Faqs page header finish

I expected to use two litres of woodstain on my last job but only needed one. Why is the coverage rate quoted on your tins different from what I achieved?
The coverage rate we quote is a recommended coverage rate, which means that the product should be applied at this rate even though we know it can be brushed out further. If you achieve too high a coverage rate then it means that the finish has been applied too thinly.

Woodstains are formulated to become thinner and thinner as they weather, which makes them easy to maintain, but if applied too thinly it will mean that more frequent maintenance will be required.

I have stained a teak table and some iroko seating with Sadolin Classic and the coating is still not dry after two days. What is wrong?
Teak, in common with several exotic hardwoods, is a naturally oily timber. These oils retard the drying of all surface coatings, and will also impair the adhesion of applied finishes.

They must be thoroughly removed from the surface prior to decoration, and this can be effected by thoroughly rubbing the timber surface with a lint free cloth dampened with cellulose thinners or methylated spirits, changing the face of the cloth regularly. Although Iroko is not oily, it contains natural chemicals which have a similar effect to the oils in teak, and the surface should again be thoroughly degreased before coatings are applied.

High solids coatings such as Supercoat and One Coat are more susceptible to this problem than traditional coatings.

I decorated my windows with woodstain a year ago, but it is peeling off the putty, which is dry and cracked. Why is this?
The use of linseed oil putty for glazing in conjunction with Sadolin timber protection is not recommended. Putty contains drying oils which are necessary in order for the compound to remain pliable.

These oils migrate into the timber and oxidise with the atmosphere unless the compound is sealed by a film-forming system, such as a traditional gloss paint. Sadolin woodstains are moisture vapour permeable, and therefore do not seal the glazing compound. The resulting loss of the oils allows the glazing compound to dry and crack, causing a failure of the glazing seal.

For this reason we recommend the use of approved elastomeric sealants (polysulphide, silicone or acrylic).

Some plywood soffits looked great when I stained them with Sadolin Classic a few months ago, now they look as though they’ve gone mouldy. What has happened?
The white deposits found on the plywood surfaces are sodium salts which originate from within the glueline of the plywood. During the board manufacture, caustic soda is added to the glue mix to render the adhesive more soluble in water. Once the glue is cured, the caustic soda becomes superfluous.

Under the influence of atmospheric moisture, it can migrate to the plywood surface and appears as a white crystalline powder. In the normal course of events, the action of rainwater washes these salts away and they are rarely visible. However, in sheltered areas, such as soffits, the salts are not removed by rain action and remain as a ‘bloom’ on the surface.

The remedy for this is to wash down the affected areas with clean water and a bristle brush (not metallic bristles), thereby removing the salts. Provided that the finish is not damaged by over-vigorous scrubbing it need not be re-treated. It may, at some time in the future, reoccur to a lesser extent before the salts are fully depleted. Again, removal is by washing.

This phenomenon seems to vary with the type of plywood and country of origin. It should be pointed out that the loss of these salts in no way affects the strength or integrity of the plywood and does not blister or crack the finish.

In warm, dry conditions, Sadolin Extra is touch dry within a couple of hours. Can I apply another coat the same day?
The simple answer is NO. Water-borne stains, paints and emulsions can be overcoated as soon as they are fully dry, and two coats can be applied in the same day. Solvent-borne coatings undergo a two-stage process – firstly the solvent evaporates away (within 2-4 hours), leaving the surface dry to the touch; the coating then undergoes “oxidative curing”, i.e. the resin/binder within the coating reacts with oxygen in the atmosphere to give a chemically hardened (or cured) surface.

This process takes as long as 12 hours, and it is therefore essential that the coating is left to dry overnight before overcoating. Applying the second coat too soon can lead to wrinkling and a soft finish which can be easily damaged.