Another Question About Linseed Oil

[Submarinerblue]

Is there any reason NOT to use acrylic paint on wood that has already been treated with boiled linseed oil? I want to paint accents on wood that has been already stained rather than try to mask off thin strips to be paintEd.

I did a few tests on pear wood that I had treated with oil and the paint appeared to go on just as well as on bare wood. I didn’t see any difference. Is there anything I’m not aware of?

 

[Bryian]

You should do a fingernail scratch test to see if the acrylic paint has adhered to the linseed oil.

 

[dockattner]

I used acrylic paint over boiled linseed oil treated wood and everything seems fine one year later (the oil was at least a month old though when I applied the paint). I'm no expert - just sharing my experience.

 

[Jimsky]

Is there any reason NOT to use acrylic paint on wood that has already been treated with boiled linseed oil? I want to paint accents on wood that has been already stained rather than try to mask off thin strips to be paintEd.

I did a few tests on pear wood that I had treated with oil and the paint appeared to go on just as well as on bare wood. I didn’t see any difference. Is there anything I’m not aware of?

This is a great question. Acrylics are water-based, and oils are oil-based, so they each have different properties and different needs (in terms of drying time, type of varnish, etc). If you want to paint one first and then the other, it is okay to paint oils over acrylics, but never paint acrylics over oils.

What you should not do is paint a layer of oils and then paint over it with acrylics. Here's why: the acrylic paint will be unable to stick to the oil paint, so it will flake off. This can sometimes happen very quickly, almost as soon as the acrylics dry, or sometimes it can take weeks. In any case, the acrylic will definitely flake off at some point.

P.S. Shellac could be a good base for acrylic paint, just saying.

 

[Recusant]

I did a landscape once and used an undercoat of oil based paint and then overpainted it with acrylic paints. It turned out fine...for about two years and then the entire surface flaked off in about a month's time. Go figure.

 

[MM2CVS9]

House painters use oil based primers for a first coat on bare wood all the time, then topcoat with acrylic finish coats. Maybe the primer is specially designed to provide more grab?

 

[Peter Gutterman]

Having had 40+ years as a restorer of period (mostly 18th and 19thc.) furniture and over ten years experience as a volunteer model shipwright at the Naval Academy museum model shop, I have had a lot of experience restoring and using shellac as a finish and finish base for oil or water vehicle. Allowed to dry thoroughly (24hrs.) it is malleable (can be reworked ad infinitum) and serve as a base for either acrylic or oil based top coats. Shellac is the most frequently encountered finish used on centuries old antique furniture as well as period ship models, and is eminently restorable. Amber shellac imparts a honey gold color to wood surfaces imparting a warm under glow to other finishes. Clear or "white" shellac is perfectly clear, and often used to seal unsightly stains before being painted over to prevent bleed through. Using a soft cotton cloth pad or "rubber" with a touch of boiled linseed oil (just a touch!) on the pad as a lubricant, shellac can be applied and polished onto a well prepared hardwood surface and brought to a very high luster or even gloss finish. This is a simple, technique ,but requires much practice and patience to achieve reliably successful results. Polishing is still a profession in England and Europe.

Pete Gutterman

 

[Jimsky]

House painters use oil based primers for a first coat on bare wood all the time, then topcoat with acrylic finish coats. Maybe the primer is specially designed to provide more grab?

Unfortunately, I am not aware, nor familiar with such primers (of cause it doesn't mean they don't exist), but they may be a special blend instead. In theory, it will be hard if not possible, to adhere anything to an oily surface, or paint (unless it is oil paint).

 

[Peter Gutterman]

Another word about finishes.
As a general rule, because of the antipathy between oil and water, you may use fat over lean but not lean over fat. However, like "i" before "e", there are exceptions.
For example: the conundrum of stains: Oil (fat) based stains are light fast , but do not penetrate wood as efficiently as water or alcohol (lean ) stains which are more susceptible to UV degradation. So as a result I prefer to use oil based stains because of their (there you go, "e' before "i") resistance to UV , with the caveat that more coats are required to get the desired depth of color In order to use a lean finish over a fat stain. The stain must not (!) be allowed to fully seal the the surface grain , and a light sanding over is desirable to to create a "tooth" for the lean finish to mechanically bond to as a final finish. I have successfully French polished or used acrylic, over well cured (!) oil based stains many times using the afore mentioned technique without my carefully arrived at stain coloring being bleached into gray oblivion over time.

