Poly coating on a non-flexible part?

[erikgreen]

Hey poly guys -

I'm coating some accessory woodwork and panels with poly, specifically Bondo resin, because I have some and it's cheap

For waterproofing, do I need to glass both top and bottom, or can I just glass the top for abrasion resistance?

This is 3/4" plywood that isn't going to flex at all. I want to just coat the wood and leave it exposed (it's furniture grade) to the sun, so I can't use epoxy.

I know you can get clear coat poly resin to use for tables and the like, so I'm hoping it's not a big deal to leave the underside unglassed (I ask because I've already done it, of course)

Erik

 

[redfury]

Re: Poly coating on a non-flexible part?

Eventually you'll have a problem, if it's allowed to soak up moisture ( humidity ) and then freezes in our winters ( expansion/contraction ). However, it should be minimal. I'd think it'll mostly depend on the ability to keep it mostly dry. I think the woodwork in my boat that was just covered with vinyl ( front seats ) has stayed in decent condition all these years because of the lack of concentrated water in the bow of the boat. They are still solid, including the underside of the deck which is exposed plywood.

I don't think I'd worry too much about it.

 

[erikgreen]

Re: Poly coating on a non-flexible part?

Yeah, I did some reading that basically confirms your thoughts.

If it gets cracked or abused there's a good chance water will get in, or if it's left to weather in the snow. If that happens though, I'll just replace or repair it.

I wouldn't want to do that on wood I couldn't see, but this stuff will be right on top, so I think I'm ok.

I'll give it a good even coat and see how it looks.

Erik

 

[Coors]

Re: Poly coating on a non-flexible part?

Read up on poly eurathane? I seem to remember sun doesn't affect, as bad.

 

[redfury]

Re: Poly coating on a non-flexible part?

Read up on poly eurathane? I seem to remember sun doesn't affect, as bad.

I work with polyurethane everyday ( hardwood floors ).

It's water resistant, but not water proof. Most have UV protection built in to avoid yellowing, though anything exposed to the sun will change eventually. I do know there is an indoor and outdoor version, so be careful what you buy/use. Personally, I like spar finishes for outdoor wood, though it can be difficult to work with as it will flash dry very quickly. The nice thing about oil based polyurethane though, is that it retains some flexibility, so it resists cracking on seams that move a little. Shellac and alcohol based finishes are too hard for anything that will expand/contract, so I'd avoid using them. I've got a Paduk floor that popped the alcohol sealer off at every seam. The floor looks like we painted white lines on the whole floor ( mind you, this was a $15,000 master bedroomfloor.

 

[ondarvr]

Re: Poly coating on a non-flexible part?

Polyester normally starts to crack and peel off after a short time and even faster when exposed to the weather, it's just too brittle without glass.