Finishing Touch: Hardwax oil
Hardwax oil (HWO) finishes have been used for quite some time in Europe and are beginning to be more widely adopted by the floor-finishing industry in North America. They are also becoming increasingly popular among professional woodworkers because of their ease of application and repair, and excellent durability.
Most woodworkers will be familiar with penetrating oil finishes of one type or another and with paste waxes – typically applied after the oil topcoat has cured. Two of the more common oil finishes are oil and varnish blends – typically linseed or tung oil based, and often referred to as ‘Danish Oils’; and polymerized linseed or tung oils, such as ‘Tried & True’ and ‘Lee Valley Tung Oil’. Noted furniture maker Sam Maloof popularized a finish consisting of equal parts of boiled linseed oil, mineral spirits and polyurethane. All these finishes are easy to apply (simply wipe on and wipe off), and they provide reasonably good protection and a natural, hand-rubbed look. However, they aren’t as durable or moisture resistant as film finishes such as lacquer, varnish and polyurethane.
HWO finishes are somewhat of a compromise finish. You get the benefits of a conventional penetrating finish but with a higher level of durability and moisture resistance found in film finishes – though not as robust as you will get with a film finish. These finishes will harden both on the surface and inside the top layer of wood pores as they cure.
They’re a much more environmentally friendly and personally safe option than most other finishes. Most of the content in these finishes consists of purified natural oils and waxes. They do contain some chemicals – typically a less toxic aliphatic hydrocarbon such as mineral spirits, and may contain lead and cobalt-free dryers. None contain biocides or preservatives. HWO finishes also eliminate fewer volatile organic compounds (VOCs) than other finishes – less than 500 grams per litre (Rubio is completely VOC free). And once they’ve dried (most after a few hours) they’re odour free.
Oli-Natura is imported from Germany. For those who favour a somewhat glossy, higher-sheen finish, Oli-Natura is a good choice. It’s the faster product to use – it dries in a couple of hours and cures in a couple of days – and it’s the most economically priced. Like Rubio, it’s sprayable without having to add any thinner. I also like that the container it comes in has a screw-on spout cover rather than the more standard paint can lid. It’s only available in a 1L size, and currently there is only one Canadian distributor, located in BC, so shipping cost will need to be factored into your purchase.
Only the Rubio product had to be pre-mixed before it was applied, but the process is fairly simple.
Duguay applied each finish to an oak board, and when dry he found there was little difference in the look of each finish. Different species of wood may vary slightly, however.
After subjecting a small finish panel of each product, Duguay let water and alcohol sit on their surfaces for 10 minutes. The Oli-Natura and SAICOS showed some slight discolouration, but a second application of finish over the samples completely rejuvenated the look of each panel.
The Oli-Natura, as well as some volumes of Osmo, come with a simple and easy-to-use cap.
Applying a hardwax oil finish
While HWO finishes are very easy to apply, it’s still important to follow the specific instructions from the manufacturer to get the best results. All four products I looked at are applied in a thin coat. Oli-Natura and Rubio are wiped off after 10 minutes or so, and typically require only one coat, whereas the first coat of Osmo and SAICOS are not wiped off. Osmo requires a second coat that you wipe off straight away after it’s applied, while SAICOS also requires a second coat that is not wiped off. One thing that I really like is that they don’t raise the grain, so there’s no need to sand between coats.
Pot life is anywhere from 2 to 4 hours, enough time to finish all but the largest projects (by the slowest woodworkers). Coverage rates will vary depending on the wood species you use, along with how careful you are in applying the finish. Likewise, dry times vary quite a bit, from a couple of hours to a day and a half. Contributing factors include the ambient temperature and humidity levels in your shop and how thick or thin a coat of finish you’ve applied.
Because these are all oil-based products, you still have to be careful about rag disposal to avoid the possibility of spontaneous combustion. Remember to immerse all your oil-soaked materials in water or in a fire-rated air-tight container.
All four brands I tried can be applied by rag, microfiber roller, or white abrasive pad – the best option for furniture unless you’re finishing very large projects such as a bank of kitchen cabinets. Only the Oli and Rubio can be sprayed. Both Osmo and SAICOS have other formulations that work better with oily exotic woods.
