Should fibreglass be coated the existing led and felt

Yes is the answer you can use one of the acrypol products designed to be applied over felt and most other surfaces as long you use it correctly As for your lead work I would not better to replace or refit exiting lead also acrypol comes with 15 year guarantee

No, fiberglass needs to be installed to new Osb 3

Hi there, you can use this liquid membrane. Sikafloor®-400N Elastic Sikafloor-400 N Elastic is a one-component, UV resistant, highly elastic, moisture curing polyurethane waterproof membrane. USE Sikafloor-400N Elastic is suitable for applications to most common building substrates including concrete, fibre cement, plasterboard, timber, and some metals. It is suitable for use as a waterproof membrane for wet areas as described in AS 4858:2004 “Wet Area Membranes”. It can be used as a waterproof membrane and coating for: Exposed roofs, decks, terraces, gutters, flashings, walls Tanks, reservoirs and pipes Shower recesses Wet areas Balconies Retaining walls Planter boxes Slab floors CHARACTERISTICS AND ADVANTAGES UV resistant and non-yellowing. Excellent mechanical resistance. Can be made slip resistant. Versatile – can be used for a flexible coating and as a waterproof membrane. Good crack bridging ability. Excellent thermal resistance. Fast curing Good resistance to a wide range of chemicals and detergents Approved in accordance with AS 3740 - 2004 “Waterproofing of wet areas within residential buildings”. Approved in accordance with AS 4020 - 2002 “Approval for Use in Pot

Yes any strong structure as long as it mat coated before application is fine