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instructor4688 05-04-2012 07:12 PM

Granite countertop underlayment
My granite installer wants two 3/4 inch thick pieces of wood glued together for under the granite. Is simple waferboard good or do I need a smoother surface such as particleboard? Thank you.

gregzoll 05-04-2012 07:27 PM

If you are using a Granite installer, they have done this hundreds if not thousands of times. They know what wood product to use, they will either tell you what to install, or they will do it before they bring the counter in off of the truck.

mrgins 05-04-2012 07:37 PM

Is this top going on kitchen cabinets? I've never heard of needing underlayment under it.

gregzoll 05-04-2012 07:47 PM

If it is a thinner slab, as some people are opting to go for, since it is cheaper than paying for the thicker slabs, they have to place at least 5/8" Exterior grade Plywood underneath it mrgins. The front of the slab has a edge, so that it appears that it is thicker, but in reality it is at most maybe 1 1/2" for the slab, but as thin as at least 1".

mrgins 05-04-2012 07:52 PM

could you also use 5/4 hard wood 12 or 16 oc?

gregzoll 05-04-2012 07:55 PM

It is just easier to use plywood, because you can get it in 4x8 sheets, same as chipboard.

havalife 05-04-2012 11:41 PM

Be sure to seal the underside of the board you use by the dishwasher, steam from the drying cycle of the d/w could cause the board to swell and crack the granite.

firsttimeremode 09-24-2012 12:06 PM

i definitely would not use particleboard, the second water touches it, it pretty much disintegrates. Im dealing with this right now with my floors. So, steam from a dishwasher or a leak under your sink would destroy the underlayment. Use plywood. like one of the posters said, 5/8 would probably work but if he told you 3/4, you better use 3/4. I was told that for my floor, to coat the underside with Thompson's Water Seal before i put it down, but im not sure if that would work for a countertop or not. Good luck.

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