Pete Gutterman

 

[danielsje]

For my models I have gravitated to my own formula for finishing that has proven stable and satisfactory over a dozen models. To seal fresh wood I use water based matte polyurethane either brush on or rub on. Preferred brand MinWax. For stain I use water based stains by MinWax. If I want to stain the wood I have two choices…apply the stain to fresh raw wood…the stain sinks more into the wood and takes on a decidedly richer tone. I can also rub water based stain over a dried base of the polyurethane. The stain does not penetrate the wood but acts as an antiquing look. I can then apply a protective coat of the poly over either option. In any case, I use water based MinWax products in whatever combination needed for the desired outcome. Absolutely no issues over time. I often use the poly as a sealant on parts as I build the model…no problems with glues adhering to the poly sealed parts.

 

[Bryian]

Unfortunately, I am not aware, nor familiar with such primers (of cause it doesn't mean they don't exist), but they may be a special blend instead. In theory, it will be hard if not possible, to adhere anything to an oily surface, or paint (unless it is oil paint).

Jim, as an old retired professional house painter, we always used oil based primers on exterior surfaces before finishing in acrylic.

 

[Recusant]

So it seems like from the responses that if one uses an oil based primer or an oil based stain that it will hold acrylic paint. I have to assume that's because either of the oil based applications sink into the surface and allow acrylic paint to "grab" onto it. Regular oil based paint might not allow the acrylic paint do that and that was why, in my landscape painting, the surface of acrylic paint flaked off. Shellac apparently is OK for acrylic. Sound right?

 

[wmgrimball]

Test first on scrap Then go ahead. As Davy Crockett said, "Be sure you're right, then go ahead."

 

[Bryian]

painting acrylic over a matt surface like primer is usually o.k, but painting acrylic over a oil gloss enamel will cause issues.

 

[Peter Gutterman]

For my models I have gravitated to my own formula for finishing that has proven stable and satisfactory over a dozen models. To seal fresh wood I use water based matte polyurethane either brush on or rub on. Preferred brand MinWax. For stain I use water based stains by MinWax. If I want to stain the wood I have two choices…apply the stain to fresh raw wood…the stain sinks more into the wood and takes on a decidedly richer tone. I can also rub water based stain over a dried base of the polyurethane. The stain does not penetrate the wood but acts as an antiquing look. I can then apply a protective coat of the poly over either option. In any case, I use water based MinWax products in whatever combination needed for the desired outcome. Absolutely no issues over time. I often use the poly as a sealant on parts as I build the model…no problems with glues adhering to the poly sealed parts.

For my models I have gravitated to my own formula for finishing that has proven stable and satisfactory over a dozen models. To seal fresh wood I use water based matte polyurethane either brush on or rub on. Preferred brand MinWax. For stain I use water based stains by MinWax. If I want to stain the wood I have two choices…apply the stain to fresh raw wood…the stain sinks more into the wood and takes on a decidedly richer tone. I can also rub water based stain over a dried base of the polyurethane. The stain does not penetrate the wood but acts as an antiquing look. I can then apply a protective coat of the poly over either option. In any case, I use water based MinWax products in whatever combination needed for the desired outcome. Absolutely no issues over time. I often use the poly as a sealant on parts as I build the model…no problems with glues adhering to the poly sealed parts.

 

[Peter Gutterman]

Sounds like a really nice well thought out and and refined process. I'll give it a try. Thanks for the tip.

Pete Gutterman

 

[Jack Jäger]

