How to Pressure Wash Dirt Away from Stone
After the snow finally melts away, it might be time to clean the dirt away from the exterior of your home. When you do get around to washing up outside, here are some hints to help you.
Pay special attention to any horizontal areas including decorative trims on windows and doors and porch roofs.
Pressure-washers look a little like cylinder vacuum cleaners. Before you buy, figure out how much pressure the water can get put under. Go for the highest possible – get a machine on wheels – water is heavy! You can get pressure-washers from catalogue shops and hardware stores. If it’s giant power you need, you may want an industrial model.
Don’t use high pressure on pebbledash or other textured effects. These walls are best left as they are until it’s time to redo the coating. Rendered (plastered) or painted walls can also be adversely affected by pressure-washers. New render can flake and old painted walls may chip and flake too. So test a small area before blasting with the pressure-washer.
Before beginning, use a stiff brush to remove loose dirt from the wall. Use an extension pole to brush areas that you can’t reach. It’s easy to make a temporary one yourself. Simply tape your brush to a broomstick with strong tape.
You may notice white deposits, most often seen on new-build brick and some stone walls in the first couple of years, especially as the walls dry out after heavy rain. These are mineral deposits that get drawn out to the wall’s surface. Don’t wash these away – you’ll simply bring more mineral salts to the surface. Instead, use a stiff wire-brush to sweep the walls clean.
You have to hold on tight to your hose so it doesn’t get away from you! Your results are directly related to the time each spot of wall gets hit by the water. So moving steadily across, slowly, is a good way to get even coverage. You may get splashed, so wear waterproofs, including eye protection, or be prepared to change. Also, start at the top, then work on down.
Take care to keep the nozzle moving. Aim it too long on one spot and the power of the water could bore a small hole in your wall. You’ll also want to steer clear of the windows and windowsills and any other parts of your wall you know to be delicate, such as a wood steps.
If you’re going to go one step further and use a cleaning solution to tackle stains on your walls, you’ll probably need to get out the ladder.
You can clean seriously discoloured stone and brick with an acid-based wall cleaner obtainable at any hardware store. Be sure to wear gloves and goggles and follow instructions with care. If there is mould growth, wash it down with a bleach solution – 1 part bleach to 4 parts water.
If the problem is contained to a few areas, try simply rubbing it away. Rub a dirty brick with a dry brick of the same shade to transfer its colour onto the brick on the wall. With stone, you need water to get colour transfer, so always keep your stone block wet.
Using bleach or a stain treatment on just one section of wall can quickly become a very big job because the change in colour means you then need to do the entire wall on that side.
Whenever you use chemicals, be sure to follow up with sustained rinsing – at least two minutes for every area. Walls are porous and may absorb cleaner beneath the surface so you have to make sure that the rinsing afterwards goes deep enough. Failing to totally rinse away chemicals leaves your wall vulnerable to attack by the acid or alkaline residue left from your cleaner.