Wood siding can benefit from a pressure wash as the grit that accumulates can be totally removed. The grit can cause damage as the wood moves with the wind and the changes in temperature. Pressure washing can also remove many stains but care must be taken. The jet of a pressure washer can actually damage the wood.
Before spray cleaning your wood siding you should ensure that you will be able to work through without having to stop to move things. Remove all furniture and plants against the siding that can be removed. Anything that could be damaged by getting wet from the spray should be moved or covered. If you have decorations hanging from the siding remove those also. Turn off the mains supplies to any outside lights in the area that you will be spraying. If you are aware of any cracked or damaged siding boards you should make a careful note not to spray wash them. Carefully close all windows and doors. If there is someone in the house they should be aware of you spraying and check before trying to leave the house.
Wood siding is not made of strong material so you should not use a very high pressure to clean it. You should also be aware that wood can be damaged if subjected to a constant spray so keep the spray moving. Use a tip for the sprayer that will fan the spray out over a wider area rather than provide a single strong jet.
Starting to Spray
You should always start spraying from the top so that there is no risk of you covering areas you have cleaned with the dirty water from the areas above. Spray with a downward angle on the spray head so you don’t force water up into the joints between boards. Introduce the spray to the wood rather than simply turning on the spray with the spray head pointing directly at the wood. Spray with a smooth side to side motion and try to cover the length of a board in a single sweep.
Be guided by the way the siding is fitted. If the siding is at 45º then you should be spraying along the board at 45º. Spray from no closer than a foot unless you have turned down the pressure.
When spraying around windows spray away from the windows. This way you will not force water through the window seating. Although not mandatory it is always a good idea to wear protective goggles while spraying. Spray bounce can be very unpredictable.
Although washing wood with a spray washer is usually enough you should be prepared to go over some areas with a scraper or sandpaper. Wait until the siding is thoroughly dry then look for areas that did not clean up as well as you expected. Clean these areas separately to give the siding that finishing touch.
Once you have the siding cleaned it will be a few years before you have to do it again.