One principal factor in the peeling process of a coating from wood is the amount of WATER or MOISTURE that infiltrates the wood siding. Many environmental factors, such as sunlight, rain (acid), heat, fungus growths, salt, hail, snow and minor property flooding, have a harmful effect not only on metals, but on wood.
Any type of wood siding needs to be protected from excessive moisture. Excessive moisture in the wood is the leading cause of paint/stain peeling.
Today’s paints and solid color stains can survive without peeling due to the unique method in which the products are formulated. Modern coatings are more durable, water- and weather resistant.
The normal exterior moisture content in wood varies, depending on its location within the home. It is also dependent on regional climatic variations due to geographical location. On average, the moisture content is generally between 9 and 15%.
When the wood’s moisture content increases, the wood swells. When the moisture content decreases, the wood shrinks. Peeling of a coating can occur when the wood actually goes beyond the normal moisture content of 9-15%. At maximum expansion, if the coating cannot expand, as in the case of old, brittle coatings, it is subject to cracking and peeling. Water blisters may also form between the wood and newer, flexible coatings.
One of the nice attributes about properly applied semi-transparent-type coatings is that no coating or film occurs. Therefore any moisture in the wood can pass as a vapor without doing any damage to the stain.
Expansion of wood due to excessive absorption of moisture and heat buildup creates a tremendous amount of stress in the wood. The wider and thinner the board, the more it will expand and contract. If allowed to get wet often enough, the wood will begin to lose its natural resins. The resin loss will then result in shrinkage.
Before applying a new coating, consideration must be given to eliminating thesources of moisture infiltration and correcting the areas that are peeling. When the wood is dry, tape-pull tests in areas not apparently affected would be beneficial in determining the full extent of the peeling. Simply press adhesive tape on the stained surface with thumb pressure, then with a jerking motion remove the tape. If the coating(s) is removed with the tape, the peeling is more extensive than just the areas that are obvious. This test should be performed in several locations on the siding.
Assuming the peeling is isolated, the next step is to remove all loose stain.
Several methods are available including stripping, scraping and sanding. I do not recommend power washing, this method drives water into the wood. I would strongly recommend sanding the entire area to be stained with 80 grit paper. The make the surface dust free. After the surface has been thoroughly prepared and is dry, apply the appropriate stain.
I would recommend Benjamin Moore Aborcoat Latex stain. Do not apply one heavy coat. If needed apply two thinner coats. If you choose to apply with a roller, make sure you back brush to make sure the stain penetrates the wood. The choice between latex and alkyd may depend on where you live. Some local dealers may advise alkyd over latex. I think latex is better on siding because it offer a more flexible coating.