I am going to install a prefab granite counter (5 ft long) over two 1 ft. wide drawer stacks. This will leave a three foot area in the center to create a desk. I've read a lot online and some postings insist on plywood under the granite. Some insist plywood is not necessary. I am worried if I don't use plywood, the 3 ft unsupported section will crack. Also, some postings recommend using metal rods to further support granite. How does this work and where would I get the rods?
I thought this would be a simple DIY but now I'm confused. Any words of wisdom?
12" overhang is okay with a granite slab. 36" opening is too much. on the back side add a 2" X 4" angle iron. You can find these as stock items at a mason yard (used for headers in brick and stone work). On the front just use a 1/4" flat steel plate. rods... get threaded rods at electrical or plumbing stores. (not very strong)
Some of your confusion and varying recommendations may come from this... Granite slabs in the West are usually 2cm (3/4") and in the East 3cm (1 1/4"). With the 2cm having 1/2" plywood underneath for added strength and then having a overhanging edge applied that is about 1.5" thick that covers the plywood from view. The 3cm is laid without plywood directly on top of the cabinets and with no overhanging edge applied. Which way is better? Neither methinks, it's a matter of preference as to the appearance.
That said, depending on if 2cm or 3cm you need plywood if 2cm. And I would think with either 2cm with plywood or 3cm without, additional reinforcement would be recommended for a 3' span.
I would confer with the vendor where you are getting the pre-fab granite for their recommendation on how best to accomplish the installation.