Hot Topics: Weatherproofing a Plywood Sign

vintage, blank plywood sign

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Original Post: How best to weatherproof vintage outdoor plywood sign?

Spock - Member

How best to weatherproof vintage outdoor plywood sign?

I picked up a really cool outdoor vintage hand painted plywood sign (2' X 4') that I am going to use as a back rest on an outdoor bench I am making. I do not know whether the graphics on the sign were painted in oil or acrylic paint.

What is the best way for me to seal, coat, or otherwise weather treat this plywood sign so as to maximize it's longevity in the outdoors. I live in NC with 4 seasons but rare snow.

Thank you

marksr - Forum Topic Moderator

The most important part would be sealing the edges so water/moisture doesn't get in between the plys!

An oil base spar poly will discolor the sign [give it an amber tone] I don't have much experience with the water base versions but they shouldn't discolor the sign. Whatever you apply will need to be lightly sanded and recoated periodically to prevent it from degrading.

pugsl - Forum Topic Moderator

Join Date: Mar 2008

I would oil poly the edges and use water poly on rest of sign. Oil seems to hold up better in weather. Edges may have to be redone yearly.

manden - Member

Depending on the thickness and shape you may want to put an edging around the outside.

Spock - Thread Starter

manden, Tell me more. The plywood sign is 1/2 inch thick and rectangular at 2 ft by 4 ft.

manden - Member

They make edging (basically a U channel) in metal and plastic

Spock - Thread Starter

Would I find such a thing at a big box store like HD, and, how is it attached to the edge - glue, nails, screws or something else?

manden - Member

Yes it should be available at the big boxes.

Pretty well any way you want to attach it.

The plastic stuff often has the ends of the U tighter than the center so it fits pretty snugly.

I would put a tiny bead of clear calk on the bottob and sides to keep as much moisture out as possible.

Marq1 - Member

Bottom line, if you want to keep it intact get it out of the elements.

There is nothing, no coating etx that will protect it outside!

Spock - Thread Starter


You know, ultimately you are exactly right. However, I can't help but wonder how this old sign, which is probably at least 40- 50 years old and has been living outside in Pennsylvania, has managed to stay in such good shape. Was it just the fact that it was painted, or did the original painters do something else to help preserve it? And if not, maybe I don't need to be jumping through hoops to mess with it as well - possibly a spray of Thompson's Water Seal and off we go and be happy if it lives another 10 or 20 years.

marksr - Forum Topic Moderator

How were the edges exposed to the elements? The odds are the sign was painted with lead based paint, that and better quality plywood would play a part in how well it held up. TWS generally lasts 6-12 months.

If using the channel that manden described I'd leave it off of the bottom. Another option would be to install a breadboard [small narrow strip of wood] on the top and sides.

manden - Member

I agree with marksr leaving it off the bottom is a good idea.

Should have thought of that myself..

No matter what finish you put on it there is some risk involved so if possible try it on a small area before doing the whole sign.

vintage sign on bench

Varnished the sign, added trim to top and sides, re-purposed cool old sign into a bench back rest. Thanks all for the suggestions.

marksr - Forum Topic Moderator

Looks sharp

What type of 'varnish' did you use? hopefully a spar varnish or spar urethane. You should carefully inspect the finish every year as you want to lightly sand and recoat before the finish deteriorates too much.

Spock - Thread Starter


I went with this:

RTG Outdoor Wood Furniture Varnish from Atlantic Boat Supply Company - a water based polyurethane that was super easy to apply and dried clear and hard. I put on 4 coats (extra on the edges) before I installed the vinyl stripping. I will keep a close eye on it as we go along but I think it is going to work well.

marksr - Forum Topic Moderator

I'm not familiar with that particular varnish. In general if exterior varnish is allowed to deteriorate too far it will need to be pretty much sanded all off [which could affect the graphics] but if you catch it early all that is needed is a light sanding and a fresh coat. Normally the varnish will look good for a year or more although that is dependent on the climate it's exposed to.