Roundtower NHL 3.5 White is a moderately hydraulic natural lime binder designed for breathable masonry, rendering, plastering, and pointing applications. Manufactured to EN 459-1 standards, it offers a balanced combination of strength, flexibility, workability, and vapour permeability, making it one of the most versatile limes for both traditional and modern breathable construction.
Its higher whiteness makes it particularly suitable for:
- colour-sensitive mortar matching,
- fair-faced stonework,
- decorative lime renders,
- and projects where a lighter finish is desired.
Compared to NHL 2, NHL 3.5 White provides increased strength and weather resistance, while still remaining significantly more breathable and flexible than cement-based mortars. This makes it particularly suitable for external rendering, general masonry, and exposed lime work where durability and vapour openness are both important.
Technical Data
| Property | Value |
|---|---|
| Product Type | Natural Hydraulic Lime (NHL 3.5 White) |
| Standard | EN 459-1 |
| 28 Day Compressive Strength | Approx. 5.51 MPa |
| 7 Day Compressive Strength | Approx. 2.5 MPa |
| Free Lime Content | Approx. 37.3% |
| Whiteness (Y Value) | 70–74 |
| Initial Set | Approx. 1107 minutes |
| Bulk Density | Approx. 0.604 g/cm³ |
| Real Density | Approx. 2.61 g/cm³ |
| Vapour Behaviour | Vapour permeable & breathable |
| Packaging | 25kg bags |
Source: Roundtower NHL 3.5 White Technical Data Sheet & Product Information.
Key Benefits
Breathable & Vapour Open
NHL 3.5 White allows moisture vapour to evaporate naturally through the wall structure, helping reduce trapped damp and condensation risks within traditional masonry.
Balanced Strength & Flexibility
Provides greater strength and durability than NHL 2 while still remaining more flexible and moisture tolerant than cement mortars. This balance makes it suitable for most external masonry and render applications.
High Whiteness
Its clean bright colour makes it particularly useful for:
- light-coloured mortars,
- decorative lime finishes,
- stone matching,
- and colour-sensitive conservation work.
Suitable for New Build & Restoration
Widely used in:
- traditional building restoration,
- breathable new build construction,
- lime rendering,
- pointing,
- and masonry work.
Excellent Workability
The high free lime content improves:
- plasticity,
- adhesion,
- workability,
- and finishing characteristics during application.
Self-Healing Properties
The free lime content contributes to autogenous healing of small micro-cracks during carbonation over time.
Cement-Free & Natural
Contains no:
- cement,
- plasticisers,
- waterproofers,
- or synthetic additives.
Typical Applications
- External lime rendering
- Pointing & repointing
- Bedding mortars
- Scratch & float coats
- Solid wall construction
- Stone masonry
- Fair-faced brickwork
- Decorative lime finishes
- Breathable new build systems
- Heritage & conservation projects
Why Use NHL 3.5 White?
Traditional masonry buildings manage moisture through vapour diffusion and capillary drying. Dense cement mortars can trap moisture within walls, increasing the risk of:
- freeze-thaw damage,
- salt accumulation,
- trapped damp,
- and masonry deterioration.
NHL 3.5 White provides a balance between:
- strength,
- flexibility,
- breathability,
- and weather resistance.
This makes it one of the most commonly specified limes for:
- external rendering,
- masonry work,
- and general-purpose breathable construction.
Typical Mix Ratios
| Application | Typical Mix Ratio |
|---|---|
| Rendering & Plastering | 2.5:1 sharp sand : NHL 3.5 |
| Pointing | 2.5:1 sharp sand : NHL 3.5 |
| Masonry Bedding | 2.5:1 sharp sand : NHL 3.5 |
| Fair-Faced Stonework | 2.5:1 selected aggregate : NHL 3.5 |
Mixes should always be adjusted depending on:
- masonry type,
- exposure level,
- aggregate grading,
- and required finish.
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 the minimum water required for workability.
Overwatering can reduce strength and increase shrinkage risk.
3. Application
Suitable for:
- rendering,
- pointing,
- bedding,
- plastering,
- and masonry work.
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.
