How to spray paint a roof. General guide to safety, choosing paint, selecting equipment such as high pressure water blasters and airless spray equipment with suggested places to find more information.

When considering spray painting a roof yourself it is most important to properly assess access requirements to ensure you will be able to safely access the roof and work on all areas of the roof without risk of slipping or falling. Most roofs will need cleaning with water which can make roofs very slippery. Anyone working on the roof must be able to safely climb on and off the roof carrying equipment without risk of falling. When applying subsequent coats of paint on a roof the previous coats of paint can be extremely slippery. If you are at all unsure about what equipment is required to access and work on your roof safely consult a professional.

Choosing the type of paint to spray on your roof may seem daunting with the range of brands and types of paint available. Most roof repaints is these days are completed with 100% acrylic water-based paint. Commonly known household brand names for these types of water-based acrylic paint would be Dulux Weathershield and Wattyl Solagard for example. The large brand-name manufacturers in Australia offer warranties on their paint products provided the paint is applied as directed, the surfaces are prepared to specifications and the correct product and paint system is used. Most large paint manufacturers offer technical data sheets, entire paint system specifications for specific applications and customer service centres who may be contacted for additional information.

For do it yourself roof repaint projects Wattyl Solagard or Dulux Weathershield or other brand-name equivalent acrylic water-based paints will be ideal and easier to use. Heavier acrylic paints designed specifically for re-coating roofs are available but these paints will require much larger airless spray machines to apply, are generally more expensive due to the fact that these heavier acrylic paints have more resins and fillers and can be applied much thicker with each coat than every day acrylic paints can be applied. Over the years I have seen roofs painted with either system that look great and outlast typical glazing on concrete roof tiles.

Tiled roofs need to be inspected carefully for cracked roof tiles which will require replacing and cracked or missing pointing under and around ridge capping which will require repair. Iron roofs need to be inspected for missing nails or screws and any rust perforations, particularly in the valleys and capping. The most common method of cleaning a roof these days prior to repainting is to use a high-pressure water blaster. In choosing a high-pressure water blaster that will clean a roof quickly and effectively don't pay too much attention to pressure specifications. Most high-pressure water blasters in the sub $5000 bracket will have a maximum pressure of anywhere between 1000 and 3500 psi but the real difference is the maximum flow capability. A high-pressure water cleaner with 3000 PSI and only 1 litre per minute flow will take ages to clean down a roof while a 1500 PSI pressure cleaner with 10 litres per minute of flow would be more effective and much quicker.

All loose paint and any chalky surface along with dirt and grime, moss and lichen build up needs to be removed by high-pressure cleaning and mechanical means. Proper care taken with preparation will go a long way to avoiding problems with adhesion, blistering or de-lamination in the future. When the roof has been prepared by removing all loose and chalky surface the next step would be to apply any pre-treatment solutions if required by the paint manufacturer for the purpose of killing off any remaining moss or lichen spores for example.

When pressure cleaning a roof with high-pressure water take care not to direct the high-pressure stream back up underneath roof tiles or underneath ridge capping or underneath the overhang in gutters otherwise water will enter the ceiling cavity with potential of causing severe damage to your property.

Once the roof has been cleaned down completely, ready for painting, recheck for any cracked tiles or missing screws or nails on iron roofs and rectify if required. At this point any cracked or missing pointing on tile roofs should be repaired using either sand and cement mix or commercially available re-pointing products.

To paint the roof the quickest way is to use an airless paint spray machine. The type of airless paint spray machine you should be considering is an airless pump that will siphon the paint directly from the paint cans on the ground so the airless is left on the ground and enough airless paint spray hose should be fitted to the airless machine to enable the person spray painting to access all areas on the roof. When spraying a roof with water-based acrylic paint at least a .017 inch spray tip preferably of the reversible type should be fitted. Larger airless spray tips such as a .018 inch or .019 inch can also be used if it is a large roof and the spray painter is experienced in using airless spray equipment. If you happen to have an airless spray machine of DIY performance available, these airless machines are usually only capable of supporting a 0.015 inch spray tip, you may be much better off considering hiring a larger airless spray machine from a hire company. Most suburban house roofs can be sprayed with two coats of a normal water-based acrylic paint in warm weather in a day if an adequate airless spray machine is used.

If at all possible an airless spray gun with an extension pole and a airless tip swivel at the end will make the job easier, safer and faster. The airless tip swivel at the end of the pole can be angled back so the front vertical edge of roof tiles can be sprayed easier. Choose a still warm day so any over spray dries quickly and does not travel, keep sections of cardboard available for holding against areas not to be painted and if a spot is too difficult to spray without masking consider simply painting that spot with a brush and or roller.

If the paint manufacturer requires a primer to be applied to the roof spray the required primer coats using the airless spray machine as directed. The paint manufacturers technical data sheet for the paint system chosen will usually specify a recommended drying time to observe before proceeding to apply subsequent coats of paint.

• Consult paint manufacturers to determine the type of paint system recommended for your roof. It is the paint manufacturer who will be offering any warranties on their coating.
• Obtain copies of the technical data sheet for the primers and top coats chosen to ensure the correct preparation and application techniques are followed.
• Think safety. Identify how the roof will be accessed, beware of power-lines, and take all measures to avoid slipping, falling or damaging a roof further.
• Use the right gear. A water high pressure cleaner with a high flow rate is important. A water blaster with high-pressure and small flow rate will take ages to clean down an average concrete tile roof. An airless spray machine needs to be large enough to support bigger than a 0.19 inch airless spray tip and be fitted with enough airless spray hose to cover the entire roof. Protect the airless spray hose on any edges such as bricks or even the guttering to avoid rub through and burst airless hose.

Because I am able to prepare and spray my own roof I prefer to use a brand name hundred percent acrylic water-based paint such as Solagard or Weathershield and re-coat the roof on a more regular basis to keep the roof looking fresher and cleaner.

If you run into problems with an airless spray gun or need to check out how to clean an airless spray unit these links to further airless spray equipment information may help.