Ever run your hand across deck railing and wonder why its so ridged and grooved? That is what happens when the soft wood fibers are blasted out from incorrect power washing. Below I will describe how to safely clean a deck without damaging the wood fiber.
The main purpose of cleaning a deck is to remove dirt, grime, mold and mildew that have accumulated over the past year or 2… or 10. A secondary purpose is to prepare the deck for a coat of stain. I don’t think that is up for discussion. Any quality wood restoration company will tell you not to use high water pressure to strip a deck. A maintenance clean will not and should not remove an existing coat of stain or sealant. Many companies still use high pressure to “strip” or blast off the existing coat of stain/sealant. This is completely wrong and visibly damages the deck more and more each time its done.
The correct way to clean a deck is to use just enough pressure to remove the mold and mildew. Sometimes a chemical cleaner can be used to help aid in the cleaning process, especially on trex and composite material. Many power washers at Home depot and Lowes have plenty of PSI to do the job but the correct nozzle needs to be use to reduce the pressure enough to safely clean wood. A higher GPM machine will make the cleaning process faster as well.
If stripping the deck and removing the existing coat is what you desire then a quality stripper should be applied with sufficient dwell time, normally 15 to 30 minutes depending on the thickness and type of sealant. Then same low pressure that was used to clean the deck can be used to loose and remove the sealant, board by board.
Although it goes against what the manufacture suggests and may void the warranty (composite decking), all decking materials including trex and composite can be cleaned using low pressure and chemical cleaners. The manufacturer suggests cleaning composite decking with a deck brush and bleach, but if you’ve ever tried this you will quickly find out that here in northern Virginia we can get some buildup of mildew. Sometimes a little pressure is needed to get the desired results.