A good block filler evens out the pitted surfaces of concrete masonry blocks. It is high in solid materials which allow the paint to fill the holes in the block without too much shrinkage. The block fillers of yesteryear weren't as easy to apply as today's new and improved formulas. The filler goes on with a conventional paint roller. Acrylic fillers work best for exterior applications while water-based formulas serve to paint indoor block surfaces. The filler then takes a top coat with a block-filler-compatible finish paint.
Clean the block by going over it with a wire brush. Brush away all dust and cobwebs. Dust the finer debris particles with a dust brush and then suck the hard-to-reach dust out of all holes and crevices using a vacuum.
Pour 1 gallon of block filler into a 5-gallon bucket and insert a metal paint roller screen. Dip the roller down into the paint and roll it up and down on the screen until the 1-inch nap fibers are loaded with filler paint. Screw an extension pole into the handle of the roller frame.
Roll the block wall up and down while applying even pressure on the roller to squish the paint into the block. Roll as close as you can get to the edges of the wall.
Dip a paintbrush into the block filler and dabble paint into the block along the wall's edges. Dabbling is accomplished by holding the brush perpendicular to the wall and then running the tips of the brushes bristles into the block repeatedly. Allow the filler to dry according to the manufacturer's recommendations and then topcoat it with a finish paint.
Pressure wash block walls that are extremely dirty. Use a degreasing agent on grease or oil stains. Apply block filler to walls warmer than 60 degrees Fahrenheit, for best results.