Bracing solid surface
It is correct that 1/4" thick material is not suitable for horizontal applications. However, the minimum distance between supports in the "bridgework" for 1/2" material is 24". Technically, a 2' X 2' square or 4 square feet of Corian® will support itself in the field with proper perimeter support. By law, a ladder structure must be built using moisture resistant MDF or plywood. The strips should be between 3-4" wide and joined with biscuits, dowels or rabbited seams, screwed and glued. Also, the supports must travel the full width of the countertop (front to back) at all cutouts, i.e. sinks and cook tops.
The standard counter thickness for solid surface is 1/2", however the exact thickness does vary, so be sure to check it before fabrication. The bridge network described above is correct for 1/2" thick solid surface, however the spacing and allowable overhangs increase with the use of 3/4 material, although finding it could be a problem. SSV by Wilsonart is installed over a solid substrate such as particleboard or MDF, however a backer sheet must be used to balance the sheet. This may be where you saw solid backing. No SS manufacturer will warrant their product if installed over a solid surface such as a sheet of plywood, PB, or MDF. This is due to heat dissipation and expansion and contraction, the two major causes of failure (cracks).
It is correct that there are no solid surface manufacturers that will warrant a countertop with a solid substrate. The main reason is heat! Solid surface is not a good conductor of heat. If a heat source is applied to solid surface, it will not dissipate throughout the sheet, but must vent through the bottom. If the bottom is fully covered by a substrate, the resulting expansion from the heat will crack the surface. Lesser extremes of heat that may not crack the surface will whiten the contact area.
Expansion and contraction of the substrate is not as big of an issue. Using a moisture resistant substrate and balancing it can minimize the expansion rate to a point where it will not affect the solid surface. Certain manufacturers will give special consideration to using a solid substrate with 1/2" or 1/4" solid surface material. In applications such as an end table or cafe table, the product will not encounter a heat source. Original Equipment Manufacturers have been producing such products for several years now. But be careful if you do this, as there truly is no warranty. My point is that people are successfully using solid substrates in specific applications.
I cannot address other materials, but with Corian, part of its cost-effectiveness is that you do not need to make your product and then surface it.
1/2" Corian is strong enough to stand on when simply applied to a frame for an end table or coffee table. 3/4" has been out of vogue for such applications for over 15 years.
Out of vogue for sure, but still in the manuals and a special order, to say the least! There are some overhangs, such as bar tops and specialty furniture that may make use of this, although it sure does sound like something an architect would demand that you do! I had the same problem three or four years ago with 1/4" Corian. The local supplier quit stocking it due to the cost of breaking it in inventory, but it was still in the manual and the architect wanted it. Luckily, I did my research before signing the contract and declined to take the job (it had trouble written all over it).
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