Water-tolerant Substrates

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The right material will resist edge swelling under laminates. May 4, 2005

Recently, millwork installed in a cafe has been rendered unusable due to substantial substrate swelling. The substrate is particleboard. It's obvious the swelling is due to moisture, and is particularly bad at most outer edges and around a sink.

I've read particleboard and MDF are the preferred substrates due to their uniformity. I'd like to pinpoint the problem. Could it be poor fabrication? Initial moisture content, poor lamination, lack of sealant at joints? Or should I have steered clear from particleboard? Where can I obtain guidelines for future jobs to avoid laminate/millwork problems?

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor D:
You might consider substituting Medex or Extira for the particleboard. They're both water-resistant substrates - in fact, I think Extira is completely waterproof. More expensive than using particleboard, but definitely cheaper than getting called back to fix it.

From contributor R:
I used to be a particleboard hater, but came around to embrace its inherent good qualities as substrate. The absolute of it is no water contact. You must create a moisture-proof barrier everywhere it might make contact. Your situation may have exposed the underside of the work to humidity. The answer is to laminate the back of everything using cheaper backer sheet. This unfaced thin laminate is impermeable, makes a professional look, and helps balance stresses to keep tops flatter.

Also, caulk the joints before tightening draw bolts. Caulk back and end splashes along the edge that meets the top with a fat bead before installation to fully fill the contact area. Do the same around the tops of the splashes at wall contact so wild splashes of liquid cannot run down behind. Use a high quality silicone around all sinks and fixtures for a flexible bond. I guess you could also polyurethane raw unseen back edges under extreme conditions, though I've never bothered. There is no way your stuff should swell after doing this, unless it was way over normal moisture content to begin with.

From contributor J:

Medite or Medite2 or similar type carries a substrate that is totally impervious to water. Same workability, but we've taken some pieces and totally immersed them in water. No change at all. Problem your having is all cuts, edges should have been sealed up with glue or a durable lacquer.

From contributor M:
Where did you get your particle from? There are different grades and densities to use. Your laminate supplier should be selling you your substrate materials. I made the mistake years ago and used particle from local lumberyard. It was much less dense and shrunk when ac was on, then over-expanded in high humidity. Good glue adhesion and using waterproof glue at seams is also very important. On large commercial tops, a backer is a wise idea also.

We did a side by side comparison with Extira and regular MDF in a bucket of water with a brick on top for several days. Obviously this is way more than should be expected of either product. We just wanted to see what would happen. Believe it or not, the regular MDF expanded less and shrank closer to its original size after drying than the Extira. The only difference was after a few days of drying out, the Extira was fine and the regular MDF had a small amount of mold on it.