Healthy Clear Coatings
We woodworkers cover a lot of project styles and applications; but which finish is best for what project? Which will give us the enhancing result we imagine, protect our project and offer easy maintenance? I’ll discuss here which types of finishes work best in what applications, plus expose some facts about today’s “healthy” finishes; healthy for you, your loved ones and our planet. To see photos of sample boards, and read some application tips, visit our website to read this article online.
What They Are, How They Work and Why You Should Use Them
Long ago and far away, woodworkers used natural solutions to treat and coat their products. Bees and carnauba wax; oils extracted from walnut, tung, flax and other plants; extracts of the lac bug, which when mixed with alcohol created lustrous shellac. Healthy finishes indeed but short on durability and requiring regular replenishment or skill to apply and maintain.
Industrial Age manufacturers developed new solutions which, mixed with petrochemical solvents, could be applied fast, cured to a hard film and required little maintenance. We makers of all stripes simply accepted the smelly solvent fume induced wooziness and the toxic cleanup of these oil-based finishes. The options were spirits-based coatings or more highly refined thinners-based coatings and lacquers. These manmade coatings, diluted and carried using petrochemical liquids, give off massive volumes of volatile organic compounds, “VOC’s”, which have since been proven to be very serious health hazards to all life forms.
Briefly, not all VOC’s are bad. Biological VOC’s, widely found in nature as “green leaf volatiles” within the scents emitted from plants, is their means of communicating with other natural creations. Animals, molds, fungi and other organisms also produce mostly harmless VOC’s. The finishes of long ago and far away fall within this group.
Manmade, or “Anthropogenic”, VOC’s are a whole different story. These, the most harmful, are notably found concentrated indoors; while not immediately toxic, in low concentrations the long term effects develop slowly and compound as they evolve. A principal source of these nasty VOC’s has been paints and other coatings whose carrier solvents were principally aliphatic hydrocarbons, ethyl acetate, glycol ethers and acetone. These coatings and carriers can outgas for months or even years depending on the product and the ventilation where it’s applied.
The Age of Awareness
Today, in what I’ll call The Age of Awareness, solutions are being found to suspend the hard-curing resins like those in the varnishes, urethanes and lacquers we’d grown dependent on, in a carrier with none of the life threatening side effects; low and “zero” VOC products which meet or surpass our expectations. Enter aqueous solvents, aka water; more highly refined petrochemical base compounds which outgas totally within days or even hours, and high solids resins needing less solvent carriers by volume, dramatically reducing our exposure to harmful VOC’s.
Since 1990, agencies like the U.S. Environment Protection Agency, the Ozone Transport Commission, the California Air Resources Board and others, then in 2003, Environment Canada, established regulations to restrict the volume of VOC’s in coatings across North America, the limits varying by a) type of substance, and b) its intended application. Consequently, coatings manufacturers have developed new compounds which generally far exceed these regulated limits. By definition, for a coating to be low VOC compliant they have to limit VOC content to less than 50 grams per litre, 60 to 70 percent less than in traditional oil-based coatings. Pleasingly, this new generation of coatings also exhibit greater durability, stain and abrasion resistance which means less frequent recoats; minimal odour; antimicrobial properties which resist mold and mildew in cured finishes; and surfaces which are easily washable and scrubbable using gentle cleaning products, no harsh chemicals.
We’ve gone full circle, rediscovering traditional coatings, successfully altered others and developed new friendly compounds that really rock.
How low is low enough?
So how do we qualify and quantify VOC’s? The benchmarks set by law limit oil-based varnishes to less than 450 grams of VOC’s per litre and thinners-based lacquers less than 550 grams per litre. By comparison, what I call “friendly finishes” are defined as follows:
No VOC’s… finishes made from natural oils, waxes, water, natural minerals, milk casein, and/or dyes from nature or earth minerals.
Zero VOC…finishes or coatings with no more than 5 grams of VOC’s per litre by volume.
Low VOC…paints and stains with no more than 200 grams/ litre by volume and varnishes within 300 grams/ litre by volume.
In reality, most manufacturers’ products are vastly below these legal limits, within the 50-150 grams/ litre range with some as low as 25 grams/litre and less.
Buyer Beware – some manufacturers legally skirt the VOC compliance issue; if a coating product contains VOC’s higher than the legal limit, they may still market it provided it’s sold in containers smaller than 1 litre. If you’re health conscious and wonder what a product contains, read the label or the health and safety literature.
