Food Grade Epoxy for Water Tanks

[KAIROS]

As a coating on the inside of plywood/epoxy water tanks, I've heard that 'Food Grade Epoxy' will seal the wood and, most important, not taint the flavor of the water.

Online I see various sources of food grade epoxy, but they seem to be for professional application to the insides of huge tanks.....large drums of the stuff.

Can anyone recommend a food grade epoxy which they know does not taint water flavor, and comes in reasonable quantities (a quart)?

Jack

[Ian McColgin]

The sheet says that QCM Industrial ships gallon containers (2 gal total) of their EAS-1.

[Tom Lathrop]

Like some others here, I have a shop made water tank coated on the inside with regular epoxy. There is no taste that I can determine. Glidden, Devoe, ICI has a "potable epoxy paint" meant for the inside of water tanks.

[Garret]

Hi -

Timely posting for me. My boat has a large single aluminum water tank (~125 gal) under the cabin sole. Custom made (fairly complex shape) & works fine, except....

It develops small white granules that clog strainers & the water tastes like [insert a nasty word of your choice]. I always filter water gotten from a hose (activated carbon household filter with at least one new cartridge/season) - this helps, but I think the aluminum is my big problem.

I've wondered if there was an epoxy coating I could use (after serious wire brushing). Does anyone know if the above-mentioned ones will adhere well to aluminum?

Other ideas? I'd thought of redoing it in SS, but that'd be expensive - particularly with good food grade stainless.

Thanks!

Garret

[StevenBauer]

I think this article would be worth reading:

http://www.epoxyworks.com/18/index18.html


Steven

[AstoriaDave]

Steven,

That link really lays out things in spades. As a longtime chemist, I had thought to caution the OP about tackling this project cold, but held off because it is an area outside of my professional expertise (I'm not a food chemist). Lots of variables in doing a careful skookum job making a tank "potable water-qualified."

BTW, that link leads to articles burried in a frame. this is the one he wants (can be downloaded as a PDF file.):

Building tanks with WEST SYSTEM® epoxy
Wood/epoxy composite tank guidelines

[Garret]

Thanks for the detailed reply! Rambling is fine by me, as it often produces interesting info. I do it myself.... Where was I? Oh -

I figured it was aluminum oxide & probably harmless. I have not scrubbed it off - other than to clean the tank when I bought the boat - as it was fairly slimy. I do have to empty the strainer on the galley sink every week or so - when it starts running slow. The water does have a strong metallic taste - to the point where we don't drink it.

Copper - interesting. I even have the skills/technology for making a copper tank. I'd have to build some internal braces though - but that shouldn't be too tough - copper pipe cut & soldered appropriately maybe. Lead free solder obviously - even if less forgiving than good old lead/tin. Wish copper prices weren't so high.

Come to think of it, the original (1941) tank was copper.... Learn something old every day!

Food (drink?) for thought -

Garret

[Garret]

Garret,

The strong metallic taste in an aluminum tank doesn't sound right at least if it is a 5000 series. Most of the good alum tanks I have drank out or been intimate with over the years are only a problem if you leave them empty or low for long periods or have a high pH water in them. Then again the water if it has quite a bit of metals or other things in it can react with the tank. Sounds like perhaps your tank is not a 5000 series marine aluminum but something else. If so this may explain why you have so much oxide build up and fouling in your system not to mention offending tastes.

As for making you own copper tanks you really don't need any framing per se other than a couple of full width & height internal baffles to control free surface sloshing and panting. Baffle location and design would be according to tank design and location. I am presuming a tank that is contained in the bilge or under settees or berths and not a large vertical wing tank. BTW copper tanks do not do well in machinery spaces unless you need warm water.

Hi -

I have no idea what grade aluminum it is, as it came with the boat. It was made at the same time as 2 fuel tanks, so I'll guess they used the same material. All are nicely made, but - as Sgt. Schultz would say "I know nothing"....:confused:

The tank sits below the salon sole & is kinda rectangular, with a bunch of tapering (it's about 6' long, 3' wide aft to 3.5' @ the forward end, 2' high at the narrow/aft end & 8" high at the wide/forward end). My guess @ 125 gal. is only a guess. Too lazy to do the math & it's too cold to fill from a measured container.

