Robson Mastic RT10
I have been using the product for almost 6 years now on the suggestion of another builder who has used it for much longer. I like it because it is easy to apply, can be applied all in one day and painted within 3-4 days. It fills the weave better and therefore takes less paint to get a smooth finish. This product was not designed for boats, but rather for waterproofing canvas that is wrapped around steam and water pipes in the construction industry. It can sustain harsh conditions and remains pliable. The only down side is that because it is basically a latex rubber compound, it can not be sanded easily, therefore you must take great care in smoothing it out with your hands before it dries or it is like sanding a rubber eraser. I have never had a boat returned due to this product. It is holding up well.