Beth n Rod 1,279 Report post Posted March 1, 2003 This article was reposted with the permission of Russell Cissell of Extreme Solutions. Thank you Russell! ------------------------------------------------------------------- I’ve noticed recently a lot of confusion with regard to the neutralization of wood during the cleaning and restoration process. I wanted to take just a few minutes to explain neutralization from the practical as well as physical standpoint. While it is not necessary to have a degree in chemistry to be proficient at wood restoration, a basic familiarity of the chemical processes that are taking place will help you understand why things sometimes go wrong for “no apparent reason”. Further, it will help you predict results and alter your process to match the job at hand. Unfortunately, I am going to have to give you a bit of background information before I can get into how neutralization affects the results of your work. -pH 101 A Danish chemist first coined the term pH. “p” for the Danish word potenz which translates to “power” and H for hydrogen. Many compounds dissolve in water and alter the concentration of ions. Substances that form ions when they are dissolved in water are called electrolytes. The three types of electrolytes are acids, bases, and salts. Compounds that produce hydrogen ions when they are dissolved in water are called acids. Compounds that produce hydroxyl ions when they are dissolved in water are called bases. The pH scale was developed as a (simplified) way of assigning a value to the level of acidity or basicity of any given substance. The scale runs from 0 to 14 with 7 being neutral. Acid 0_1_2_3_4_5_6___7___8_9_10_11_12_13_14 Base __________________Neutral______________________ Anything with a value less than 7 (for simplicity) can be called an acid. Anything with a value over 7 can be called a base. The further you go from 7 toward either end of the scale indicates the relative strength of the acid or base. Sodium Hydroxide, a common ingredient in wood strippers, ranges on the pH scale from 12.0 to 14.0 so it is very “Basic”. Oxalic, 0.1N, used in many brightener/neutralizers hits the pH scale at 1.6 so it is acidic. “Acids” are substances that dissociate in water to produce hydrogen (H+). An example of a common acid is sulfuric acid, H2SO4- In solution, H2S04 dissociates to form hydrogen and sulfate ions. Some other examples of acids are lemon juice, orange juice, aspirin and vinegar. Acids all share some common properties. For instance the term “Acid” comes from a Latin word that means, “sour.” You will find that most acid solutions will taste sour. On a side note, tasting a solution to determine if it is in fact an acid is not the best method! Acids share some other properties that are much safer to test for. Here are some examples: Acids turn litmus paper red. Acids react with many metals to form hydrogen gas. Acids react with carbonates to form C02 (carbon dioxide gas). “Bases” are substances that produce hydroxide ions (OH-) when dissolved in water. An example of a common base used in wood restoration is sodium hydroxide, NaOH. In solution NaOH, dissociates to form sodium ions and hydroxide ions. Common types of bases are most soaps, household ammonia and lye. Like Acids, Bases share common characteristics. The following are four characteristic properties of all bases. Basic solutions taste bitter. Basic solutions are slippery to the touch. Bases turn litmus paper blue. Bases neutralize acids. Anytime you combine an Acid with a Base the chemical reaction that takes place is called “Neutralization.” This process of neutralization creates “Salts” Salts When an acid reacts with a base, two products are formed; water and a salt. A salt is an ionic compound composed of positive ions and negative ions. The ionic bond is what keeps salts in their molecular form. The “salts” that are produced are not simple table salt (Sodium Chloride) such as is found in seawater. Chemically speaking the term “salts” is used to classify a whole group of ionic compounds. These ionic compounds are created during the complete or partial neutralization of acids. Salts can also be created by the direct combination of elements, reactions of salts and acids, or reactions between different salts. The term “salts” can further be broken down into two sub categories: Acid Salts and Normal Salts. While “Normal Salts” are created during complete neutralization, “Acid Salts” are created during incomplete neutralization. Certain soluble salts (principally sodium, potassium, magnesium, and calcium) that have the property of combining with acids to form neutral salts are called alkalies. Unlike acids and bases, salts vary greatly in all their properties except their ionic characteristics. Salts may taste salty, sour, bitter, astringent, sweet, or tasteless. Solutions of salts may be acidic, basic, or neutral to acid-base indicators. The reactions of salts are numerous and varied. Because of their ionic nature salts cause or enhance chemical reactions. Being ionic means that salts have an imbalance in the electrons that they contain. This imbalance facilitates the transfer of electrons from other molecules. This transfer of electrons is the very basis of a chemical reaction. In some cases this transfer of electrons is a very desirable thing. When it comes to the curing of a freshly applied stain or sealer it can cause reactions that are not conducive to the performance and longevity of the finish. Having said that I want to take a look the chemistry behind the restoration process. Because wood, especially cedar and redwood, tends to be slightly acidic, understanding the neutralization process becomes very important. When a contractor strips a solid colored stain or paint, often times they will use a stripper that contains a caustic, or base, such as sodium hydroxide. After the wood has been stripped the pH will still be very high (basic) and the wood may take on a dark appearance. It then becomes necessary to neutralize the wood to restore a more natural pH and color. Proper neutralization is crucial for the finish to cure out and perform optimally. If the wood is too caustic or basic it can react with the oils in the stain and produce a form of soap. This reaction will drastically alter the curing process of the finish and result in premature failure. If the wood is too acidic it can cause decolorization of the stain or prevent proper penetration and adhesion. In general most finishes are more tolerant to acidic conditions then basic conditions. As you read before, the neutralization process produces salts. These salts can have varied and unpredictable effects on a finish. It is not enough to simply neutralize. You must also thoroughly rinse the wood prior to the application of the finish. Substrate preparation accounts for about 90% of a finishes performance. If there are salts left behind by the cleaning process, you are asking for trouble when the finish is applied. The tricky thing about salts is they have a way of changing on you. Again, as mentioned earlier salts can be created from a reaction of other salts. Because of this it is difficult to know exactly what type of salts you will have when you return and thereby impossible to predict how a finish is going to react to any salts left behind. An example of this can be found when looking at color shift. Color shift is a term used to describe the process wood (especially cedar and redwood) goes through after it has been over treated with oxalic acid. The chemical process that takes place draws the natural coloring of the wood to the surface. This is an unnatural state for the wood and in a short time the natural colors in the wood will migrate or shift away from the surface of the wood. This can result in an uneven or splotchy appearance. In some cases the shift can be such that the wood will take on a whitish “dead” look. The absolute best advise I can give with regard to the cleaning and neutralization process is to rinse, rinse and rinse. When you are certain that you have rinsed as much as you can, rinse everything one more time. The extra couple minutes it takes you to rinse well is nothing when compared to the time it takes to strip off and reapply a finish that failed because you didn’t rinse well enough. Best of Luck Russell Cissell Share this post Link to post Share on other sites
Beth n Rod 1,279 Report post Posted July 20, 2003 Important reading, if you missed it the first time... Share this post Link to post Share on other sites
Claude 14 Report post Posted July 30, 2003 A great pH article. Tell me something. I walked up on a porch the other day and the homeowner had cleaned it with a sodium percarbonate cleaner (Armor All from Wally World) His porch had that dead white appearance. Would I have to reclean the porch then neutralize right afterwards or what would I have to do to get this porch in shape to seal? And where is a good place to get Oxallic or Citrolic for neutralizing? Share this post Link to post Share on other sites
ron p 500 Report post Posted July 30, 2003 it sound's like it was not rinsed very well. If water bead's on the surface you'll need to strip it, then nuet. Beth here sell's citrolic acid. A better pre-carb[efc38] and other great restoration chem's. Her store is SEE DIRT RUN Share this post Link to post Share on other sites