The most widely used solvent/thinner in use for surface coatings is water. Second to that is low aromatic white spirit, or isoaliphate, a petrochemical refinement in which the most dangerous aromatic hydrocarbons have been removed. Synthetic isoaliphate solvents have been created using extracts from citrus fruit peel and contain limonene. None of these solvents are particularly safe by themselves or in extreme volume but used in coatings as recommended, pose little risk.
An application tip or two
To apply oils, waxes and wipe-on finishes I use white synthetic ultrafine abrasive pads (Scotchbrite or equivalent) not paper towel or lint-free clothes. The mild abrasive action burnishes the wood and resultant surface, enhancing the film building process. As I swirl the finish on in a figure eight pattern, followed by going with the woods grain, it is thinned by friction ensuring it gets well down into the woods pores. Unlike paper or cloth, there is almost no risk of the pad deteriorating in use, compromising the cured finish. Also, because of the pads porous structure, risk of spontaneous combustion of a used pad is far less than with a paper or cloth applicator. I buy pad material from stores that rent square pad buffers for flooring installation. The pads I buy are 3/4″x 12″ x 18″, easily cut with scissors, yielding many small hand applicators or hand buffs. Most of the applicators I use are cut less than 2″ square.
I always wear disposable nitrile gloves, keeping my skin and nails clean, protected from drying and cracking and from absorbing chemicals through my pores and into my circulation system.
Prepping the samples
With a couple of noted exceptions, all the 7/16″ × 4-5/8″ × 11-5/8″ sample boards I used were ash sanded to 180-grit. Only the waterborne varnishes needed a quick scuff sanding with 400-grit paper between coats.
I applied each product with a fresh 1-1/2″ square pad of white Scotchbrite (or equivalent) ultra-fine abrasive. Each sample received three coats of product, except two as noted, leaving the surface as recommended by the manufacturer for each application. My shop temperature at the time of this evaluation averaged 25°C with between 51 and 58% humidity depending on the day.
Four main categories
I’ll break the products I’ve examined here into four groups, defined by how they interact with wood; drying oils, soft film finishes, waterborne film finishes (varnishes) and microporous surface coatings.
These protect the wood from inside by penetrating deeply, enriching the wood’s grain, figure and natural tone but will darken over time. They build little film, adding only subtle durability. Oils cure through exposure to the air (oxidization), building sheen according to the number of coats applied. Any resulting film is a soft, breathable membrane, easily refreshed by adding more oil or top-coating with wax or a sympathetic film finish once fully cured. The oils I tested here amazed me by penetrating completely through their 7/16″ thick sample boards; no other finishes absorbed this completely. Well suited to food prep woodenware (cutting boards, salad bowls, etc.) which you’ll want to recoat regularly for appearance. They’re also fine for children’s toys and furniture, secondary components for furniture or cabinetry (legs, stretchers/stringers, cases) or conversely, where you expect the surface will see abuse and you want easy regular refreshment with the same or a compatible product.
Homestead House pure Tung Oil
No VOC’s – 250ml $13.00 / 500ml $23.00 /
1 gallon $69.99
With a thin consistency and a greenish colour, this has a faint new-mown grass scent. I maintained a damp film, letting it sit for 30 minutes before wiping dry. Each coat seemed to only absorb moderately. Any bloom could be wiped away easily. Each coat could be applied 24 hrs. apart. The resultant surface shows a yellowish soft golden colour, transparency and sheen free.
Lee Valley Pure Tung Oil
No VOC’s – 250ml $13.90
This is a thick liquid with a golden colour and sweet, nutty aroma. The first coat seemed to absorb very little but I let it setup and removed all trace product after 10 minutes. After 24 hrs. I repeated the process for each of the next two coats. I was rewarded with a rich, softly pleasing film finish, likely the result of a higher solids content than others in this group.
Soft Film Finishes
Natural “drying oils” based, these products have been processed using heat, called polymerization, altering their chemical structure. Different from their oxidizing cousins, each polymerized coat bonds and layers to its previous coat, creating a durable, breathable membrane. These can be easily maintained by applying more thin coats as preferred. The result is an enhancing transparent coating with little applied tone, though this will deepen over time, dependent on the number of coats applied.
Tried & True Danish Oil
Zero VOC’s – 473ml $17.95 / 946ml $26.50
Polymerized linseed oil-based, this food-safe product has a thin liquid consistency, a golden colour and a sweet nutty aroma. It absorbed really well. For each coat I maintained a wet surface for 5 minutes then wiped thoroughly, buffed dry and let each coat set for 24 hrs. It cured to a soft golden sheen with clarity. No doubt more coats would build the sheen. It would be excellent for kitchenware, furniture, children’s toys and any interior natural wood surface, except maybe flooring.
