Cracks at Sink Corners in Plastic Laminate

Tops in a science lab show cracking at sink corners. Info here on movement issues, and on chemical-resistant laminate material. April 11, 2008

We recently installed island style countertops in a science lab. The counters had chemical resistant sinks that were recessed into the counter and epoxied in place. These four counters were installed late summer (New Mexico) and we were just informed about the cracks in the laminate. The cracks radiate out from the corners of the sinks.

We used Formica laminate (standard grade) and contact cement (Permagrip brand from a canister). Does anyone have any ideas as to why this happened? We've been in the cabinet/countertop business for about 25 years and thought we'd seen just about everything. I know that laminate does shrink and expand, but we've never seen it to this extent. The counters were quite large... about 58" x 132".

Forum Ressponses
(Laminate and Solid Surface Forum)
From contributor A:
Do the sink openings have sharp or rounded corners? If sharp, that is probably the problem.

From the original questioner:
We did discuss the corners of the sink cutouts. They have a 1/4" radius... However, we have done literally thousands of cutouts where the corners have been square (typical with cooktops) without any problems.

I did forget to mention that the substrate is plywood with a backer sheet on the bottom.

From contributor R:

It sounds like you should be okay with the radius corners and the backer sheets. Honestly, there are a lot of variables.

Plywood does not move much. The laminate could be trying to move over a stable core. This may be true, especially if the glue line is in question. Is there adequate coverage to both surfaces that meet the manufacturer's specs? Was the open time exceeded or insufficient pressure applied to complete the bond? I won't even speculate if the epoxy used affected the laminate or contributed to the issues.

My recommendation would be to ask your Formica distributor to submit a top or representative sample to Formica. They should have a NEMA lab capable of testing the laminate for acceptability as well as the performance of the glue line.

Perhaps you could replace one as goodwill pending the outcome of appropriate testing. With so many variables in play, I wouldn't get my hopes too high that someone will bail you out. Research the NEMA specs for laminate and recommended bonding procedures. Visit and search under HPL.

From contributor S:
First, did all of the tops do the same thing? Are they cracked in the four corners of every sink? If so then you could have a laminate that is trying to expand, and with a strong substrate, it picked the weakest point to crack. I once relaminated a bunch of metal desks and run offs. The laminate cracked straight across the middle of the run offs. Never did figure that one out, just did them again. If you do have to do them over again, you might want to try putting wood glue around the sink, just about an inch all around.

From contributor V:
The size and substrate are working against you here. Laminate is a wood product made from paper, and the paper has a grain that follows the sanding scratches on the back of the sheet (but not related to them). The laminate will expand and contract just like a piece of wood, more across the grain than with it. Plywood does not expand or contract much at all. I am guessing that the laminate shrunk and the plywood did not. Radius or not, it will give at the weakest spot. I did a kitchen island on plywood once and replaced it in less than a year. Second time around I used particleboard and that did the trick. That was over 15 years ago.

I think this is a specifier problem and not a fabrication problem, unless it was your idea to do it this way. The last lab tops we did were full 1" thick Pionite. Many of the other p-lam manufacturers make a full thickness lab top also and the price is not that bad. Cut to size, put an edge on it and sand and polish. More $ to buy and less labor to fabricate. Trespa is another company that makes full thickness lab grade tops.

From contributor C:
Did you use chemical resistant laminate? I don't remember what Formica's offering is, but Wilsonart's is called Chemsurf. Formica has a helpful technical hotline.