Wipe-on finishes are popular for a variety of reasons, the biggest of which is the ease of application. Wipe-on oils may take a little more time to apply and to dry than do some spray finishes, but provide a different look, and feel, which is often preferable for the amateur. Wipe-on finishes work beautifully when there is no need to meet high volume production standards: ease of application is added to a need for very little equipment. Wipe on finishes are basically a low tech in application, so can be done in any home shop with reasonably decent ventilation. Please note that last requirement, for some wiping finishes contain lots of materials you'd rather not breathe on an intensive basis for more than a minute or so. If shop or finish room ventilation is poor, get a respirator--not a dust mask, a respirator.
Some Massive Over-Simplification of Wipe-On Finishes [b1]
Danish oils are among the best known of the wipe-on oil finishes. The compounding is simple, with a few tricks from each manufacturer to add to their particular label's allure: usually, an oil, linseed or tung, is polymerized and sent out, with or without added color, stabilizers, or different ingredients. Danish oils give a satin finish. Wiping varnishes include a resin varnish with the oil, and give a faster build-up of a harder finish. Wiping varnishes provide a semi-gloss finish, and can be, with extra work and some steel wool, induced to provide quite a high gloss.
In reality, the above is nearly enough to know to select the finish you want--if you can interpret the manufacturer's claims. We'll look at those shortly, but the all-important parts of any finishing job are, first, deciding what finish to use, and, second, prepping the surface for that particular finish. Even more important is deciding whether or not to fill the wood first.
Too, it's not that difficult to make your own wipe-on finishes. Select a full strength poly or other varnish. Thin it about 50-50 with the appropriate thinner, and you've got a start. Work from there to see what suits your tastes best, but remember that if the full strength calls for three coats, you'll need five or six of the thinned coats to equal that depth of appearance and protection. If you desire, increase the strength of second, third and successive coats from 50-50 to 66-34 or 75-25 to build depth faster.
Oil Finishes Don't Suit Some Woods[b1]
Open-pored woods such as oak and hickory and mahogany don't do as well with wipe-on finishes as do closed pore woods such as cherry and maple. If you're willing to put in the effort filling ring porous woods, then they'll finish as well as any other with wipe-ons, but you eliminate one of the great advantages of wipe-on finishes, the ease of application. No more "wipe it on with an old cotton sock and wipe it down with an old T shirt." First, you've got to fill the wood, which can be a lot of work. Most times, you'll then need a sanding sealer, too. After which, a light sanding, clean-up and then going through the process of applying the wipe-on oil works well.
Prepping The Wood[b1]
Sanding Sheets Getting the wood ready to accept a coat of finish is always the first step. Scrape all glue off near joints--or anywhere else it got dripped. Sand the finish from 100 grit through 180 to 220 grit, going step-by-step: that is, go from 100 to 120 to 150 to 180 to 220. Dropping a grit or two may look like a way to speed up, but going, for example, from 100 to 180 grit means you've got to take that much more time with the 180, and use that much more 180 grit paper, to get the same results. The idea is to eliminate visible scratches. Sand with the grain whenever it is possible, during hand sanding.
Using a random orbit sander is a great way to reduce overall sanding time, while getting a swirl free job. If you're blowing off the surface, wear a dust mask, of course, but also make sure you have a good, clean filter in the air compressor line. At this point in the job, tiny blobs of oil from the compressor lube will penetrate the wood surface beautifully, and really mess up your results. I like to add two small, maybe unnecessary, steps at this point. First, I go over the surface with my hand, feeling for rough spots. By this time, if you get a splinter, you've got problems other than with the finish. Then, if I'm using oil based finishes, I like to wipe down with a coat of mineral spirits: this seems to serve as a degreaser (at least in my mind), and shouldn't really be needed, but I've been doing it for years. As always, make sure you have plenty of ventilation, no open flames and so on. Let dry well before the next step.
Finish clean-up with a tack cloth, using care in the corners and in detail carvings.
Raising Grain [b1]
Raising grain isn't an overwhelming problem with wipe-on finishes, but you want to keep an eye on any kind of roughness after the first coat. After the first coat is wiped off, wiping down with more finish and 0000 steel wool is a good idea in such cases (do not use steel wool if you're using water based finishes. Substitute a super fine grade [600 grit or finer] of wet/dry sandpaper, or one of the abrasive fiber pads). When you do have to reduce raised grain, you need to apply some effort, and you may have to spend half an hour or more getting it back to the 'baby butt' smooth you want for a fine finish. Wipe off any standing oil when you're done with the steel wool. Let dry. Wipe down with a solvent laden rag, after drying, and then wipe down with your tack cloth again.
At this point, just keep applying coats. Depending on the brand of wipe-on you've selected, the build-up may be fast or slow, but each coat takes about 24 hours to dry ready for the next application, so if you go the six or seven coat route, expect to spend at least a full week of time waiting for things to dry. Apply. Wipe off carefully, five, ten or 30 minutes later, as the manufacturer directs.
Keep applying until you have the look you want. Let dry for at least 48 hours, and put the piece into use.
Wipe-on finishes do not protect well from abrasion and lots of wet, but when the finishes are damaged, the repairs are quick and easy. Wipe-on varnishes are more protective in those areas than are the nearly straight oils, but these finishes are not meant for high abrasion areas, nor are they meant for use where water is apt to be a problem. For most in-home and around-the-office uses, they're great--and if accidents happen, a bit of new application over the old usually fixes things. For projects to be used in kitchens and baths, select another finish.
Most manufacturers advertise their wipe-on finishes as "tung oil" and provide little large print label information on other ingredients. If you read the smaller list carefully, you'll find the hardeners, and other necessary products. As one who at one time had to use straight linseed oil to beautify and protect the walnut stock of an M1, I can assure you that straight oils are going to demand an excessive amount of work for the results, even without a Drill Instructor breathing down your neck. The addition of resins speeds the set of the oil (driers are used in boiled linseed oil), and varnish resins make them a little more use as a protector…our M1 stocks always suffered finish damage when used in the rain. So we spent a lot of time wiping on more raw linseed oil.
For a deep appearing, easy to repair finish, wipe-on oils are hard to beat and are much easier to apply than are straight oils.