I have to say right up front that wood restoration using chemical strip methods is a project best hired out to qualified professionals. The pressure washing equipment, chemicals, safety equipment and best practices for all of the above are not common knowledge. Also, knowledge and experience in working wood through various stages of chemical ph balance manipulation is necessary to avoid damaging the home.
Exterior wood restoration is kind of like stripping a gigantic piece of furniture, and can be done in many ways. One of the most effective methods is chemical stripping. When done properly, the chemicals do the majority of the work, and the washing is done with relatively low pressure. The worst thing you can do is to use too much pressure and tear up the wood.
There are a couple of relatively easy ways to get the chemicals onto the house. Downstreaming uses a suction tube at the pressure washer machine to draw the chemicals into the flow through the pressure hose to the wand, after the pump. The “dwell” method is another way, and it is a bit easier to control the results.
For our current wood restoration project, we are using the dwell method.
Chemical stripping is a two step process, referring to the need to apply and rinse two chemicals. The first is the stripper, and the second is the neutralizer, or sometimes called brightener.
The stripper step is often a sodium based chemical such as sodium hydroxide, which raises the ph level of the wood. The second step is an acid component which neutralizes the ph level and restores the natural color of the wood. With both of these steps, it is important to wet vegetation and other surfaces in the area that the rinse water might get to.
Most important is the personal protection of the person or people applying the chemicals and rinsing them. The photos in this post show the extremes we go to for personal protecion. No exposed skin. Period. Stripping chemicals are hot, and have a real capacity to burn skin, especially after hours of grinding on your skin through wet clothing. It is important to limit the amount of applying chemicals and rinsing overhead.
The stripping process in a nutshell: protect yourselves; apply stripper from the bottom up using a pump sprayer; let dwell for 20 minutes; rinse before it dries and do so at low pressure from the bottom up and then top down; apply neutralizer and let dwell for 20 minute; rinse until all runoff water is clear.
For stubborn areas, you can reapply your stripper, or agitate with a stiff bristle brush and rinse again.
Chemical stripping has the tendency to raise the grain of the wood that has been stripped. This is sometimes called “furring” of the wood, referring to loose wood fibers left on the wood after final rinse. Light sanding will smooth the furring out and remove the loose fibers. After several days of dry time, the home can be refinished.
Please leave a comment if you have questions on how to safely strip exterior surfaces for wood restoration.