Builders Tips: Waterproofing A Flat Roof

Working in layers
Should you decide to apply an all-over surface treatment, you will find numerous materials you may use. First you would apply an initial layer of liquid proofing to the roof surface, which you'll be able to reinforce with non-rotting fabric mesh, and then another layer, allowing it to solidify and form a tough, waterproof yet flexible sheet:
1 - Remove any stone chippings and moss or algae from the surface. It's a good idea to apply a suitable fungicide to kill any remaining traces of growth.
2 - Then apply the very first coat of liquid proofing, making use of a soft broom.
3 - If you are using reinforcing mesh, unroll it into the wet waterproofing and stipple it into the surface making use of a wet brush. Overlap the edges of strips by about 2Omm.
4 - When the first coat has dried, apply a second all over the roof, and then a third. You may give this last coat additional protection with a covering of white reflective stone chippings or sharp sand, which you apply when the previous coating is still slightly tacky.

If flashing has merely lifted away from the roof, tap it back in place with a piece of wood. If it has pulled away at the top, where it is tucked into a mortar joint along the wall, the job of repairing it'll involve far more work.

Loose flashings
Where metal flashings have pulled away from a roof/wall junction, rake out the old mortar along the chase into which the flashing fitted. Then reposition the flashing, wedging it into the chase, and repoint with fresh mortar.

Missing flashings
If the flashing is porous or is missing altogether, fit a length of self-adhesive flashing tape. Brush on the special primer initial and leave it to turn tacky. Then cut the flashing tape to length, peel off the release paper and bed the tape in place along the junction. Tamp it down with a block of wood and a hammer to ensure that it forms a proper bond.

By: Jim Smithy

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Brisbane Home Builder is a builder in Brisbane also serving Rockhampton, Gladstone, Bundaberg and Townsville. With over 50 years combined experience they offer home renovations, decking, patios and much more.