I have mold growing on Douglas Fir Timbers. Does anyone know of effective ways to stop and even reverse this? Some of the timber are final dimension so I can't plane much wood away.
Also, just in the case I have to live wth these dark stains, does anyone know of cool finishes that will hide the mold stains yet look attractive. ( i have considered stains but i am avoiding the look of heavyly pigmentd suface finishes, i am after something more evocative of milk paint )

tHANKS

Anthony

Mold eh? Welcome to the Pacific coast.
The most readily available mold fighter is household bleach. It will kill the mold and bleach the wood to remove some or all of the stain depending on how dark it is. Use a fairly strong solution (1/4 cup to gal of water) or stronger as needed. You will notice that the bleach gives the wood a yellowish color, which you may not care for.
Another solution is oxalic acid. This available thru chemical supply houses, paint suppliers and some hardware stores it is also the active ingredient in many commercial deck/wood bleachers. Oxalic will give the wood a more orange cast than bleach which I think looks more natural.

Over time the natural darkening of the wood will obscure the color changes caused by either method. It is also best to treat the entire piece and not just the molded and stained areas. And I have learned that sanding the affected areas before bleaching seems to improve the effectiveness.

Final note: none of this is magic and you may have some residual stain left. You can try sanding or planing but my experience is that bad stains go deep and repeated bleachings will help but at some point its best to leave well enough alone.

And don’t forget eye protection

good luck

Are they just raw timbers or are they assembled in a frame? Are they indoors or outdoors?

The timber are raw, I am cutting joinery so they are in my shop, which has a woodfire burning most of the time (and a 24" fan to make sure i have good circulation throughout. I'm not sure what the temp is but i am usually dressed in a t-shirt or sometimes a light sweater while working in there so its pretty warm.

PS
I did try bleach but the mold came back after about two weeks. Perhaps I'll increase the bleach to water ratio. I will also try the O. Acid.

Anthony,

I doubt bleach will give you any long lasting results. The problem is that the water in the Bleach/water solution penetrates into the wood and supplies moisture for continued mold growth while the chlorine simply stays on the surface.

You can try the O. acid or try Tim-bor a commercially available borate based wood preserver. It will have better penetration qualities in liquid form and can also be applied
to kill surface mold as powder. It is a natural pesticide as well as fungicide. I have never used it personally. If you try it let me know how it works.

http://www.custompestcontrol.com/Timbor.html