weathering proof was laid to our house,6 months back.Laid Kerala tiles.Now everything got powdered.need advice

Answer 1

Without full info., I believe you have an RC (reinforced concrete) roof and top off with unglazed clay roof tile, which is quite a common roof system in Southern India. You are experiencing efflorescence, whereby the lime content from the RC roof is being absorbed by the unglazed clay tile (I guess the water absorption rate of the tile to be higher than 8%). Everything looks powdery now but you can't do much. You can try cleaning it but are not sure when the efflorescence will stop. However, you can wait a while longer till you are sure efflorescence has stop, then clean it. You can also change the tiles to a lower water absorption clay tiles or glazed clay tile but I don't think anybody can give you a guarantee on this. Didn't you waterproof the RC roof before laying the clay tiles? Hope this helps.