Waterproofing Products in South Africa, Honestly Compared

The five families of waterproofing product

Bituminous waterproofing — Derbigum and the torch-on family

Derbigum is the name most South Africans know and it is manufactured locally; Index, a.b.e. and several importers supply the same class of product. Within the family the meaningful distinction is not the brand but APP versus SBS and the thickness. APP is the plastic-modified version, harder and more UV-tolerant. SBS is rubber-modified, stays flexible at lower temperatures and tolerates movement better. Both come in 3 mm and 4 mm, both are laid single or double layer, and that choice matters far more than which manufacturer's name is on the roll.

Two layers of 4 mm, correctly lapped, on a roof that does not pond, gives fifteen to twenty years. A single layer laid over a failed system gives three to five. The detail is on torch-on waterproofing.

The place a torch-on roof most often fails is the upstand at the edge, which is why the detail on parapet wall leaks matters more than the name on the roll.

Liquid acrylic, Flexikote and membrane cloth — what the tin does not say

This is the family sold as “waterproofing paint”, and it is where most of the confusion in the category lives. Duram's Flexikote and Rainkote, Dulux Waterproofing, the Prominent and Plascon equivalents and a long tail of house brands all sit here.

The important point is that the tin on its own is not the system. These products are specified to be applied in coats with an open-weave polyester membrane cloth embedded between them. Used that way they are a reinforced liquid membrane and a legitimate, if shorter-lived, waterproofing system. Used without the cloth, as a thick paint, they are a water-shedding coating and nothing more — which is why so many of them are judged to have failed when they were never installed as a system in the first place.

Expect eight to twelve years when reinforced, correctly primed and not ponding; considerably less on a roof that holds water. The full comparison against sheet membrane is on waterproofing paint vs membrane.

Rubberised coatings — liquid rubber, Flash Harry and bitumen emulsion

Black, brush-applied, cheap per litre, and genuinely useful in a narrow role: re-coating an existing bituminous surface that is sound, and sealing gutters. Flash Harry and the a.b.e. range are the familiar names.

The role is narrow because these products have very little elongation and no reinforcement. Applied over a crack that moves, they crack. Applied as the primary waterproofing on a roof, they are the cheapest way to have to do the job again in three years. They are a maintenance product sold at a price that makes people treat them as a system.

Cementitious tanking — Cemflex, SikaTop and the slurries

Cemcrete's Cemflex, the Sika SikaTop range, the a.b.e. cementitious products and the imported equivalents. These are cement-based, mixed with a polymer liquid, and they bond into the substrate rather than forming a film over it. That is the whole point: they work under hydrostatic pressure, where coatings simply get pushed off.

Their limitation is movement. A cementitious tanking coat is rigid, so it belongs on structures that do not flex — retaining walls, basements, planters, pools, water features — and not on a roof deck that expands in the sun. See basement and cellar waterproofing.

Silane and siloxane repellents

Sold as façade creams and water repellents. They are not waterproofing in the membrane sense: they line the capillaries in masonry so liquid water cannot travel through, while leaving the pores open so water vapour still can. On a porous face-brick or plastered elevation taking Cape driven rain this is the correct product, and a film-forming paint is not.

They do nothing about cracks, joints or standing water, and they are invisible once applied, which makes them easy to sell and hard to verify. Get the active content and the expected service life in writing.

On masonry already carrying salts, the repellent goes on only after the salts are dealt with — efflorescence and wall salts explains why.

What contractors use that is not on the shelf — Sikalastic and cavity drain

Three categories sit outside the retail range and are worth knowing about, because they are the right answer often enough:

• Polyurethane liquid membranes — Sikalastic and its competitors. Much higher elongation and UV tolerance than acrylic, which is why they are the sensible choice on balconies and decks that flex and get walked on. Several times the price per square metre.
• Cavity drain membrane — studded HDPE sheet that does not resist water at all, but drains it to a channel and a sump. The reliable answer below ground where the water table is high.
• Bonded sheet membranes for wet areas — thin flexible sheet taped at corners and penetrations, under the tile bed. The only correct way to waterproof a shower. See shower waterproofing.

The full system-by-system breakdown, with what each one costs installed, is on waterproofing systems and waterproofing prices.

How to not waste money in the aisle

1. Identify the fault first. More waterproofing product is bought for rising damp and condensation — neither of which any of it treats — than for anything else. Start at the four types of damp.
2. Buy the system, not the tin. If the data sheet specifies a primer and a membrane cloth, those are not upsells; without them you have bought a different and much weaker product than the one on the label.
3. Check coverage, not price per litre. A 5-litre tin at half the price covering a third of the area is not cheaper.
4. Match elongation to movement. Anything crossing a joint, a crack or a change of material has to stretch. Rigid products on moving substrates is the single most common specification error.
5. Respect the weather window. Most of these products need a dry substrate and a dry cure period measured in days. A Cape winter rarely offers one, which is why so much waterproofing applied in June has failed by August.