I was concerned about support, because the current tank rests directly blocks on the frames. This leaves 16" or so unsupported between them. Unless I went with very thick copper, I'd have to provide support. Maybe the best way would be to put stringers along the frames for support if I go with copper.

With this big a tank, it does spend a lot of time not completely full. I could go with separate tanks, but with current cruising limited to New England, isolating bad water isn't an issue.

Thanks for the info!

Garret

[Garret]

I realize I've hijacked this thread. My apologies.

To help make up for that a bit, here's some info I've found. Most available epoxy coatings are for commercial/municipal use: 250,000 gal. tanks. So - the problem will be to find product available in small quantities.

Sherwin Williams (http://news.thomasnet.com/fullstory/24510) & PPG (http://corporateportal.ppg.com/NR/rdonlyres/3F9E39DC-FEB4-403D-B4BD-D50372158516/0/aquaponnsf.pdf) offer coatings. Both seem to focus on coating steel & cement (picture tall water tower), but I'd bet they'd work on regualar epoxy as well.

Nuflow (http://www.nuflowtech.com/products/epoxylining.aspx) is another one. And one for brewery tanks (http://www.sscoatings.net/brewcoat.htm). If it's good enough for beer, it's good enough for me! ;) This one has small qty pricing on the site: $200US for 2 gal. - plus shipping I imagine.

HTH

Garret

[BarnacleGrim]

What kind of aluminium are beer and pop cans? They are perfectly fine, even with acidic contents and during long storage.

You'd need a tig welder and a lot of time to figure out how to put it together and not just burn holes, but it seems a lot cleaner than epoxy. I'm guessing they avoid using things like Bisphenol A when making food-grade epoxy.

[Bob Adams]

I'm pretty sure beverage cans have a sprayed lining. My boat might not be much, but the Monel tanks are finestkind.

[RFNK]

I'd recommend having a tank made up from food-grade poly. The poly imparts no taste to the water, the poly is cheap and should last a very long time. There are plenty of companies around that do this. Rick

[PeterSibley]

I'm planning egg crate style containers to hold individual 4 litre /1 gallon jugs .Cheap ,easy to clean and replace .Easy to carry in a dinghy ,transperent .....so I can see the condition .I'll keep them away from light .

[BarnacleGrim]

What about filtering the water going into the tank? It should keep a lot of slime forming bugs out of the tank.

[Garret]

What about filtering the water going into the tank? It should keep a lot of slime forming bugs out of the tank.

I always do that - with an activated charcoal household filter on which I put a hose fitting on one side & a male fitting on the other. Attach it to the hose, rest it on the deck with the male end stuck in the deck filler, turn on the water. Actually, I flush a couple of gallons through the filter first.

Makes it easy.

[KAIROS]

I think this article would be worth reading:http://www.epoxyworks.com/18/index18.html

Thanks Steven, and all. At the link above, you must scroll down to the link titled "Wood/epoxy composite tank guidelines (http://www.epoxyworks.com/18/tanks.html)".

As Tom Lathrop mentioned there are many good composite ply/epoxy tanks that don't significantly taint water flavor. I have tasted epoxy in water though....I could only drink the beer aboard. I think the reason my hair is now thin on top is because I showered for months on a ship where the water tanks had been repaired with epoxy. I had to hold my breath to avoid becoming nauseous. I suppose it was not mixed or cured properly as the article above mentions.

The article also hints that the chemicals in what we think of as structural epoxy may leech into water and may not be healthy whether we taste them or not. I'm thinking of building as the article recommends so that I end up with a strong tight tank, then coating the inside with several coats of 'potable water epoxy'.

I am building the tanks to rest on the frames under the main cabin berths.....very complex shapes. If I go for a simple shape (rectangle or cylinder) I'd have to build complex bracing anyway, and I'd loose half of the volume. If I do it right, I can get 30 gallons of water with a tank on each side, and use only half of the length of each bunk.....leaving the other 3 feet on each side for other storage.

When/If I need more capacity for a voyage, I'd choose a variation of what Peter Sibley said (1 gallon flasks). Very comforting not having all your water 'eggs' in one basket, and as he says easy to take ashore for filling.

