Understanding the Bleeding of Wood Extractives.

Wood extractives are compounds present in the softwood and heartwood of a tree that contribute to such properties like color, odor, decay and insect resistance, density, and flammability. When used for log homes, naturally occurring extractives in the wood can migrate to the surface and discolor paint and finishes (water soluble extractives) as well as create adhesion issues (oil soluble extractives) for many coating types.

The organic components of the extraneous materials are referred to as extractives because they can be removed by extraction with solvents without altering the cellulose/lignin structure of the wood. Extractives include tannins and other polyphenolics, coloring matter, essential oils, fats, resins, waxes, gums, and starch. Depending upon such factors as species and growing conditions, the total extractive content of wood substance may range from less than 1% to 30% in extreme cases.

Wood Species and the Level of Extractives 

All wood species contain wood extractives; however, there are a handful of wood species that are characterized as extractive-rich woods. This group includes Redwood, Western Red Cedar, Walnut and Mahogany. The second group of wood species that also contains higher levels of wood extractives but less than extractive-rich woods include Southern Pine, Douglas Fir, Spruce and Cypress.

The percentage of extractives in trees is generally low, but a high concentration is found in knots and heartwood of the tree. Knot bleeding can occur when a knot contains an excessive number of extractives. In these cases, the extractives consist mainly of rosin, fats and turpentine, and these extraneous materials can make up as much as 50% of the knot by weight. The ratio of extractives can change with the season and weather (if the tree is stressed).

Extractives Affecting Wood Color

Staining or discoloration of wood may result from chemical processes that convert originally colorless or light-colored extractives into intensely colored products. Most of the “chemical stains” result from oxidation of certain wood extractives during air seasoning or kiln drying. Some resins can bleed out of the wood, as seen in pine wood. Sometimes the extractive can react with foreign material.

Using Cedar Wash For High-Extractive Wood Species

Cedar Wash is a wood cleaner with a high pH solution, which can dissolve, soften, loosen, or react with different types of extractives found in extractive-rich woods used in log homes. If a chemical is soluble in a liquid, it is easier to remove than a chemical that is only softened by that liquid. Being soluble is preferred as this means the particles are broken down to become so tiny we can no longer see them. Cedar Wash is designed to remove surface resin oils and high concentrations of water-soluble wood extractives such as sugar and protoplasm, in addition to dirt, grease, grime, pollen, and surface mold and mildew without harming the wood.

Cedar Wash was developed by Perma-Chink Systems as a Ready-to-Use cleaner specifically formulated for preparing the surface of wood species that contain high levels of wood extractives and resin oils. It is also safe for chinking and sealants.

• Easy to use, Ready-to-Use formula.
• Low environmental impact
• Designed specifically for Western Red Cedar, Redwood (Softwoods), Walnut, and Mahogany (Hardwoods)
• Removes resin oils and wood extractives from the surface of the wood