Roundtower NHL 5 is a high-strength Natural Hydraulic Lime (NHL) designed for demanding applications where increased durability, faster setting times, and higher weather resistance are required. Manufactured from naturally hydraulic limestone and conforming to EN 459-1, NHL 5 provides a breathable, cement-free binder suitable for exposed masonry, limecrete floors, retaining walls, chimney work, and severe weathering environments.
Unlike cement mortars, NHL 5 remains vapour permeable, allowing traditional masonry to continue managing moisture through evaporation and capillary movement. This makes it particularly suitable for older solid-wall buildings where breathability remains important, but where greater strength and weather resistance are needed than would typically be achieved with NHL 2 or NHL 3.5.
Technical Data
| Property | Value |
|---|---|
| Product Type | Natural Hydraulic Lime (NHL 5) |
| Standard | EN 459-1 |
| 28 Day Compressive Strength | Approx. 6.2 MPa |
| 7 Day Compressive Strength | Approx. 3.54 MPa |
| Free Lime Content | Approx. 21.9% |
| Initial Set | Approx. 312 minutes |
| Vapour Behaviour | Vapour permeable |
| Bulk Density | Approx. 0.775 g/cm³ |
| Real Density | Approx. 2.75 g/cm³ |
| Fire Classification | Non-combustible |
| Packaging | 25kg bags |
Key Benefits
High Strength & Durability
NHL 5 is the strongest commonly available natural hydraulic lime grade and is suitable for:
- exposed masonry,
- limecrete floors,
- chimney stacks,
- retaining walls,
- and marine or coastal environments.
Breathable & Vapour Open
Unlike dense cement mortars, NHL 5 remains vapour permeable, allowing moisture vapour to evaporate safely from the wall structure rather than becoming trapped within masonry.
Suitable for Exposed Conditions
The higher hydraulic set makes NHL 5 particularly suitable for:
- driving rain exposure,
- frost-prone locations,
- coastal environments,
- and permanently damp conditions.
More Flexible Than Cement
Although stronger than NHL 2 and NHL 3.5, NHL 5 still remains more flexible and moisture tolerant than OPC cement mortars, reducing stress concentrations within traditional masonry.
Cement-Free & Compatible With Historic Masonry
NHL 5 contains no Portland cement and remains compatible with:
- stone masonry,
- traditional brickwork,
- lime-built structures,
- and breathable construction systems.
Typical Applications
- Limecrete floors
- Chimney stacks & flaunching
- Wall copings & parapets
- Exposed rendering
- Coastal & marine masonry
- Retaining walls
- Foundations
- Structural masonry repairs
- Damp-prone buildings
Why Use NHL 5?
Traditional masonry buildings manage moisture through vapour diffusion and capillary drying. Dense cement mortars can trap moisture within stone and brickwork, increasing the risk of:
- freeze-thaw damage,
- trapped damp,
- salt accumulation,
- and masonry deterioration.
NHL 5 provides a balance between:
- breathability,
- durability,
- strength,
- and weather resistance.
This makes it particularly suitable where greater exposure or loading conditions require a stronger lime binder while still maintaining vapour permeability throughout the wall assembly.
Typical Mix Ratios
| Application | Typical Mix Ratio |
|---|---|
| General Masonry | 2.5:1 sharp sand : NHL 5 |
| Pointing | 2.5:1 sharp sand : NHL 5 |
| Limecrete Floors | 2.5:1 aggregate/sand : NHL 5 |
| Exposed Render | 2.5:1 sharp sand : NHL 5 |
| Copings & Chimneys | 2:1 sharp sand : NHL 5 |
Mixes should always be adjusted depending on:
- exposure level,
- aggregate grading,
- masonry type,
- and substrate strength.
Installation Overview
1. Surface Preparation
Substrates should be:
- clean,
- stable,
- dust free,
- and appropriately dampened before application.
2. Mixing
Use clean sharp well-graded aggregates and only enough water to achieve a workable consistency.
Overwatering can reduce strength and increase shrinkage risk.
3. Application
Suitable for:
- bedding,
- pointing,
- rendering,
- masonry construction,
- and limecrete applications.
4. Curing
Fresh lime work should be protected from:
- frost,
- rapid drying,
- heavy rain,
- and direct sunlight
during curing.
5. Storage
Store dry and off the ground. Use within the manufacturer’s recommended shelf life.
