Inulating Roof with White Wash

[irfan]

Hi,
Some one told me that white wash is also a good insulator for roof. If a layer of Calcium Carbonate is quoted over roof then it will reflect the sun rays. In this way heat will not effect the interior of house. is it correct or not because it sounds very easy and could be done with a very light budget.

[htg engineer]

Never heard that before, what would stop it washing off when it rains?

White surfaces do reflect the sun, but wouldn't that mean your house wouldn't be heated by the sun - which would cost you more as you'd need the heating on more?