Lead-Acid Battery Acid and Epoxy

[bristol27]

Does anyone know the long term effects of battery acid dripping onto epoxy (which coats fiberglassed plywood & foam)?

I may be using lead-acid batteries which means I must protect the battery compartment from acid spills. The lead-acid in batteries is 35% sulfuric-acid / 65% water (I believe). My research indicates there are certain epoxies that will withstand battery acid...others that will not. I can't seem to find data on West System's resistance to battery acid, however from reading around, it doesn't seem that any epoxy has true long term protection from acid spills.

I've considered are stainless steel battery trays or perhaps buying acid resistant plastic and gluing these together to make a tray (again, the glue needs to be acid resistant). Even with sufficient trays, I could see that some acid could 'jump/squirt' onto the epoxy-fiberglassed plywood side walls, attack this material.

I am also considering switching to AGM to avoid the entire issue (among of other benefits they provide - no need for dedicated ventilation, no off-gassing, smaller size, no distilled water refilling, etc.)

I am planning to install batteries in a sealed (but ventilated) area below my navigation station and engine compartment. Here's an image of the area in question:

Battery compartments templated. The compartments are the inboard area, to port and starboard. Shelves will be built low along the hull to hold the batteries.

If you'd like full details on the compartment, I have an write-up on my battery compartments here - http://www.bristol27.com/projects/battery-compartment

[CharlieJ]

Why not phone the Gougeon's and ask? Their tech support section is always willing to answer questions like this.

Or simply put the batteries in a battery box made for the purpose, and fastened down.

[bigd14]

Can you just use one of those close fitting plastic boxes that fits in your battery tray? It should trap incidental spills pretty well. I don't know what size batteries you are going to use, but I found a great box at the chandlery for 2 6v trojan batteries.

Doug

[bristol27]

Why not phone the Gougeon's and ask? Their tech support section is always willing to answer questions like this.

You're right, this is likely what I'll do tomorrow. I also wanted to ask here as well, because I appreciate a second pair of eyes on the entire set-up.

Can you just use one of those close fitting plastic boxes that fits in your battery tray?

Yes, I think that's a good option for lead-acid batteries. The 6V Costco batteries I saw measured 32.7cm (12.875") L x 17.145cm (6.75") W x 23.18cm (9.125") H. If I add the battery boxes size to the battery, the length extends beyond the compartment's planned locker face (I already built the side walls for the face; the photo is a little old).

So...silly me, I should have added the battery box size to my wall calculations, but didn't. This is making the smaller AGM's look more and more desirable (despite their cost, more delicate charging cycle, etc.). AGM's wouldn't need battery boxes, because they are enclosed (right?).

[Tallystick]

You could paint the compartment with PSX-700. http://ppgamercoatus.ppgpmc.com/product ... PDS_AI.pdf

Acid won't hurt polysiloxane. Not sure if it's sold in quart sizes. Although I may have some leftover I could give you if you don't need it ASAP.

[bristol27]

I called West System epoxy today to find out if their epoxy would stand up to battery acid. I asked them to tell me both the real world applications and technical tests they performed on West System epoxy and sulfuric acid. Here was their technical support person's answers:

• Overall, it's resistance to sulfuric acid is pretty good. People often build battery storage boxes, lined with fiberglass and several clear coats of west system epoxy (three or more coats) He did mention there were problems if the battery where to rub into the fiberglass below and expose the ends of fiberglass. I guess any spilled acid may wick into the fiberglass threads and cause problems with the epoxy.
• Another real world example is companies that recycle batteries where there could be spills. They use epoxy to coat the walls of 'battery spill zones' and they say it holds up quite well.
• West System did some chemical resistance testing 12 - 15 years ago. They cast epoxy cylinders in 10cc plastic cc syringes, 2 - 3 inches long (or the length of normal compression test samples they use for other compression tests). They ground the ends smooth of the samples as well, then fully immersed the samples in a jar of sulfuric acid for 8 weeks. The samples were weighed before and after exposure. They saw the 105/205 mix gained 1.9% and the 105/206 gained 2.1% in weight. They noticed that there was an initial .5% weight gain after just a couple days of exposure, then linear growth up through the 8 weeks. There was nearly no loss of hardness in the epoxy. After compression tests, they said that compression strength was 95% for 105 hardener with West System. 3 - 1 hardeners performed a little better at 97-98% of original compression strength,

Based on the above input from West System, I believe it is safe to use epoxy to coat the battery tray and battery compartment with epoxy. I will be sure to use a healthy number of clear coats. I also feel a bit more comfortable with AGM batteries, as a spill is less likely to occur and the epoxy less likely to be tested.

[Lloyd]

Good info. Thanks for checking this out for us.