Faqs page header preparation

Do I need to use a timber preservative before I stain my wood?
Many hardwoods (e.g. oak, teak and iroko), are naturally durable, and have their own natural resistance to decay/rot. Most softwoods and “cheaper” hardwoods are not durable, and must be treated with a preservative if they are to be used outside. Some of these timbers are treated in the factory to stop them rotting, but if this has not been done, Sadolin Wood Preserver and Quick Drying Wood Preserver are ideal for use as superficial preservative pre-treatments.

Why can’t I use white spirit to clean down surface prior to painting or woodstaining?
White spirit tends to smear contaminants such as grease, resin and oils over the timber surface rather than remove them. This is why we recommend the use of methylated spirits or cellulose thinners. White spirit can also have quite a ‘greasy’ feel to it and can add to problems with adhesion of subsequent coatings, especially water-borne ones.

There are a lot of knots in the timber I’m using. Should I use a knotting agent?
The phenomenon of resin exudation is natural and highly unpredictable, being dependent both on timber species and timber grade/quality. The traditional answer was to apply Shellac Knotting and ‘seal’ in the resin.

However, many years of research and on site experience have shown that this method is not completely effective, even with paints, with which it is traditionally used.

The moisture vapour permeable (sometimes referred to as microporous) finishes attempt to deal with the problem in a different manner by allowing resin to filter through the finish without blistering or peeling of the finish, hence full protection is maintained.

In the short term, resin exudation tends to look unsightly, but within a year or so the excess resin becomes exhausted and exudation ceases. The initial resin should be cleaned from the timber using a lint free cloth dampened with cellulose thinners or methylated spirits.

The new windows I’m coating already have a basecoat applied, do I just apply finishing coats of woodstain?
If the base satin is in a good condition and the windows have not been exposed for longer that about 12 weeks, then you would only really need to apply two coats of the finishing woodstain such as Sadolin Extra. Many base stains are formulated to offer only temporary protection to the timber during installation of the windows and if they have been exposed to weathering for more than 3 months then it would be best to sand back to bare timber and apply the full coating system, such as Sadolin Classic followed by Sadolin Extra.

What are the best fixings to use with Sadolin woodstains?
Because of the vapour permeable nature of Sadolin wood stains, iron or steel nails are not ‘sealed off’ from air and moisture, thus rusting of the nails can still occur. Rainfall then washes the rust away, and is seen as a brown ‘tear-like’ discolouration of the timber.

Any loose or rusty nails, screws, etc. should be replaced with galvanised or non-ferrous fixings, which will not corrode, even if exposed to the weather.

Wherever possible it is preferable to use lost head nails, but if this is impractical, nails should be punched home, and remaining holes filled with a suitable woodfiller.

My new timber has only been exposed for a few weeks and is dry and clean, can I just go straight ahead and apply your coatings?
As soon as timber is exposed to light, a substance known as lignin which binds together the timber fibres begins to be degraded. As this happens the fibres on the very surface of the timber become loose and friable.

Although this is not generally apparent to the naked eye, greying of exposed timber is a tell-tale sign that this is occurring. If these fibres are not removed by thorough sanding prior to coating under the stresses of weather they can detach from the main body of the timber taking the coating with them.

However, research has shown that even after only 2-3 weeks, and before any real colour change is seen, damage may already been done to these fibres and sanding is therefore recommended prior to coating.

Is washing down with water sufficient to remove the algal growth from the cladding before I re-decorate?
No, using water or an ordinary detergent will not kill off the spores present in the timber surface, even though the algal/mould growth may appear to be removed, and they would then grow through any newly applied coating.

You will need to use either a proprietary fungicidal wash or a solution of one part bleach to two parts water. This needs to be scrubbed onto the surface and allowed to ‘work’ for a minimum of 20 minutes before scrubbing off and rinsing with clean water. Allow to fully dry before redecoration.

Can water-borne stains and paints be removed by burning off?
Yes, however, this is not an easy task. The preferred method would be to use a chemical stripper to soften the finish, remove with a metal scraper, followed by thorough sanding.

How do I remove lead paint?
Some old paint coatings may contain lead which is poisonous to humans, and before removing or preparing existing paint coatings it is important to determine whether the paint concerned contains lead. Remove all such coating materials in accordance with the appropriate legislation. A guide on “How to remove old lead paint safely” is available via the British Coatings Federation Ltd.
(Tel. 01372-360660).