I use Osmo Polyx Oil on almost every project. I generally sand to 180 with an ETS 150/3 and 220 on end grain with a RTS 400.
If it still looks waxy or wet a few minutes after applying, wipe it off and buff it out with a clean cloth. I use Brawny paper towels. Lint isn't an issue because the finish is in the pores. Change paper towels frequently. I fold them in quarters and go through a roll per project. If you leave Osmo on the surface, it dries glossy and on top of the wood. However, it is NOT a build finish. It's supposed to be a penetrating finish.
Festool's STL 450 surface control light is outstanding to apply raking light for inspection.
Osmo does have special instructions for Walnut if it's likely to be exposed to water like a table top.
FINISHING WALNUT WITH OSMO POLYX OR OSMO TOP OIL
The Osmo Polyx Oils (3054 and 5125) and Osmo Top Oil (3058) all provide a beautiful & durable finish on the many varieties of Walnut. It must be understood, however, that the grain character of this wood, regardless of variety, grade or cut, causes it to require special preparation and/or application to ensure proper protection from water-spotting. Water-spotting on oil-finished Walnut is because of the physical characteristics of Walnut, not failure of the oil or oil/wax finish.
Failure to understand and follow the below is likely to cause water-spotting to be an ongoing issue with any Walnut table, cabinet, flooring or other surface subject to liquid exposure.
Walnut is known as a semi-ring porous grain wood. Translated into lay terms, this means that it has bands of very fine pores or pits through most of the wood. These pores appear to be just the right size to readily wick water. Our best understanding is that the cured oil/wax finish cannot ‘bridge’ or ‘block’ these pores enough to counter the wood’s natural tendency to wick water. (Remember, these pores transported fluids from leaves to root and back during the tree’s life.)
These pores must be ‘grain-filled’ or ‘stopped’ PRIOR to or during finish application to achieve satisfactory resistance to water-spotting. Many woodworkers will probably have their own techniques for managing this characteristic.
We know of two techniques to achieve this goal:
1: Use a wood filler of the brand and color of your choice using standard filler application and sanding techniques. A possible objection to this technique is that Walnut color-changes over time, whereas the filler probably won’t. Another possible objection is with Claro Walnut, which can exhibit more color variation than American Black Walnut; it may be harder to match with available fillers. Filler is probably the only choice with Walnut flooring; flooring contractors will be quite familiar with the process. Standard application techniques for the Osmo product of choice are then used.
2: One can also use a modified application technique with the Osmo product to achieve the same goal. It is probably not practical for flooring. Along with significantly decreasing the water-spotting, the below technique can create a beautiful polished luster that is hard to achieve with our standard application techniques.
After sanding the surface to the desired dry grit, use wet-dry sandpaper wetted with the finish to abrade the surface of the Walnut to create a fine ‘slurry’ of sanding dust and finish. With the wetted paper, work the slurry into the grain structure using some vigor. Buff dry with clean cotton cloths before the slurry begins to get sticky.
Choice of sandpaper grit is up to the finisher, although 220 grit is likely to be the coarsest available in wet-dry form. There are many choices in finer grit, but be aware the higher the grit, the glossier the end result.
One should plan on two or three coats using this method, using 220 or finer to choice. No brushed coats are required.
Remember, all oil-soaked rags, paper, gloves etc are self-combustible and require proper disposal to avoid risk of fire.
Allow the finish to cure for at least two weeks in normal interior conditions before covering or exposing it to water.
Care and maintenance are the same as with other techniques.
