Q.: We placed a concrete wall for which the architect wanted an exceptionally smooth surface on the top 2 to 3 feet. We formed most of the wall with standard steel-faced forms but used hardboard at the top. When we removed the forms, the concrete surface in contact with the hardboard was soft and dusty. The rest of the wall looked fine. Are there chemicals in hardboard that retard concrete setting?
A.: Jerry Ford of Symons Corp. says that if surface appearance is critical, concrete shouldn't be cast against untreated hardboard because wood sugars in the product can leach out and retard concrete setting. Using form release agents on hardboard also can cause problems. The product data sheet for Magic Kote, a Symons form-release agent, advises avoiding use of the product on untreated Masonite. Ford says this is because the form-release agent softens the material.