Painting Acrylic on top of cured Marine Spar Varnish

[John_Smith]

I know there are "old" posts about this, but, our products and procedures are going through some drastic changes these days with the EPA and other things.
Take for example; a routed sign made with cypress, cedar or redwood, properly sealed and clear-coated with 3 coats of Marine Spar Varnish. (NOT polyurethane). I'm wondering about the adhesive factor between the acrylic and varnish over a long period of years of outdoor exposure with minimal maintenance.
At what point in time, would the acrylic start to separate from the varnished surface.
Question #2; although the acrylic is top-of-the-line in quality in UV endurance, would a coat or two of the same Spar Varnish over the acrylic graphics be recommended.
The bottom line is to preserve the natural look of the wood and the painted graphics equally. Not to have one fail prematurely before the other.
First hand experience would be preferred - not guess work.
(and, there is no specific state or location involved as this could apply to any place in the world).

 

[John Miller]

a routed sign made with cypress, cedar or redwood, properly sealed and clear-coated with 3 coats of Marine Spar Varnish. (NOT polyurethane). I'm wondering about the adhesive factor between the acrylic and varnish over a long period of years

Sorry, but you've lost me, you speak of a carved sign with 3 coats of spar varnish then talk about the adhesive factor between acrylic and varnish. Acrylic paint? Acrylic as in plastic? Check your varnish specs or contact the spar manufacturer and get their opinion.

 

[signbrad]

Acrylic is a somewhat generic term.
Acrylic enamel, acrylic latex, acrylic lacquer? We use acrylic polyurethane (car paint).

I would not hesitate to put Matthews Acrylic Polyurethane on top of spar varnish that has cured and has been sanded thoroughly. But acrylic latex on top of varnish? I would probably not put acrylic latex paint on top of spar varnish.

About clear coats on raw wood

Back in the 70s when we started doing redwood signs, we quickly learned that clear coats did not hold up well on raw wood. Nor did oil-based enamels like One Shot lettering colors. A house painter told me back then that he would never seal a redwood deck or cedar siding with varnish—it turns white and peels in about a year, especially at edges of the boards where the finish is the thinnest.
We tried various types and brands of clear on raw redwood and cedar signs, but nothing was satisfactory.

Has the situation changed? I don't know. The water-based and water-borne coating technologies have advanced greatly. There are even water-based clear coats. Do they hold up outside? And for how long? I don't know. I don't experiment any more with jobs for customers. I've had to re-do too many projects because of using a material that was "recommended" by someone. If I can't see a finished sample that is five or six years old and still looks good, I don't use a product. I let others experiment.

The house painter I mentioned above told me that commercial painters don't use on raw wood ANY finish that dries to a hard shell. The finish will not move with the wood as the grain opens and closes. It is not flexible, and it will crack. Flexibility is one of the reasons latex coatings were developed in the first place—they are stretchy. Another fact about latex coatings is that they are semi-permeable. That is, they allow residual moisture in the wood to escape through the finish. A clear or pigmented coat that dries to a hard shell, sealing the wood, will trap the moisture, but it will force its way out through the finish anyway in hot weather, causing blisters.

Having said all that, I repeat that I have not kept up with the advances made by paint companies. I used a water-borne primer by Sherwin Williams on a 10'x30' painted sign on a metal building. The building was constructed of prepainted panels, probably factory painted with a PVDF coating (polyvinylidene fluoride) so I was skeptical about long-term adhesion of any water-borne coating to such a hard finish. But the paint seemed to grip the wall well (I washed the wall thoroughly first), and it seemed to dry incredibly hard for a water-based coating. It was about 80 dollars a gallon if I recall. The finish coat was all latex by Sherwin Williams, too, and the graphics were done in water-based acrylics by Nova. It was not my job, so if it failed it would have come back on my boss, not me. However, it looks great after six years.

The bottom line for me is that I don't experiment anymore. And if someone highly recommends a product, I want see what it looks like after a significant period of weathering.

Brad in Kansas City

 

[John_Smith]

thanks Brad - I'm in the same boat as you. I haven't been keeping up with the advances (degradation) and changes either. I am a painter - I paint things - that's what I do. Probably less than 1% of my signwork and other projects are painted with a brush (I don't spray) been doing it since the early '70s.
This question isn't for my work. It is for a budding young artist that has already pumped out dozens and dozens of hand-routed signs using this method. I'm just trying to gather some ammunition from other professionals to assert my tutoring. She insists on doing it her way. At least I got her away from that Helmsman stuff. I guess when she starts getting Call-Backs on her work, she'll see the light.
This is exterior grade (with UV inhibitors) Acrylic Enamel paint onto varnished routed wood signs. The varnish is Cabot Marine Spar applied as it should be.
Thank you for your time,
John

 

[Billct2]

I have used 2 part marine varnish successfully on exterior wood projects for many years. I also have done gold leaf/painted names on wood boat transoms over varnish. They would apply multiple layers of varnish and the scuff it before I lettered it using size and one shot. They would then apply multiple layers over it when done.

 

[John_Smith]

yes sir, Bill - that is the standard method for gilding and 1-Shot lettering enamels.
I'm talking about Acrylic water based paint applied to a varnished wood project.

 

[Johnny Best]

If the marine varnish is sanded it should take a latex water base paint should "grab" and hold up well. But to put latex water base right onto a varnish finish without a tooth to grab onto might cause a problem.
Note: Spar varnish lets the wood expand and contract. Marine varnish protects from the wheather and contains oil, solvent, ultra violent additives and drying agents. The solvent evaporates so acrylic latex would not have a problem being applied on top but sanding is important.
"Spar" is from the sailboat terms referring to mast and sails. So they added that name to varnish for the brightwork on the boats.

 

[John_Smith]

totally agree about the scuffing - I seriously think that is not being done in this case. (I'll double check).