Three important considerations are involved in surface preparation: surface condition requirements, evaluation of surfaces, and methods of surface preparation. All barrier systems require a surface free from holes or protrusions. Because many waterproofing barriers and most protective barriers exert stresses on the concrete while they shrink during curing or cooling after application and when they undergo ambient temperature changes in service, the concrete itself must resist these stresses without failing.
Unless the barrier manufacturer specifically recommends the surface be wet, there should be no free water on the concrete surface. In many cases, this can be evaluated by dragging one's finger along the surface. If moisture is picked up, the surface is too wet. An alternate method is to press an absorbent paper very tightly against the concrete. If the paper darkens, indicating a pickup of moisture, there is too much water present for successful application of most barriers.
How do we know if the concrete is strong enough to withstand the stresses exerted on it by barrier materials? The strength of the concrete at and near the surface can be evaluated by a pull-out test in which a 2-inch-diameter core hole is drilled to a depth of 1 inch and a pipe cap is bonded to the concrete. After the bonding agent cures, the pipe cap is attached to a hydraulic jack which pulls perpendicularly to the concrete surface. The force required to pull the concrete apart or to break the bond of the pipe cap to the concrete is recorded. For epoxy and polyester protective barrier materials, the tensile strength of the concrete should be at least 200 psi and perhaps more depending upon recommendation of the manufacturer.
