Exterior Decorating: Surface Preparation Before Painting

Damp, heat and frost while paint is drying are the enemies of the painter working outdoors. Damp will cause the paint to peel: a hot sun will cause blistering: and frost will cause gloss paint to become flat.

Work, therefore, in dry, warm weather after a dry spell. Do not start before the dew has cleared, and stop before it returns.

If you must paint during a wet spell, work on the dry side of the house and first wipe over the surface with a dry cloth.

When painting windows, check that putty is not loose or cracked. If it is, replace it.

Remember that preparation, though hard work, is the only way to get good results.

With oil-based paints, allow overnight drying between coats. Emulsion and cement-based masonry paints can normally be recoated in 1-2 hours.

Wood

(a) New softwood

1. Smooth with glass-paper.

2. Apply knotting to knots and resinous patches, to prevent resin bleeding through.

3. Prime with a good quality primer.

4. Fill any holes or splits with water-resistant filler or stopping and when it is hard, rub down with glass-paper. If holes are not sufficiently filled after rubbing down, repeat until the surface is level.

5. Dust off any particles, especially in crevices where the paint-brush can pick up dust, which will cause little lumps in the finished surface.

6. Apply an undercoat.

7. Apply at least one coat of gloss paint — two for extra protection.

(b) Previously painted woodwork

(i) In poor condition (e.g. peeling and possibly bare in places):

1. Remove all the defective paint by scraping, burning off or using a paint remover.

2. Remove any remaining paint with coarse glass-paper. Using a scraper to clear out angles and corners.

3. Rub down with medium glass-paper to get a smooth surface.

4. Apply knotting to knots and resinous patches.

5. Prime the surface.

6. Fill any cracks or holes with filler or stopping, rub down the filled areas and touch them in with undercoat.

7. When the filled patches are dry, lightly rub down with medium glass-paper and apply an undercoat.

8. Apply a gloss coat — two if you want extra protection.

(ii) In reasonable condition: Rub down with medium glass-paper, and continue as for stages 6, 7 and 8 in (b) (i) above.

(c) Hardwoods and cedar cladding — clean finish.

1. Use a Skarsten scraperto remove any old linseed oil or sealer on hardwoods, sandpaper cedar, or use Translac ‘Colorbac’, to remove grey powdering.

2. If any filling is necessary, use putty stained to match the timber.

3. Rub down with glass-paper and apply two coats of preservative.

4. Varnish if required.

Stone and brickwork, rendering

(a) Previously painted stone or brick

(i) If using cement paint:

1. Brush off loose particles and grime with a stiff brush.

2. Fill any cracks or holes with mortar and allow to dry out.

3. If the old coating is powdery or loose, apply a coat of primer-sealer or stabilising solution.

4. Apply two coats of paint.

(ii) If using emulsion masonry paint:

1. Make good any holes or cracks. Brush off any loose particles.

2. Seal with thinned coat of emulsion or proceed as for stage 3 above.

3. Apply two coats of emulsion.

(iii) If using gloss paint:

1. Remove flaking paint with a scraper or wire brush.

2. Repoint where necessary and allow to dry out.

3. Apply sealer to any bare patches.

4. Apply an undercoat (when covering a dark colour with a light one apply two).

5. Apply a coat of gloss.

(b) New stone or brick

(i) Cement paint:

1. To prevent efflorescence — salts in the wall working through to the surface, where they appear as whitish deposits — apply a special sealer. The supplier will advise which one to use.

2. Apply two coats of paint.

(ii) Emulsion masonry paint:

1. Fill any holes and joints and allow to dry out.

2. Apply the correct sealer (with some makes, this can be made of emulsion thinned with water).

3. Apply two coats of emulsion masonry paint.

(c) Old rendering and pebble-dash

(i) Cement paint and emulsion masonry paint: As for (a) above, except that a soft brush, slightly dampened, should be used to brush down pebble-dash, and you may have to use a stippling brush to paint pebble-dash and stuccoed surfaces.

(ii) Gloss paint:

As for (a) above, except that there will be no repointing.

(d) New rendering and pebble-dash

(i) Cement paint and emulsion masonry paint: As for old rendering and pebble-dash.

Metal

(a) New ferrous metal (steel, cast iron, etc.)

1. Wipe off any oil or grease with a rag dipped in turps substitute.

2. Remove any rust with a wire brush, then dust off.

3. Apply a coat of the correct metal primer (when buying metal primer, tell your paint merchant what kind of metal you are priming and where it is situated).

4. Lightly rub down and apply an undercoat.

5. Apply at least one coat of gloss finish.

(b) Old ferrous metal with extensive rust

Thoroughly scrape and wire brush the surface. An electric drill with a wire brush attachment will cut down time and effort. Continue as for stages 3,4 and 5 in (a) above.

(c) New galvanised metal

1. Wipe off any oil or grease with a rag soaked in turps substitute.

2. Apply a coat of calcium plumbate, or a similar special primer, which will provide a key for the paint.

3. Continue as for stages 4 and 5 above.

(d) Old galvanised metal

Chemical paint removers may damage the galvanising, so remove loose paint with a wire brush. Use the brush carefully as scratches in the metal will allow rust to form. Continue as for (c) above.

(e) New non-ferrous metal (aluminium or alloys)

1. Clean off oil or grease with a rag dipped in turps substitute.

2. Apply the appropriate primer.

3. Continue as for stages 4 and 5 in (a) above.

(f) Corroded non-ferrous metal

1. Lightly scrape off or wire brush away the corrosion, which shows as a white crystalline deposit. Do not scratch surface.

2. Apply zinc chromate or a similar primer.

3. Continue as for stages 4 and 5 in (a) above.

Other surfaces

(a) New hardboard

Gloss:

1. Fill nail holes and joints and rub down.

2. Brush off and apply a coat of hardboard primer or aluminium primer.

3. Apply an undercoat.

4. Apply a gloss coat.

Note: paint the back and edges of the hardboard to keep out damp.

(b) Old hardboard

Gloss:

1. Fill holes and joints, rub down, scrape off loose paint and brush off loose particles.

2. Touch in bare patches with primer: then continue as for stages 3 and 4 in (c) above.

22. June 2011 by admin
Categories: Painting, Preparation | Tags: , , | Comments Off on Exterior Decorating: Surface Preparation Before Painting

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