Q. Can polypropylene fiber additives (such as Fibermesh) be used instead of welded wire mesh in concrete slabs?

A.A lot depends upon what kind of reinforcement you need.

Polypropylene fibers can help reduce the initial shrinkage which occurs in concrete during the first two days of curing. But these fibers do not permit wider spacing of control joints over what is specified for unreinforced concrete. If the concrete does crack, the fibers will not hold the pieces in alignment as well as welded wire mesh. The fibers should not be counted on to resist stresses due to extreme temperature change or as a replacement for any steel 1/4 inch in diameter or larger.

Other fibers, such as nylon, alkali-resistant glass, and steel can provide significant gains in strength, but the mixes and applications should be carefully designed by an engineer.