Roundtower NHL 3.5 Grey is a moderately hydraulic natural lime designed for breathable masonry, pointing, plastering, and rendering applications where a traditional grey lime finish is required. Manufactured to EN 459-1 standards, NHL 3.5 Grey provides an effective balance between strength, flexibility, vapour permeability, and durability, making it one of the most versatile limes for both restoration and breathable new-build construction.
Compared to NHL 2, NHL 3.5 Grey develops higher early and long-term strength, making it more suitable for exposed external work and general masonry applications. At the same time, it remains significantly more breathable and flexible than cement mortars, allowing traditional masonry to continue managing moisture naturally through vapour diffusion and capillary drying.
Technical Data
| Property | Value |
|---|---|
| Product Type | Natural Hydraulic Lime (NHL 3.5 Grey) |
| Standard | EN 459-1 |
| 28 Day Compressive Strength | Approx. 4.27 MPa |
| 7 Day Compressive Strength | Approx. 2.16 MPa |
| Free Lime Content | Approx. 27.7% |
| Initial Set | Approx. 975 minutes |
| Vapour Behaviour | Vapour permeable & breathable |
| Bulk Density | Approx. 0.643 g/cm³ |
| Real Density | Approx. 2.68 g/cm³ |
| Colour | Natural grey |
| Packaging | 25kg bags |
Key Benefits
Breathable & Vapour Open
NHL 3.5 Grey allows moisture vapour to move safely through the wall structure, helping reduce the risk of trapped damp, condensation, and masonry decay within traditional solid-wall buildings.
Balanced Strength & Flexibility
Provides greater durability and weather resistance than NHL 2 while still remaining more flexible and moisture tolerant than OPC cement mortars. This balance makes it suitable for most general masonry and external render applications.
Traditional Grey Finish
The natural grey tone makes it particularly suitable for:
- traditional stonework,
- historic masonry repairs,
- conservation projects,
- and mortar matching where a softer natural grey finish is desired.
Suitable for Internal & External Use
Commonly used for:
- pointing,
- rendering,
- bedding mortars,
- plastering,
- and masonry repairs
in both traditional and breathable new-build construction.
Improved Workability
The free lime content improves:
- plasticity,
- adhesion,
- workability,
- and finishing characteristics,
making the mortar easier to apply and finish than many cement-based mixes.
More Compatible Than Cement
NHL mortars accommodate slight building movement and thermal expansion better than rigid cement mortars, reducing stress concentrations within softer masonry units.
Cement-Free & Breathable
Contains no Portland cement or synthetic waterproofers, helping maintain vapour openness throughout the wall assembly.
Typical Applications
- Lime rendering
- Pointing & repointing
- Bedding masonry
- Scratch & float coats
- Stone wall repairs
- Chimney work
- Solid wall construction
- Traditional & heritage buildings
- Breathable new-build masonry
Why Use NHL 3.5 Grey?
Traditional masonry buildings rely on vapour permeability and capillary drying to regulate moisture naturally. Dense cement mortars can trap moisture within stone and brickwork, increasing the risk of:
- freeze-thaw damage,
- trapped damp,
- salt migration,
- and masonry deterioration.
NHL 3.5 Grey provides a balance between:
- durability,
- flexibility,
- breathability,
- and weather resistance.
This makes it particularly suitable for:
- exposed external render,
- masonry repairs,
- general-purpose lime mortars,
- and traditional buildings requiring breathable construction methods.
Typical Mix Ratios
| Application | Typical Mix Ratio |
|---|---|
| Rendering & Plastering | 2.5:1 sharp sand : NHL 3.5 Grey |
| Pointing | 2.5:1 sharp sand : NHL 3.5 Grey |
| Masonry Bedding | 2.5:1 sharp sand : NHL 3.5 Grey |
| General Lime Mortar | 2.5:1 aggregate : NHL 3.5 Grey |
Mixes should always be adjusted depending on:
- exposure level,
- substrate strength,
- aggregate grading,
- and masonry type.
Installation Overview
1. Surface Preparation
Substrates should be:
- stable,
- clean,
- 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:
- pointing,
- bedding,
- plastering,
- rendering,
- and masonry work.
4. Curing
Fresh lime work should be protected from:
- rapid drying,
- frost,
- heavy rain,
- and strong direct sunlight
during curing.
5. Storage
Store dry and off the ground. Use within the manufacturer’s recommended shelf life.
