Cleaning Log Home Logs
Just as you wouldn't wax your car prior to waxing it, you shouldn't stain your log home prior to removing all mildew, dirt, dust, pollens and other contaminants. It's not that unusual to spend as much time (or more) prepping your logs to be stained as on the staining itself. Don't take shortcuts.
Log Cleaner & Water
If an inexpensive log cleaner (soap) and water cleans your logs to your satisfaction, you won't need any of the below methods. When determining what cleaning methods to use, start out with the easiest, least expensive system first. For example, why assume your home needs to be cob blasted when a soap scrubbing and rinsing will give you what you want? If your first choice doesn't give you your results, proceed to a more aggressive method. Some cleaners may work by spraying a log surface then either pressure washing or hosing off. At times, hand scrubbing may be necessary.
Note: Bleach will not remove a stain or dirt, but will often remove some mildew, and in doing so, will also brighten your logs. Bleach should never be used at full strength. A dilution of 1 part bleach to 4 parts water often works well.
You'll hear different recommendations on whether you should have your home pressure washed or not. Theres no uniform answer to this. If pressure washing can be the quickest method with stellar results, it should at least be considered before employing the cob blasting (below) method. It could be much quicker, easier and definitely is more cost effective. One fallacy is that you're saturating your logs with water as a result of pressure washing. This isn't necessarily true. On hard, sound, rot-free logs, you're only introducing water into the top fibers of the wood. Your decision should be dependant on the results you want and whether or not your gaps are conducive to allowing water in your home. If you choose to go with a pressure washing, and your home has numerous gaps that will allow water to infiltrate, foam backing rod (the same as a what is used prior to chinking) can be plugged in place beforehand. Because the interior of your home doesn't face the elements of Mother Nature, pressure washing generally isn't necessary except for on the exterior. The one exception could be if after your walls are stacked, a long period of time goes by before the roof is erected. This exposure could cause some mold and mildew to form, particularly in a damp or humid environment. Remember, mildew does not damage or weaken wood, it's just unsightly.
The amount of pressure used will vary tremendously. A low setting of 500 - 1000 psi could be sufficient to simply remove UV graying that's taken place over a few months. Something closer to 2500 - 3000 psi may be necessary on some logs. Remember, the higher psi used, the higher the probability that some fuzzing of the wood could take place. If you choose, this end effect can be buffed or sanded off.
While solvents aren't as popular as they once were, they could be the necessary means depending on the type and amount of finish you're removing without going to the more expensive cob blasting method. Since a potassium hydroxide, sodium hydroxide or methylene chloride based strippers are generally used, protective gear (including eye-wear) should always be used. After applying the stripper, let it stay in place as long as recommended by the manufacturer, then pressure wash off. Generally a lower pressure setting can be used (1000 - 1500 psi) to remove the chemical than with pressure washing alone. In addition, a rinsing with an oxalic acid following a high pH level stripper should be done in order to return the pH level of the wood back to where it needs to be to properly accept a stain. Proper care should be given to surrounding grass and foliage as well. Wetting down the areas you want to protect, covering with plastic tarps and rinsing again after the project with water normally does a good job of protecting your plants.
Remember: ALWAYS apply a stripper (or any cleaner) from the bottom and work up then rinse starting with the top. This process will help eliminate any spotting effect caused by upper logs dripping on lower ones. In addition, when pressure washing off a stripper, make sure not to spray the water on the logs that have not yet had the stripper applied. Strippers always work best on dry wood, and usually work better (and quicker) in warm weather.
While one wouldn't use a sand blaster on a log home due to the potentially severe damage it can do to your surface, media blasting over the years has evolved into a very popular, solvent free finish removal system. A modified sand blaster and a large air compressor (125 CFM or greater) is used to blast your surface with blasting media at a very high velocity and relatively low volume. Coverage one can expect from a 40-pound bag of can vary from 40-50 square feet up to 150+ square feet. Factors include amount of pressure (psi), size and effectiveness of compressor, hardness of your logs, moisture content, experience of the applicator and most important, the type and amount of finish you're removing. While the media won't rough up your log surface to the extent a sand blaster will, it also won't leave your home with a “hand-sanded" finish. You can always choose to buff or sand your log surface lightly after a cob blasting to minimize the effect of the pitted texture blasting may leave. This blasting media is biodegradable and won't harm your plants. Blasting media should not be recycled through the blaster. Re-introducing the media back into the equipment could also add small rocks and bark which could damage it.
Hand sanding or by mechanical means (planer, angle grinder, orbital, etc.) gives you the best results but also is (by far) the most time consuming. A good sanding or grinding of your logs will provide a very smooth finish which means your logs will stain substantially lighter since the stain (oil or latex) won't soak in as deep. Your coverage will also substantially increase from 200 - 300 SF per gallon to as much as 450 SF per gallon. After a sanding, make sure to brush or sweep off any dust particles prior to staining so it doesn't interfere with adhesion. For log ends we use a 36 grip aluminum oxide grinding disk.