It dampens the unit, reducing its water demand and the potential of premature dryout. This prepares the unit surface to absorb paste from plaster. Immediately prior to plastering, the wall should be pre-wetted. If it is readily absorbed, then the surface is expected to bond well with stucco. Potential for bond can be quickly checked by a simple test: sprinkle the wall with some water to see how it absorbs. ![]() Partial bond will create undesirable stresses and can lead to delamination and cracking of the stucco layer. The entire surface must have uniform bonding potential or you can run into problems. Older walls may have bond-inhibiting characteristics, in the form of paint, sealer, or some other coating or dirt on the surface. This is generally not a concern with new walls. If contamination is present on the substrate surface, good bond is inhibited. Concrete masonry surfaces are both absorbent and textured, two things necessary for bond. ASTM Standard C 926, Specification for Application of Portland Cement-Based Plaster, permits direct application of stucco to solid surfaces like concrete and masonry as long as bond is sufficient. ![]() ![]() Portland cement adheres well to lots of materials, especially to other materials made from the same type of ingredients. As such, they have a great affinity for each other. Stucco is made from the same materials as concrete and concrete masonry. With a substrate of concrete or concrete masonry, is it necessary to use lath? ![]() Metal lath is regularly used over stud wall construction with or without sheathing materials. This question probably arises because plaster is often attached to wall surfaces that have metal lath affixed to them.
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