Woodworking Articles & Tips

Wet Sanding with ArborOil?

By Malcolm Gillett

Many woodworkers like to use oil finishes but have trouble achieving a glass smooth finish. In this article, Malcolm details how to use Arbortech's ArborOil and the "Wet Sanding Method" to achieve a level, smooth finish, on all types of timber.

Many woodworkers like to use oil finishes instead of lacquer, varnish, polyurethane or water-based finishes mainly because oil finishes are much easier to apply, and are much more forgiving when mistakes happen. However, one of the main drawbacks of an oil finish is that one cannot achieve a glass smooth finish on open pored woods as one can when applying a lacquer, varnish, polyurethane or other topcoat finish.

The term "glass smooth" may be somewhat confusing, as many people associate this with producing a high gloss finish. This is not true. You will not get high gloss sheen when using any oil finish. Glass smooth refers to how level the surface is, the 'evenness' of the light reflection and how smooth it feels. When using a topcoat finish on open pored woods, you can either build up the finish by applying multiple coats and sanding back down until the pores have been filled or you can first apply a paste filler to fill the pores, then apply a topcoat finish.

Oil finishes are thinner and contain much less solids than topcoat finishes, therefore it would not be practical to apply multiple coats and sand back until the pores have been filled. This would take much too long. Also oil finishes need to penetrate the wood in order to work properly.

Once the finish penetrates, the solvents evaporate and the resins solidify actually making the wood itself harder. If the pores have been filled with paste filler (which is usually silica - very finely ground glass), the oil finish will not be able to penetrate the filler.

While leaving the pores open when using an oil finish is OK, and many times even desirable on some pieces of woodwork (like a chest of drawers, chair or clock), for other pieces (like conference tables, dining tables, pianos, jewellery and music boxes) may look much better if the pores were filled so a glass smooth finish can be obtained. In the end, it still comes down to solely a matter of taste.

By Wet Sanding, the oil is mixed with the sawdust that has been created by the sanding; this makes a slurry or paste. As one continues to sand, the paste is forced down into the pores of the wood. Basically the open pores of the wood are filled by using its own sawdust in combination with the oil, which works as not only a finish but also a binder to hold the sawdust down in the pores and level the surface.

The reason why a higher sheen is achieved is simple. Once the pores of the timber are filled, more light is reflected off the surface at a "similar angle", due to the surface being smoother. In contrast, when the pores are open, the light is reflected at random angles due to the unevenness of the surface. This scatters the reflected light and results in a lower level of sheen.

Aesthetics also come into the equation with wet sanding. The even surface that results from wet sanding gives a smooth, almost satin-like feeling when handling the object. This tactile response is an additional bonus and one which adds to the overall quality finish that comes from wet sanding applicable wooden surfaces.

SUGGESTED METHOD

1) Prepare the wood by sanding through the grades of coarse, medium, and fine sandpaper. Make sure to wipe off all sawdust after sanding. Note - It will help if the surface is wiped over with damp rag or even wet the surface to raise the grain and lightly sand again.

2) Apply a generous amount (almost flood the surface) of ARBOROIL to the surface.

3) Immediately after the ARBOROIL has been applied (while it is still wet on the surface) sand with the 320 grit and work into the pores. Continue to oil and wet sand until you feel enough of the paste has been worked down into the pores. It is better to use 320-grit silicon carbide wet and dry paper rather than 600 grit. The 320-grit paper will create the paste quickly and the paste will fill the pores. Continue to oil and wet sand until you feel enough of the paste has been worked down into the pores.

4) There will still be a substantial amount of paste left on the surface. Don't wipe it off right away. Let the surface harden until touch dry, then wipe off the excess paste using a lint free rag. Wipe against the grain, trying to cut the paste off at the surface, this way the paste in the pores will remain and not be pulled out. Leave to dry further.

5) Before you continue, there may be a small amount of paste that is still on the surface. This needs to be removed, if not visible now, it will be when you apply additional coats. Leave until the mixture has hardened enough to sand and then with clean 320 grit, remove the paste on the surface. You need only to take a few passes, just enough to remove any excess paste that has remained.

6) Wet sanding need only be done until the grain has been sufficiently filled and generally only one or two applications are necessary. Now it is just a matter of applying additional coats of ARBOROIL (without wet sanding) until you achieve enough protection and the desired sheen. Usually two to four additional coats after the wet sanding coats will produce the required sheen. The coats should be applied wet on wet (to allow deeper penetration of the oil) and smoothed and buffed with a soft cloth with a small amount of friction applied.

After the last coat has been applied, ARBOROIL will dry with friction and fully cure in about 12 -15 hours. A final coat of ArborWax (Clear, High Build, or Burnishing) will increase

Copyright © Arbortech Pty. Ltd 2002 ===========================================

Reprinted with permission from http://www.arbortech.com.au