As we mentioned in “Moisture – The Exterior Curse (Part 1)”, there are three difficult exterior issues that affect paint appearance and longevity and they are all caused by excessive moisture. Below we further explore those exterior issues as well as how to minimize the moisture problem and renew the substrate with quality paints and coatings.
Tannin is a naturally occurring, water soluble substance found in many varieties of wood. Tannin can be pulled to the surface in the presence of water and leaves behind a brown or tan stain. Tannin staining issues are more likely to develop from red cedar, cypress and redwood. While these stains do not harm the integrity of the paint film, they are unsightly.
The best way of preventing tannin staining is by applying a tight film of paint over the substrate minimizing the ability of water to penetrate. In the past, solvent-based alkyd primers were the choice to prevent tanning staining. However, solvent-based primers tend to become brittle, crack and peel with age.
There are acrylic latex primers that have been specifically designed to combat tannin staining and peeling issues on exterior wood substrates. Some premium products perform best when applied in two coats with twenty-four hours in-between coats, which help prevent tannin bleed.
Efflorescence is often a white or tannish, powdery deposit on concrete or masonry substrates. While typically not structurally damaging to the substrate, it is unsightly and destroys the paint on the substrate. Efflorescence occurs when moisture migrates through concrete and masonry substrates, dissolving salts contained in the material. The moisture deposits the salts on the surface of the substrate and evaporates, leaving the powdery deposit.
Prior to rectifying the ruined painted surface, the source of the moisture must be found and stopped, or the process will reoccur. Once the moisture has been stopped, remove the existing efflorescence and loose paint by using a stiff wire brush. Clean the surface to remove all the dirt, debris and other contamination. The masonry must be clean and dry before the appropriate primer is applied. Follow with one or two finish coats of premium finish paint/coating as noted in the proposal/contract or project specification.
Source: Painting Pro Times, 4/13/16. Author: Matt Ferring. Moisture – The Exterior Curse