When logs go through the planer, as most new, smooth wood does during the milling process, the heat of the planer melts the natural sugars in the wood creating a barely visible film called mill glaze or mill scale. This little talked about film creates a barrier that interferes with the penetration and adhesion of wood finishes, which in turn can create long term issues with finish durability and performance.
When wood finish is applied to lumber that still has mill glaze, penetrant stains will often look spotty and show a decrease in performance. Film forming glossy or satin finishes may start to peel soon after application, have a spotty appearance and decreased durability and performance against the elements. To protect your investment initially and avoid costly re-do expenses, it is extremely important to remove mill glaze from wood before applying any type of finish.
Removing mill glaze can be done in a number of ways; LogFinish.com suggests the two options below:
1.Washing with a wood cleaner:
The easiest way to remove mill glaze is to wash with a wood cleaner designed to remove mill glaze and clean wood. Wood cleaners formulated specifically for use on wood will maintain the proper pH balance of wood while removing mill glaze. Cleaners that contain oxalic acid, like X-180 Weathered Wood Restorer or sodium percarbonate like All Wood Cleaner do a great job of removing mill glaze. Most products that remove mill glaze are best applied with a pump up sprayer and then washed off with a pressure washer at no more than 500-600 psi. Do not use bleach unless specifically recommended by the wood finish manufacturer. Bleach is caustic and dramatically affects the pH of wood, which can cause spotting, streaking and all manner of application problems.
2. A light sanding:
If you have the people power and/or a small surface to remove mill glaze from, use a fine to very fine grit sand paper to give the wood surface a light sanding. After sanding, be sure to use a vacuum or leaf blower to make sure all the sawdust from sanding is removed from the wood. Even small amounts of fine sawdust left on logs can cause a lot of problems when staining, preventing stain from being absorbed and creating an uneven finish. This results in decreased finish performance and durability.
Removing mill glaze is the essential first step in a quality wood finish application. Questions about your specific project? Leave a question in the comments section below, send us an email at [email protected], or give us a call at 888-208-2248.