Type A · Barrier protection

Spray applied tanking systems

Spray applied tanking puts a continuous, seamless barrier onto the structure. Because it is sprayed rather than laid, it follows complex geometry without lap joints — which makes it a genuinely better answer than sheet or hand-applied systems on the vaulted, irregular substructures common under Victorian London.

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The system in section

What is actually behind the wall.

EXTERNAL GROUND LEVEL MODEST, KNOWN HEAD 30m TO THE RIG — 230V ONE CONTINUOUS PASS FINISHED ROOM 1 2 3 4 5 6
  1. Prepared substrate. Old finishes and any failed historic tanking taken off back to sound masonry. A barrier is only as good as what it is stuck to, and spraying a new coat over a failing one simply inherits the failure.
  2. Cementitious fillet. Formed in the internal corner so the barrier turns a radius rather than a right angle. A sharp internal corner is a thin spot in any coating, and thin spots are where the first pinhole appears.
  3. The barrier coat. HydraFlex, sprayed in one continuous pass at uniform thickness. There are no laps and no cold joints anywhere in the run — which is the entire reason to spray rather than brush on a vaulted or irregular substructure.
  4. Renovation plaster. Salt-resistant finish over the barrier. Ordinary gypsum on a wall that has carried damp for a century blows within a couple of winters.
  5. Screed over the barrier. The floor build-up sits on top of the coat, so the barrier is continuous under the whole room rather than stopping at the wall line.
  6. Sprayed from a peristaltic pump. The rig stays up at the top of the stairs — 30 metres of hose and a normal 230V socket — so no plant sits in the room being coated and nothing heavy is carried down into the cellar.
A Type A barrier in section. Sprayed in one continuous pass, the coat has no laps and no cold joints — which is the whole argument for it on vaulted and irregular substructures.

Where spraying wins

Hand application leaves laps, and laps are where barrier systems fail. On a flat, square wall that is manageable. On a barrel-vaulted coal cellar with arched openings, stepped haunches and a dozen changes of plane, it is a long list of vulnerable joints.

A sprayed system covers all of it in a uniform thickness with no joints at all, and it does so quickly — which matters when the structure is exposed and the weather is not on your side.

Outside is better, when outside is available

A barrier can go on either face of a wall, and that choice matters more than the material does. Applied externally it sits on the positive side — the side the water is on — and ground water presses it against the structure. Applied internally it sits on the negative side, where the same pressure spends the life of the building trying to push it back off. Given a free choice, every barrier system would go on the outside.

You rarely get a free choice. An existing London cellar has a pavement, a neighbour or somebody's garden on the far side of the wall, and excavating to reach it would be a larger job than the waterproofing. That is why our Type A work is usually internal and usually sprayed: the constraint is access, not preference, and a sprayed coat is the best answer available on the face we can actually reach.

Where there is a dig — a new basement box, an underpinned extension, a lowered floor with the excavation still open — the answer changes, and so does the material. On a new wall that is flat and regular, a self-adhesive sheet on the outside face is the stronger system, and the objection to sheet stops applying: the laps fall in straight runs where they are designed to, rather than round an arch. We use Wykamol SureProof for that, and it is in the materials below.

Both are Type A and both are barrier protection under BS 8102. Which one is right is settled by whether anyone can get to the outside of your wall — a question about your site rather than about waterproofing, and one we answer at survey before recommending either.

What it demands in return

A barrier system is only as good as what it is stuck to. The substrate has to be sound, clean and properly prepared, and any existing failed tanking generally has to come off rather than be sprayed over. Where the structure is moving, or where the head of water is high and not fully understood, Type A is the wrong choice and we will say so — a barrier that fails has no second line behind it.

This is the honest limit of the system, and it is the reason we survey properly before recommending it.

The rig, and why it matters

We spray with an InoBEAM M8 peristaltic pump. The pump type is not a detail — it decides what can be sprayed and what the coat is like when it lands. In a peristaltic pump the material never touches an impeller or a piston; a roller squeezes it along the inside of a hose. A two-part cementitious membrane with crystalline additives arrives at the wall chemically as it left the hopper, rather than sheared by the pump on the way.

It delivers up to 8 litres a minute at 15 bar, through 30 metres of hose and 20 metres of lift, off a normal 230V socket. That combination is what makes it usable in somebody's home: the rig stays at the top of the stairs, nothing heavy is carried down into a Victorian cellar, no plant sits in the room being coated, and there is no generator running outside a family house all day.

The practical result is a whole vaulted cellar going on in one uninterrupted pass at a consistent film thickness. No cold joints where a bucket ran out, no laps where a brush had to stop and start, and a uniform build over arches and stepped haunches that hand application cannot match. The same pump also handles grouts and injection mortars, so structural repair and waterproofing happen on one visit rather than as two contractors blaming each other.

Where we use it

Sound structures with a modest, well-characterised head of water; vaulted and irregular cellars where jointing would otherwise be extensive; and as part of a combined approach where a barrier to one element sits alongside drained protection elsewhere.

On site · our own photographs

A barrier going on the side you can almost never reach.

Every other photograph of Type A work on this site would be of an internal coat, because that is what an existing cellar allows. This was a job with the dig still open, so the membrane went where a barrier actually wants to be — on the outside, with the ground on the other side of it.

