How to apply liquid rubber properly, step by step

We get called to look at failed liquid rubber roofs perhaps a dozen times a year. In every single case so far, the product was fine and the process was not. It was applied over a surface that was never properly cleaned, or without primer, or with primer meant for a different surface, or in two coats instead of three, or into the first coat before it had cured.

So here is the sequence, in the order we do it, written for somebody who is going to do their own garage or outbuilding. If you want the certified system with the full guarantee behind it, that has to be applied and certified by an approved applicator, which is a separate thing.

The surface has to be clean, sound and dry. Sweep it, wash off dirt, algae and chalking, and let it dry properly. Every bit of loose rust, flaking paint, blistered old coating and lifting lap has to come off, because your new membrane will be exactly as well attached as whatever is underneath it.

• Bonding Liquid Super+ on concrete, screed, plaster, brick, roof tile, Harvey tile, slate, old torch-on, sound painted surfaces and wood. About 6 m² a litre.
• Etch Primer Rust Supreme on every kind of metal: raw steel, galvanised, Chromadek, IBR, corrugated, zinc, and painted metal too. About 6 m² a litre, more on pitted or rusted sheeting.
• Never both, never neither, and never the wrong one. Galvanised sheeting primed with a masonry bonding liquid is the single most common way to waste a weekend and a drum.

One coat of primer across the whole area, not just the leaky bit. Let it do what the label says before the sealant goes on.

This is the step that separates a professional job from a DIY one, and it costs nothing but patience. Before you coat the open field of the roof, go around and treat every weak point on its own: every bolt head, screw, washer, lap, ridge, valley, upstand, flashing, pipe penetration and crack.

Work the sealant into and around each one with a brush so there are no air pockets, then let it set. Those details are where water enters. The middle of a sheet almost never leaks.

Brush or roller, straight from the drum, no thinning. Coat one, cure. Coat two, cure. Coat three. Cross the direction of each coat over the last one so you cannot leave a thin lane. Work in the cool of the morning, not onto a metal roof at two in the afternoon, and stop early enough that the last coat is not curing through the night dew.

Two coats is not three coats with a saving. It is a different, weaker product that happens to look identical for about eighteen months.

Do not apply into rain, onto a damp surface, or when rain is forecast within the curing window. A water-based product that has not cured yet will simply wash off, and you will watch it go.

1. 1No primer. The membrane is perfect and it is not attached to anything.
2. 2The wrong primer. Masonry bonding liquid on metal, or etch primer on concrete.
3. 3Two coats instead of three, usually because the drums ran short.
4. 4Coating over rust, blisters, chalking paint or lifting laps that should have come off first.
5. 5Working too hot, too late, or into weather, so a coat never properly cured.

Every one of those is free to avoid on the day and expensive to fix afterwards, because fixing it means going back to a sound surface and starting again.