Building Fiberglass Fresh Water Tanks

From a wood boat guy, this plastic fantastic stuff is a new experience. Building the trimaran has brought out some new and interesting challenges. The most recent being the water tanks. After I recovered from the sticker shock of having tanks made to fit, I have decided to try building them. I have gotten fairly proficient at laying glass, and epoxy is my poison of choice. I have seen boats with fiberglass water tanks, so I know it is done. My question is coating. Is there any specific method or material that should be used to coat the inside of the tank? Is there any specific type of epoxy that should not be used to glass a water tank? My plan is to form flat panels and glass them together. I have searched for info online, but have not found the answers I need so I am open to any sources on this as well. Any warnings?

[cat man do]

Mate, none that I can warn you of.

All my tanks are done in Ply /epoxy, lighter and stiffer than solid glass panels, making sure that all limber holes got several coats on the endgrain, and the flat parts were glassed with 200gsm plainweave, and then given another coat of resin when the glass was green.

Heres some info, but i'm sure you'd have seen it.

http://westsystem.com/ewmag/18/pdf/tanks.pdf


Diesel tanks done the same way.

Epoxy was the resin of choice for water tanks on all boats I've worked on with composite tanks.

Have Fun

Dave

Thanks for that link. I had not read it before. Interesting they tell you this is how to do it, but don't do it. Hard for me to get a controlled environment to build them. That is why I was wondering about coatings. Since I have seen glass tanks on production boats, I am wondering if these are poly instead of epoxy? does poly have the same potential problem of leaching chemicals?

[cat man do]

I'd hazard a guess that they'd be poly.

Hard to imagine a production builder spending the extra $$$ on epoxy.

Dave

HMMMM? Good point. Maybe now I have a use for all that glass matt I have stored

[cat man do]

Not for a second suggesting I'd go that way.

I just hate polyester resins.

Dave

I am not fond of poly, but then again, my experience with it is limited.
So, are the tanks you have screwed together and epoxied inside an out? Just so I can get a clear picture.

[Stevens 47]

I am in the construction phase of building in epoxy tanks for both water and diesel. What I like about doing this is that I use as much of the boats hull. When I glass over the hull, by the very nature of the construction I will be creating a stronger form, in the style of bulkheads. My boat came with 300 US Gallon SS tanks under the settee's. I will use the furniture and the hull to contain the new plastic making a flange on all sides. I will build in baffles after the flange and bottom and all the sides are built then I will build a top with all the inspection hardware built in and bolt and epoxy that to the flange, same for my diesel tank. For the water tanks I am thinking of using Marlon thru holes for the fill's and exits. For the diesel I will use stainless glassed into the top.

Jack

Jack, so I understand, are you going to use the hull as one of the tank walls? And, are you using epoxy and ply, or epoxied glass mat?

[Stevens 47]

I noticed that you are planning on using matt? If it is not stitched and is held together with a binder it will not be compatible with epoxy, the binder is broken down in the ester's. My choice would be to use a biax cloth (all so much stronger than matt) to do the bending if you are going the epoxy route.

Jack

[Stevens 47]

Yes the hull and the ply as a form much like pouring concrete. As a matter of fact the diesel tank is in the bilge and about 65% of it will be glassed against the hull should be very strong and add an additional strength to the hull. See my earlier about matt verse's biax. I have been using biax really great stuff.

Jack

Thanks Jack. I have lot's of mat around, and was only saying I would use it with poly (I know about the binder issue). I still have about 20 yds of 40oz cloth left, and that was what I was originally planning to use, but the article Cat-Man-Do provided discouraged the use of epoxy for potable water tanks. With that in mind, I was considering the use of poly resin, and with that, using up some of the glass mat I have around. Saving my cloth for other projects.

[SkiprJohn]

For freshwater tanks even if they are built of polyester it is a good idea to coat the interior with epoxy to get rid of most the funny taste.
Could anyone describe the concern about using mat with epoxy resin? I've been using it for years and it never seems to have been a problem. Is there something I need to know about?
Regards,
JohnL

Yes, the binder in the mat reacts with the epoxy, and will cause the area to weaken. There may be some mat out there with a different chemical binder in it, but I do not know. All the books say simply don't do it. The Gudgeon Bros. article says that chemicals can leach from the epoxy if the mix and cure is not 100% perfect, and advise against coating the inside of a potable tank with epoxy. They also say that people do it, and have been quite successful. If I had a more ideal work area, that could be temperature controlled, and dust free, I would not be so hesitant, but working on deck out in the elements, I do not think I could get the epoxy to properly mix and cure so it would not leach into the water.

[mike d.]

KAI NUI there is/was a polyester resin for water tanks that imparts no taste or odor to the water you have to find the right supplier i imagine to get it. i believe if i remember right it was used in the whole process lay up to inside finish.

regards mike