Mold on Green Lumber

Quick drying should contain most mold problems encountered on freshly-sawn green lumber arriving at the kiln. June 13, 2014

We are a large kiln drying facility in western WI purchasing roughly 100,000 to 200,000 feet of green lumber per month drying roughly 1.4 million a month with our own sawmill stock. We have received some loads in our yard the last few weeks that have shown some initial signs of mold and slight stain. We usually have the white woods into the kiln within 48 hours of arriving in our yard. The problem is when the stock comes off the truck with mold and stain we can re-grade this stock and de-grade against it but our purchasing agent wants us to S2S a sample of this stock to our hit miss product of 15/16" to see if the stain will be in after drying. We know that it will S2S out at 15/16" in the green. Are there any kind of studies that shows and quantifies the results if the stock has mold or stain in the green it will be worsened or enhanced during drying. We can run tests and show the results here but if there have been studies done on this I would love to take a look at them.

Forum Responses
(Commercial Kiln Drying Forum)
From Gene Wengert, forum technical advisor:
At this time of year the sugar content right under the bark is fairly high and so mold can grow. When the temperatures are warm mold will grow in just a few hours. There is also a lot of sugar in the sapwood near the bark that will feed mold. The mold does not go deep into the wood. Other fungi may go into the wood however. Rapid drying will stop the mold quickly. So make sure you get a low RH in the kiln ASAP.

The S2S stuff is not too good, as the bad color can develop only after drying. That is, it may look ok green, but can have bad color later. Nevertheless, initial rapid drying (low RH) will eliminate almost all color problems. To make sure that the low RH is provided for the entire load, often a kiln is loaded only half full initially. I think you recall this procedure from when you were in a drying class.