"Joe AutoDrill" wrote in message
...
I need to glue two large pieces of granite together at the edge.

I will not need to see the bottom of either part so I want to make a large
overlapping "plate" to span the "crack" and hold the two pieces together.

The edge is about 30" in length and I figured an 18" square "patch" or
"plate" below glued to both sides would work. The material isn't thick
enough to use lag bolts and a plate.

...Thinking either construction adhesive or Gorilla Glue.

I'll put the plate on from below and press it up using bracing. I'll have
a lot of weight on top to keep the pressure constant overnight or longer.

I'm thinking of using an aluminum plate simply because it's easy for me to
get and easier to move around.

Any suggestions or thoughts?

My first thought is, good luck! g

Aluminum has three times the thermal coefficient of expansion as that of
granite. If this is an indoors application, and if the place where you do
the gluing is roughly the same temperature as the place where you will use
it, you probably won't have a problem. If the temps are much different, the
aluminum will try to shear off of the granite.

It's difficult to glue anything to aluminum without preparation. A thin
layer of aluminum oxide begins to form within a few seconds of cleaning it,
and it's a very weak layer.

Epoxy is used for gluing granite and other masonry materials, but a strong
epoxy often is brittle and the shearing problem will be worse. The
construction adhesive you're talking about is, I think, recycled chewing gum
g, and it's less susceptible to brittle shearing but it's also a lot
weaker. I'd call the maker of Gorilla Glue before even considering the use
of it here. It's fairly reactive (a moisture-curing polyurethane) and I'd
want to know how it sticks to these materials. I always ask for an engineer
when I make those calls, and I eventually get one. Elmer's makes the same
product under a different name, so I'd call them first.

We'll keep our fingers crossed for you. d8-)

--
Ed Huntress