There is a difference between boiled linseed oil and raw linseed oil .Raw linseed oil can be used to treat wood, (traditionally it was brushed or rubbed on hurley sticks and cricket bats) but it contains no external driers such as Cobalt Octoate or Zirconium Octoate or previously Lead, (in medieval times a portion of lead oxide was 'boiled' into the raw oil to aid drying by oxidisation). Without such it never truly 'dries'. Usually what happens is its carrier, often white spirit, evaporates off and there is a bit of very slow oxidisation, after a while the surface of the wood feels dry but it is unstable and prone to movement. If it is then painted over even with an oil based paint sooner or later it will move and the top coat will 'mud crack' (think of a dried out pond). Worse still If you paint over it with a high solids water based acrylic the movement will cause cracks and the (relatively) high pigment to binder ratio will cause flacking. Even boiled linseed oil compared to a varnish such as a polyurethane will probably dry too slow to be overcoated in any meaningful short time
Since the 19th. Century oil based paint and varnishes have employed metal soaps to chemically dry them, once fully dried they cannot conventionally be dissolved and are generally stable. However as said above if these surfaces are very glossy the will give further coats adhesion problems and obviously make bad priming surfaces. But, even to linseed oil resin, if you where to add a lot of fillers and a bit of pigment to bump up the solids along with the proper driers you can make a very good primer that can be overcoated with virtually any type of paint water or oil based, although not anything with very strong solvents such as two pack epoxy. Shellac is a different cattle of fish altogether. Shellac is a natural resin deposited by a beetle, (least I think it is a beetle), anyway the natural polymer has a very short chain length (the shorter the chain length the harder and more brittle the polymer) when after it is dissolved in alcohol and applied it dries very hard and is quite crystalline in structure and scratches easily by todays standard, but does give a lovely finish. You probably could get away with painting over it as it usually has a very thin film surface and is very stable.
Overpainting any gloss needs to be done to a well flatted surface to give a bit of mechanical adhesion. I have used linseed oil resin to make many paints and primers that are easy brushed, very waterproof and durable with good heat resistance, there main draw backs are, even with the proper driers, they dry slow by todays standards. They do produce good decorative gloss finishes, however whites made with them they yellow terribly.

 

[Peter Gutterman]

Very elucidating! And instructive. The chemistry and physics behind finishes, in particular the ones dating back centuries, even millenia is fascinating and a necessary study especially for restoration and conservation. Shellac (yes ,a deposit from a beetle) dries and does not polymerize, like alkyd resin finishes ( varnish). A shellac finish can, therefore, be amalgamated using alcohol ,or a similar solvent, some being water soluable, that will disconnect its molecules and allow it to be softened and reworked on a surface without removing it altogether, allowing it to be conserved and restored, retaining its color ,acquired over time, and traces of its crackled surface to be retained as evidence of its antiquity. No such luck with old polymerizing (varnish) finishes, where the surface must be slowly and gently abraded to the point where the top obscured layer is removed and the remaining surface polished back to clarity. Both approaches are time consuming and require a great deal of patience and care. The latter being agonizingly slow, produces a lot of toxic dust and no small amount of joint wear. Wear a mask, use fine grades of sandpaper to start with and be prepared for the long haul. Remember, whatever scratches you put in you will have to polish out. old well worn sandpaper is best.

A word about the light fastness of alcohol and water vehicle stains. I was referring to aniline powders or concentrates dissolved in water or alcohol., which can produce nice fast drying and penetrating stains but are susceptible to UV. I have not tested the light fastness of commercially available water based stains like Minwax brand but I believe them to be, thanks to modern chemistry, more durable and light fast as demonstrated by danielesje.

Stay away from solvent vehicle finishing products as much as practicable. In nearly every contemporary case a more environmentally and non poisonous water based substitute is readily available, easier and safer to use and give very satisfying results. Thanks again to danielesje for his very useful and helpful information on this topic regarding model building.
I am happy to receive any correction to, or informed analysis of, my comments . Beyond personal experience I am no authority.

Pete Gutterman

 

[bill36]

Is there any reason NOT to use acrylic paint on wood that has already been treated with boiled linseed oil? I want to paint accents on wood that has been already stained rather than try to mask off thin strips to be paintEd.

I did a few tests on pear wood that I had treated with oil and the paint appeared to go on just as well as on bare wood. I didn’t see any difference. Is there anything I’m not aware of?

Linseed oil, the oil of the flax(?) seed, is an OIL. Acrylic is water based, at least you can thin it with water. Oil and water do not mix; at least without an emulsifier. Eventually the acrylic will peel off the oiled wood. It may take a year or two, depending upon how much oil is in the wood, but you can almost guarantee it will not hold in the long run. Use an oil based paint for whatever it is that you want to do.

 

[Peter Gutterman]

Linseed oil, the oil of the flax(?) seed, is an OIL. Acrylic is water based, at least you can thin it with water. Oil and water do not mix; at least without an emulsifier. Eventually the acrylic will peel off the oiled wood. It may take a year or two, depending upon how much oil is in the wood, but you can almost guarantee it will not hold in the long run. Use an oil based paint for whatever it is that you want to do.