Tried & True Varnish Oil
Zero VOC’s – 473ml $26.50 / 946ml $38.50
Polymerized linseed oil blended with modified pine resin, this is a heavy liquid with a high solids content, a deep golden colour and a sweet nutty aroma. The first coat absorbed moderately; after 60 minutes I wiped away the surplus and buffed the surface dry. I repeated this after 24 hours for each coat. Its water-resistant film finish has a rich tone and a rich semi-gloss sheen. Also food-safe, it’s well suited for interior trim/millwork, furniture and cabinetry.
Tried & True Original Finish
Zero VOC’s – 473ml
$26.50 / 946ml $38.50
Polymerized linseed oil blended with beeswax. Food-safe, a gel/ paste with a golden colour and sweet/nutty aroma. Absorption of this very viscous finish seemed minimal but developed nicely as I let it sit for 60 minutes then wiped and buffed the surface dry. Likely, letting it cure longer between coats would advance the total cure. It produced a rich tone with a soft sheen. I expect this would be excellent for turned woodenware finished on the lathe.
Waterborne Film Finishes (Varnishes)
These hard, thick coatings are typically applied to natural wood tabletops, trim and furniture; they cover well but penetrate little. Acrylics, alkyds, acrylic fortified polyurethanes and polyurethanes are all polymer resin-based, curing through chemical action to form durable coatings which bond to the woods fibres, fill its pores and harden.
VOC under 90 g/L – .95 litre $18.00 / 3.78 litres $64.00 /
18.9 litres $294.00
A clear, pure, waterborne, cross-linking acrylic for both interior and exterior use, UV stable and mildew resistant. It can be applied by brush, roller or spray. A very thin milky coloured liquid with a faint sweet/acrid “ammonia” scent, the first coat absorbed well leaving good film. I was able to scuff sand after 30 minutes but waited 4 hours to recoat. Three such applications yielded an exceptionally natural hard film with depth, clarity and a pleasingly soft sheen. This can also be applied over stone, concrete and masonry.
Emtech EM2000 Varnish
VOC 23 g/L – .95 litre $26.00 / 3.78 litres $82.00
Available in gloss, semi-gloss and satin all at the same pricing
This is an interior/exterior alkyd varnish of waterborne hybrid alkyd resins. My sample is “satin”, requiring steady stirring to suspend the silica (ultra-fine sand) matting agents. A creamy liquid with a milky colour and muted crisp acrid aroma; I’ve no doubt, like other such emulsions, the gloss and semi-gloss versions are clearer and thinner due to less matting agents. User friendly, it can be applied by spray, synthetic brush, pad and closed-cell foam roller. Designed for fine furniture and cabinetry, woodturners enjoy this as an on-lathe padding finish; it’s also fine for moisture and UV exposed woods such as window and door trim. With 34% solids by weight, it builds well; the first coat over bare wood absorbs nicely, drying to the touch within 20 minutes. Scuff sanding and recoat time is after one hour; I applied three coats in an afternoon. It flows and levels well, produces a light golden film with a soft sheen, brilliance and clarity.
Varathane Premium Diamond Wood Finish
Low VOC – Less than 275 Grams/ Litre
319 g aerosol $12.50 236ml $11.99 946 ml $23.99 3.78L $59.99
Available in satin, semi-gloss and gloss (as tested)
A waterborne urethane acrylic designed for interior furniture, cabinets and trim which can be applied by synthetic brush, foam pad, or conventional / HVLP sprayers. It has a milky colour and consistency (~/= 27% solids) and a light acrid aroma. Fast drying, so short working time, it levels well and produces a good sheen with a recoat time of +/- 2 hours depending on temperature and humidity. Three coats applied in a day with scuff sanding between (220 grit) yields a deep gloss finish with a warming, natural tone to the wood.
Vermont Natural Coatings - PolyWhey - Furniture Finish
VOC 180 g/L – Quart $37.99 / gallon $121.99 Available in gloss, semi-gloss and satin
Uniquely, PolyWhey uses whey protein, a by-product of cheese making, to produce a polyurethane polymer. Waterborne, it is designed for interior applications including furniture, cabinetry, toys, trim and woodenware. It can be applied to bare wood and over cured oil and water-based stains and finishes. My gloss sample was a milky colour liquid with a whole milk consistency and an acrid aroma. It can be applied by synthetic brush, pad or spray. I pad-applied a thin wet coat and let it dry two hours, followed by a second coat. I scuff sanded before my third coat, which cured to a crystal clear gloss, enhancing the wood’s tone, character and texture.
