In the second Bench Test contractor Jeff Burns uses WonderBoard by Custom Building Products.



The regular three-step process for applying stucco entails basically the following: After felt paper and chicken wire are attached to the plywood inner wall, a scratch coat is applied to fill in the chicken wire. A 48-hour wait period ensues while the scratch coat cures. Plaster crews then return to the building site to apply a brown leveling basecoat. A much longer second waiting period is needed before applying the final surface, color coat of stucco.

I recently used a product called WonderBoard, manufactured by Custom Building Products, of Seal Beach, Calif. It enabled me to turn a residential project into a one-step process with no waiting period before the final color coat is applied. For 34 years, the product has been used entirely as a backer board for tile, marble and stone-1/2-inch-thick cement aggregate that is enclosed in panels on both sides by fiberglass. The product has worked well as a water-repelling backer board.

In stuccoing, WonderBoard replaces both the chicken wire and scratch coat, and the brown leveling coat. The board also comes previously cured, removing the need for any delays once the crew puts it in place.

The final and only surface coat of stucco can be immediately applied directly to the board.

In the three-step process, shrinkage occurs in the base scratch and brown coats, and that underlying shrinkage, in turn, produces cracks in the stucco surface. By replacing the underlying coats with WonderBoard, cracks can be eliminated. Also potentially eliminated are ripples and waves on the surface. This is accomplished via bypassing the underlying scratch and brown coats-which can be toweled on with only so much precision-and replacing them with the flat WonderBoard.

The use of this product may also eliminate certain eventual discolorations in the stucco surface. Too-fine cement aggregate employed in the old scratch and brown coats contain a lot of lime and that lime often eventually "effervesces" to the surface, producing stain-like discoloration.

Bakersfield home

A 3,500 square foot home in Bakersfield, Calif., is the subject for the WonderBoard Bench Test. For this custom home, stucco was chosen for the rear exterior and the WonderBoard product was green-lighted for the application.

Current construction codes and practices, in order to provide necessary sheer value strength, involve the stucco going over 1/2-inch-thick plywood sheets. The WonderBoard panels could replace the plywood. An advantage would be that it is one-third the price of plywood and has 50-percent more sheer value than plywood. Tests have demonstrated 2x4 studs behind plywood panels start collapsing when applied pressure reached 420 pounds. By comparison, the studs behind WonderBoard panels did not start collapsing until the pressure went past 600 pounds, according to the manufacturer.

For the product to qualify as a substitute for plywood, Custom Building Products needs to arrange for independent engineering tests and then be "published" in the building industry.

The 2,500 square feet of stucco on the home did indeed turn out crack free and this was a successful bench test. W&C