pH Strips
By Sean Gahan
A lot of time and effort in our newsletters and training seminars is devoted to making sure that our customers understand the importance of surface preparation prior to applying a finish to their log home. The cleaning process is the basis for how the finish system will perform and look for years to come.
Currently, there are two cleaning solutions that Perma-Chink Systems recommends for preparing the wood surface prior to the application of a finish. The first of the two options is a 1:3 bleach-water solution plus the addition a detergent like Ivory soap, Spic-N-Span or TSP (trisodium phosphate). There are two parts to this solution. The purpose for bleach is to sterilize the wood surface; however, most people do not realize that bleach does a lousy job of cleaning, hence the addition of a detergent.
The second option is the use of Lifeline Wood ReNew™, a white powder that contains a detergent. Lifeline Wood Renew forms hydrogen peroxide (H2O2) when dissolved in water. Both of these solutions do a great job of removing foreign matter from the surface of the wood and sterilizing it.
The cleaning solution should always be applied starting with the bottom log and proceeding to the top log. Using this method ensures that each log below where you are applying cleaning solution already has cleaning solution on it and thus reduces the potential for streaking. Allow the solution to remain on the surface of the wood for 15-20 minutes and begin rinsing with a pressure washer. Rinse the wall starting with the top log and proceed to the bottom log. Rinse the house thoroughly to ensure all the cleaning solution is removed.
With this said let’s address a few important questions.
Question #1: What color is a solution of bleach and water?
Question #2: How do you know when all the cleaning solution has been rinsed off the log surface?
The answer to the first question is colorless. Most cleaning solutions have very little color associated with them, especially when they are diluted with water. So this leads us into the second question. Without a visual indicator, how do we know when the wood surface is free of cleaner residue? To answer this question we must utilize a quantitative tool that enables us to determine when the surface is free of cleaner and furthermore that our rinsing process is complete.
The first thing that you must know is that both of the recommended cleaning solutions that were discussed above are bases and have an approximately pH range of 11-12.
pH is a method that determines whether substances are either acids, bases or neutral.
To do this we are actually measuring the concentration of hydrogen ions in solution with either a pH meter or pH paper and using the following equation:
pH = -log [H+]
Armed with this information, pH strips will serve as our quantitative tool to indicate that we have thoroughly rinsed the cleaning solution from the wall.
Before you start rinsing the cleaner solution off the logs, use a pH strip measure the pH of the rinse water to determine your baseline pH. This number typically falls between 6.5 and 7.5. The objective in rinsing is to reduce or dilute the pH of the cleaning solution (pH = 11-12) that is on the wall to the pH of the rinse water. Rinse the house until you think that you have removed all the cleaning solution. When you believe that you have reached this point, take a few pH strip and measure the pH of the water dripping off the wall at 4-5 places.
Continue rinsing until the pH off the wall measures 6.5-7.5 (Ideally: 6.8 – 7.4). Remember that this number will be defined and limited to the pH of your rinse water.
The failure to remove the cleaner residue entirely from the wall surface can result in many detrimental problems with the finish systems.
This would include premature failure due to a lack of adhesion. This lack of adhesion stems from a chemical reaction between the residue and lignin, a component of wood, resulting in a loss of the wood’s structural integrity.
Secondly, a high concentration cleaner residue on the surface of the wood can increase the migration rate of tannins, components within wood, to the surface of the wood. These components in the presence of metals such as iron can produce blue-black discolorations. The problem is that these discolorations may not show up for many months and they are almost always located underneath the finish.
pH strips can be purchased at Perma-Chink Systems stores, pool supply stores, aquarium shops, or discount stores (i.e. Walmart). This tool can save you a tremendous amount of time and money when it is used properly. Contact Perma-Chink Systems if you have questions concerning the surface preparation steps or the use of pH strips. We are here to help you.