HWO finishes infiltrate the pore structure of wood, so it’s important to remove all surface dust. After sanding, vacuum thoroughly and then follow this up with a tack rag or, better yet, a cloth dampened with mineral spirits to remove any residual dust. If there is any raised grain, gently rub over the surface with a bit of Kraft paper (aka ‘brown paper sandwich bag’).
All these products can be used over grain fillers on open-grained wood, but make sure you use a ‘stainable’ filler.
HWOs are among the easiest finishes to maintain. For minor scuffs just apply another thin coat. For a water mark or stain, sand the affected area just enough to remove the affected area and then spot finish. So, unlike a film finish, it’s unlikely you’d ever have to do any major resanding to repair a small blemish.
Like any finish, these have a maximum shelf life for unopened products – from 1 to 2 years (Rubio) to at least 5 years (Osmo). Once opened, shelf life is about 1 year (3 years for Osmo). You can extend the shelf life of these products by adding an inert gas, such as Bloxygen, to the product container after each use.
The choice is yours
I tried four types of hardwax oils, applying the product on ash, oak and walnut, carefully following the manufacturer’s instructions.
Product application is quick and easy for all four brands, and most importantly, the results are consistently beautiful and durable. Only one product, Rubio, needed to be premixed. None had overly obnoxious odours, though it’s still advisable to wear respiratory protection as you would when applying any finish. When the samples were placed side by side, I found it difficult to tell the finishes apart. The Oli-Natura had a slightly brighter sheen than the others, while the Rubio had a somewhat duller sheen. Like any oil finish, they do impart some darkening to wood; on the lighter ash I didn’t find it unappealing. They do an excellent job of highlighting the natural grain features of wood.
I did some ‘real-world testing’ – subjecting the wood samples to a 10-minute standing water and alcohol spill, and using the samples as coasters for a couple of weeks. In my standing water and alcohol test only the Oli-Natura and SAICOS showed some slight discolouration. However, a second application of finish over the samples completely removed the discolouration. I didn’t notice any abrasion to the finishes from hot coffee cups and (the occasional) beer bottle.
Osmo, also manufactured in Germany, is probably the more widely known HWO, as it has a nationwide dealership. The product is virtually odour free during application, and it has the longest shelf life. Like SAICOS, it requires two coats. It’s also available in 5mL, 0.125L, 2.5L, and 10L sizes. Osmo produced a sheen in between the Rubio and the Oli-Natura and SAICOS (a matte sheen is also available). The Polyx-Oil that I tried is their original HWO. They also have a low VOC (50 grams per liter) version (#5125), a sprayable version (#1101), plus 15 transparent colours and 10 intensive colours. Some of the volumes are available in a screw-on spout cover.
Rubio is imported from Belgium, and is the only two-part finish, consisting of a container of oil (Part A) and a smaller container of hardener (Part B). You mix the two together in a ratio of 3 to 1. While it only requires one coat, it has the longest dry time (24 to 36 hours). Rubio is the only HWO that is completely VOC-free. Rubio is sprayable and is available in 350ml and 3.5L sizes, and in 54 transparent colours. There are about a dozen dealers across Canada.
SAICOS is the third product from Germany. The sheen it produced was most like Oli-Natura (matte and high-gloss sheens are also available). It has the second lowest VOC emission level and almost no odour in use. It’s the most expensive of the four (based on a single coat application). SAICOS is also available in .125L, 2.5L, and 10L sizes, and in 10 colours. There is an additive (#3242) available that provides UV protection and a sprayable version of the product (#3063). There are about two dozen SAICOS dealers in Canada, mostly in BC.
If you like a hand-rubbed look to your woodworking projects, then HWO finishes may well be worth considering.
Oil Plus 2C
|215 sq. ft./L
|260 sq. ft./L
|500 sq. ft./L
|150 sq. ft./L
|Mix and stir
|< 450 g/L
|Shelf life (unopened)
|Shelf life (opened)