Causes:
Peeling on surfaces composed of mortar, brick, building
block or concrete is commonly caused by efflorescence.
Soluble salts present in the material are dissolved by
water and carried to the surface as the water evaporates.
As these salts push on the surface paint, peeling results.
Efflorescence occurs on brick walls of new construction. A
common building practice is to treat new brick or concrete
with muriatic acid, rinsing with water to clean away
excess mortar. Rinsing removes only those salts on or near
the surface. After painting, salts remaining within the
bricks will absorb the moisture and travel to the surface,
causing peeling.
Peeling can also occur when alkyd or oil paint is applied
over unetched concrete. Alkyd resins that come in contact
with an alkaline surface form a soap film between the
concrete surface and the coating. This process, called
saponification, results in softness and loss of adhesion
of the alkyd coating.
Solution:
Remove all evident efflorescence before repainting.
Sandblast or wire-brush all flaking or chalking paint from
the damaged area. If necessary, apply a solution of 5%
muriatic acid or undiluted vinegar. Rinse with clean
water.
Fill all cracks with masonry patching compound, latex
concrete patch, or caulking compound. If the surface is
very porous, apply an alkali-resistant primer or block
filler.
Cover with latex housepaint.
To prevent recurrence of efflorescence on interior walls,
the exterior walls should be sealed.
NOTE: Extraneous water sources must be removed
before painting (e.g., migration at ground level, often
caused by poor drainage). |
