Preparation . . . from www.painting-effects.co.uk

Preparation.

General.
Plaster: Walls & ceilings.
Pre-painted surfaces.
Bare timber.
Bare metal.
Miscellaneous

General preparation.
All surfaces should be sound, clean, dry, and free from oil and grease.

Flaking or peeling paint should be scraped, filled with a proprietary filler, and then spot-primed when dry.
Alternatively, the paint can be removed using liquid stripper (solvent or caustic) or heat (blow lamp or heat gun).
Cracks should be raked-out with a shave hook or similar tool to widen the crack and then filled with a proprietary filler.
This allows the filler to "key in" to the surface of the crack, which, in turn, prevents the filler from falling out.
Nail holes, dents etc. should be filled with a proprietary filler, or "stopping", allowed to dry, and then abraded.
The surface can then be spot-primed to kill the suction of the bare filler before painting.
Scratches and other minor defects, can be filled with fine-surface filler, allowed to dry, and then spot-primed.
Mildew should be removed using a proprietary fungicidal solution or thick, neat bleach, applied with a synthetic brush.
This should then be rinsed off, several times, with plenty of clean water & allowed to dry thoroughly before painting.
Efflorescence can be sealed with a coat of alkali-resisting primer or oil-based undercoat so that it does not reoccur.
Water-stains (ironmould) can also be sealed with a coat of alkali-resisting primer or oil-based undercoat.
Bitumus surfaces: cooking or nicotine stains can also be sealed with alkali-resisting primer or oil-based undercoat.
Corrosion or rust should be removed using a wire brush or mechanical tools (electric sander etc.).
Refer to the bare metal section for further details including the use of metal primers.
Grease should be removed using turpentine or white spirit applied by brush or cloth.
If this treatment does not cure the problem, wipe the surface with "fullers earth" powder on a damp cloth before painting.
Dirt should be removed using sugar-soap, following the manufacturers instructions.
A mild detergent can be used as an alternative to sugar-soap if necessary (rinse thoroughly).

*** IMPORTANT ***
Wood and metal surfaces, especially pre-1960, may have been decorated with paints containing lead pigments
The preparation of such surfaces can be hazardous

	*Plaster walls & ceilings.* The preparation of plaster walls & ceilings is dependent upon the previous treatments that they have received.
	1) Plaster that has previously been wallpapered.

All existing wallpaper (including lining paper) should be removed before painting.
Failure to do so will result in a poor finished result with a limited lifespan.
All traces of adhesive (paste) should also be removed using warm soapy water, or if necessary, a steam stripper.
If adhesive is not removed, subsequent coatings will craze or crack due to the differing surface tensions of the 2 substances.

2) Plaster that has previously been painted.

Previously painted plaster is an ideal surface on which to create specialist decorative paint-effects.
Refer to the General section for specific surface defects.

3) Newly plastered or bare plaster surfaces.

New plaster must be allowed to dry out thoroughly before being painted.
If the skimming (topcoat) plaster has plasterboard beneath it, it is referred to as being "dry-lined", or "a studded wall".
The skimming plaster is usually only a few millimetres thick, and will dry out within 1 week under normal drying conditions.
If the skimming (topcoat) plaster has a bonding coat beneath it ("wet plastered") the drying time will be considerably longer.
In this instance, the use of vinyl emulsion is not recommended, as it will not allow the plaster to "breathe".
In time, the vinyl emulsion may blister, crack or even peel, due to efflorescence being trapped beneath the paint.
Contract emulsion (latex) with a matt finish is recommended for the first 6 months to allow the efflorescence to escape.
Unfortunately, this is not a suitable surface for (subtractive) paint-effects such as ragging-off and sponging-off.
Additive paint-effects, such as ragging-on and sponging-on can be used without any detriment to the plaster.
The first coat of paint applied to bare plaster should be thinned (to manufacturer's specification) to improve penetration.

	*Pre-painted surfaces.*
	Previously painted surfaces are an ideal for creating specialist decorative paint-effects. Abrading the surface with sandpaper is usually all that is required unless the surface has defects (blisters, flaking paint etc.). Refer to the General section for specific surface defects.

Bare timber.

Hardboard and Fibreboard (MDF) should be prepared in the following manner:
1) Ensure that the surface is dry, and free from dust, oil and grease.
2) De-grease with turps or white spirit to remove any oil or grease if necessary.
3) Punch any nail heads below the surface of the timber, fill the holes, and abrade the filler when it has dried.

