MC-Bauchemie MC-Crete 820
A water-based surface set retarder that lets precasters and architects reveal decorative aggregate to a controlled depth, cleanly and repeatably, on both formwork faces and green concrete.
What is it?
A liquid, water-based surface set retarder (surface deactivator) from MC-Bauchemie that delays hardening of the outermost cement paste so the aggregate underneath can be washed out to a chosen depth.
Where is it used?
Architectural precast panels, precast and in-situ retaining walls, decorative paving and landscape concrete, and feature wall production where an exposed-aggregate look is specified.
Why use it?
It gives a consistent, gradable exposed-aggregate finish (light, medium or deep) without acid etching, honeycombing or hand-tooling, so panels match batch to batch.
How is it applied?
Brush or spray a single uniform film onto the formwork inner face before pouring, or onto freshly stripped green concrete within an hour of demoulding, then wash off after 12 to 24 hours.
About MC-Bauchemie MC-Crete 820
MC-Crete 820 is MC-Bauchemie’s answer to a problem every precaster and decorative-concrete contractor knows well: how to expose the aggregate for a textured architectural finish without damaging the concrete or fighting inconsistent results from panel to panel. It is a water-based surface set retarder, sometimes called a surface deactivator, that you apply as a thin liquid film. Wherever the film sits, the very top layer of cement paste is prevented from hardening on schedule while the rest of the concrete cures normally. Once the element has gained strength, that soft skin of paste is simply washed away to reveal the sand and stone beneath, giving the crisp exposed-aggregate look designers ask for.
For Indian projects, the appeal is control and repeatability. The product is supplied in retardation grades that let you target a set exposure depth, so a facade specified with a medium etch on drawing one behaves the same on the hundredth panel off the bed. Because it is water-based, it works with common formwork release agents and suits both the negative method (applied to the mould face for face-down casting) and the positive method (applied to green concrete for face-up work and in-situ walls). Space Arc Engineering supplies MC-Crete 820 as an authorised MC-Bauchemie distributor and can support application across Delhi NCR and pan-India, which matters when a finish this visible depends on getting the film weight and wash-off timing right.
The technical insight
The mechanism is chemical, not mechanical. A conventional set retarder slows cement hydration throughout a mix; MC-Crete 820 instead confines that effect to a paper-thin zone at the surface. The active chemistry keeps the calcium-silicate-hydrate reaction in the top skin of paste from developing, so while the body of the element sets and gains structural strength on its normal curve, the paste in contact with the retarder film stays soft and unbonded. That soft layer only extends a few millimetres deep, and the depth is what the grade controls: a lighter formulation deactivates paste to roughly 2 to 4 mm, a medium grade to 4 to 7 mm, and a deep grade to 7 to 10 mm. When you wash the surface, the unhydrated paste flushes out and the aggregate that was embedded within that zone is left standing proud, uniformly, across the whole face. Because the retarder never penetrates deeper than its rated zone, the parent concrete keeps its full design strength and durability. Timing is the other half of the physics: wash too early and you cut past the retarded band into sound concrete; wait too long and even the retarded paste starts to knit, making it hard to remove. The 12-to-24-hour window and a high-pressure jet are what turn that chemistry into a clean, predictable finish.
