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Timber
is a dimensionally unstable material which expands and contracts with
changing moisture content. Exterior timber surfaces erode by ultra violet
light, normally changing to a grey colour leaving cellulose fibres exposed
on the surface. Timber also provides a source of nutrient for mould
growth. A protective system for timber needs to combat these three sources
of aggression, viz. water, ultra violet light and mould.
Some timbers contain resins and oils which can affect the performance
of paint - i.e. resin pockets in pine which can soften and bleed through
paints; oils in teak which can prevent penetration and adhesion of paint;
anti-oxidants in totara and matai which inhibit the drying of oil-based
paints.
Reconstituted timber products are subject, to a greater or lesser
degree, to the same degradation as timber. The majority of these products
contain wax to improve water-resistance and wet-strength. These waxes
can be dissolved in hydrocarbon solvents present in oil-based paints
and then be deposited on the film surface when the solvent evaporates.
This wax layer can upset the gloss and finish of the paint system and
seriously retard the drying of oil-based paints by blocking the ingress
of oxygen needed for curing.
Surface preparation:
- Remove all moss and mould:
Thoroughly clean down to remove all loosely adhered material. Treat
areas of moss or mould infestation with
Resene Moss & Mould Killer, correctly diluted with clean water.
Leave for up to forty eight hours to achieve full kill.
For heavy infestations further applications may be needed. Wash thoroughly
with clean water to remove all residue.
- Sand timber surfaces:
Always sand along the grain to remove minor imperfections and any
loose surface fibres. Loose fibres can be assumed to be present if
the timber is left exposed to the weather for more than one week.
Remove dust.
Sharp edges on timber are very difficult to apply paint to, as paint
tends to flow away from edges, leaving weak spots. For best results
these sharp edges must be sanded to a rounded profile.
NB: All sanding dusts can be harmful and appropriate protection
should be worn. In particular dust from old lead or chromate based
paint can be injurious to health if inhaled or ingested. Seek expert
advice if the presence of these materials is suspected.
- Optional:
Resene
TimberLock is a multi functional timber treatment that improves
the dimensional stability of the substrate, as well as improving its
fungal, water and ultra violet light resistance. Its use improves
the durability of subsequently applied topcoats. It is especially
recommended on cedar and old weathered timber that is to be painted.
Apply to bare areas, one coat of Resene TimberLock Preserver/Conditioner
at the spreading rate of 5-10 square metres per litre depending on
the timber porosity.
Allow twenty four hours to dry. Remove excess Resene TimberLock by
wiping with a turps dampened rag. Follow label instructions at all
times.
- End grains:
Always coat end grains (i.e. underneath the doors) as this prevents
moisture penetration into the timber surface which will eventually
crack the paint film.
- Moisture:
Generally timber should not be coated when its moisture content is
above 17%. Contact Resene if this is
suspected.
First coat:
For a painted finish, prime the timber with Resene
Quick Dry Acrylic Primer Undercoat at approximately 12 square metres
per litre.
Ensure all nail holes, damaged or split timbers are filled with a suitable
filler and applied in accordance with the manufacturer's instructions.
Spot prime filler when dry, with Resene Quick Dry Acrylic Primer Undercoat.
If the surface you propose to paint is already painted and in good condition,
then you can go straight to the Topcoats below.
NB: If staining is evident after the application of Resene Quick
Dry Acrylic Primer Undercoat, apply a further coat of Resene
Enamel Undercoat.
Topcoats:
We recommend you proceed
with two coats of either Resene
Enamacryl (Gloss) or Lustacryl
(Semi-Gloss) - waterbased enamels at approximately 12 square metres per
litre. These products perform like solventbased paints with the added
benefits of non-yellowing, fast drying and low odour when compared to
solventbased paint.
Follow label instructions at all times.
Clear/stained finish:
Because of their low UV resistance, clear finishes in exterior
environments are not recommended. For interior joinery and once the
surface preparation is completed - apply three coats of Resene
Aquaclear.
For a stained finish use Resene
Waterborne Colorwood, reduced if necessary to the desired colour
with Waterborne Colorwood Reducing Base. For a natural finish, the colour
of the timber is enhanced by the application of Waterborne Colorwood
Reducing Base first. Follow this with the three coats of Resene
Aquaclear.
Follow label instructions at all times.
Cleaning up:
Cleaning up waterbased paints is different to solventbased
paints - click
here for detailed instructions on clean up.
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