MC-Bauchemie Oxal WPw WTA
A WTA-certified salt-storage render that lets damp, salt-laden masonry breathe, dry out and hold a finish — instead of blistering and re-efflorescing every monsoon.
What is it?
A factory-mixed, hydrophobized mineral finish render built to the German WTA restoration-plaster guideline, applied as the top coat of MC-Bauchemie’s Oxal system for salt- and moisture-damaged masonry.
Where is it used?
Rising-damp and salt-efflorescence-affected brick, stone and block masonry — heritage facades, basements, plinth walls, boundary walls, godowns and industrial sheds near coastal sites or high water tables across Delhi NCR and India.
Why use it?
Ordinary cement plaster traps migrating salts at the surface, where they crystallise, push off paint and keep re-appearing every monsoon; Oxal WPw WTA’s open pore structure stores those salts harmlessly inside the render while its hydrophobic skin sheds rain, so the wall keeps drying instead of relapsing.
How is it applied?
Hand or machine-applied by trowel or spray over the Oxal porous base coat (spatterdash plus a base render such as Oxal PGP WTA), mixed at 25 kg powder to 5.6 L water, in a minimum 15-20 mm total system thickness, cured and then finished with a breathable paint.
About MC-Bauchemie Oxal WPw WTA
Old masonry across Delhi NCR and much of urban India carries a problem that new-building waterproofing products were never built to solve: rising damp. Groundwater and monsoon moisture move up through brick and stone by capillary action, carrying dissolved chlorides, sulphates and nitrates with them. Plaster over that wall with an ordinary dense cement render and the salts have nowhere to go — they crystallise just beneath or on the surface, pushing off paint, blistering the plaster and staining the wall again within a season or two, no matter how many times it gets replastered. This is exactly the failure mode the German WTA (Wissenschaftlich-Technische Arbeitsgemeinschaft für Bauwerkserhaltung und Denkmalpflege) restoration-render guideline was written to address, and it’s the problem Oxal WPw WTA is engineered around.
Oxal WPw WTA is the finish coat of MC-Bauchemie’s Oxal restoration render system — a factory-mixed, hydrophobized mineral render applied by hand or machine over a porous base coat on salt- and moisture-affected masonry. Rather than sealing the wall, it deliberately stays open: a highly porous structure gives it the capacity to store crystallising salts harmlessly within the render body, away from the visible face, while its hydrophobic skin still sheds wind-driven rain. Space Arc Engineering stocks and applies the Oxal system for heritage facades, basements, plinth walls, boundary walls and industrial sheds across Delhi NCR and pan-India projects where conventional replastering keeps failing on the same damp, salt-loaded wall.
The technical insight
The WTA guideline sets a fundamentally different benchmark than a standard waterproof plaster. It mandates a minimum total porosity in the hardened render (here ≥40 vol.-%) and a minimum air-pore content in the fresh mortar (≥25%), so the cured render carries a network of macropores large enough to physically host crystallising salts without the pressure build-up that blisters ordinary plaster. Hydrophobization is layered on top of that open structure to cut liquid-water uptake from rain without closing the pores to water vapour — so residual moisture already in the wall can still diffuse outward and dry. That combination — porous and salt-absorbing, yet water-repellent and vapour-open — is the opposite design logic to a sealed waterproof coating, which is why the two product types aren’t interchangeable on a genuinely salt-damp wall.
