I bought a piece of granite approx 40 inches by 40 inches and 3/4 inch thick and was just going to use it as a garden table. It is unfinished (polished on top but raw edges). I can place it on a three brick columns. However, should I worry about providing better support, i.e. a sheet of plywood cut to fit within one or two inches of the edge?

Another piece is 1-3/8 inch and I may use it as an island countertop in my kitchen. It is approx. 30 inches by 40 inches. Will a “normal” cabinet base unit be able to support this weight or should I install 3 or 4 2×4 legs?

Thanks,
Don

Hello Don,

3/4″ granite is fine for exterior use but do not put a plywood substrate because the plywood will swell after exposed to normal exterior moisture. This will make the substrate uneven and do more harm then good.

If you don’t dance or pound on it, the use of 3/4″ is no problem on three brick columns as you mentioned. If you think someone might sit on it, then you need to provide more support. For this you must use stainless steel angle 3/4″ wide x 3/4″ tall x 1/8″ thick, and make a frame which is 6″ less than the perimeter of the granite table. This is costly.

Regarding your second questions about 1 3/8″ granite, you do not need additional support because granite this thick is very strong. It also weighs about 20 pounds per square foot so although your cabinet can support it, just be sure to apply some basic Newton logic and make sure that it is properly anchored to the cabinet so that the weight doesn’t logically tip the granite over.

Best wishes,
Tom Cordova

Follow up:

Thanks for the answers to my support/weight questions. I do have two small follow-up questions. I am guessing that you are specifying stainless steel angles for rust/corrosion resistance but would wrought iron be acceptable? I’m thinking of just finding a table about the right size and placing this granite on top. The second minor question has to do with anchoring the kitchen island granite piece. Would you use, say, construction adhesive on battens to keep the piece from shifting. or?
Thanks again,
Don

Hello again Don,

If you put 1/16″ neoprene shims or 1/16″ thick plastic between the rod iron and the granite, that should be adequate for your personal situation and avoid the rust and oxidation transferring to the granite. I can’t answer the second question about the bonding material adequately because I would need a lot of details. I suggest using your best judgment.

“Liquid Nails” make a very good adhesive but you need to be sure it is the brand that says, “Made for stone”. Do not use the cheap stuff.

Best wishes,
Tom Cordova

This entry was posted on Monday, June 12th, 2006 at 1:25 pm and is filed under Answers to Granite Questions..., Installation Issues. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.