We just bought a 21-year-old house. There is a strong chalky smell on the main floor. The basement, crawl space and upstairs bedrooms don't really smell. The worst is the garage. We air it out all day, but after closing windows and doors you can smell it again. There are tiles in the smelly areas. Any chance it is the tiles or the grout? Is there a non-toxic, green sealant one can use on both the tiles and the grout?

Chalky smell usually comes from new concrete, not 21 year old. I do think a clear sealer will help. I used a drum of sealer for my foundation and inside concrete walls and floors. I don't think you will find anything 'green' though. I used a garden sprayer and got it all over me and didn't feel any sting or felt that I inhaled anything bad. Since it's made for interiors, I am sure it had to pass some guidelines for safety.