Subtops Under Solid Surface Countertops

Solid surface is not installed over a subtop, but over (at most) widely spaced mounting strips (and let the installer worry about those). September 26, 2006

I'm a one man custom cabinet shop that offers subtop with our cabinets. In our 2 years of existence, we have yet to have someone install a solid surface top on our cabinets, until now. Does solid surface require a sub-top? Does it depend on the type? If it does, what do you recommend (type of material and thickness)?

Forum Responses
(Laminate and Solid Surfacing Forum)
From contributor K:
Corian more than discourages the use of any substrate under 1/2" or 3/4" material and does not allow 1/4" to be used for tops. The reasons for this are several. First, it does not need it. Corian is strong enough. Second, Corian expands and contracts with heat; wood with humidity. The movement may be small, but the forces can be great. Third, a substrate would trap localized heat, say from a hot pot, increasing the possibility of failure. A cross support every 20 to 24 inches is all that is required.

From the original questioner:
Thank you for your help. I guess I need to know also if we need to build up. We build a euro box with only a 1/8" reveal at the top. Is most Corian a slab material or does it have a lipped self edge?

From contributor L:
Contributor K, this is not a challenge, but a sincere question. I thought that I'd seen Corian used in bath/shower installations. How do those survive?

From contributor K:
You can machine it to whatever configuration you wish. I am not familiar with the edge treatment to which you refer.

Most shower/tub surrounds are 1/4" material applied to drywall or other backer. The expansion is covered with expansion joints. (A silicone batten joint.) Hot pot pressed against the wall is a rare occasion!

From contributor B:
Avonite *used* to insist on substrate strips, but have backed off in the past year. I put 1 1/2" wide strips of 1/2" MDF in front, back and middle under 1/2" SS with 1.5' built up edge, mostly just for preferred overhang. Lately I'm selling 3/4" Mystera a lot - no substrate, no build-ups - just cut, route and polish. Most shops around here aren't using substrate at all on any SS products.

From contributor U:
I would have the surface supplier supply his own substrate and take care of his top finished. I make cabinets and do SS and would not want a sub top in place. I have power seams under the tops where required and the sub top would just get in the way, plus I will allow for my own edge treatment, not try and meet something someone else set up.

From contributor J:
Contributor K is correct. Your best course is to furnish your cabinets and install them level. Let the countertop installer worry about everything else above your cabinets. When I install 1/2" thick solid surface countertops on kitchen cabinets that are about 34-1/2" high, I use two layers of 1/2" thick plywood strips cut 2" wide, which are concealed by the 1-1/2" thick front edge of the countertop. I leave off the second layer of plywood in the area of any deck seams, and instead bond a second layer of solid surface material as a reinforcement below the seam. The result is a stable but open support structure that dissipates excess heat far better than a solid subtop. Finish countertop height ends up at the industry standard of 36". Face frame cabinets that are a little higher may require just one layer of 1/2" plywood strips, but the principle is the same.