edge of the lamination - shame too - it was a DOUBLE OGEE
edge detail - in Labrador Antique - the job was a total loss - all because
the knuckelhead cutting the sub tops was too lazy to cut the plywood a little
small - so there would have been a gap between the stone and the plywood...

but no.......

anyways.....

again

hth

kevin
PoorOwner
Original Author
14 years ago
Hi, thanks for the tips, in your picture, do you have 1/4" gap there? It looks very close the plywood and granite edge. Could be the angle of the picture, though.

The section I am working on is 93 inches just short of 8 feet. 30"+30"+30" cabs, The middle 30 is a 4" drawer that is like a desk you can sit in. I am a little worried about it, but then dishwashers are one big 24" bridge also. As least I have a tiny 4" high cab hanging in between. As long as no one sits on it, I hope. As far as flatness, I am doing my best. In your picture, did you not show us that you will spread the dabs of glue? Or is that how it goes on? hopefully if I get the whole surface flat within 1/16th inch or less, it will balance out any voids.

for the plywood do you put the "A" side up? I am not sure if I can find ACX in my local stores.. What's the importance of ACX, waterproof and less voids I am guessing?

Julie, thanks for the pic also, I also want that kind of edge.. I was told it's called baldwin edge.. many names for similar things I guess.