OMG thank you for posting this about Delta mat.I did my house foundation with it a few months later I saw a museum's foundation built with it but exposed to the sun.I touched it and it started crumbling.I had nightmares because I thought that this is a junk product and never knew the fact that it not suppose to be exposed to UV light LOL I basically had nightmares because I spent money and hard work fixing my house.Now I know that I am safe because none of mine is exposed to UV light.