Home built in 1829. Old sandstone foundation. Purchased 5 years ago and basement looked in great shape. After 2 years, colors began to show through white-painted latex walls (previous owners tried to cover) - tested positive for 5+ molds. Have bleached, scraped, etc... still coming through. Just put on new roof, new seamless gutters. Do not get water coming into basement. How do I get mold off permanently without having to spend a small fortune?