Issues like minimum coating thickness necessary, shipping restrictions, applicator certification costs, and the epoxy's moisture tolerance are often overlooked in the evaluation of different solutions. The following is not exactly a waste water example, but it is relevant as it concerns adhesion of a coating on a water saturated concrete surface under continual submersion. A coating system is the selection of products and the order of which they are applied to the hull to offer this protection. Typically, this consists of a sealing coat to seal and prime the natural hull surface, followed by several barrier coats to keep the water out, and topped off with a coating of antifouling - a toxic product designed to keep the hull free of weed and barnacles. In the tropics the boat owner can expect to renew this top coating every 12 months.
Most hull types can have problems with their coating systems of one sort or other.
Ferro-cement hulls are no exception. Even more common is a phenomenon where small paint blisters form on the hull, mainly in the solid sections of the keel. These blisters lift the coating reducing the protection afforded and promotes premature fouling of the hull, not to mention the addition labor and cost each year of repairing the paint system. Over the past few years I have taken a special interest in hull coatings and attempted to resolve the problem in my own sailing boat, Lilly Ann, a Hartley 38 South Seas Ferro-cement sloop. I contacted many of the leading marine coating manufacturers in Australia, to seek an understanding of the problem and the possible solutions.