Flat roof leaking badly - Cromapol held out awhile until now

[cc120]

If I use the Britannia Aquashield High Build, https://www.rawlinspaints.com/home/...nts/3070-britannia-aquashield-high-build.html, as some gaps/holes could be wider than 3mm, which cheap scrim / alternative could I use under the paint?

Could I paint, put scrim then paint again?

Or should I use the two items below instead:

[URL='https://www.wickes.co.uk/Acrypol-%2B-Waterproofing---Grey-2-5kg/p/167556'] Acrypol + Waterproofing - Grey 2.5Kg[/URL]


https://www.wickes.co.uk/Acrypol-+-Waterproofing---Grey-2-5kg/p/167556
28.00
Quantity:

• 

Acrypol Flexible Reinforcement Scrim Tape - 150Mm X 20M

29.00
Quantity:

Buy together:57.00

 

[cc120]

It is a tar roof.