We own a post and beam built in 1987. The beams were green pine sealed with linseed oil and thinner. We have a house ventilation system which we use in the winter to solve moisture problems but in the summer we keep the windows open. For the last several years we have had an increasing mildew problem (the previous owners who built the house will not admit to having the same problem). The mildew only shows on the beams; the walls and woodwork are clear of mildew. The wall have paint and the woodwork is stained and sealed with poly. What we would like to know is why we have this problem and what we can do to solve it. I am hoping that the guild members (who have been tremendous with past roof problems)will have some advice. Is the lineseed oil causing the problems? Is there some product that works particularly well? I have tried a 10/1 mixture of bleach.

Anne

Anne...

I'm no expert, soo...

The first thing that comes to mind is humidity. Given the age of the frame, I would expect the timbers to have acclimated to ambient humidity by now. Assuming of course that the sealeant is not doing an incredible job of holding in the moisture. A pin type moisture meter will quickly confirm if this is the case.

I would not be surprised if the relative humidity of the house in the summer is the cause of the problem. A relative humidity meter will make fast work in confirming if this is the case. If it is, I think increasing air flow through the home MIGHT help, by AC might be needed.

Other possibilities: If part of the living space is below ground, the cool floor and walls would very likely condense water from the "fresh outside air". Conventional wisdom says open the windows...and "air out" basements in warm weather. I think conventional wisdom in the case is all wrong. Warm outside air holds a relatively large amount of water. Bring this "fresh air" into a cool living area and the RELATIVE humidity will increase. Mold and such love such an environment.

Moisture seeping through concrete walls and floors are another possible source of moisture.

Anyway, to boil this down to fewer words: There is moisture. Determine the source of the moisture. It's coming from the timbers, or somewhere else. Test timbers with pin type moisture meter and ambient inside air withe relative hudidity meter.

Hope this wordy reply is of some value to you. Let me know how it turns out.

Joel

Anne

I have a few observations. Living in Western Washington as I do, one becomes well acquainted with molds, mildews and fungi. Mildew on the woodwork is a common problem here. On and in both houses and boats.
I think you may be onto something re: the linseed oil. Mildew needs food and linseed oil would do nicely.
I also think that Joel has a point about moisture and I would be curious as to whether you see more mildew in summer or winter
It occurs to me that warm moist air on summer morn may condense on wood surfaces chilled by the cool night air
Is the floor plan open and do you have a good hood over the cookstove? (downdraft vents don’t count)
Very likely the mildew was in the beams when the house was built.
The bleach is a good idea but you may have to use it in greater concentrations and volumes that you care to inside.

Good luck J. Buday