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Preparation of new timber surfaces
With new timber surfaces:
- Remove surface contamination, such as dirt etc with a stiff
brush.
- Make good any cracks with an appropriate filler.
- Treat any organic growth with a fungicidal treatment.
- Apply a stain-blocking product directly to knots, or use a product that is self-knotting to stop
discoloration of paints.
- Because of their oily nature, some hardwoods – such as cedar
and iroko - should be wiped over with white spirit solvent. In
extreme cases, the natural oil content can stop traditional
oil-based paints from drying.
- If the surface is weathered, grey and friable, then thoroughly
sand clean and apply a stabilising sealer before the
finishing coats.
- If you are applying a natural finish – varnish, lacquer or
wood stain – then you may need to use a colour equaliser if the surface appearance is variable.
- Apply an appropriate primer or basecoat, then a finish. Some
products for use outdoors are marketed as microporous to
allow wood to dry out if it accidentally gets wet – these will
not be effective, though, if water is entering the wood through
design defects.
- Do not paint over intumescent strips to the edges of doors.
- Do not paint over silicone mastics.
Preparation of previously painted timber
surfaces
With previously painted surfaces:
- Remove all defective paintwork to leave a firm edge.
- Sanding, burning-off, or solvent-based paint removers can be
used, but see the note below under Health and Safety on
lead-containing paints..
- Caustic-soda paint removers are effective where the previous
paint is very thick, but full immersion in caustic baths can
cause problems of distortion and efflorescence when the wood
dries out.
- If the surface has been exposed and is grey and weathered
thoroughly sand until clean, and then apply a stabilising sealer before the finishing coats.
- Abrade sound gloss painted surfaces to provide a key for
subsequent coats, then wash down and allow to dry.
- Treat any organic growth with a fungicidal treatment. Areas
where there is a need to provide long-term protection against
organic growth may also require the use of a finish that is fungicidal.
General issues
- Unless approved by the manufacturer, do not apply any coating if
the ambient temperature is below 5oC or if other adverse weather
conditions such as rain are likely to occur before the paint
dries.
- Only use products supplied by a single manufacturer.
- Where it is necessary to paint children’s play goods, use a
product that is specially formulated to be child safe.
- Some products for use outdoors on garden fencing, sheds and
furniture are specially formulated to be plant and pet friendly,
and should be used if this is an important requirement.
- If uncertain of your skill in obtaining a good finish with
liquid gloss paints, then use a non-drip product.
Health and Safety Notes
- Paints applied to older buildings may contain lead-containing
pigments and preparation of these surfaces will require care.
Test kits for lead paint are available through most trade and retail
outlets, and should be used if in any doubt. Advice on the safe
preparation of old leaded paint is also available from coatings
manufacturers and suppliers
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