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How to Waterproof an External Balcony

There are many ways and products to waterproof an external balcony - if the screed timber is in place than a hard-wearing durable product will have to be used.

If we are using a cold applied liquid product (depending on the finish and product used) the final coat will need either a sand finish for foot traffic or tiles, matting, composite/timber decking.

The build-up or waterproof layers whether it is a mastic asphalt, rubber, GRP(glass reinforced plastic), liquid coating, rubber system is the same as with a roof, only some slight changes will be put in place.

With regards to mastic asphalt - this would need to be a heavier grade (i.e.: rec-duty/pave grade) with either solar coating or left with a 3mm granite built into the asphalt.

Felt roofing can also be applied in a built-up system with either a further top layer of walkway felt applied once the system has been put in place.

Single applied membranes such as single ply/rubber roof systems will need a matting, decking, or easy grass finish for highly foot trafficked areas, as these two systems are highly susceptible to punctures with a lot of foot movement.

GRP systems require a 600g matting embedded into the two-part resin, then the top UV coating added or roof tiles etc laid on top of the system.

GRP and mastic asphalt are the two systems best suited to balcony types as those are the two hardest wearing and most robust systems in the marketplace to date.

Detailing around handrail posts are similar to all roof SVP’s (soil vent pipes), the upstands as well as the perimeter details must all be 150mm above the balcony system.

A common mistake on all balconies is the detail, where the upstands are not above the ‘leisure deck’ surface and a damp splash back accrues at the wall junctions. With the lack of spaces, the correct system must be put into place to allow for all these changes.

If you need any more information about waterproofing external balconies, Southern Liquid Systems would be delighted to help you. Just call us on 0207 7818153 and one of our team will be happy to help you.