Kiln Drying Color Change
Experts and sawyers discuss the various reasons wood from the same batch might end up with slightly different colors. September 6, 2010
Question
I am currently in the middle of a project in which I have been sawing/drying red oak and turning it into tongue and groove flooring as well as installing it. When I was hired to do the job I began by using some red oak that was air dried, but I only had about 1/2 of the needed material so I sawed the rest up and had it kiln dried since I needed it quickly.
Half the room has been laid with the air dried material and now that I have made the rest of the flooring out of the kiln dried material I am noticing that it seems to be tinted more dark grey-ish. Is this common? Unfortunately half the floor is already laid so I cannot mix the material together. I've yet to sand or stain the floor so perhaps I can stain it so the difference is not noticeable?
Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Chances are that the color is due to enzymatic stain, but it could also be the common blue stain fungus. Slow drying or no drying will encourage these two stains. In either case, the color develops or begins to develop as soon as the tree is cut down. So, did the second batch of logs sit in the woods for a while during warm weather? Or did the logs sit at the sawmill? Did the sawn lumber sit too long before drying or did the sawn lumber dry too slowly at high MCs (slower than about 2.5% MC loss per day) from the moment it was sawn?
From contributor O:
This is a little off the subject but along the same line. Vacuum dried wood normally looks brighter than conventionally dried wood. Is this due to inhibited enzymatic staining because of quick drying, reduced caramelization due to lower temperature or reduced oxidation due to less air?
From Gene Wengert, forum technical advisor:
Contributor O is indeed correct, but only if the lumber or logs are fresh.
From the original questioner:
The kiln dried wood only sat for about a week after being sawn, and it was indoors. The air dried wood sat for over a year but it was also indoors. Both came from logs approximately the same age which had been cut for around two years. I assumed the color change was due to the heat causing some kind of caramelization. It’s hard for me to imagine it being due to fungus since it occurred in every piece that was kiln dried which came from two different trees. The whole batch was tinted grey-ish, while the air dried wood was more red/golden. What is enzymatic stain and would it cause a color change in only the kiln dried wood? I believe the kiln got up around 160 degrees.
From Gene Wengert, forum technical advisor:
High heat causes the wood to brown and not gray. Perhaps there were two different oak trees, one being northern red oak (Quercus rubra) and the other being black oak or another species within the 20 species that are in the red oak group. You can read a lot about the enzymatic stain in the archives, but heat over 75 to 80 F when the wood is wet and not drying makes ideal conditions for graying.
