backing for carpet

[pablojani 10]

I have a handmade rug that was made about 30 years ago but is still in good condition. When it was made we stitched a piece of hessian to the back but the hessian frayed and I recently removed it from the back of the rug. Now I am looking for a sort of rubber/latex backing in liquid form that one paints onto the back of the rug. I know such stuff exists as we put it on the back of a carpet previously but the place where we bought it is no longer. Does anyone know of anything like this and where I can get it?