Our house has a lap type siding that looks like clamshell molding. We has the paint stripped off using a pressure washer since the paint was falling off anyway. So, now the grain of the wood is raised. I know we can sand the grain, but how do we fill it? The bare wood is rough even when sanded. I've mixed drywall mud in paint to thicken it for interior repairs. Any idea how to make some affordable thick paint to build up and smooth out the siding on the exterior?