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svDragonfly 11-08-2008 12:50

Crack in fiberglass water tank…

Just found the first big issue on our new to us Beneteau 411…

The forward integrated fiberglass water tank has a crack along the top seam. Speaking to a few people at the boat yard they seam to think if the crack is at the top of the tank I should re-glass as a repair. Any one out there with more experience care to recommend the steps or technique to doing the glass job my self.

S/V Antares 11-08-2008 14:22

Check out the West System repair manual (Not west Marine) It has some good detail on this type repair. The main issue is if it is a corner. There are special fiberglass "Tapes" in rolls that are designed to make fairly severe bends. West system has these.

Free On-Line User Guide:

Fiberglass Boat Repair & Maintenance (002-550) - $4.95

Fiberglass Boat Repair & Maintenance

Roy M 11-08-2008 16:10

A crack may have developed because someone stepped on the tank when the boat was being built, or because of insufficient stabilization leading to flexing, or because the boat has an infestation of malevalant spirits that need appeasement. At any rate, the crack has to be properly repaired or it will continue to haunt you. If you don't feel secure about your repair skills, hire someone who IS skilled. It will probably mean emptying the tank because you are going to have to grind the edges of the crack to expose clean, solid substrate for the repairing materials to bond to. That will intoduce stuff into the contents of the tank. This might be a good opportunity to build in a cleanout/inspection port in the tank. Hopefully, you will be able to expose the damaged area so as to determine the extent of damage, and to easily make repairs. Or, in the case of malevalent spirits, you will have a fixed sole of exotic hardwood permanently covering the area of the crack. Then, you REALLY want someone, with small, delicate hands, who can perform surgery in very tight spaces with minimal overhead clearance. Best of luck!

TexSail 11-08-2008 17:32

The West System (Gougeon Brothers) is good stuff. I believe that West Marine does sell the stuff, but is unrelated otherwise. Their system uses epoxy with glass and is quite strong (and pricey). If the crack is along a straight seam, I suspect that a roll of 4" glass tape and a quart of the West System 105 resin and one of their hardeners would work. Follow the directions to the letter. Good luck.

svDragonfly 12-08-2008 10:19

so how many layers of the 4" in glass do you add to reinforce a corner?

The crack is only 3 inch long but it seams I should reinforce the intire 6 foot length, would a 50 foot roll of the 4 inch tape be enough for the job? How much epoxy, and hardener would it take.(how large a container?)

TexSail 12-08-2008 10:44


Originally Posted by svDragonfly (Post 192885)

so how many layers of the 4" in glass do you add to reinforce a corner?

The crack is only 3 inch long but it seams I should reinforce the intire 6 foot length, would a 50 foot roll of the 4 inch tape be enough for the job? How much epoxy, and hardener would it take.(how large a container?)

I would think that a 50 foot roll of tape and one quart of epoxy (they sell hardener in volumes to match the quarts and gallons) would leave you with plenty for another job. The stuff keeps for years.

Roy M 12-08-2008 13:17

If the crack is only a few inches long, simply grind or file, or sand the edges of the crack and the surrounding surfaces back about two or three inches to remove any wax or other barrier coats. If you can lay a strip of three inch masking tape on the INSIDE FACE of the tank (assuming you can reach there), that would be perfect to keep the resin from dripping down into the tank until it cures. Purchase a WEST System repair kit with some fiberglass cloth or tape, enough to completely cover the crack three or four times, layered. A small amount of epoxy will go a very long way. Wet out the sanded fiberglas tank section, place a piece of fiberglass atop the crack, and resting on the surrounding tank parts that have been sanded. Then brush the cloth with enough resin to wet it thoroughly. Use a heat gun or a hair dryer at low setting to speed up the cure. When it is just hard enough to be gummy, mix a second batch of epoxy. Wipe the surface of the partially cured epoxy with alcohol or acetone to ensure a good bond, then layer the remaining pieces of fiberglass cloth with wet epoxy. Use a spatula or 'glass squeegee to press out the excess epoxy and any air bubbles. Let it cure naturally. Pat yourself on the back, but clean your hands first.

svDragonfly 12-08-2008 15:08

I am not sure how bad the damage is yet, the previous owner had covered the area with something, and it was empty. So I am going to have to get in there and scrape away the previous repair (term used lightly). I would like to be able to determine what caused it; was it a strike to the corner when a drawer fell out or was it some sort of stress along the edge like some one standing at the center of the tank, etc.

When you talk about grinding fiber glass do you mean going at it with a grinding wheel on an air tool, or do you just hit it with a stainless steel brush on a hand drill?

Roy M 12-08-2008 15:25

Adhesives and other coatings, like paint, need a base to adhere to. It must be slightly roughened, clean of dust and oils and waxes. You achieve the roughness with a file, sandpaper, a grinder, or any abrasive applied with copius amounts of elbow grease to achieve the proper surface. Grinders are fastest and use the least elbow grease. A stainless brush on a drill motor MIGHT work, but probably not as well as more traditional (and harder) methods. just use 60 grit sandpaper if you aren't sure, then clean it with acetone or alcohol. Get ALL of the previous "repair" removed and do it right this time so you can forget about it and get on to other maintenance adventures.

S/V Antares 12-08-2008 16:25

All good info here. Also the West System has Fast , med and slow cure hardner, (part B) The slow stuff is good in hot weather and gives you some time to work before it "kicks". Buy the West System Mini pumps as it gives you perfact mixing ratios for the quart or galllon group,


wear gloves and do not scratch your nose until finnished!

forsailbyowner 12-08-2008 16:57

the golden rule for fiberglass is it must be ground back and feathered 12x the thickness of the glass. So if its quarter of an inch thick must grind back 3 inches to get proper strength going from pointed edge to pointed edge. Also very important to do chemical wash with acetone multiple times. Ps best way Ive found to clean up anything on hands etc is alcohol.

Luders33 02-09-2008 16:04

I thought that west system epoxy was not safe to use for potable water tanks. I was told that old fashion polyester resin was safe.

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