Mill Glaze is a phenomenon that occurs during the milling process of the wood. Wood generally has an open porous cell structure that is very accepting of wood finishes. This porous structure is altered during the planing process that makes the wood glossy smooth or mill glazed.
Blades on these planners rotate at very high speeds and crush the open cell structure, which transforms it into a closed structure that prevents the penetration of any coating. To achieve maximum bond of our coatings to the wood we recommend that the glaze be removed by sanding or applying TSP, bleach and water solution and then lightly power washing the surface.
Various “Mill Glaze” removers are also available on the market. Mill glaze removers use a wetting process and some type of physical abrasion to open the closed cell structures.
An easy demonstration to see if there is mill glaze is to sand a small area with 60 to 80 grit sand paper, wipe off sanding dust, place a drop of water on the sanded area and a drop of water on the wood surface without prep. You’ll be able to see the absorption in the area where you have sanded.