Cleaning Algae, Mildew and Mold with a Pressure Washer

Every Spring it seems our house's vinyl siding, porch, and deck attract dirt, algae, mold and mildew, and needs a cleaning. Prior to buying a pressure washer I used a hose which did an okay job. I've stepped that process up a bit now!

No, this isn't about cleaning siding, but I'm starting with this photo to show you the power of a pressure washer. This is a shot where I've removed years of surface crud from unfinished pressure treated wood. The new looking wood is where I have given the steps a good close up blasting. It's slow work doing this kind of cleaning, but the results are amazing. But please do read further down in this article to learn about the damage that pressure washers can do to wood. Also, see below for the complete rehab to these steps. Note: You can click on all photos to enlarge them.

Here's a typical shot of what the side of our garage looks like before pressure washing (after our harsh New England winters), showing lots of dirt, algae, mold and mildew on the vinyl siding. This side gets particularly bad, as our driveway snow plowing leaves 4 foot piles right up against the vinyl siding.

Here's a shot after using the pressure washer with detergent made for cleaning dirt, algae, mildew, and mold from siding, wood, and driveways, etc.

And here's the cleaned siding looking especially bright on a sunny day.

I Fell in Love with my Pressure Washer
This year I bought a pressure washer to refinish my deck (that deck article is here), but I also used it to clean many other things around the house. It's pleasing to use, as the work is easy and the results are immediate. I was going to put the pressure washer (some call them "power washers") on, after using it for the deck refinishing, as it was cheaper than renting, for the amount of time I needed it, but I fell in love with it, and I have kept it! By the way, this is also a good strategy to get tools past the budget department (joke, but not really)!

It's a Nice to Have
It's not something you use all the time, but it's nice to have when you want it, and it's the kind of tool you can feel great about loaning out to the neighbors. You might even want to go in with a neighbor, to reduce the cost of ownership.

I've never used a pressure washer before, so I can't compare this model/brand to others, but this one seemed to work very well for my needs. It's a Husky 2600 PSI, 2.4 GPM, Axial Cam Pump, Pressure Washer, which has a 173cc Kohler Courage XT-7 engine. I got it from Home Depot for about $320 (Spring, 2009).

Here's the wand, which feels much like what you would use at a self-service car wash. The water pressure feels about the same too. I think the tubing from the machine to the wand is 25', one upgrade I might make is to get a longer tube, which means you don't have to move the machine around as much.

Here's shot of 2 of the nozzles that this Husky power washer comes with. There are 4 provided. One is for soap application (not shown) and the other 3 vary in the spray focus (0 degree, 25 degree (not shown) and 40 degree). The more focused the pattern, the more force the spray has. All of these can rip through the surface of wood, so never ever point them at humans or pets, they could rip a hole right through them! The nozzle you use and the distance from the surface you are cleaning determines the spray strength. There isn't a control on the wand for pressure, it's either on or off. The only problem I found with the nozzle "caddy" (shown above) is that the nozzles would fall off the posts that they are supposed to be stored on.

Here's a top down view of the detergent reservoir. The uptake tube is above it here, and when in use, the tube is inserted into the detergent tank.

Gas and Cleaning Solutions

Here's what you'll need to get started. Zep makes a few varieties of cleaning products for vinyl siding, driveways, concrete, brick and wood. Be sure that you get a detergent made for pressure washers. These detergents come in concentrate, so you'll need a container to dilute the cleaning solution with water in, thus the empty milk jug on the right. Never use bleach in your pressure washer, as it can damage the pump and other parts.

A few More Sample Uses

Garage steps before shot. These steps are stained with opaque gray, below the crud.

Garage steps after shot. I intentionally removed some of the loose stain with the powerwasher, in order to prepare the wood for a new coat of stain.

Here's a before shot showing algae on our front porch (the wood is wet here, as I took this photo after initial wetting with the detergent. Dry they didn't look this bad).

