Exterior Wood Finishes vs Exterior Fasteners

Natural Linseed oil is as old as Lewis & Clark ... so what if an exterior wood finish product has natural Linseed oil in it? Enter "Photosynthesis" ... which occurs when the suns untraviolet rays come into contact with your newly finished exterior wood surface at specifically 72-1/2 degrees Fahrenheit (or 22-1/2 degrees centigrade). Why should this occurence be a problem for you?

At this specific temperature, usually intensified on the side of your structure that has the greatest sun exposure time of the day, is when a phenomenon happens that creates fungus growth on any surface that doesn't absorb the natural Linseed oil completely. Your Cedar, Redwood, Fir, or other common natural wood siding will absorb all the Linseed oil by design as its intended to do, but the exposed heads of fasteners have no means of "absorbing" the Linseed oil film that is left and exposed to the elements. "Natural" Linseed oil comes from flaxseed, and is "sticky" in consistency when left exposed on the surface. However, "boiled" Linseed oil is not sticky and/or tacky ... so it doesn't cause adhearance of foreign matter or organic growth such as fungus. For example, wooden tool handles have been coated with "boiled" Linseed oil for years, eliminating checking and cracking of the wooden handles for long term serviceability. But "boiled" Linseed oil is more expensive and requires added processing for its intended purposes. "Natural" Linseed oil seems to me more common as an additive in some wood coating finishes.

So what does this mean to you? Fungus and/or moss growth on the metal fastener finishes of your outdoor wood structure eventually leads to dark brown/black streaking running down your wood from the heads of the fasteners when moisture is present (rain, night dew, sprinklers, etc.) Everytime the sun comes out and hits at the 72-1/2 degree mark, another dose of photosynthesis takes place, encouraging more fungus growth to occur at these locations.

So the fix is ...? Entry of high end synthetic wood finishes into the market has resolved this potential problem, eliminating the cause for fungus growth. Also the use of "boiled" Linseed oil resolves this problem as well if you wish to save your wood surface from potential cracking and/or checking when exposed to the suns ultraviolet rays that can dry it out quickly when the summer time heat kicks in.