Dishwasher steam and countertops

Q: I built a kitchen countertop using 1/4-in. oak parquet flooring glued to a 3/4-in. plywood substrate. Although I finished the parquet with epoxy, the area over the dishwasher delaminated almost immediately. What can I do to prevent delamination in the future?

Oscar Wehmanen, Houston, TX

A: Johannes Boonstra of Akzo Coatings in Troy, Michigan, replies: Most dishwashers expel steam through a port in the door, so you should design the countertop so that it won’t capture the steam exhaust. The dishwasher should fit tightly in its opening, and the countertop shouldn’t overhang the steam exhaust.

Choose a countertop substrate that is manufactured using moisture-resistant adhesives, such as exterior-grade plywood. Then you should seal the underside of the substrate with a nonpermeable coating. Chemical-resistant coatings, such as one- or two-component polyurethanes or twocomponent epoxies, are best-suited for this purpose. Two or three coats should be enough to keep the moisture out of the substrate.

From Fine Homebuilding 95, pp. 16 May 1, 1995