Due to the amount of resin used in their construction, primers are unable to penetrate deep into the wood.
For internal use: Hardboard primer, thinned acrylic primer/undercoat or thinned emulsion.
For external use: Hardboard primer or aluminium wood primer.
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Hardwood, Softwood, Chipboard, Blockboard and Plywood should all be prepared in the following manner:
1) If possible, use a moisture meter to ensure that the moisture content of the timber is less than 18%.
If the moisture content is higher than 20%, any paint applied over it may flake off or blister.
2) Punch any nail heads below the surface of the timber, fill the holes, and abrade the filler when it has dried.
3) Prevent resinous stains from bleeding through the paint by applying 2 coats of shellac or styptic knotting to all knots etc.

The following primers are suitable for 1st coating bare wood:
All purpose wood primer.
White wood primer.
Pink wood primer.
Lead-free primer.
Aluminium wood primer.
Acrylic primer/undercoat. (Not emulsion)
Calcium plumbate primer can be used on both timber and metal, and is therefore ideal where the two are combined.
e.g. A metal window frame with a wooden outer frame.
Primer used on hardwoods should be thinned with the appropriate solvent to aid its penetration.
The ultimate wood primer (white lead) is only available for grade 1 & grade 2 listed buildings, due to its lead content.
Many thanks to the health & safety bods for that one ! Sarcasm

Particularly oily or resinous timber should be washed with cellulose thinners or turps & primed with aluminium wood primer.

Bare metal.
Ferrous metals contain iron (e.g. cast iron, wrought iron, high tensile steel, mild steel, stainless steel).
Non-Ferrous metals do not contain iron (e.g. aluminium, brass, bronze, copper, lead, zinc).
Galvanised metals have been coated with a thin layer of zinc to prevent corrosion and should be treated as non-ferrous.

Ferrous metals should be prepared in the following manner:
Remove all traces of rust and millscale before priming using a wire brush or mechanical hand tools.
Bead-blasting, shot-blasting, flame cleaning and acid pickling give far greater results. Use these methods where possible.
Remove any oil, grease or ferrous sulphate by degreasing with naphtha, white spirit, turps or an emulsifying agent.

The following primers are suitable for 1st coating ferrous metals:
Zinc Chromate, Zinc Phosphate and Zinc Dust.
Calcium plumbate primer can be used on both timber and metal, and is therefore ideal where the two are combined.
e.g. A metal window frame with a wooden outer frame.
The ultimate metal primers (metallic & red lead) are only available for grade 1 & 2 listed buildings, due to their lead content.
Many thanks to the health & safety bods for that one ! Sarcasm

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Non-Ferrous metals should be prepared in the following manner:
Aluminium: Use emery cloth and turps to etch and degrease the surface.
Primer: Zinc Chromate.
Brass, Bronze & Copper: Use emery cloth and turps to etch and degrease the surface. (do not dry abrade)
Primer: Etching Primer.
Lead: Allow to weather for several months, or use emery cloth & turps to etch & degrease the surface. (do not dry abrade)
Primer: Etching Primer.

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Galvanised metals should be prepared in the following manner:
Allow to weather for several months, or degrease the surface with turps. (do not abrade)
Primer: Calcium Plumbate, Etching Primer or Zinc Chromate.

Miscellaneous.
Acoustic Board and Insulation Board should be prepared in the following manner:
1) Ensure that the surface is dry, and free from dust, oil and grease.
2) Punch any nail heads below the surface of the timber, fill the holes, and abrade the filler when it has dried.
Primer: Glue size, hardboard primer, thinned acrylic primer/undercoat or thinned emulsion.
Brickwork, Building Blocks ("Breeze Blocks"), Cement Rendering, Concrete and Stonework:
1) Make sure that the moisture has dried out. Use a moisture meter if available.
2) Remove any efflorescence with a wire brush.
3) Remove any mildew or mould with a fungicidal solution or thick, neat bleach.
Primer: Stabilising solution or alkali-resisting primer.
Expanded Polystyrene (ceiling tiles & wall insulation sheets):
Should not be coated with any flammable material. (e.g. wallpaper or oil-based paints) This would be a fire hazard.
Fire-Proofed Boards should be prepared in the following manner:
1) Ensure that the surface is dry, and free from dust, oil and grease.
2) Punch any nail heads below the surface of the timber, fill the holes, and abrade the filler when it has dried.
Primer: Alkali-resisting primer. (water-based paint may draw out the salts of the fire-proofing and cause efflorescence)
Paper and Fabrics should be prepared in the following manner:
Ensure that the surface is dry, and free from dust, oil and grease.
Primer: Glue size, thinned acrylic primer/undercoat or thinned emulsion.
Plastics should be prepared in the following manner:
Use silicon carbide paper (wet & dry) and detergent to etch and degrease the surface.
Primer: None. (use finishing paint)