could be ashfelt,fibreglass etc its hard to say tbh,but they will all cost you a bomb!it could be acropol which is a fibreglass based paint(normally light blue/grey in colour) that comes in a tin around £60 for a 10ltr tin which if you spread it on thick enough,usually with a brush or broom would be cheap enough and probably something you could have a go at yourself as the instructions are on the tin.however for me if you dont have the experience or a diy head on you,it could get very messy!!and once its on ITS ON!theres no going back.personally i would go with the tried and tested way and have it felted by a proffessional.if it is already watertight i dont see why 1 layer of green mineral wouldnt be sufficeint providing you prime it properly and last a good five years minimum,it all depends whats already down to be honest and thats the same for the acropol by the way.i would normally charge around 250 to go over the old felt with 1 layer on a standard garage (15-20 sq metres) providing theres no water damage to the boards beneath the felt,because then its a case of stripping the lot,renewing the boards then 1 layer of black and 1 layer of green which i would normally charge around 650-750 to do,so if you use that as a rough guide for pricing it up against other options avaliable on the market you should be able to work out whats best for you.hope i was of some help anyways
jimbobly
November 2012