pressure washing - i've done quite a bit of pressure washing and here's a few tips i have learned. like everything else different techniques work better for different people. but these are what have worked well for me.
how much pressure do i need? this will vary with the size hose tip you use ( more on that later ) and the horsepower of your washer. obviously you're going to use more pressure for removing paint from concrete than you would for cleaning a wooden deck. the pressure is controlled by the speed of the pressure water motor. when washing decks a good rule of thumb to use for pressure ( since every deck is going to be different depending on the type and age of wood ) is to find a spot on the deck that is aged but out of the normal line of sight. under a deck or on the back or side is usually a good point to look. i start with the washer on idle and slowly move the engine rpm up until i see the water starting to damage the wood and then back the motor down to my second previous setting.
which size hose tip do i use? with my commercial washer i have 4 tips to choose from. they are sized in degrees. i have 0, 15, 25 and 40 degree tips. usually the tip numbers are in small print on the side or front of the tip. the higher the number of tip the wider the spray pattern is going to be and the wider the pattern the less effective your cleaning will be. on my washer the 25 tip is perfect for most decks. since i've been using a washer so long i'll usually go with the 15 because it's faster but i would tell anybody else to start with the 25 tip. the smaller the tip the slower you can set the engine rpm so a little experimentation will be needed to get the right combination. the horsepower of the engine and the speed you move the wand will help dictate the right combo for you. keep in mind the distance you keep the tip away from the surface will also dictate the cleaning power you have. so whatever distance you use in your trials is the same distance you should use when you start cleaning the rest of the deck. 6 to 12 inches usually works for me.
what type of pattern should i use for cleaning? ALWAYS clean parallel to the way your deck boards are laid. just like sanding, always clean with the grain and not against it. Never stop or start your spray in the middle of a board. i always start at one end of the deck and walk down the length of the deck always keeping the wand at a 90 degree angle to the surface and the same distance from the surface. if you have to stop in the middle of a board stop moving your feet and continue moving the wand. that will slowly move the wand away from the surface and will apply less pressure as it gets farther from the deck. this will give you more of a " blended " end line. when resuming do just the opposite. start back over the clean section and slowly bring the wand closer to the working surface. if you just stop or start the wand you'll leave a VERY distinct mark on the wood that you will probably not be able to get out. i always try to adjust my spray pattern so it will cover about 2/3 of a board. i put the middle of the spray pattern over the decking joints so i get down on the sides of the decking as i'm cleaning. on my next pass i overlap the pattern just a bit to help blend the spray patterns. on 2x4 decking i can usually just hit every joint. on 2x6 i usually set the pattern to wash one joint, one pass down the middle and then the next one down the next joint. it's always better to overlap your patterns too much than not enough.
do i need to clean the deck first? some pressure washers have an automatic cleaner download option on them. mine does not so i usually don't pre-clean. i have found that if you set your washer up correctly with the right tip/pressure combo cleaners aren't needed. but if you want to clean the deck either use a garden sprayer or the download option on your washer. follow manufactures directions for cleaning but normally you don't want to let the cleaner dry before to start washing. if it's going to be a 2 day project at least flood the deck with water from your garden hose after cleaning.
what do i seal my deck with? i've never had any luck with clear sealers. see what type of products are available in your area and pick a semi-transparent color ( always use products designed for the type of wood you are staining and for outdoor use ) if you want to see the grain or a solid color if you want more of a painted look. the semi-transparent stains can easily be applied with a garden sprayer designed for harsher chemicals. if you have access to an airless sprayer this is your best option. pick the right sized fine pattern tip. use the same pattern to spray that you used to wash. all the same rules of washing will apply to application of the spray as well. so when you clean you'll also be getting some stain spraying experience. solid stains will need to be either applied by hand or sprayed with an airless sprayer ( semi-transparent stains have a water-like consistency and solid stains are more like latex paint ). you'll need to increase the pressure and tip size on the sprayer but everything else is similar to what we just discussed. i would not recommend trying to apply semi-transparent stains by hand. it's messy and you're probably going to end up with a blotchy finish. make sure you compensate for overspray so cover up everything close to the deck with plastic or drop cloths. also be careful with autos or houses nearby or the wind will help you stain your neighbors house right along with your deck. try and pick a calm day for your spraying project.
if you're renting or borrowing a washer it's a good idea to go ahead and do your driveway and sidewalks at the same time. just up the pressure but use the same techniques. i almost always use a 15 tip for concrete but this will also varying according to the size washer you have and the condition of your concrete.
