There are two reasons to wash the outside of your house; the first is to get it ready for painting. The second is just to make it look nicer (though it’s also a good idea to remove mold or mildew on a regular basis).
If you really, really want the exterior of your house to look clean, no matter what kind of siding you have – vinyl, aluminum, wood, brick, or even asbestos concrete shingles, get ready to spend some time and major effort. The best way to most types of siding is to take a bucket of soapy water, a stiff bristle brush on the end of a long pole, scrub it down, and Rinse it off with the hose.
There are a couple of exceptions we know of. Wood shingles do not have to be washed. They don’t even have to be sealed unless you live in an area where there’s an abundance of sunshine or an abundance of rain; there, sealing will slow down the bleaching process. The other exception is for the only siding we know of that is even uglier than asbestos concrete shingles. By some strange coincidence, like asbestos concrete shingles, it is found widely in the state of New Jersey: we’re talking about those sheets of faux brick or stone block stamped out of the same composition stuff you find on most pitched roofs in the East.
Pressure Washing Your Siding
The next best method for cleaning siding is pressure washing, also known as power washing, where you use a high pressure pump creates a high velocity stream of water that blasts dirt away. This is a good way to clean a house exterior or prep it for a new paint job. Spraying water and, in some cases detergent or other solutions does a pretty good job of removing dirt, grime, and chalk-like residue from deteriorating paint from the surfaces of siding and trim. It’s not a better alternative to hand scrubbing, unless your prime concern is to avoid hard work.
A pressure washer is okay for most siding materials, but full pressure should not be used on masonry for fear of blasting mortar from between the bricks. Care must also be taken with pressed board siding for fear of injecting water into dings in the wood, thereby encouraging rot and warping. Care must also be taken with stucco, which can easily be damaged.
If your home is huge, you don’t want to use either method unless you’re making the project a lifetime task. If the place is two stories or more, you will probably want to hire a contractor rather than risk tumbling off a ladder.
Cleaning Mildew from Siding
Pressure washers come in various sizes, from about 1,200 to 3,000 pounds of pressure per square inch. The stronger ones, of course, work faster, but they should probably be restricted to materials like vinyl that can withstand the pressure and which have no paint to peel off. Less pressure is more appropriate to other materials. The washers can be rented, and it’s advisable to get one that allows you to mix cleaning materials with the water.
Power washers will not remove mold or mildew, so you will have to do that by hand prior to using the pressure hose by scrubbing it off by hand. To determine whether blackish areas are mildew or dirt, apply a little bleach solution (one part bleach to four parts water) to the area with a spray bottle. Mildew will disappear; dirt won’t, but it should come off with scrubbing. If you’ve had your portable grill too close to the house, it could be soot. Repeated applying foaming bathroom cleaner to brick and then repeatedly rinsing it should get it off of brick, and we would think that would also get it off of other types of siding. Whatever you’re using, and whether it’s dirt, soot, or mildew, rinse it off when you’re done cleaning it.
Take the precaution of wearing eye protection when using a pressure washer and keep the stream clear of electric motors or transmission lines. Protect or move plants and breakable materials beforehand and clear away obstacles.
You can’t operate the device from a ladder, and you may not even be able to use an adjustable extension to wash high areas, as that takes a good deal of muscle and coordination. Take that into consideration before you rent the machine. The nozzle should be no more than 36 inches from the target. You can slowly work in closer until you find the sweet spot, but get no closer than a foot or you could damage the surface. Keep it away from windows.
Working from the top down, start with soffits, overhangs, gutters, and downspouts. Then steadily move it across the siding from side to side, directing the stream downward. If you’re using a solution, follow up with a clear water rinse using a garden hose, not the high pressure device.
Stucco should be cleaned annually, as its rough surface is a dirt magnet. This is especially true for light colors that show dirt more than darker colors. A lower pressure power cleaner may be used, but used with care. A good cleaning solution is a bit of dishwashing detergent, a cup of washing soda and a cup of borax mixed with two gallons of hot water.
To avoid damage to stucco surfaces, don’t use concentrated jets of water; use the open jet setting to flood the side of the house with a curtain of water.
A lower-pressure power washer may be used on brick siding, though best results may be obtained by first spraying an oven cleaner on the bricks. If this doesn’t get heavy grime off, try using turpentine, mineral spirits, or paint thinner, which might also be effective in removing paint spots. Latex paint spots will come off more readily than oil-based paint.
If you’re unlucky enough to have cement asbestos shingle siding, it’s only because that stuff never seems to wear out; they stopped making it decades ago. It’s easy to clean, but it’s so brittle that you have to be careful – even a high pressure water cleaner can crack a shingle.