How To Renovate Old Boat Tanks

One of the questions that I have been repeatedly asked when surveying vessels, particularly older ones, is "Can I repair the old tanks as I don't want plastic or stainless in its place?" Well, of course you can but you just have to do the job properly because the last thing you need is a bodged job dripping fuel or water all over the place, filling up the bilges. The main priority of course are safety issues and you can rest assured that if a fire or damage is caused via leaking tanks your insurance will almost certainly be considered null and void. In many cases, the tank will be beyond redemption but the tank may well be put to use to enable a new tank to be molded from the old one, depending of course on your own skills with GRP and the spare time you have to do it in.

There are several stages in repairing tanks and certain criteria to take notice of before we begin the job in hand. Fuel tanks have a different function to water tanks but the repairs for both must be adequate, safe and strong. Materials must also be taken into account and a decision made whether the repair can be considered viable financially, though in most cases, the price of a new tank is fairly horrendous.


One of the questions that must be answered fairly early on in the piece is 'Will this be an internal repair or an outside repair?' Naturally, the job may well make all the difference if inspection panels can be lifted right away to allow access for repair. The other, critical question is. 'Where is it leaking and how bad is the damage?' This can be extremely tricky and often very misleading. A tiny pin prick leak on the edge of a tank can run several feet along pipes, down gradients and drip morosely somewhere quite different giving you a bum steer! The problem can be added to by rain or pipes leaking from above giving the leak an added dimension. Worse still, and most unfairly, a tank can leak from several places at once but can exit downhill in quite a different spot! Beware too, the flange leak or tap that leaks undetected back along the pipe, down under the tank bottom giving the misleading impression the problem actually to the tank itself. Proper leak identification is critical before you go to the huge problem of actually removing the tank itself only to find it wasn't worth it all! Sounds horribly obvious doesn't it, but you'd be surprised. Don't be fooled also by tiny pinprick leaks. In steel and aluminum tanks a pinprick is sometimes only indicative of a much greater problem inside.

Many tank leaks are caused by corrosion that is the inevitable result of water lying undisturbed inside at the bottom for years. Steel tanks suffer greatly from this and often the pinprick leak is the first sign that the paper-thin bottom is about to fall out, plus whatever the contents are. Aluminum tanks have their own problems too. Many alloy tanks are seconded into use by people and often they are not marine grade aluminum alloy. This means that if they are left standing in seawater, their chances of surviving the ultimate corrosion and failure are virtually nil. The wrong grade alloy literally melts in seawater! Much damage can be caused by aluminum tanks standing on rubber mats or cushioned by rubber inserts under steel retaining strops. Certain brands of rubber contain chloride and this too chomps away at aluminum alloys at an alarming rate. Leaving wet rags on top of alloy tanks is also bad news as the resulting poultice corrosion that produces a horrible white sticky substance is also highly corrosive. The same goes for nuts and bolts and any tools left on top of tanks, dissimilar metal corrosion is alive and well in these cases, all wreaking their own particular havoc!

Now that I have succeeded in frightening y'all to death, what do we have? The leak has been identified, assessed and the odds are the tank will have to come out in most cases. It is a bit of a pain but generally it is a good thing because you can check all the hidden unseen areas that are behind it and clean it up at least whilst the tank is out. One chap I knew did the same and found a heavy oiled bag behind the tank. Upon opening he found a .45 automatic handgun and couple of boxes of bullets …. what I want to know is how the hell did the previous owner forget about that? We'll never know, I suppose, maybe he never knew? It was probably his wife's! Once the tank is out though a lot will become clearer. The next stage is about to evolve and we can actually get to grips with the beast.


Assuming the tank to have been initially emptied of content, we can now decide, can we repair internally or not? Remove any inspection panels and make a decision whether it is possible to work inside. Being able to see what you do is vital. If you do have enough room to see and work that's great. However, one steadfast rule remains for all tanks, great or small, fuel or water, glass or metal, copper or steel, they must all be spotlessly clean, no grease, no rust, no dust, no slime, no powder, no particles , no nuthin. Did I make myself clear? Cleanliness is next to godliness in these cases, a good repair starts spotless. Once cleaned, it must be degreased thoroughly. In the case of steel, copper, brass and alloy it helps if it is shiny bright metal too! If the bottom appears to be leaking two layers of CSM (Chopped strand mat) about 1.5 ounce mat will usually suffice ensuring that the glass is raised about ¾ inches above the bottom all round inside.

If further investigation of the bottom leak shows weaker metal and a larger hole appears (or several) then it will be best to ensure the repair is approached from the outside. This can be achieved by backing up the wetted fibreglass mat by a stiff piece of cellophane covered card that, in turn, is stuck firmly to the bottom of the tank with plenty of sticky tape. This ensures the glass will not sag or droop or even fall off under its own weight whilst curing. Be generous in the patch size, the larger the better. Curing can be facilitated by heating with a hair dryer or even adding a little extra to the resin / catalyst mix. NOT, however if epoxy resin is being used ….. strict measures only please! Allow a minimum of 12-15 hours, preferably overnight. Please note: In the case of petrol tanks, they must be steam cleaned before any repairs are undertaken

Remember, in the case of the fuel tanks, it is critical for the repair to be completely degreased. The resin will almost certainly not adhere and the process will have to be re-done once more. Degreasing can be done with trichlorethylene, carbon tetrachloride, detergent solution or a proprietary degreaser. Don't shortcut this step ….. you can't say you weren't warned!

Sealed tanks of course, must be repaired from the outside and it may well be worth considering, to completely glass over the whole tank, especially if you use a couple of layers of fine cloth and used filled resin to fair it off. You can give the tank a completely new lease of life, especially if you paint it a bright new color afterwards. However, be careful that any corroded pieces cannot break away in the future, potentially blocking pipes, filters and causing the engine to stop at a very awkward time. One further suggestion in this scenario to make good and certain that no particles are loose is to pour 2 to 3 liters of resin / catalyst mix down the filler pipe via a funnel to seal the bottom completely and preserve forever any loose flakes or dust after glassing the outside. It is so cheap to do and it is worth the extra effort!


A leaking seam may seem an impossible job but with patience it is a breeze. Clean thoroughly all around the seams and degrease. Simply repair right around the whole seam overlay on both ends of the tank.


Where water tanks are repaired with general purpose resins (polyester) the residue of styrene that is present (about 50 parts per million) imparts a "taste" to the water. It is not harmful as such but quite undesirable and the taste will hang around for some time. In boats or caravans the water does not get used so quickly and it can take time to flush away. However, certain resins that are recommended for drinking water supplies can be used. Check with your resin supplier for advice. However, always cure water tanks for at least seven days and repeatedly flush with hot water, which removes much of the styrene taste. You can also have the tank steam cleaned at your local garage for a reasonable fee … it is well worth it.


On a boat it is vital to have something always to hand for repairing a sudden leak or pipe break. There are several varieties of epoxy two part putty and epoxy tapes for pipes available. However, ensure that the temporary repair does not end up permanent, some of these putties really work well, even soaked in fuel or water.This is one boat repair that you dont want to end up leaving wont repair itself, for sure!

With ever rising costs today, new tanks are really expensive, several thousands in the case of large yachts and it is always satisfying to be able to make a safe, efficient repair for the fraction of the cost of replacing them. It takes a bit of extra effort but think of the hundreds of hours of work you'd have to do to pay out extra hundreds of bucks for new ones!

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