MC-Bauchemie Oxal WPw
A breathable, salt-storing WTA restoration render that lets damp, saline masonry keep drying instead of trapping moisture behind a film.
What is it?
A one-component, hydrophobised, highly sulphate-resistant mineral finishing render — the top coat of MC-Bauchemie’s Oxal WTA restoration render system for damp, salt-affected masonry.
Where is it used?
Basements and plinths with rising damp, heritage brick or stone facades, boundary walls near saline groundwater, and any masonry showing efflorescence or flaking plaster.
Why use it?
Its engineered pore structure gives salts somewhere to crystallise other than the wall face, and its high vapour permeability keeps letting residual moisture escape.
How is it applied?
Hand-floated or machine-sprayed over a compatible base render, built up to 15-30mm total system thickness, then cured roughly a day per millimetre before top-coating.
About MC-Bauchemie Oxal WPw
Oxal WPw is the finishing coat in MC-Bauchemie’s Oxal WTA restoration render system, and Space Arc specifies it on damp, salt-laden masonry across Delhi NCR and pan-India heritage and infrastructure work. It solves a problem every conservation contractor knows: decades of contact with saline groundwater or seepage leave old brick and stone saturated with dissolved salts. Ordinary cement plaster seals the surface, the trapped moisture has nowhere to go, and within a season the wall blisters and efflorescence blooms straight back through fresh paint. Oxal WPw does the opposite by design — its fresh mortar carries an air void content of 25 percent or more and its hardened porosity runs to 40 percent or higher, so salts crystallise inside that pore network rather than on the visible face, while high vapour diffusion keeps a drying path open outward.
It ships as a 25kg factory-dry-mixed bag, gauged at 25kg powder to 5.6 litres of water, and finishes as a fine, close-textured coat with a 1mm maximum grain size — fine enough to float or sponge to a heritage elevation, with enough body to cover minor substrate irregularities. It sits over, not instead of, a compatible pore-filling or preparatory base coat from the same Oxal system; together they carry the WTA 2-9-04 classification and CS II strength rating under EN 998-1. It is therefore not a stand-alone patch-repair plaster but the visible, breathable skin of a layered system built for walls where the underlying problem is salt and moisture rather than structural damage.
The technical insight
The mechanism worth understanding is the difference between a sacrificial pore structure and a barrier coating. A waterproof render tries to stop salts reaching the surface; on capillary-saturated old masonry it usually fails partway, and crystallisation pressure just behind the coating is what delaminates the plaster. Oxal WPw’s ≥40 percent total porosity is deliberately coarse and interconnected so salts crystallise well inside the render body, away from the paint film, while its documented high vapour-diffusion rate keeps a continuous drying path open. The trade-off is that the render absorbs and stores salt load over its service life, which is exactly why MC-Bauchemie specifies it as a full 15-30mm system rather than a thin decorative skim — there has to be enough render mass for the pore reservoir to do its job.
Where it is used
- Rising-damp and salt-affected basement and plinth walls
- Heritage brick and stone facade restoration, including protected structures
- Boundary and compound walls exposed to saline groundwater or coastal spray
- Interior walls showing efflorescence, flaking, or hollow plaster
- Bridge abutments and retaining walls carrying salt-loaded moisture
- Industrial plinths near saline process water or chemical storage
- Re-plastering after a horizontal damp-proof-course injection
- Machine-applied restoration on large elevations where coverage speed matters
Key advantages
- High salt storage capacity keeps crystallisation inside the render, not on the visible face
- High vapour diffusion lets residual wall moisture keep drying outward
- Hydrophobised surface sheds driving rain without closing the working pore structure
- Meets WTA data sheet 2-9-04, a recognised benchmark for restoration renders
- Fine 1mm grain gives a smooth, paintable finish for heritage work
- Machine-sprayable, speeding coverage on large elevations versus hand plastering
- One-component, factory-proportioned mix removes on-site mix-design guesswork
- Natural white base takes mineral silicate paints without a separate skim coat
Limitations & considerations
- Manages salt and moisture symptoms, not the source — chronic rising damp still needs a horizontal barrier injection or DPC
- Minimum 15-30mm system build means it isn’t a thin skim-coat or quick patch
- Short ~30-minute working time at 20°C drops further in Delhi NCR summer heat, so batching discipline matters
- Restricted to a 5-30°C application window, needing planning around peak summer and cold winter conditions
- Natural-white finish still needs a compatible mineral topcoat for colour and added weathering
- A specialist layered-system product best left to an authorised applicator, not a DIY patch
Selection & best practice
Batch to the stated 25kg powder to 5.6 litre water ratio and mix mechanically — don’t loosen the mix with extra water, which dilutes the pore structure the product depends on. Apply only over a compatible base coat from the same Oxal system, never onto sound cement plaster or bare wall, and keep to the specified 15-30mm total thickness rather than a cosmetic skim. Work within 5-30°C, shield fresh render from direct sun and wind for the first day, and respect the roughly one-day-per-millimetre interval before top-coating. On genuinely damp walls, pair it with a horizontal damp-proof injection — the render manages salt and vapour, the injection stops the water; specifying only one is the most common reason restoration renders under-perform on-site.
Specifications
| Product type | One-component hydrophobised, highly sulphate-resistant restoration finishing render |
| Standard compliance | WTA data sheet 2-9-04; strength class CS II per EN 998-1 |
| Maximum grain size | 1 mm |
| Mixing ratio | 25 kg powder : 5.6 L clean water |
| Air void content (fresh mortar) | ≥ 25% |
| Total porosity (hardened mortar) | ≥ 40 vol-% |
| Working time | Approx. 30 minutes at 20°C |
| Consumption | Approx. 1.1 kg/m² per mm thickness |
| Pack size / colour / shelf life | 25 kg bag; natural white; 12 months in unopened pack, cool & dry storage |
Industry use cases
Heritage & conservation
Restoration of a colonial-era Lutyens Delhi bungalow facade where the brief called for a breathable, reversible mineral repair, not a sealed render.
Residential basements
A Gurugram basement wall with recurring salt bloom from saline groundwater, replastered over a bonding base coat after the seepage source was fixed.
Boundary & compound walls
An NCR compound wall with plinth-level efflorescence, re-rendered in sections using machine application for faster coverage.
Infrastructure
Bridge abutment masonry exposed to salt-laden runoff, restored alongside crack-injection work in a larger rehabilitation contract.
Institutional buildings
An older institutional building interior wall with flaking, salt-stained plaster, restored to a maintainable, breathable finish.
Frequently asked questions
What does the WTA certification mean for a buyer?
Will Oxal WPw permanently stop rising damp?
Can it go directly onto old cement plaster or a bare wall?
How soon can it be painted?
Does it have to be machine-applied?
How is this different from a waterproof plaster or coating?
How we position MC-Bauchemie Oxal WPw
Oxal WPw is the finishing half of a two-part system: it goes over Oxal VSM WTA, the higher-strength (CS IV) bonding base render in the same Oxal restoration range, and Space Arc typically supplies the pair together. Within the wider Oxal masonry range, injection products like Oxal VP III HS grout cracks and cavities — a different problem on the same wall, not a substitute for this render. Genuine alternatives are limited: WTA-certified, salt-storing restoration renders are a narrow specialist category, and Fosroc’s Indian catalogue doesn’t compete here directly — its Renderoc range targets structural concrete repair mortars, not breathable masonry restoration renders, so it isn’t a like-for-like swap. A specifier is really choosing between restoration-render brands with WTA credentials, and Oxal WPw’s documented porosity and vapour-diffusion data make it easy to defend on a heritage or conservation submission.
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