Torch on again

Hi

I need to patch an existing felt roof and I would like to use "Jewsons" version torch-on (not that it matters that it is Jewson, could be Wickes but I think the staff are good at Jewsons - gave me a jacket). The existing roof has a rubber coating - smooth, not mineral finished felt. The roof is clean.

Can I go straight over the existing felt with the torch-on? If I primed the roof, would I get away with one sheet? Some of the felt is loose, so should I nail this down before felting or just leave it to float?

Its only a temporary fix but it would be nice if it would last a couple of years.

Any experience appreciated.

P.S.

If I did the whole roof with two-layers of torch-on, but leave the existing felt down, would that be a permanent repair? I read something to this on a flat-roof company's web-site.