Water tank painting is a job that often gets neglected by boaters. Many boat owners are taking an ‘out of sight, out of mind’ attitude to their water tanks. Water tank painting and care is an important part of boat maintenance, with serious negative effects on both your personal health and your boat’s health if it is not done routinely. We strongly recommend that you do not drink or cook with your tank water unless you are certain that the water system is in good condition. We normally check water tank annually and touch up any minor issues. Full re-paints are carried out every 3 years or less. This is for water tanks that are integral to the hull. Plastic and stainless steel water tanks do not need painting.
Why Water Tank Painting Needs To Be Done.
Crawling into a boat water tank to paint it is not exactly most people’s idea of a fun weekend. Yet it is important to maintain and check your water tanks at least yearly for a few reasons.
Firstly: your health. As mentioned above, all water tanks get build ups of biological matter from bacteria and micro-organisms. This can cause sickness in humans, depending on the exact organisms present. Another cause of sickness in humans comes from integral mild steel tanks painted with bitumen or other paints. As these coatings degrade over time, they flake off into your water supply. Constantly ingesting bitumen and other harsh paint chemicals is not good for your body. While rust causes obvious discolouring to your tank water, it is the least toxic constituent of water from a badly maintained tank. By the time the rust is visible in the water, the bitumen or paint has already gone through the water system.
Secondly: the health of your boat. Integral water tanks should be checked every 3 years. They are painted with bitumen and other water tank coatings, which do eventually degrade. Once these degrade, they offer no rust protection . Corrosion sets in rapidly as the water levels go up and down in the tank. This kind of tank needs to be regularly repainted to avoid expensive hull repairs and overplating down the line. When water tank painting is carried our regularly, there is no risk to you health or the integrity of your hull.
On initial inspection, this water tank, didn’t look too awful. There was some obvious corrosion, but it was far from the worst we had seen.
Once emptied the rust becomes more apparent During cleaning, this same tank began to show some serious problems. There were holes in the steel between the vertical wall of the bow well deck and the water tank. Luckily for the boat owner, there were no holes below the waterline despite some heavy pitting.
We overplated the holes in the tank by welding from inside the tank to give a seamless finish outside. As the Floating Boatyard has full equipment on board, if we discover emergency works which must be carried out we can offer these without delay.
Preparation for Water Tank Painting
There is no substitute for climbing inside the water tank through the access hatch. Most of the water tanks have an access tank which is suitable for this, but if not a larger one can be fabricated by our team. All existing rust will need to be mechanically removed. We also remove all loose and flaking bitumen or paint – as with boat painting, preparation is big part of successful water tank painting.
This is a water tank a customer had been drinking from, the heavy corrosion is clearly visible. You can also see the bubbling and peeling bitumen which will inevitable find its way out of the boat’s taps.
This is the same boat’s tank after it has begun to dry, the extent of the rust is clearly visible now. The rust in the centre was approximately an inch thick, there was also around half an inch of old bitumen. This had collected when a previous coat of bitumen was applied too thickly and it had pooled in the centre.
The same tank after rust removal. We took this water tank back to bare steel as the old bitumen was so badly degraded. When water tank painting, some old bitumen can be left on the steel if it is still in reasonable condition.
Applying Water Tank Paint
Once clean and all loose old bitumen has been removed, water tank painting can begin. Most integral water tanks have traditionally been painted with a bitumen-based paint. Bitumen requires the worker applying it to wear full safety gear. When using this chemical in enclosed spaces such as a water tank, it is vital that the person applying the bitumen takes regular breaks for fresh air. Bitumen also needs to be left to cure for at least 7 days, then flushed with multiple tanks of fresh water to remove any taint.
One of our team taking a breather (literally) while blacking a water tank.
The key to water tank painting is to ensure the correct coverage of bitumen. Too thin will cause weak spots in the protective coating, leading to premature rust. Too thick, and the product will slowly roll down the tank to the lowest point, leaving a pool of bitumen that will never cure correctly, tainting the water in the tank. The temperature of the product and the steel on which is being painted is vital to this. Warm bitumen is thinner and flows faster than cold bitumen.