Ideas for plugging a hole in granite vanity

I am guessing that your sink weight is causing the pressure, making the cracks worse. If I am right on this then the first thing you need to do is build a simple way to support the sink using wood or whatever - I have 2x2s that are screwed to side cabinet and pushed up to support it. So that will cost you $3. If side walls are not close enough you have to build a box.

Now to fix the cracks you will need a knife grade epoxy. I have used Tenax brand in the past to "glue" granite corner shelves in the shower. Pretty easy to use. Epoxy will be about $20-$30.

And for some reason (conspiracy) the big boxes don't carry any knife grade epoxy. You will have to hit the interwebs for this. Just search for knife grade granite epoxy if you want to read reviews or whatever. Basically you will get the activator and the putty. You put a little activator in the putty and wipe it on the granite. If you are doing the top then you might need to by color matching kit (which is more expensive than epoxy). Basically it is hard in 30 mins and can be used the next day. Once epoxy is on it is permanent and harder than the granite. If you arent worried about looks your sink area could be cured of the crack as long as you get the epoxy in the right places.

The makers of those tops will have the seam adhesive to join the tops permanently. If they are anything like Corian by Dupont, they want to protect their warranty. You may need to do some convincing to an installer to sell you the adhesive you need. It can be done, I have done it before. It takes a router or a belt sander to get the joint down flush after the glue squeezes out.

More later if you go that route.

12-9-13 addendum

The bond is really strong, but it is always best to insure the joint is stable on both sides. This can be done with silicone under both halves. While silicone is still fresh, position your halves and use shims from the underside if needed. From the looks of it you may not have the luxury of getting a clamp block at the back edge but you may at the front. Have everything ready, and clamp the front and shim the back like you are ready to glue. Get it right at this point after this step there is no turning back. Use a straight edge of some sort to insure surface are flat and true. Remove all clamps that block access to the joint. apply your bonding cement and reset the clamps. The stick(s) I have referred to are small hardwood scraps, maybe 1/2" square to 3/4" square and 4 to 6 inches long. When this is placed on the glue joint it will spread the glue a little, but it will sand out with the rest of the joint.

After all this is said, any of this is for worst case scenario. If the joints line up perfectly as it sets on the cabinet, which it looks real good in the picture you offer, all you need is to apply the glue and let it set which will only take minutes to set, and hour to finish.