I can taste polyethlene (or something) in poly water tanks. And, getting a company to build two unique poly tanks (two complex molds) for 30 gallons of water would make for some valuable water per gallon :D.

[nautiguy]

I'm also in the process of building a wood water tank so that I can shape the tank to fit the curves of the hull.
I coated the inside with a saturation of penetrating epoxy which serves to protect the plywood. I then found out (in a conversation with Steve Smith of Smith Company, maker of CPES) that the epoxy will allow water vapor to migrate, think blisters on a fiberglass hull. So I am now in the process of coating the inside of the tank with 3 coats of Interlux barrier coat. When the odor is completely out-gaussed there should be no residual odor or taste.

[SV Papillon]

I contemplated this but after doing the math on material cost for marine ply epoxy etc and looking through the several hundred "stock" size arrangments offered by plastic tank manufactures it was a wash. I will loose about 10 gallons per tank with the closest ones to fit what I need verses building to fit but they are less in cost than materials to build. The rep said it is much more for a custom tank so in that case it would make sense.

Ex: $190 for 30 gallon wing tank that fits to the hull under a sette, what I thought was a really weird shape but they had one that was close.

Jake

[KAIROS]

.....So I am now in the process of coating the inside of the tank with 3 coats of Interlux barrier coat. When the odor is completely out-gaussed there should be no residual odor or taste.

I doubt that the Interlux product is much different as far as use for potable water than most other what we might call typical epoxies used in boatbuiding (west 105/205 for example). If you're comfortable with disregarding recommendations for epoxy used for contact with potable water, have at it. Note that for commercial boats regular epoxy may be illegal in water tanks and might need to be replaced for resale. That article (http://www.epoxyworks.com/18/index18.html) above seems to reasonable basic information. Also, no epoxy is waterproof....it just slows water down.


I contemplated this but after doing the math on material cost for marine ply epoxy......Ex: $190 for 30 gallon wing tank that fits to the hull under a sette, what I thought was a really weird shape but they had one that was close.

Is the company Tank Depot? After I figure the shape I will check with them. I think I've looked at every tank they sell and don't see one that works yet. There's other companies, sure. Depends on whether they've had demand for a particular shape from a plastic boat factory.

By the way, how did you figure the shape? I'm just measuring dimensions at each rib to get section shapes, then interpelating between them with 3-D software to get the volume.

[KAIROS]

I don't have any idea who Steve Smith is but if that is in fact what he told you and not a misinterpretation then I have call BS. Epoxy is one of the ultimate barrier coatings since it is essentially 99% solids. GRP hulls with osmotic blistering are usually stripped of the gelcoat, dried out and re-coated with several applications of EPOXY. Epoxy is really a remarkable substance and a reliable barrier coat or insulator for water, electricity, most chemicals. If moisture migration is taking place it's due to a failure in the application. Enough said and good luck

The Gudgeon's don't claim that their (West System) epoxy is waterproof now. It slows migration to a crawl. For a barrier coat it is probably the best you can do, but as a glue only resorsinal is considered waterproof. Only an issue for bonding below the waterline. I use epoxy for all glueing though.....I need it's gap-filling qualities. CPES is a different animal than most epoxies. Not an adhesive. Made to penetrate and seal wood.

[PeterSibley]

I have to wonder if wax wouldn't be better and certainly cheaper .

[wizbang 13]

Only slightly off topic, my fuel tank is ply/epoxe. 40 gal diesel. Quiet, no condensation. Water, monel has got to be best.

[SV Papillon]

Is the company Tank Depot? After I figure the shape I will check with them. I think I've looked at every tank they sell and don't see one that works yet. There's other companies, sure. Depends on whether they've had demand for a particular shape from a plastic boat factory.

By the way, how did you figure the shape? I'm just measuring dimensions at each rib to get section shapes, then interpelating between them with 3-D software to get the volume.

Most of them seem to be re-sellers
I tried plastic-mart
this there catalog (HTTP://WWW.BOATTANKS.COM)
lots to choose from.

I just measured and drew it out by hand, then calculated volume.

good luck
Jake