What is Sapstain – Blue Stain?
The term sapwood stain and blue stain is used in many articles related to rotting and wood preservation. This term should be understood as a first step in understanding wood decay and rot.
What is Sapstain?
A tree consists of many parts, but for this brief treatise two terms will suffice, heartwood (physiologically dead wood located near the center of the tree) and sapwood, which are found on the outer periphery of the tree (physiologically active). Sapwood carries water and nutrients through the tree and is therefore a perfect environment for sapwood growth.
When a board or wood is cut from a log, mold spores can come into contact with the nutrient-rich wood with its inherent high moisture content and begin to multiply and spread across 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 checked, it can penetrate the wood with tendrils and carry the infection deep into the wood or joists. They will eventually release enzymes that break down the wood and then serious decay begins. We are talking about wood that is moist (uncured) and in a nutrient-rich environment. Many people speak of dry rot; but in reality there is no such thing. This is a misnomer. as wood must have a moisture content between 30 and 60 percent for the decay cycle to begin.
Prevent sap stain
To prevent the sapwood stain from discoloring the wood and to prevent further degradation from decay, many sawmills soak the product in a fungicide to prevent mold from attacking the wood. This is particularly important in humid areas of the United States and 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 with the sapwood stain will absorb the wood finishes more than the unaffected areas. Therefore, when finishing such an infected piece of wood, you will have to use several coats of wood finish to match the look. For high-quality products such as furniture or trim, sapwood-infected wood is discarded.
If wood that has mold is being installed, it should be washed thoroughly before applying any type of finish. We are talking about a superficial layer of mold, not a stain that has penetrated deep into the wood. Use a mixture of three quarters of water, one quarter of household bleach, and 1/4 cup of liquid dishwasher detergent that does not contain ammonia. Never mix bleach and ammonia as it will emit 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 chemistry and experiment with mixing various chemicals as they could emit dangerous fumes … and more!