Preventing Mold Formation on Freshly Sawn Pine

Surface dryness is the best answer to preventing mold from getting a foothold on sawn softwood. Here are tips on how to achieve it. April 18, 2010

I have a sawyer friend that has a problem with his lumber molding after he mills it, even though he's using a mold spray. The lumber is under a 50' X 70' shed. What can be done to stop the mildew?

Forum Responses
(Sawing and Drying Forum)
From contributor S:
The wood needs to be stickered right after sawing. It also needs to have as much airflow through the pile as possible.

From Professor Gene Wengert, forum technical advisor:
I suspect he is not using a mold spray that is designed for wood. In fact, most of today's chemicals do not control penicillin mold and some other molds very well. There are a few chemicals that do indeed control molds, but it is worth noting that these are stronger and more dangerous than the more standard chemicals used for woods. There is a great deal of work on this subject that has been done by the University of BC and the Western Canadian Lab (Forintek). I recall several articles in the Forest Products Journal.

Because molds and mildew need moisture to grow, quick surface drying will stop them unless the moisture returns. If mold is developing, it is also likely that some blue stain is also forming, which would go deeper into the wood. Shipping undried wood and not developing staining is a complex subject that cannot be covered with a short answer.

From contributor L:

One way to lessen the stain is to cut the timber in colder weather. Won't eliminate the problem due to the many factors that Dr. Gene references, but it will mitigate the extensive stain you'll see in summer cut pine. That said, some people actually like "Denim Pine".

From contributor A:
In the summer when we saw pine, it goes on dry stickers. The bundles are set out in the sun where they can get the most wind. For pine we want to keep free of mold, we load the kiln about half full and crank up the heat and fans. With really nice boards we lean them against the shed and flip them every few hours so that the sun dries them down quite a bit. Your friend's shed is not getting enough air flow.

From contributor S:
We saw pine all year long with no problems. Air flow, air flow, air flow - that is your best mold and blue stain prevention.

From contributor M:
Also, removing/sweeping all sawdust off helps the lumber dry. Virtually every response speaks of moisture and drying the lumber as quickly as possible. Mold/mildew can not grow without moisture.

From contributor D:
I have a row of 5 3x3 poultry house fans mounted to posts - sort of a makeshift drying shed. We cut pine through hot, humid summers with no problems. I only run them for a few days to get rid of surface moisture and keep the cost down, but it really works. Airflow is better than trying to spray the lumber in my opinion.