A shored and propped excavation alongside a basement wall, with timber walings and adjustable steel props, before waterproofing is applied
The excavation, shored and propped before anything is applied. Getting to this face of a wall is most of the cost, which is why external work only makes sense when there is already a dig.
A worker applying black self-adhesive waterproofing membrane to the outside face of a basement wall in an open excavation
The membrane going on. Cold applied and self-adhesive, so there is no torch, no gas and no hot works in an excavation under somebody’s house.
Black self-adhesive membrane on a basement wall showing printed white guide lines that set the overlap between adjacent sheets
The printed guide lines set the width of every lap. A barrier is only as continuous as its overlaps, and this is what stops that becoming a matter of judgement at four in the afternoon.
The protective release liner being peeled back from self-adhesive membrane where it is dressed into an internal corner
The release liner coming off at a corner. Corners are dressed as a detail in their own right rather than folded — the same discipline as the internal work, on the opposite face.
Self-adhesive membrane running down a basement wall and turning onto the floor slab to form a continuous wall-to-floor junction
The sheet turned off the wall and onto the slab. The wall-to-floor junction is where barrier systems are won or lost, and it is continuous here before anything is backfilled against it.

Swipe for the rest → 5 photographs

Systems and materials

What we install, and why that one.

We specify Wykamol systems for this work. Every product below carries its own datasheet and, where it exists, a BBA certificate — read them rather than taking our word for it.

Wykamol HydraFlex two-part flexible tanking membrane in a 20kg tub

Flexible tanking membrane

Wykamol HydraFlex

A two-part cementitious tanking membrane — powder and a high-concentration polymer — that stays flexible once cured. That flexibility is the reason we specify it over a rigid slurry on older masonry: it bridges cracks in the substrate rather than telegraphing them, and it keeps doing so down to −5°C. It is thixotropic, which is what makes it behave properly through a spray line instead of running off a vaulted soffit.

  • Two-component, elastomeric
  • Crack-bridging to −5°C
  • Radon barrier tested
  • 20kg unit, up to 6m²
Wykamol Technoseal liquid damp proof membrane

Damp proof membrane

Wykamol Technoseal DPM

A liquid-applied damp proof membrane for floors and for the wall-to-floor junction, where a solid floor meets a wall that has no continuous DPC. It is the material we reach for when the problem is a specific interface rather than a whole tanked box, and it links a new floor DPM back into the wall system so the two are actually continuous rather than merely adjacent.

  • Liquid applied
  • Floor and junction detailing
  • Black and white grades
Wykamol SureProof self-adhesive membrane applied to the outside face of a basement wall and turned onto the slab

External barrier — new build

Wykamol SureProof Membrane

A sheet, not a spray, and the exception that proves the rule. Every other barrier we fit goes on the inside of a structure that already exists; this one goes on the outside of a new one, in the open excavation, before anything is backfilled. That is the positive side of the wall — water pressure holds the membrane on rather than trying to peel it off — and an open dig is the only chance a building ever gives you to work there. We specify it on new basement boxes and underpinned extensions where there is a dig to work in. It is no use whatever on a Victorian cellar with a neighbour on the far side of the wall, which is most of what we do, and that is exactly why it sits here alongside the sprayed systems rather than instead of them. The primer is not optional and the laps are the job.

  • Self-adhesive, cold applied
  • Cross-laminated HDPE on polymer modified bitumen
  • External, below ground, new build
  • BS 8102 Grades 2 and 3
  • 1.05 × 19.05m roll, 20m²
Wykamol HydraDry Universal Mortar bag

Fillets, making good, penetrations

Wykamol HydraDry Universal Mortar

A waterproof mortar for the work either side of the membrane: forming the fillet at the wall-to-floor junction, making good around service penetrations, and packing out a substrate that is too irregular to take a barrier coat. Unglamorous, and it is where a Type A system is usually won or lost — a barrier is only as continuous as the corner it turns.

  • Waterproof cementitious mortar
  • Fillets and penetrations
  • Substrate preparation

Technical downloads

The paperwork behind the specification.

The full technical library, including the drawings manual →

Common questions

What people ask us about spray applied tanking.

Is sprayed tanking better than brush-applied?

On coverage, yes, and the reason is joints. A brush has to stop and start, and every stop is a lap; on a barrel-vaulted cellar with arched openings and a dozen changes of plane that is a long list of vulnerable lines. A sprayed coat goes on in one pass at uniform thickness with no laps at all. What spraying does not do is rescue bad preparation — a sprayed coat over a dusty or unsound substrate fails exactly as fast as a brushed one, and rather sooner than people expect. The preparation is still the job; spraying just makes the coat itself better.

Is basement tanking the same as waterproofing?

Basement tanking is one kind of waterproofing, not a synonym for it. Tanking is BS 8102 Type A: a continuous barrier bonded to the structure, which resists water. Waterproofing also covers Type B, where the concrete structure itself does the work, and Type C, where a drained membrane collects water and removes it instead of resisting it. Tanking is the right answer on a sound structure with a modest and well-understood head of water, and the wrong one where the head is high or the substrate is a hundred and thirty years old and still moving. Ask which type is being proposed and why — "tanking" on a quotation with no reasoning behind it is a word, not a design.

Is tanking a permanent fix?

It can be, provided the design was right for the water and the substrate was properly prepared. The failure mode to understand is that a barrier system has no redundancy: if it develops a defect, water arrives in the room, and locating the defect behind a finished wall is difficult. That is why we do not recommend Type A where the head of water is high or where the structure is likely to move.

Can you tank over existing failed tanking?

Usually not. A new barrier bonded to a failing one inherits the failure, and the original problem — whatever caused the first system to let go — is still there. In most cases the old system has to be removed and the substrate prepared back to something sound. If that is not practical, drained protection is normally the better route.

How long does spray applied tanking take?

The spraying itself is fast, often a day or two for a typical domestic cellar. Preparation is the longer part — removing old finishes and failed systems, making good the substrate, and dealing with anything the survey found. Expect the preparation to take several times as long as the application.

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Where we work

Across London and Surrey.

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