We have a recent job completed at a local hospital and we got called back to replace a large nurses station countertop, for what the suits called 'poor worksmanship'. What happened was the top of the self edge was showing at the edge of the top. We obviously couldn't make the top like that and upon investigation we found that either the laminate 'shrunk' of the substrate 'grew'.

We are using 1 1/8" PB with backer and GP grade Formica laminate on the face. All items are stored in the racks in our heated shop at all times and delivered weeks prior to using it.

The atmosphere at the hospital is typical hot hospital, 75 and above I think.
We are using Wilsonart 950 adhesive and using the same procedures as always.

We have never seen this before, first hand, just heard about it.

Question is.'What causes it and what can we do to prevent a re occurence??

Thanks guys,

Tom in PA

Could be a combination of the core expanding ( think humidity) and the laminate shrinking. One way to help reduce this is to use a pvc adhesive rather than contact. It forms a riged gule line. You can get this if you make the product in the winter with low humidity and when the warm humid weather hits things grow.

Tom:

You may find this article useful, especially "Moisture Resistance and "Handling and Storage".

Joe

The top laminate is shrinking and the flexible bond of the contact cement is letting it. P-lam is a wood product (paper) and that paper also has a grain that aligns with (but not related to ) the sanding scratches on the back of the sheet. The sheet will expand and contract just like a solid piece of wood, more across grain than along the grain. These tops can be repaired in the field if they will let you. You will need to peel of the self edge and replace with the same color in V32 grade. Also check your compressor to see it you are putting moisture out in the spray air. We sometimes had this problem with cabinet doors when we laminated with contact cement, in the winter. It would look like the edging was starting to come off, a tiny gap. Close inspection showed the p-lam to have shrunk. We cold press all layup with PVA in house now and the problem is gone. Panels are much stiffer too.
PVA layup of counter tops can be a bit tricky because of the different shapes required. 5x12 cold presses are hugely expensive, we have a 50" x 100" that suits us just fine.

At some point the substrate will also shrink, but the suits will prob not want to hear that. I know because I do a ton of hospital work.

If you have to make the tops over than spray very lightly, or not at all, near the self edges. 3-4 clear inches should do it. Same with the sheet. Spread yellow glue at the self edges and index the top sheet. A few strips of flakeboard and some spring clamps to finish the job. The sheet now has to move somewhere else. Also do the PVA glue at any seam, shop seam or field seam. You don't want the same thing happening there.
I had a post here somewhere about "glue lace" on the p-lam seams, that may also help.

I was at the hospital in question this past weekend doing an install on some Mystera window sills and we had a chance to inspect some of the work on the first floor that we had done earlier, at the begining of winter. All tops, doors etc are perfect, just as they had left the shop. The temp on the first floor is more relaxing than the patient floors which seem to be sweltering.
We then went and checked all the work on the first floor and the ground floor and found no other shrinking / swelling at all in any items which put my mind at ease, somewhat.
We did replace one big 3 section top 3 weeks ago but have not had a chance to re-inspect.
Thanks for the input guys,

Tom in PA