I recently poured a small test section of a counter top concrete mix from Menards. i poured it in a melamine form. when i took it out the bottom (which would be the finished top) is darker around the edges and is lighter in the middle. does anyone know what causes this. is it just not cured all the way. it has been 3 days. I did not caulk the edges of the mold because i was just looking to see what color it came out to be. could the melamine have sucked off water?