There is a product on the market called Magic Scupt. It is made by Wesco in California (916)-635-1270 and is great for that application. We use gallons of this stuff and it does come in small kits. It gives you about a 4 hour working window and is easily worked like clay. With a little warm water you can blend it in so you won't see the seem at all. Then we color it with some oil paint(comes in a tube and you can get it at any craft store). The good thing about oil paints is that you can put it on heavy and blend it down with a rag or paint thinner. Good luck!