CONCRETE HORIZONTAL SURFACES

Surface of concrete floors vary depending upon age, degree of finishing or trowelling, presence of surface curing compounds and the type of contamination from use prior to painting. Because of this, it is difficult to obtain consistent painting results on concrete floors.

Below Grade Concrete Floors may be particularly difficult to paint because of moisture entering the surface from the underside. Prior to painting such floor areas, the surface should be tested for moisture. The test can be done by taping a piece of plastic (about 1 metre square) and allow to remain on the floor for a minimum of 24 hours before removing. If there is moisture on the plastic when removed then there is moisture migrating to the surface in sufficient quantity to cause paints to peel. Such surfaces are generally a problem to paint satisfactorily unless the source of moisture can be eliminated by improved drainage.

NOTE: Do not use concrete curing compounds when concrete floors are to be painted. If curing compounds or release agents have been used, as in Tilt-Up construction, they must be removed prior to painting unless they are known not to adversely affect paint adhesion.

CONCRETE MASONRY UNITS

All mortar joints and the bricks and blocks must cure for at least 28 days prior to application. Concrete blocks and bricks will typically have very porous surfaces and may require the application of a block filler to obtain a filled even surface for the topcoat.

CONCRETE VERTICAL SURFACES

Tilt-up and Pre-cast concrete are normally treated with a release agent and special care must be taken when painting. The release agents used often also act as a curing agent on the top surface of the slab. Some release agent contains a resin, which oxidises and powders quite rapidly, especially in direct sunlight. Once the surface is no longer glossy and has an overall chalky residue on the entire surface, then after proper surface preparation and all the chalky oxidised material is removed the surface should be ready for painting. Until this has taken place and the powder washed off, the surface should not be painted either with water based or solvent based paints or a loss of adhesion will likely result. It is always recommended, when possible, to find out if and what type of release or other surface agent has been used and to follow the directions of the manufactured for coating.

Poured-in-place concrete often contains steel clamps, rods or ties that need to be cut back and spot primed with an anti-corrosive primer prior to painting.

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