Logs that have been exposed to the sun may have slight gray areas on them and dirt, dust and mold spores are probably on most of the logs. It is important to start with a clean, uniform surface before applying a coat of stain, since dirt and discolorations will show through semi-transparent stains and the stain will seal in any blemishes. Cleaning also opens up the pores of the wood, allowing better adhesion of the stain. This is especially true if there is a mill glaze present on the logs. Not only will the mill glaze reduce the stain’s performance, but caulks and chinking will have a difficult time adhering to mill glazed wood.
Aggressive cleaning of a new log or timber home is not required. A light cleaning with Log Wash and a pressure washer will usually remove the dirt and mill glaze, as well as clean the surface to prevent the formation of mold under the stain. If the new logs have started to gray from sitting unprotected in the sun, a percarbonate cleaner like Wood ReNew will restore the wood back to its original color. Log Wash and Wood ReNew are much safer products to use compared to bleach solutions which destroy wood fibers.
The leading cause of stain adhesion failures and discolorations appearing under the semi-transparent stains is inadequate rinsing of a bleach-cleaned surface. Bleach (sodium hypochlorite) solutions are alkaline (high pH). Wood, on the other hand, is slightly acidic (low pH). Whenever low pH materials are exposed to high pH solutions, chemical reactions occur. Often these chemical reactions are minor and do not affect either material, but in the case of wood, exposure to bleach solutions may result in several irreversible reactions that may not become apparent for several months. Once the wood fibers are damaged or destroyed, a stain will not properly adhere to the surface and eventually will chip or peel. Even when used at a low concentration, a bit of bleach residue left of the wood will eventually result in discolorations due to iron tannates coming to the surface under the stain.
Occasionally, steel straps used to bundle the logs during transportation will leave iron stains that need to be removed with OXcon oxalic acid. Whenever oxalic acid is used, be sure to clean the entire wall to avoid blotches and streaks.
We never suggest media blasting new construction, but if that is what your log home manufacturer recommends, be sure to use a fine grit media to avoid damaging the surface of the wood.
Congratulations on your new home and happy cleaning!