How To Pressure Wash A House Before Painting

One of the most argued about points in the painting and decorating industry is do houses need to be washed before painting? Some swear by washing the house first, others say it’s unnecessary. What is the correct answer?

The truth is, there is no correct answer if you prefer to wash your house before painting it, fine, if you don’t that’s fine too. The next question is almost always, should you use a pressure washer to wash a house? Again there are 2 schools of thought, one says no it causes damage, the other says yes it’s a quick and easy way to clean the exterior before painting.

How Often Should You Paint The Exterior Of Your House?

The frequency in which you should paint the exterior of your house depends on the weather and climatic conditions your house is exposed to. Here in the UK for example, we get an average of 1500 hours of sunshine per year, plenty of rain and strong winds etc. Taking all of those conditions into account, you should repaint the exterior of your home every 7 to 10 years.

Of course, there are other factors to consider here, if the last paint job wasn’t done correctly, you might need to repaint sooner. Also, different materials have different criteria too. For instance:

Material	Frequency of repainting
Brick (if painted)	15 to 20 years
Cement fibre-board	10 to 15 years
Render	5 years
Wood siding	3 to 6 years
Aluminium siding	5 years

Should You Pressure Wash A House Before Painting?

As we said earlier there are 2 very different perspectives on this, we believe that anything that saves time is the best way of doing things so we’re very definitely in the yes camp. The reasons why are stated below.

• A thorough cleaning
  Using pressurised water lifts much more dirt and debris than a sponge or cloth.
• Deals with mould and mildew
  Very stubborn stains like mould, mildew and damp are lifted much easier with pressurised water.
• Clears flaking paint
  Peeling and flaking paint lifts off easily with the power of a pressure washer.
• Saves time
  Using a pressure washer can reduce the time it takes to clean a house by up to 75%.

Reasons for not using a pressure washer to wash a house include the high-pressure water can damage wood, mortar and bricks. All of which is true, but so can washing by hand if your house is in disrepair. Our advice is to inspect the building before washing and make good any repairs that are needed.

Safety Tips Before Starting

There is a correct process to follow to ensure your safety and the safety of your home and family. Let’s look at personal safety first. Including the house, surroundings and plants etc. Before using a pressure washer you should always:

• Wear PPE
  Always remember the high-pressure water from a pressure washer can cause serious personal injury. So it’s best to always wear gloves, goggles, facemask, long-sleeved shirts, long trousers, boots or closed in shoes, and never under any circumstances direct the spray towards any person, animal or plant.
• Cover any electrical equipment
  Water and electricity do not mix. Always cover any fuse boxes, vents, air conditioning units, alarms, outdoor lighting, junction boxes etc. with plastic sheeting sealed with masking tape.
• Remove any trip hazards
  You’ll need all of your concentration to operate the power washer, so be sure to remove any pot plants, tools, cables, toys, hoses etc. to prevent any accidents.
• Cover plants
  Any large established plants that are in the ground should be covered with plastic sheeting or old blankets, cloths etc to protect them from blast damage. Wet the soil around any plants to dilute the detergent runoff that will inevitably occur.
• Ensure children and pets are safe
  Keep pets and children indoors if possible, or at least away from where you’re working. It is so easy for injuries to happen with high-pressured water jets.
• Protect windows and doors
  Prevent accidental damage to doors and windows by covering with plastic sheeting secured with masking tape.
• Inspect the building
  Before any pressure washing begins, make sure there is no damaged or loose mortar, bricks, wood, aluminium etc if you find any damage repair it and allow to set completely before washing.
• Keep the pressure low
  It’s always best practise to start with the lowest pressure possible and increase if needed. For cleaning the exterior of a house, an electric pressure washer is your best choice. As electric machines tend to be lower powered than petrol machines.
• Always use the correct nozzle
  Remember the correct nozzle is always the least powerful nozzle, you can always up the power if needed.

Now let’s get the pressure washer out and get started on the house cleaning. We’ve come up with an easy to follow step by step guide to safely wash the house with a pressure washer.

Guide To Pressure Washing A Home Before Painting 

1. Rinse the building
   Using the 25-degree (green) nozzle, spray the entire surface from around 10 to 12 feet away from the building. This should remove any loose dirt and debris. If you find some areas are not lifting, move slightly closer to the building to increase the pressure. Be sure to cover all the areas you intend to paint. Keep the angle of the nozzle at about 30-degrees and never spray directly straight at the surface, to avoid damage.
2. Apply the detergent
   Using the 65-degree (black) or detergent nozzle, apply the detergent from the bottom up to ensure even coverage, once the entire area is covered allow the detergent to work for 10 to 15 minutes. Don’t allow the soap to dry out, respray any areas that are drying too fast. If you have one, now’s the time to use a brush attachment and give those hard stains a gentle scrub.
3. Rinse the detergent away
   Change to the 40-degree (white) nozzle or the 25-degree (green) nozzle and starting at the top of the building rinse all of the soap and dirt away. Never spray directly at the wall, keep at an angle and keep the nozzle moving constantly.
4. Allow the building to dry
   Be sure all of the building is dry completely before painting. This will ensure no damp is sealed into the building and allow the paint to protect the building as it should. The building should be allowed to dry for at least 24 hours, longer if necessary. Touch dry is not necessarily completely dry, wood and brick surfaces are absorbent and require a longer drying time than aluminium etc.

How Soon After Pressure Washing Can You Paint The House?

This depends on the materials washed, the weather, and the temperature and moisture content in the air. The best way to tell is to invest in a moisture meter, these can be picked up relatively cheaply from all decent builders merchants or online. If you don’t have a moisture meter or don’t want to get one, we have an approximate drying guide to help, but remember this is not 100% accurate, much depends on climatic conditions.

Material	Approximate drying time
Brick	24 to 72 hours
Render	24 to 48 hours
Cement fibreboard	24 to 48 hours
Wood siding	24 to 72 hours
Aluminium siding	2 to 4 hours

If your building is constructed of various materials, it’s probably best to err on the side of caution and allow anything between 3 days and a week before painting, after pressure washing. But don’t go over a month before painting or the house will probably need washing again.

Why Is It Necessary To Allow Houses To Dry Before Painting?

This is not just some dodgy builder or decorator’s trick to stretch jobs out, there are genuine reasons why materials have to be completely dry before paint can be applied to them. The main problems are:

• The paint won’t adhere
  If there is moisture or damp on the material, the paint can’t adhere to the surface sufficiently causing premature peeling or patches. Sometimes the paint won’t dry if the surface is too damp.
• Moisture can get trapped under the paint
  This can lead to rot, mould, mildew and many other problems associated with damp. If not treated correctly, damp and mould can cause structural damage.
• Internal damp
  If damp is trapped beneath the paint and can’t escape it will eventually go inward and cause problems inside the house.
• The paint doesn’t last as long
  Damp walls can lead to the degradation of the paint, meaning it will need to be repainted sooner than would otherwise be necessary.

Frequently Asked Questions