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Two years ago during construction of a new garage/loft I installed a 33 foot glue-lam beam (approx. 20 2x6's sandwiched together). Before I could get a roof on the structure we had a couple of early rain storms which stained the beam with dirty streaks. I quickly got the building weather tight and haven't thought much about it until now. I'm finally getting around to the interior of the building and have started trying to clean up the beam as it will be a show piece of the room. Getting out the dirty rain streaks is proving very difficult. So far I've tried cleaning with TSP and using a palm sander with 60 grit paper and I can get it out but it's taking me roughly an hour and several sheets of paper to get one foot and I have to do both sides of the beam-almost 70 feet. Is just the inherent hardness of a glue-lam that's causing me trouble? Any suggestions on how to clean up the beam more easily? And once it is clean, what to you suggest as a finish?
Not being there is is difficult to appraise the situation. But here goes...You'll need to use a mild solvent. I'd try denatured alcohol and a course scrubby (artificial steel wool). Just do a test patch and don't use too much of the alcohol. Just dip the scrubby in it. If that does not work, take it up a notch to mineral spirits. Make sure you've got adequate ventilation – – think about wearing a respirator, solvent fumes are heavier than air and will come off the beam and go right for your lungs. Both if these will tend to raise the grain on the wood a bit, so if successful a light sanding will be appropriate.
An alternative and "less toxic" cleaning formula is as follows:
( Add to a gallon of "hot" water)
2 tablespoons gum turpentine
4 tablespoons boiled linseed oil
This formula works best if it is hot enough to require that you wear rubber gloves. Wring out a soft clean cloth in the solution and wash the wood. Wipe dry. One advantage to using this mix is that it also serves as a sealer (linseed oil).
As far as a finish goes, any good satin urethane will do nicely – urethane is better than poly in this instance because it has more flexibility and can handle the expansion and contraction of the beam.
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