Here's the after shot. You can see there is some very minimal lifting of lose paint. Loose paint will come off whether you want it to or not.

Gutter Cleaning

Here you can see the section I've cleaned in the middle. Be careful not to spray up and under shingles. And don't use powerwashers to clean shingles. You'll damage shingle surface.

Here are the gutters, and the rest of the front of the house, after powerwashing.

Here's a before shot of a hidden part of the house. I was surprised to see how dirty it was. I did this work in the spring. In the summer and fall this area is covered by large bushes, so you don't usually see it, and either did I. By the way, I've since cut back all foliage about 2 feet from the house. You should do this too, to allow the house to dry, and it keeps ants and other bugs from having easy routes to enter your house.

Here's an in progress shot. You can see where I've pressure washed the vinyl siding above the dryer vent and up, and then I cut one swath down the middle of the siding to show the immediate cleaning difference. Yes, that's a dryer vent. You can read about that energy saving dryer vent here.

Here's the after shot. I'm not sure why the right bottom is darker. Some permanent damage my have happened to the siding? All dirt and algae has been removed. It was overcast this day, so my photos seem a bit gloomy, but boy did the siding shine a brilliant white when the sun hit it. I did all of the exterior surfaces and siding in one day. One thing you want to avoid is shooting the spray up and behind the siding. It's best to work spraying the siding straight on, or at a slightly downwards angle. You'll need a step ladder to get up high and still spray downwards. For getting the second story, switch to a more focused nozzle to give you pressure to really get up there.

Speaking of technique, read the directions carefully on the cleaning solution bottle. Application of the cleaning solution should be with a low pressure soap nozzle, and from the bottom up to avoid staining The cleaning/removal of the detergent should be from the top down with a medium pattern/pressure nozzle. Your pressure washer's manual, and the detergent bottle will have detailed instructions, so I'm not going to cover proper technique fully here. It is though very important to read the whole manual as there are important safety and usage notes, that will keep you from damaging yourself or the washer.

Resurfacing Old Pressure Treated Wood Steps

Here's a shot where I'm removing years of surface crud and weathering from unfinished pressure treated wood steps. The new looking wood is where I have given the steps a good close up blasting (about 2 inches from the wood). It's slow work, as you have to move slowly to really get an area cleaned well, but the results are amazing.

Here's a side by side, before and after shot. I was really blasting this wood hard, to bring it down to clean wood. In doing so, experts would say that I've damaged the wood, which is true. You can see that the soft grains of the wood have been completely blasted away, leaving deep grooves, where the harder wood grains remain.

Here's a shot after the wood has dried. You can see that fibers of the wood have lifted and that the boards have become furry. Expert powerwashers say they use the right chemicals and only use a few hundred pounds per square inch (psi) of pressure to do this kind of cleaning without damaging the wood. I used 2600 psi, at close range! I like to live on the wild side. I'm a rebel!

To remove the fur, and to smooth out the ridges, I first pounded down all of the popped up nails, and then sanded the boards with a 6" Rigid brand random orbital sander, using 60 grit (aggressive) sandpaper.

I quick brushing and vacuuming cleans up the wood dust, in preparation for staining.

Here are the cleaned steps ready for opaque deck stain which will match my deck.

I used this stuff (Sikkens, Rubbol Solid DEK). It's an opaque stain. To me, it seems to go on even thicker than exterior paint. I love the almost rubbery surface it makes. Just one coat seems to do the job well. The manufacturer recommends 2 coats (one that acts like a primer, and then a finishing layer). I also used it with my deck project.

For quick painting (as I like to slap it on and be done with it), I'll use a piece of cardboard to keep things from getting painted/stained the shouldn't be.

And here we go, the final smooth steps are now a favorite hangout for my son and I. Don't mind the shoe issue. He put them on himself, "good for you son!".

