7. Wood was installed directly over foam or foil-faced insulation board.Water can travel in behind the siding of the house through various routes but has to travel out through the wood, pushing the paint off. Even if the paint remains on the surface, this moisture can cause other problems. Large overhangs, proper caulking, and a 12-inch minimum ground clearance may decrease the chance of water getting in behind the siding. Additional suggestions to prevent paint failure in this situation include the following:
- Driving small wedges (1/16 inch) under every sixth row of siding may permit water to escape and reduce the moisture problem. However, wind-driven rain may also use this as an access and aggravate the situation.
- Back priming (painting the back of the siding before installation) may help reduce/prevent paint failure.
- Install roofing paper (15- to 30- lb felt) beneath the siding. Note: The best solution is to attach furring strips to the studs through the insulation board, making air spaces behind the siding. Furring strips also make a nice home for bugs, if you do not screen the bottom. A spacer-type webbing called "cedar breather" is sometimes used under wood shingles and may have merit for use under siding.
8. House has no interior vapor barrier.The absence of an interior vapor barrier is related to the problems of high levels of humidity inside the house during the heating season and wood that was installed directly over foam or foil-faced insulation board. Driving wedges under the siding may be the easiest solution. Applying certain interior vapor- retarding paints and installing electrical outlet gaskets may also be effective, especially on the upper floor of a multi-story house.
9. Wood siding is dirty.If the siding is dirty, the surface of the siding should be power washed or cleaned with detergent and a stiff bristle or brass brush and rinsed well. Never use steel or iron, which causes iron stain and may glaze the surface.
10. Wood has mill glaze.Mill glaze can be caused by several factors. For example, if during planing to make smooth wood, the planer blades were dull, running too fast, or pressing too hard on the wood surface, the surface of the wood can become hardened or resins may be drawn to the surface causing a glaze. Whatever the cause, the surface appears to be case hardened. If a drop of water beads up on the wood surface but does not on a lightly sanded surface, you may have what is commonly called mill glaze. If you have mill glaze, the smooth surface must be lightly sanded or power washed to remove the hardened surface. Oddly enough, controlled wetting of new siding with a garden hose may promote better adhesion to the redried wood. The water releases the stresses in the wood. You can also create a type of mill glaze by sand blasting or using a wire wheel on the wood surface. Mill glaze is not a problem on rough-sawn siding.
11. Brown stains appear on the surface of the paint.Paint does not have to fall off to fail. Moisture traveling through wood pulls water-based extractives through the paint, leaving brown stains on the surface of the paint. If the wood is kept dry, the waterbased extractives in the wood will not bleed through paint. Keeping all moisture out may be difficult. Oil-based primers usually block extractive stains better than latex primers and may be a better choice on redwood and cedar; however, oil paints can increase mildew. Compared with oil-based primers, latex primers produce a more flexible paint film with better durability and can be used when extractive staining is not a problem.
12. Wood has decayed (rotted).Decayed wood can result if the wood has been wet for extended periods. If the wood is soft and spongy, it is degraded to the point that it will never hold paint and should be replaced.
In summary, note the following to prevent house paint failure (not applicable to semitransparent or solid-color stains):
- Install siding properly.
- Sand or power wash the surface of the wood if it is smooth.
- Apply paint during recommended weather conditions and temperatures.
- Treat the surface of the wood with a paintable water-repellent preservative (especially the end grain).
- Prime the surface of the wood with a stain-blocking primer.
- Properly apply caulking material.