[bigegg]

I've registered on here just to ask a question which is puzzling me from another forum, and hope someone can help...

https://www.youtube.com/watch?v=ycQDH8OYvWY

is a youtube video showing metalworking in Haiti.
around 3.20 onwards, portland cement powder is added to a sand mold on what will become the inner surface of a cast aluminium pot.
I am unsure if this is just done to improve the surface finish of the pot, or whether a chemical reaction would occur which would leave a protective surface on the pot - perhaps to prevent damage from acidic foods.

 Thanks for any help/comments