- Q. I’m working on a project with a 2-inch thick colored concrete topping slab installed over a 5-inch thick structural slab on grade. There will be #15 felt installed between the two slabs, so they can move independently. I am considering using fibermesh to minimize cracks in the topping slab. If I use fibermesh, can I omit the usual welded wire mesh? Also, I have heard that there is a type of sealer that can be mixed into the concrete to help preserve the color and finish of the topping slab. Do you know about this product?
A.Jay Meunier, contracting specialist at S.T. Griswold and Co. in Williston, Vt., responds: Fibermesh is typically not used in conjunction with wire mesh. The function of either fibermesh or wire mesh is to reduce the physical size (width and length) of the cracks that appear in a slab as it cures and shrinks. For a 2-inch thick colored topping slab, it would be best to use a micro-fiber, which is smaller in diameter than the standard fiber and more easily worked. Even with fibermesh, the topping slab will still require control joints to reduce the risks of random cracking.
I do not know of a sealer that can be mixed into the concrete to preserve the color or finish. If the concrete is colored by adding pigment to the concrete mix, or if pigment is broadcast onto the fresh concrete (the "dry shake" method), then a wax-based curing compound containing compatible pigment should be applied. This type of pigmented curing compound will form a heavy film, and is typically available from the pigment supplier.
If the concrete is to be colored by painting or staining after finishing, the slab should be wet-cured and curing compound should be avoided. We have found that stained slabs are susceptible to surface contamination and discoloration, and require that activities on the slab be kept to a minimum.
