Prepare to Paint Outside


Painting the exterior
Whatever way you look at it, the full scale outside painting of a house is a major operation, particularly if the home is weatherboard or has a paint finish over cement rendering. There can be no cutting corners. With the paintwork constantly exposed to the elements, sunshine and rain can soon damage a poor finish, or have disastrous effects on a cheap paint.
Of course, your full scale painting task will be much easier if you have carried out regular maintenance and touching up of the paintwork every 12 to 18 months, or as problem spots have appeared. But even so, there comes the time when everything must be done again from scratch.
The amount of preparation required and the amount of work to be done will, naturally, govern the amount of time you must allow for the work.
A person should be able to cover the walls and woodwork of an average house with one coat in two full days. So, for example, in an extreme case where a lot preparatory work, difficult trim, and two coats are needed, you might be faced with a 10-day job. On the other hand, if it is basically a touch-up or maintenance job, you might only have to spend one day.
Let’s look at some of the more common problems. Things like painting over knots, all kinds of new surfaces, cleaning old surfaces, repainting surfaces that have become damp, greasy, rusty or powdery and so on – and see if we can give you some advice that will help you do a better job, a longer lasting job.

Woodwork
The successful painting of exterior woodwork depends on thorough preparation beforehand. The surface should be closely inspected and repairs carried out before the application of primers, undercoats and top coats.
New timber
Strict attention should be paid to end-grain, which is the most common cause of paint failure. Moisture which penetrates the board through the end-grain will travel along, swelling the grain as it goes, and so cause the paint film to lift. All end grains should be primed with at least one coat or primer. The importance of this cannot be stressed too much.
Note all areas where end-grain is open, where cracks have occurred in the boards and where there are knots. Force primer well into the open end or crack, and then fill with sanding putty.

There are three methods of treating knots.

  • Heat knot gently with a heat gun, and keep on heating almost until the wood is scorched. At this stage, scrape the liquid resin from the knot. When cool, sand to a smooth surface, then apply one coat of aluminium paint. This will place a heat-reflecting barrier over the knot. Then proceed with the priming operation.
  • Tap or drill the offending knot from the board. Fill the hole with a piece of doweling or shaped wood well coated with primer. Tap the plug in while the primer is still wet. Fill any remaining crevices with sanding putty. Sand to a smooth surface and proceed with the priming operation.
  • The most popular, because of the large amount of work involved in the other methods, is to sand the area of the knot to a smooth surface and apply a coat of primer. This may be the only method possible when the surface to be painted contains a large number of knots.

When end-grains, cracks and knot holes have been treated, sand the entire surface to a smooth, even finish. This is best achieved with a power driven sander, either rotary or orbital type. Dust down thoroughly and proceed with application of your primer.

Removing old paint
Sanding: Power driven sanding is preferred. The two types are the rotary and the orbital. For large areas, the rotary is preferred. When using it remember to use only the edge of the disc and not to press the disc into the surface.
Burning: The heat gun is the quickest and most effective method of removing old paint from exterior surfaces. Particular care should be taken to avoid damage from fire, especially when working neat eaves of roofing were there may be inflammable materials such as birds’ nests, straw and so on.
Always have a hose or a bucket of water at hand in case of accidents. With normal care there is little risk involved, but remember that accidents happen when least expected.
When burning off, apply the gun to a section of surface, moving the hot airto and fro over the surface until the paint
commences to soften or melt. Still keeping the same motion with the hot air, scrape the softened paint from the surface using a flat paint scraper or shavehook.
And a word of caution . . . paint scrapings may ignite, and ignite grass or articles on the ground. It is a good idea to wet the grass and shrubs before starting work.
After burning off, the work is thoroughly brushed down with a wire brush, and finally sanded down, to leave the surface free from old paint or roughness. The last operation is to dust down.

Previously painted in bad condition
Paintwork is in bad condition if it is chalking excessively, flaking, blistering or where there are numerous open end-grains or knots causing paint failure over large areas. In this case, it is necessary to remove either the entire film, or enough of it so that a sound base remains. Note nails which have sprung or become loose and punch these back, using a hammer and nail punch.
Damaged or rotting boards should be cut out and neatly replaced with new timber. Before replacing the board, prime it all over with primer and apply two coats of primer to the ends. This is most important to prevent moisture from getting into the surface through the end-grain.

Dampness and dry rot
Whichever method is used to remove the paint, note carefully those areas where the wood is damp, or grey, in appearance.
If the wood is damp, it must be allowed to dry out before proceeding with the painting. A grey appearance indicates rot, and this should be removed by sanding until the wood presents a fresh new appearance.

Wrought Iron
Iron gates should be straightforward, but screen doors and fly screens can be awkward to get at. Where possible, remove the door or fly screen – if not, mask the door or window behind the screen.
Wire brush or sand loose paint and treat rusted areas with a rust removing preparation. Swab the preparation on to the surface and wire brush while still wet. Hose the surface to remove all traces of the rust remover.
As soon as the surface is dry apply one coat of metal primer all over and when this has dried follow with your finishing coat. Special paints are available which will retard the action of rust on iron or steel.

Brickwork, cement, asbestos cement, stone
It will always be a better paint job if new cement and fibro-cement can be allowed to weather for at least three months before painting. This is to allow the action of the weather to remove from the surface those salts which would be harmful to the paint film. The painting specifications for these surfaces are detailed in the application instructions.
When previously painted surfaces are in bad condition, wire-brushing or power sanding may be used to remove old paint.

Aluminium
New: To the clean, dry surface apply one coat of all-metal primer. When dry, apply roof paint.
Previously painted: Remove any areas of loose and flaking paint by sanding or wire brushing. Spot prime bare areas with an all-metal primer, then apply roof paint.

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