Resources Outdoor Cleaning with Pressure Washers (By Briggs & Stratton)
The link above seems mainly a source to drive people to buy, through their site, pressure washers, but it does have lots of great basic videos. Also it shows you all the things you can clean, which was also a good reminder to me that I have more stuff to clean. They have videos showing how pressure washers can be used to clean: siding, brick, stucco, decks, fences, concrete, vehicles, boats, remove paint, outdoor furniture, grills, pools, spas, and lawn and garden equipment.

They also have great videos on technique, key features, operation, maintenance and winterizing. I was going to say that I didn't know who provides this site, but I see now at the bottom of the site it says "Briggs & Stratton" who are the engine providers for a few different brands of pressure washers. Okay, I give the site more credit now. Check it out. I'm about to go through it more thoroughly too!

My Standard Disclaimer: This is what I did. This does not mean this is the best way, the right way, to building code, or even safe for your needs. So you are on your own with your project. I make no promises about the information presented here. I'm just a do-it-yourselfer, not a professional at all, sharing my story. So if something goes wrong with your project, you are on your own. Good luck, and have fun!

All content and photos, copyright 2009, Dover Projects.
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  1. Nice article and great photos. Very nicely done!


  2. Great job man! Get those "Honey-Do's" out of the way and feel good about it!

  3. I am in the market for a pressure washer and came across your article..It was a lot of help..Loved the pic of your son with the shoes on wrong..Brings back memories of my two sons at that age!!!

  4. I ran across your site while looking for trouble-shooting info for the exact same power washer that you have here. My husband and I acquired it spring of 2009, just like you! Let me begin by saying that I love this power washer except for one problem that may be particular to only ours! And I really enjoyed your article and I, too thought the picture of your son was adorable! Great finish!
    I think we may have a problem with the amount of ethanol in the gas here in FL because if the washer sits for any time with gas in it, it will not start! We took it in for warranty covered repairs, but I just pulled it out of the garage to use it and when I pressed the primer, the gas came out of the air filter cover!!! I called the guy that repaired it and he said it's probably a needle stuck in the fuel filter and to tap it, to shake it loose, but this did not work! Any ideas? I'd like to have our washer running as well as yours! Thank you for taking the time to develop this site and share your experiences.

  5. NEW!!! DOVER PROJECTS ON FACEBOOK! Join in with your DIY spirit! Click on the BIG blue box for "Facebook, Dover Projects" in the right column above! See you there!--Peter

  6. Can this technique be used on mold-infested INDOOR wood? My basement ceiling joists, etc are mold-covered due to a water problem in certain walls and the rim joists . Just certain sections of the wood flooring underside and beams have mold; it is spreading and I wondered if using a pressure washer indoors would be dangerous because of splattering mold everywhere. We realize we have to correct the source of the water but were wondering if this technique would work on removal of the mold.

  7. Excellent read. I like your style...have a good one!

  8. I'm very impressed with the amount of improvement the pressure washer creates! Wow!

  9. Nice. Thanks for sharing. Craigslist here I come!

  10. I also have the same dilemma with my porch and vinyl siding, and it's a bit surprising since it only appeared this weekend. I think the change of temperature as a huge factor as to why this happened. We tried several solutions for this problem, and the pressure water was also great in helping us deal with it. We did power washing and was very surprised with the result.

  11. Informative as always. Thanks for sharing. The wood and home look 100% better! It's nice what a powerwashing can do. The shoe comment made me laugh! :)

  12. This technique will work but i don't think it will kill the root cause which is creating the mold, you can do this several times but it will come back, it is better to find the reason behind it.

  13. We removed the Sheetrock and insulation after Sandy, I was thinking of preasure washing the interior walls that now have green mold appearing. I was thinking of powerwashing the mold away, drying in 24hrs and hitting the wood with Shockwave via spray and brush.

    What are your thoughts.

  14. what a fantastic write up. God bless you indeed for sharing this. x

  15. Good pressure washing skills, no gouges to deck surface. I have never seen paint that makes the wood look like a composite deck, thanks for sharing.

    Pressure Washing HQ

  16. Sooooo much help and info. Thanks so much for your articles.


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