What is Sapstain – Blue Stain?
The term sapwood stain and blue stain is used in many articles related to rot and wood preservation. One should understand this term as a first step in understanding the degradation and rotting of wood.
What is SAPSTAIN?
A tree consists of many parts, but two terms will suffice for this brief treatise, heartwood (physiologically dead wood located near the center of the tree) and sap, which is found on the outer periphery of the tree (physiologically active). Sapwood transports water and nutrients through the tree and is therefore a perfect environment for sapwood growth.
When a board or lumber is cut from a log, mold spores can come in contact with the nutrient-rich wood with its high inherent moisture content and begin to multiply and spread over the surface of the wood.
As they spread, they create a stain that is normally blue, but can actually be different colors. Over the years I have seen not only blue, but also black, red and yellow.
If this mold/stain is not controlled, it can penetrate the wood with tendrils and carry the infection deep into the wood(s). They will eventually give off enzymes that will break down the wood and then you will have the start of some serious decay. We are talking about wood that is moist (not dried) and in a nutrient-rich environment. Many people talk about dry rot; but in reality there is no such thing. This is a misnomer. since wood needs to have between 30 and 60 percent moisture content for the decomposition cycle to begin.
Prevention of sap stain
To prevent sapwood stain from discoloring the wood and to prevent further degradation from decay, many sawmills dip the product in a fungicide to prevent mold from attacking the wood. This is particularly important in the humid areas of the United States and its use is highly recommended for high-quality, valuable lumber.
Wood that has a high propensity for sapwood stain will not have a uniform finish. The area that has the sap stain will absorb the wood finishes more than the unaffected areas. So when you finish such an infected piece of wood, you’ll need to use a series of coats of wood finish to even out the look. For high-quality products, such as furniture or trim, sapwood-infected wood is discarded.
If you are installing wood that has mold present, it should be thoroughly washed before any type of finish is applied. We’re talking about a surface layer of mold, not a stain that has penetrated deep into the wood. Use a mixture of three quarts of water, one quart of household bleach, and 1/4 cup of liquid dishwashing detergent that does not contain ammonia. Never mix bleach and ammonia as it will give off dangerous fumes. This formulation can be sprayed using a pump sprayer. After 15 to 30 minutes, it can be washed with a pressure washer.
Remember that once the stain penetrates deep into the wood, it cannot be removed with bleach or any other product. It is there to stay. Always remember not to play chemist and experiment with mixing various chemicals as they could give off dangerous gases…and more!