Prompt Natural Cement is a fast-setting natural cement manufactured by Vicat in France from argillaceous limestone fired at relatively low temperatures and ground without Portland cement or synthetic additives. Produced for over 150 years, it remains one of the only true natural cements still manufactured at industrial scale.
Unlike OPC cement, Prompt remains vapour open and compatible with lime-based construction while offering extremely rapid setting, high early strength, and excellent resistance to water and salts. This makes it particularly suitable for heritage restoration, tanking, rapid repairs, marine environments, and gauging lime mortars.
Technical Data
| Property | Value |
|---|---|
| Product Type | Natural Cement |
| Manufacturer | Vicat |
| Raw Material | Argillaceous limestone |
| Setting Time | Approx. 1–5 minutes |
| 24 Hour Compressive Strength | Up to 20 MPa |
| Vapour Behaviour | Vapour permeable |
| Colour | Warm ochre/light tan |
| Packaging | 25kg bags |
Key Benefits
Extremely Fast Setting
Sets within minutes, making it suitable for:
- rapid repairs,
- fixing work,
- water ingress,
- and emergency stabilisation.
Breathable & Lime Compatible
Remains vapour open and can be blended with:
- lime putty,
- NHL mortars,
- and traditional lime systems.
High Early Strength
Develops rapid strength gain suitable for:
- structural patch repairs,
- tanking,
- chimney repairs,
- and exposed masonry.
Water & Salt Resistant
Performs well in:
- damp environments,
- marine applications,
- basements,
- and tidal zones.
Natural & Cement-Free
Contains:
- no Portland cement,
- no fly ash,
- and no synthetic additives.
Typical Applications
- Tanking & waterproofing
- Rapid masonry repair
- Marine & coastal work
- Chimney repairs
- Lime mortar gauging
- Basement repairs
- Roman cement restoration
- Structural patch repairs
Why Use Prompt?
Prompt combines:
- rapid setting,
- breathability,
- moisture tolerance,
- and compatibility with traditional masonry.
Unlike dense OPC cement, it allows moisture vapour to move through the structure while still providing extremely fast curing and high durability.
This makes it particularly suitable for:
- heritage buildings,
- damp environments,
- and specialist conservation repairs.
Typical Mix Ratios
| Application | Typical Mix Ratio |
|---|---|
| Rapid Repair Mortar | 2:1 sharp sand : Prompt |
| Tanking Render | 1:1 sand : Prompt |
| Gauging NHL Mortars | Small % Prompt added to NHL mix |
Mixes should always be adjusted depending on:
- required set time,
- substrate,
- and exposure conditions.
Installation Overview
1. Surface Preparation
Substrates should be:
- stable,
- clean,
- dust free,
- and dampened before application.
2. Mixing
Only mix small batches and apply immediately due to the rapid setting time.
3. Application
Suitable for:
- repairs,
- rendering,
- tanking,
- fixing,
- and specialist masonry work.
4. Curing
Protect fresh work from:
- frost,
- rapid drying,
- and excessive heat.
5. Storage
Store dry and sealed within the manufacturer’s recommended shelf life.
