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- User Guidelines - Preparing NHL Mortar - Part 2: Consumption, Protection & FAQ
This second part of the Saint-Astier® User Guidelines covers consumption tables, protection of freshly applied NHL mortars and answers to frequently asked questions.
NHL products are purchased by weight but mixed by volume. Always confirm densities and ratios with the supplier or project specification.
| Binder | Average density | Mix 1:2 | Mix 1:2.5 | Mix 1:3 |
|---|---|---|---|---|
| NHL 5 | 700 kg/m³ | 350 kg | 280 kg | 240 kg |
| NHL 3.5 | 610 kg/m³ | 305 kg | 244 kg | 203 kg |
| NHL 2 | 560 kg/m³ | 280 kg | 224 kg | 186 kg |
| Lime putty | 1,350 kg/m³ | 675 kg | 540 kg | 450 kg |
| OPC / White cement | 1,450 kg/m³ | 725 kg | 580 kg | 483 kg |
Field reminder: Because Saint-Astier® NHL has a low bulk density, weight-for-weight it can produce significantly more mortar than ordinary Portland cement.
Freshly applied NHL mortar is at its most vulnerable between application and full cure. Protection is a fundamental requirement, not an optional step.
Direct sun, heat and strong wind may inhibit hydration and carbonation, leading to shrinkage or friability.
Remedy: use fine-mesh debris netting and mist lightly in hot or windy conditions.
Excessive rainfall, low temperatures or persistent damp can slow the initial set and leave mortars vulnerable to frost.
Remedy: protect wall heads, manage drainage and use scaffold sheeting when needed.
Water expands when freezing. If the pore structure is saturated, the mortar may not be able to accommodate this expansion.
Remedy: cover with hessian and tarpaulins, and provide supplementary heating if necessary.
Wind can significantly reduce the effective surface temperature of fresh mortar, increasing frost risk.
Remedy: use scaffold sheeting on the windward face and record min/max temperatures daily.
| Wind-chill reference Wind speed | +5°C | 0°C | -5°C |
|---|---|---|---|
| 7 km/h | +2°C | -2°C | -7°C |
| 14 km/h | -1°C | -7°C | -12°C |
| 21 km/h | -4°C | -10°C | -16°C |
| 36 km/h | -10°C | -15°C | -23°C |
| 50 km/h | -12°C | -17°C | -26°C |
| 64 km/h | -13°C | -19°C | -28°C |
Answers to common on-site questions about preparing and using Saint-Astier® Natural Hydraulic Lime mortars.
The number indicates the minimum compressive strength at 28 days in N/mm². NHL 2 is the softest and is often used for sensitive historic masonry. NHL 5 is more hydraulic and is suited to more exposed situations.
Yes. Saint-Astier® NHL mortars can be reworked for up to 24 hours. Keep the mortar covered overnight and add as little water as possible when re-mixing.
Excess water is a common cause. Check the sand grading, as fine sands absorb more water. Improve workability through longer mixing rather than adding water.
Use a sharp, well-graded sand from 3 mm down to 0.075 mm, with less than 15% fines between 0.075 and 0.150 mm. Avoid clay-contaminated or mono-granular sands.
Protection should remain until the cured mortar reaches approximately 8% moisture content. Use a calibrated moisture meter rather than relying on visual appearance.
Yes, with suitable precautions. Use scaffold sheeting, monitor wind-chill and provide heating if required. Do not apply if frost is forecast within 48 hours unless proper protection is in place.
Lime putty can improve immediate workability and shorten mixing time, but it may reduce final strength. Do not exceed 10% of NHL binder weight, and do not use it with NHL 2.
Clay can behave as a binder and alter the effective binder-to-aggregate ratio. This can make the mortar unpredictable and potentially too rich.
This guide is provided for general information only. Specifications should always be project-specific and issued by the relevant specifier. Site conditions, substrate type, exposure, sand grading and workmanship must be assessed before application.