Microporous Surface Coatings
These “new” coatings engage with the wood on a molecular level. Designed for interior applications, they reinforce the wood’s surface structure, reject liquids yet allow moisture vapour to be absorbed and released without compromising the wood’s structure or appearance. Maintenance, largely unnecessary, is easy if required. Unlike traditional finishes, requiring large amounts be applied for proper coverage and density, these “microporous” coatings must be used very sparingly to gain the best result, soooo… A) despite their price these are exceptionally cost effective and B) the volume of applied VOC’s and chemicals is so low that outgassing occurs within hours, not weeks or months like others, hence safer wood products and environments far quicker.
Osmo PolyX-Oil Pure 5125
VOC less than 50 g/L – .125 litre $26.00 / 1 litre $160.00
A clear finish based on natural vegetable oils (sunflower, soya, thistle) and waxes (carnauba, candelilla), paraffin, drying agents and water repellants, this is an oily liquid with a pinkish colour and a faint acrid odour. Working only a few drops well into the wood surface using a swirling pattern with my synthetic pad, I created a uniform film on the surface, left it for 35 minutes then wiped it off thoroughly. I repeated the process after eight hours then again for a third coat. The result was a rich wetted look with clarity and little sheen, accentuating the grain and drawing out the wood’s natural reddish tones. Designed for interior wooden floors and furniture (even children’s toys), it’s resistant to most common liquids and stains.
Rubio Monocoat Oil Plus 2C
Zero VOC’s – 1.3 litre Pure 2C $203.80 / 1.3 litre Colour $260.30
Costly at first glance, Monocoat has a reputation for 11 times the coverage of other finishes; 1 litre equaling 3 gallons of conventional coatings, plus it’s completed in one-third the time so a big labour saver. Available in “Pure” plus over 40 standard colors which can be blended for custom shades – Rubio’s one application (Monocoat), two-part solution uses a linseed oil base plus an accelerator, boosting the cure rate; fully dry after 24 hours, 80% cured in 48 hours and washable after 5 days. Monocoat is water, solvent and VOC free.
Part A, is an oily, lightly coloured liquid with a sweet/acrid scent; the accelerator, part B, is a thick, clear odourless liquid containing isocyanates so skin protection and adequate ventilation are important. Out of curiosity I allowed a dab of each part to dry on glass separately. “A” formed a wrinkly skin as you’d expect from an oil product while part “B” dried rock hard and crystal clear. Designed for interior floors and furniture it is durable, resistant to wear, water and heat, fine for kitchens and bathrooms. I sampled both “Natural” and “Pure” products…
Natural; part A has a slight green hue. I mixed 3 parts resin to 1 part accelerator, applied a tiny amount, spread it into a thin overall coat, waited 15 minutes and buffed the surface off. That’s it. It dried hard in 24 hours to a straw yellow tone, a satin finish with subdued clarity. A very muted result.
Monocoat Oil Plus 2C – Pure; as above except having an amber colour. 24 hours after application my sample board softly glowed with a golden hue, a semi-gloss finish with tremendous depth and clarity; very enhancing without altering the wood’s natural character.
I hope now you have a better view of the finishing options available to you, and are well equipped to understand what’s in a can and what its contents will bring to your future projects. Today’s coatings, and those that have stood the test of time to become the basis of today’s finishing products, perform really well and are both user and environmentally friendly, far nicer than their hazardous petro-based predecessors. And now you know how to pick just the right one, every time.
|Broda – CBR Products||cbrproducts.com|
|Heritage House – Homestead House Paint Co.||homesteadhouse.ca|
|Kunos – Livos Plant Chemistry||livos.ca|
|Lee Valley – Lee Valley Tools Ltd.||leevalley.com|
|Osmo – Osmo Canada||osmo.com|
|Rubio Monocoat – Exotic Woods Inc.||exotic-woods.com|
|Target Coatings – Wood Essence Distributing||woodessence.com|
|Tried & True Wood Finishes – Lee Valley Tools Ltd.||leevalley.com|
|Vermont Natural Coatings – Randalls||randalls.ca|
When it comes to choosing a finish everyone’s needs are different, but my particular needs are largely satisfied by three products. I enjoyed using Varathane Professional Clear Finish, as it sprays nicely and is a nice finish to the touch. Osmo Poly-X Oil Pure will be used again in my workshop. It wipes on very nicely, providing me with a simple, user friendly way to apply a finish to small and medium sized objects I create. And I’ve always been a fan of Emtech EM2000 Varnish, as it’s easy to apply with virtually any method, adds a warming amber cast to woods like cherry, mahogany and sapele, and I have never had a bad result while using the product.