Where it is used
- Finish coat over rising-damp and salt-efflorescence-affected brick, stone and block masonry
- Facade and plinth restoration of heritage buildings and monuments with visible salt blooming
- Basement and below-grade plinth walls with capillary ground moisture
- Boundary and compound walls in coastal zones or areas with saline/brackish groundwater
- Industrial sheds, godowns and warehouse masonry near the coast or with high water tables
- Interior finish coat completing the Oxal WTA system over a spatterdash or porous base render
- Renovation of old lime- or cement-plastered facades that keep re-blistering after replastering
- Temple, gurudwara and institutional masonry with chronic damp staining
Key advantages
- WTA-certified — built to the German restoration-plaster guideline, so it’s engineered specifically for salt-damp masonry rather than adapted from a generic waterproof plaster
- High total porosity (≥40 vol.-%) gives the hardened render real salt-storage capacity, keeping crystallising salts buried inside the coat instead of blooming at the surface
- Hydrophobized finish sheds wind-driven rain while remaining vapour-open, so moisture already inside the wall can keep diffusing out and drying
- CS II strength class per DIN EN 998-1 keeps the render appropriately matched to old, softer masonry rather than over-strong modern renders that trap stress and crack
- Fine 1 mm maximum grain size gives a smooth, paintable finish suited to both heritage facades and everyday plastered walls
- Frost, weathering and moisture resistant for long-term exterior exposure once cured
- Roughly 30-minute pot life at 20°C and a simple 25 kg : 5.6 L mix ratio suit typical Indian site working conditions
- Installed by Space Arc’s trained applicator team, so layer sequencing and thickness — both critical to WTA performance — are executed correctly on site
Limitations & considerations
- Must be installed as part of the full Oxal WTA system (spatterdash/porous base coat plus this finish coat) — it is not a standalone waterproofing skim coat
- Rated performance depends on a minimum total system thickness of 15-20 mm; thinner applications won’t deliver the specified salt-storage porosity
- Does not fix the underlying moisture source — leaking pipework, poor drainage, or a failed damp-proof course still needs separate remediation
- Natural white finish only, and must be overcoated with a breathable mineral or silicate paint rather than any film-forming decorative coating
- Application is temperature-limited to 5-30°C (air, substrate and material), which needs planning around peak Delhi summer heat and monsoon humidity
- As a specialist restoration render it costs more and needs trained applicators, unlike routine cement plaster
Selection & best practice
Hack off all contaminated or blown plaster back to sound masonry well beyond the visible damage line, rake and clean joints, and confirm the substrate is a mineral surface suited to the system. Apply the Oxal base coat first — a spatterdash plus a porous base render such as Oxal PGP WTA — before finishing with WPw WTA at its specified minimum system thickness (15 mm over spatterdash, 20 mm over a porous base render, up to 30 mm total). Avoid over-troweling or polishing the surface, which closes the pore structure and defeats both the salt-storage and breathability the WTA system depends on. Respect the working temperature window of 5-30°C, cure at roughly 1 day per mm of thickness before overcoating, and finish only with a mineral, silicate or other breathable paint. Because incorrect layer sequencing or under-thickness application voids the system’s rated performance, have Space Arc’s applicator team execute the full build-up rather than treating WPw WTA as a standalone skim coat.
Specifications
| Product Type | Factory-mixed, hydrophobized mineral restoration render (WTA-certified finish coat) |
| Compressive Strength Class | CS II per DIN EN 998-1 |
| Maximum Grain Size | 1 mm |
| Mixing Ratio | 25 kg powder : 5.6 L water |
| Air-Pore Content (fresh mortar) | ≥ 25% |
| Total Porosity (hardened mortar) | ≥ 40 vol.-% |
| Total System Layer Thickness | 15-20 mm minimum (per base coat) up to 30 mm maximum |
| Consumption | ≈ 1.1 kg/m² per mm of thickness |
| Pack Size | 25 kg bag |
Industry use cases
Heritage & Conservation
Facade and plinth restoration of old masonry buildings and monuments suffering rising damp and visible salt efflorescence, where the render must stay period-appropriate in texture and colour.
Basements & Plinth Walls
Below-grade and plinth-level masonry in bungalows and commercial buildings with capillary moisture and rising salts from ground contact.
Industrial & Warehouse
Godowns, factory sheds and boundary walls near coastal sites or with saline/brackish groundwater where salt blooming keeps damaging paint finishes.
Religious & Institutional Structures
Temples, gurudwaras and older institutional buildings with thick masonry walls showing chronic damp patches and plaster delamination.
Residential Retrofits
Older bungalows and independent houses in Delhi NCR being renovated where damp-stained walls keep failing repeated cement replastering.
Frequently asked questions
Will Oxal WPw WTA make my wall completely waterproof?
Can WPw WTA be applied directly onto brick or stone as a single coat?
How thick does the render need to be applied?
Will the salt patches and blistering come back after this render is applied?
Can it be painted, and with what kind of paint?
How is this different from a normal waterproofing plaster?
How we position MC-Bauchemie Oxal WPw WTA
Oxal WPw WTA is one part of a designed system, not a solo product — Space Arc pairs it with the Oxal base/spatterdash coats (such as Oxal PGP WTA and Oxal VSM WTA) that go on first, and with Oxal VP I T injection grout and Oxal BS-V injection-hole filler where masonry cracks or voids need consolidating before rendering. Specifying the full Oxal line rather than mixing brands keeps the base coat, render and any grouting chemically and mechanically compatible, which matters for a system whose performance depends on layer sequencing. For rising damp at its source rather than at the wall surface, Fosroc’s Dryzone damp-proof-course injection cream is a genuine complementary option specifiers reach for — but Fosroc does not carry a like-for-like WTA-certified, salt-storage restoration render, so projects needing this specific technology stay within the MC-Bauchemie Oxal range that Space Arc stocks and applies.
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