Understanding Stripping and Cleaning Chemicals
Sodium Hydroxide, Sodium Percarbonate and Sodium Hypochlorite are the three main cleaning agents used in log home and deck restoration. Each chemical has its place in the cleaning process, however, knowing when and how to use each one is often misunderstood.
Sodium Hydroxide, the strongest of the three, can be used either as a mild cleaner or when mixed properly, an aggressive stripping agent. Sold over the counter, it is one of the main ingredients found in oven cleaners, dish washing liquid, stain removers, degreasers and deck cleaners as well as a host of other products. City municipalities even use it in the purification process of drinking water.
In deck and log home restoration it is used to remove mildew, grayed out wood fibers and oil based stains and sealers. With proper dilution it can be applied to the wood preferably by spraying but also can be brushed on. It is very important to note that proper safety measures be taken when using this method and all instructions should be closely followed. Never mix water into Sodium Hydroxide. Instead, always mix the chemical into the water slowly and carefully. Mixing water to the chemical first causes a reaction that produces an enormous amount of heat and fumes. Safety goggles and gloves are mandatory as well as other protective clothing. Also, this chemical will kill grass and plants as well as stain glass, siding and other surfaces. If you are not sure about how to use this product, it is strongly recommended to find a professional who does. This is nothing to play with.
If there is no sealer on the deck or if only traces remain, a mild solution of Sodium Hydroxide and a good surfactant can be applied and allowed to dwell for a predetermined length of time. This allows the mixture to soften up the surface contaminants and degraded wood. A scratch test can be preformed to determine how easily the deck will clean up. If it is hard to remove, either more mixture will have to be applied and/or more dwell time allowed. If it is determined to be at a point that it can be removed, then a pressure washer will be used to remove a very thin layer of the degraded wood and any stain or other contaminants such as mildew, grill grease, flower pot stains, etc.
Care must be taken when using a pressure washer. If someone is not familiar with using a pressure washer, irreversible damage to the wood can occur causing costly replacement of decking boards or handrails.
Actually, less than 1000 psi / of pressure is needed. Water pressure is not as important as water volume. The more water, the more cleaning and rinsing power. At the very least, 4gpm is needed to properly remove the unwanted material. This rules out most homeowner type pressure washers which usually rate less than 3gpm (gallons per minute.)
Sodium Percarbonate is the same chemical found in the popular "Oxy Clean" products advertised on television. A non-chlorine cleaner, it is a good choice as a deck cleaner when a less aggressive cleaning or stripping is needed. Although it may remove some stain residue that may be left intact, it is better suited for the removal of mildew, dirt, light grease spots and gray, degraded wood. It will not harm grass or most surfaces if properly rinsed.
It is mixed to a predetermined solution depending on the severity of the job, allowed to dwell and removed with a pressure washer as with the Sodium Hydroxide. With this product it is advised to only mix what can be used in a couple of hours as it looses it cleaning power.
This is a good, less aggressive cleaner that can be used where there may be delicate plants and flowers in the area or animals in close proximity. Safer for the homeowner to use than that of the more aggressive strippers, it will clean the wood well enough that a sealer can be reapplied with decent results.
Sodium Hypochlorite is chlorine found in typical household bleach. Used as a disinfectant and sanitizer, it is excellent in removing and killing mold and mildew. It does little however in removing dirt and other contaminants.
Many homeowners and some less informed contractors use only bleach to clean decks and other wood surfaces.
There are a few things that need to be considered when using this method for cleaning wood.
Most importantly, chlorine bleach (Sodium Hypochlorite) is one of the main chemical compounds used in paper mills to brake down the wood fibers in the paper manufacturing process. Chlorine disintegrates the lignin in the wood which is the glue that holds the wood fibers together. Once the lignin is removed the fibers are reduced to a pulp that then is extruded through a series of rollers that expels the water and leaves a paper substance after it dries.
The point is that too strong of a chlorine mixture can destroy the wood fibers in the deck or log home.
If bleach is poured onto a piece of wood and allowed to dwell any length of time, you can take a stick and actually scrape away a significant layer of the wood. If you examine it, you will find that it has turned the wood to pulp. Not only does this destroy the wood, but it is almost impossible to rinse all of the bleach from the wood. If you put bleach on your fingers and try to rinse it off, you will find that it is very slippery and very hard to remove it from your fingers. This indicates a high ph level. The same thing is true with the wood. So there ends up being a bleach or stripper residue left on and in the wood. Not the ideal situation to be applying a new finish.
Since these chemicals are hard to completely rinse from the wood even after copious amounts of rinse water, the wood will still have a high ph level. To counter this, the wood has to be neutralized to lower the ph level in order to stop any damage to the wood and also keep from interfering with the new finish. To do this Oxalic Acid is used. Applied by sprayer, the acid lowers the ph level of the wood and at the same time brightens the wood. This process whether intentional or not, is often overlooked by the homeowner as well as the uninformed painter during the deck or log home restoration process leaving residual amounts of chemical in the wood. Again, not the ideal situation to be applying a new finish.
Also, chlorine by itself does little for cleaning dirt and other contaminants. Therefore a detergent must be added. TSP (trisodium phosphate) is a good cleaning agent if mixed properly. TSP is a derivative of borax and care must be taken when applying to any surface.
Be sure to never let it dry on glass or certain metals.
Chlorine does have its place in the cleaning process. Mixed properly and applied sparingly, it is the best method of not just removing mold, mildew and algae, but also killing the mildew spores deep into the wood cells. Used properly, chlorine can do an excellent job without damaging the wood, but it must be used correctly and must be neutralized to achieve good results without damaging the wood.
Remember, the key to a long lasting stain is properly cleaned and dried wood. Anything that will interfere with the performance of the sealer; existing stains, dirt, mildew, chemical residue or moisture must be completely removed using one of the cleaning methods, neutralized with an acid bath and allowed to dry. Dry is defined as moisture content of at least 15% or lower. Anything higher and the oil stain will not absorb properly into the wood. And the more stain absorbed into the wood, the better the performance of the finish. Remember, preparation and more importantly, proper preparation, is the key to a good and lasting finish.