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Ponding on felt roof ( concrete underneath)

I have a commercial flat roof of 1000 sqm. Its good built up felt on a solid concrete base ( roof underneath). But in one corner there is ponding ( several large puddles) covering a 13m x 6m area - 10mm deep ( max 15mm) and has started to leak.
Question is:- fill in the pond depression before re felting or EPDM as is ?
To overlay with EPDM is possible, but I worry it will not seal well at the edges with the felt ( as I would not encapsulate the whole roof in EPDM) - and ( years later) water will seep under again.
To multi layer on new felt till the puddle has gone is possible - but its a random height repair - and I may make an island, instead of a puddle - and just push the puddle elsewhere.
Flooding level with bitumen is an option ( and cap sheet over) , but rare to find someone to do hot bitumen.
Level off with cement / mortar is easier to do, and then cap sheet over the top is my preferred option. Felt is also easily repaired in the future if necessary, so is appealing.
How would you solve this ponding issue in a leaking, felt on concrete roof ?
Would you be happy with mortar, level off and re felt ? Will the cement stick to the old felt enough to be a secure base for the new cap sheets ? Or will I be re felting onto a ' loose blob' of cement ? Thanks !

1 Answer from a MyBuilder Roofer

Best Answer

I personally would strip a workable area then prime the indentation then screed over till it is level with the area you have stripped then allow to dry prime ready to refelt
Any questions please don't hesitate to contact me
Many thanks Dominic


Answered 5th Aug 2017

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