Best wood finish/coating for marine ply battery box?

[the evil stepson]

I'm using 18mm marine ply to house my AGM batteries & just wanting to know what is a really good finish to protect it in the harsh marine environment where long service life is required? I'm after a finish that will last as long as possible, yet be somewhat easy to re-apply down the track if needed.

From what I can gather wood finishes go bad very quickly as appose to say on steel outside because wood contracts & expands, so automotive 2K clear with it's UV blockers probably won't last all that long. Also UV is bad for alot of indoor finishes like oil based PolyU, however direct sunlight will be only a small % during the day. I tried a 2 part floor board polyU on another project, very tough, but I have no idea what it is like in a partial outside marine environment.

I also heard that some prime the bare wood with 2part epoxy then 2part polyU, but it sounds like a real mess to re-apply down the line.

The box may get a bit wet from water spraying up at times if that helps.
thanks

 

[Steve_S]

I have very successfully used Marine Grade Clear Urethance. It is Oil Based not water based and soaks into the wood pores, requires a minimum of 2 coats, 3 is better with the second coat receiving a fine sanding first to create a strong gloss finish. It "STINKS" so you want to apply it in a garage not in your house, well unless you wanna be single. Take 12-24 hours to dry between coats too. It already has UV blockers so there is no issue there.

Water-Based Urathanes with UV Blockers can be bought too, they are faster to apply because they can be recoated within 4 hours +/-. With water based I would suggest no less than 3 coats, 4 is better. I use on floors, woodwork and cabinetry, my home is ALL WOOD finish, there is only 6 sheets of drywall used in my house.

IF there is any potential of Water Splash etc, then go with the Marine Oil Based Urethane, do 3 coats and never worry about it again. It will just take 3 days to get 3 coats on it. Do not try to warm it to cure it faster, the results will not be good. BTW: Oil Based Urethane is getting Very Hard to get because of the VOC's, ventilation is critical, you'll get Wasted & Loopy inhaling that stuff in no time...

 

[Sillyputty]

wood finishes go bad very quickly as appose to say on steel outside because wood contracts & expands

While solid wood does this, marine plywood does very little of it. In my experience as a cabinetmaker (indoor finishes) and sign maker (exterior) the reason for clear finish degradation is 1) sunlight, 2) moisture, and 3) substrate movement. Paint generally holds up better than any clear or semi-clear finish, and is easily re-coated. The clearer finishes hold up better if they are 1) not applied too heavily, 2) have UV protection built in, and 3) expand and contract (are flexible to some extent) to accommodate any wood movement.

Also, for clearer finishes with less gloss I've been using wipe-on finishes with good results, and most can be "refinished" quite easily after they have been cleaned and lightly buffed w/steel wool. Finishes with a higher gloss and thicker applications (paint and varnishes) can often fail in patches, which requires either complete removal or the finish or patching the areas damaged and then recoating.

Whatever finish you choose, my experience has been that applying more, lighter coats is much better than applying fewer, thicker coats.

 

[BobH]

2 part epoxy. If you don't like the color, paint over the epoxy after a light scuffing with a scotch bright pad. If the wood is completely epoxy sealed on all sides, especially the ends/edges , then it will probably outlast you or the boat. That's how epoxy/plywood cored boats are made. There are plenty of those still in service after decades of exposure (Usually painted since UV rays slowly degrade uncovered epoxy).

 

[Hotdog]

Penitrating epoxy and some paint to make it easy. Or just boiled linseed oil if you don't mind reapplying ever other month or so

 

[CholeBur]

In general, as far as I know, oak is considered the most durable tree and the most used in marine conditions. But, it needs to be properly lubricated and made, so I advise you to call the master. I once also decided to make furniture in the kitchen. I didn't want to call anyone, I thought I could do it myself. As a result, I incorrectly attached the rivets to the wall, which caused the whole cabinet to collapse on me. I broke my arm then. After that, I trust the masters from this company https://mitersawjudge.com/best-wood-lathe-reviews-and-buying-guide/ absolutely everything. They are professionals, working in their field every day

 

[mmtech]

If the battery is below the deck use a plastic battery tray or box. If it has to be wood use epoxy resin but remember if it has to be where it is exposed to the weather it has to be sanded and be coated with a oil based paint.

 

[seahaul]

just paint it with something like West systems epoxy, don't thicken it. Put 3 coats and then If you want you can paint it after.

 

[mmtech]

If is exposed to sun light and you do not paint it the uv wull brake down epoxy and you will have one big mess. I know what i am talking about. 42 years of working with epoxy i have seen the results when it is not protected.

 

[floydo]

As the OP asked, prime the bare wood with 2part epoxy then 2part polyU....Two part polyurethane is incredibly durable as a topcoat...1 part is very good...His choice...Really what the paint does is protect the epoxy from UV......