Where it is used
- Architectural precast facade and cladding panels needing a uniform exposed-aggregate texture
- Precast retaining wall blocks and modular wall units cast face-down against treated moulds
- In-situ concrete retaining walls where a decorative aggregate face is specified
- Decorative concrete paving, plazas and landscape hardscape features
- Precast bridge parapets, balustrades and boundary panels
- Feature walls and interior/exterior wall panels in commercial and institutional projects
- Face-up and face-down precast production where matched batches must repeat over long runs
- Signature entrance walls and monument concrete requiring a controlled etch depth
Key advantages
- Delivers a graded, repeatable exposure depth (light, medium or deep) so panels match across a full production run
- Avoids acid etching and its handling, disposal and surface-damage risks
- Water-based formulation that is easy to brush or spray and compatible with standard formwork release agents
- Works for both negative (mould-face) and positive (green-concrete) methods, covering precast and in-situ work
- Leaves the parent concrete at full design strength because retardation is confined to a shallow surface zone
- Economical coverage, with one litre treating roughly 4 to 10 square metres depending on grade
- Backed by MC-Bauchemie technical support and Space Arc application guidance for consistent site results
- Produces a genuinely architectural finish that hand-tooling or sandblasting struggles to match for uniformity
Limitations & considerations
- Wash-off timing is critical; too early cuts into sound concrete, too late lets the retarded paste re-bond and resist removal
- Requires high-pressure water jetting (roughly 80 to 120 bar) and a stiff brush, so a wash-out facility and water management are needed
- The exposed finish is only as consistent as the mix design and aggregate; poorly graded or dirty aggregate shows immediately
- Not a set retarder for the concrete body; it only affects the surface skin and is not a substitute for a mix admixture
- Film weight must be uniform, as heavy or thin patches translate directly into uneven exposure on the finished face
- Wash water carries cement fines and must be collected and disposed of responsibly, especially near drains or landscaping
Selection & best practice
Choose the grade to match the specified etch: light for a fine sand-textured look, deep where large decorative aggregate must stand proud, and always cast a sample panel first to confirm the depth against a real mix. Apply a single, uniform, continuous film at 0.1 to 0.3 litres per square metre; on the negative method coat the mould face over the release agent before placing concrete, and on the positive method spray the green concrete within about an hour of stripping. Protect treated surfaces from rain before the pour or before wash-off, since water will disturb the film or start premature washing. Wash between 12 and 24 hours after placement using a stiff brush and a high-pressure jet, working consistently across the panel so exposure stays even, and adjust the exact hour based on ambient temperature and how the sample behaved. Collect and dispose of the cement-laden wash water properly. For large facade orders, lock in one grade, one film rate and one wash-off window as a written method statement so every panel repeats.
Specifications
| Product type | Water-based liquid surface set retarder (surface deactivator) |
| Application method | Brush or spray, single uniform continuous film |
| Application rate | 0.1 to 0.3 litres per square metre (grade dependent) |
| Coverage | Approx. 4 to 10 square metres per litre (grade and surface absorption dependent) |
| Light exposure grade | 2 to 4 mm aggregate exposure |
| Medium exposure grade | 4 to 7 mm aggregate exposure |
| Deep exposure grade | 7 to 10 mm aggregate exposure |
| Wash-off timing | 12 to 24 hours after placement, using stiff brush and high-pressure water jet (approx. 80 to 120 bar) |
| Packaging | 25-litre and 200-litre drums |
Industry use cases
Architectural precast
Facade and cladding panel manufacturers use the mould-face method to reveal a uniform aggregate texture that repeats identically across a full glazing bay or curtain of panels.
Infrastructure and civil
Precast bridge parapets, balustrades and in-situ retaining walls get a durable decorative aggregate face without acid etching or after-the-fact tooling.
Landscape and urban design
Plazas, promenades and hardscape paving take a slip-textured exposed-aggregate finish that also improves grip underfoot in public spaces.
Commercial and institutional buildings
Feature walls, entrance monuments and boundary walls use a chosen etch depth to create a signature stone-in-concrete look on visible elevations.
Precast production yards
High-volume face-up and face-down casting lines rely on the graded retardation to keep long production runs consistent panel to panel.
Frequently asked questions
Is MC-Crete 820 the same as a normal concrete set retarder?
How do I decide between the light, medium and deep grades?
When exactly should I wash off the retarded surface?
Can I use it on both the mould and on already-cast concrete?
Will it work over my formwork release agent?
What coverage and pack sizes should I plan for?
How we position MC-Bauchemie MC-Crete 820
MC-Crete 820 sits in MC-Bauchemie’s MC-Crete family of concrete and formwork products, alongside their formwork release agents which pair with it directly on the mould face for the negative casting method. For teams standardising on Fosroc, the closest equivalent in our range is Fosroc Conplast SR, a water-based surface retarder built for the same exposed-aggregate job in face-up and face-down precast; either brand achieves a comparable result, so the choice usually follows an existing project specification or approved-vendor list. Where a project also needs curing, sealing or protective coating of the finished aggregate face, we can pair MC-Crete 820 with curing compounds and decorative concrete sealers from our Fosroc and other brand lines. Space Arc supplies and applies across Delhi NCR and pan-India, so we can match the retarder, release agent and finishing system as one coordinated package.
Fosroc Conplast SR — Choose Conplast SR when the project spec or approved-vendor list is standardised on Fosroc, as it delivers the same water-based exposed-aggregate finish for face-up and face-down precast work.
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Source MC-Bauchemie MC-Crete 820 for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.