expansion of felt on roof after rainfall

[carocris]

After a bit of advice.
The other day i began putting down underlay felt on a flat roof, pinning with galvanised nails as instructed. It was all nice and flat. i couldn't crack on with the next layer which was to be applied using cold bitumen as the skies opened up. The felt has now expanded with the rainfall and buckled up in places as the nails have held it.
Will the felt shrink back flat once it dries out?

 

[9fingers]

I cannot imagine the felt has been affected by water.The felt is a fibrous material impregnated with bitumen and is waterproof.

I presume you have a temperature effect or some interaction between the felt and the cold cement if you have applied it yet.

The last flat roofing I had done used the nailed on underfelt and a torch-on top layer.

Bob

 

[devonwoody]

Timber movement?

 

[OLD]

Is the expansion due to water vapour coming through the deck and being trapped by the felt.
I had a flat roof applied to my shop recently they used felt with large holes all over it then hot mastic for the next layer which flowed through the holes and it was then stuck to the deck with dabs that had voids between them this was to contain any water vapour.