I have pulled up the ugly astro turf on my front porch, and I have used stripper, mineral spirits and a power washer to remove the glue and as much residue as possible. I think the concrete will still be a brownish color. How can I whiten the porch (which is in good condition)? Is there some kind of bleaching solution, or is the answer to use some kind of resurfacing technique--like a thin veneer?