Liquid rubber vs torch-on vs acrylic: an honest comparison

One says torch-on, because that is what proper waterproofers use. One says a liquid rubber membrane, because it is seamless. One says an acrylic roof coating, and is half the price of the other two. All three are certain. None of them explained why.

Here is the thing that would have saved you the confusion. Each of them recommended the system they install. That is not a conspiracy, it is just how a trade works. So the useful skill is not picking a winner in the abstract, it is knowing what each system is actually for, and then judging which fits the roof you have.

We install one system, Rubber Sealant liquid rubber, on every substrate we work on. We are going to tell you where it is the right answer and where it is not, because a system in the wrong place fails and takes our name with it.

Read across that table and a pattern appears. Torch-on wins on sheer mass, on a big flat empty deck, done by somebody excellent. Liquid rubber wins everywhere the roof gets complicated, which is nearly every residential roof in the Northern Suburbs. Acrylic is not really in the same category and should not be sold as though it were.

It is also why we specify three coats. Not because three sounds thorough, but because three coats at the correct spread rate is what gets the membrane to the thickness the guarantee is written against.

We do not install torch-on. We are honest about why: it is not our system and we are not going to pretend otherwise to win a job.

What we do a great deal of is overlay failed torch-on with liquid rubber, and it is one of our most common jobs. A twelve year old torch-on flat roof in Durbanville, blistered in the middle from trapped moisture, shrunk back at the upstands, splitting along the laps. The old membrane is not the enemy. Once it is cleaned, the blisters cut and treated, the laps and upstands made good and a primer applied, it becomes a perfectly sound substrate for a seamless membrane that then has no joints at all.

That is a fraction of the cost and disruption of stripping the deck, and it removes the failure mode rather than repeating it. The alternative offer, a fresh torch-on layer over the old one, gives you a brand new set of laps in the same places.

1. 1Is the deck sound? If the concrete is spalling or the timber is rotten, no coating of any kind is the answer. Structure first.
2. 2How complicated is the roof? Count the penetrations, upstands, corners, box gutters and abutments. Above about four or five, a seamless liquid system is a materially better bet than anything with laps.
3. 3How much does it move? Metal roofs, timber decks and anything with long spans expand and contract daily. Flexibility matters more than thickness there.
4. 4What is on it already? Failed torch-on, old acrylic, weathered asbestos, rusted metal: each of those changes the preparation, not usually the system.
5. 5Will anybody walk on it? Regular foot traffic needs a protected or trafficable specification, and that has to be said upfront.
6. 6What does the guarantee actually cover, and is the company that issued it going to exist in ten years?

The system matters less than the preparation, and the preparation matters less than whether anybody diagnosed the roof first.

We inspect, diagnose in writing, and specify Rubber Sealant liquid rubber if it is the right answer. Flat roofs and torch-on overlays start from R265 per square metre, metal and tile from R240, asbestos encapsulation from R310, and wall and damp detailing from R290. Three coats, all details taken in, guarantee in writing.

If your roof is a big simple deck where a first class torch-on job would genuinely serve you better, we will say that too, and you should get that quote from somebody who does it every day.