Roundtower NHL 3.5 Coarse (Premix)
Roundtower NHL 3.5 Coarse is a ready-mixed lime mortar manufactured from Natural Hydraulic Lime (NHL 3.5) and coarse kiln-dried sand, blended in a controlled factory environment to provide a consistent, breathable mortar for masonry, pointing, and rendering applications. Supplied in a pre-blended 2:5 lime-to-sand ratio, it eliminates on-site batching while maintaining the durability, vapour permeability, and workability associated with NHL 3.5 mortars.
Designed for both traditional and modern breathable construction, NHL 3.5 Coarse offers greater strength and weather resistance than NHL 2 mortars while remaining significantly more vapour open and flexible than cement-based alternatives. This makes it particularly suitable for external masonry, exposed elevations, stonework, and general-purpose lime construction. (roundtowerlime.com)
Technical Data
| Property | Value |
|---|---|
| Product Type | Ready-Mixed NHL 3.5 Lime Mortar |
| Binder | Natural Hydraulic Lime (NHL 3.5) |
| Mix Ratio | 2:5 (Lime : Sand) |
| Aggregate | 5mm Kiln-Dried Sand |
| Yield | Approx. 13.5 Litres per 25kg Bag |
| Render Coverage | Approx. 1.4m² @ 10mm Thickness |
| Brick Coverage | Approx. 25 Bricks per Bag |
| Water Addition | 4–5 Litres per 25kg Bag |
| Open Time | Minimum 8 Hours (Weather Dependent) |
| Standard | BS EN 998-1 & BS EN 998-2 |
| Packaging | 25kg Bags |
| Vapour Behaviour | Breathable & Vapour Open |
Key Benefits
Ready-Mixed for Consistency
Factory-controlled blending ensures a consistent mix ratio throughout the project, reducing variability and improving reliability compared to site-mixed mortars.
Breathable & Vapour Open
Allows moisture vapour to move naturally through the wall structure, helping masonry dry out while reducing the risk of trapped moisture and damp-related issues.
Increased Durability
The NHL 3.5 binder provides greater strength and weather resistance than NHL 2 mortars, making it suitable for more exposed locations and external applications.
Suitable for External Masonry
Particularly suited to:
- stone masonry,
- brickwork,
- pointing,
- bedding mortars,
- and coarse render base coats.
Excellent Workability
The combination of NHL 3.5 and carefully graded coarse aggregates provides good workability, adhesion, and ease of application for both masonry and rendering work.
Cement-Free Construction
Contains no Portland cement, maintaining compatibility with traditional building materials and breathable construction methods.
Typical Applications
- Pointing stone masonry
- Repointing brickwork
- Bedding stone and brick
- External lime rendering
- Scratch and float coats
- Chimneys and exposed masonry
- Heritage restoration
- Conservation projects
- Breathable new-build construction
Why Use NHL 3.5 Coarse?
Roundtower NHL 3.5 Coarse provides the convenience of a ready-mixed mortar while delivering the balanced performance associated with NHL 3.5.
Compared to NHL 2 mortars, it offers:
- increased durability,
- improved weather resistance,
- and greater compressive strength,
making it better suited to exposed elevations and external work.
The coarse aggregate grading makes it particularly suitable for:
- bedding masonry,
- wider pointing joints,
- and base render coats,
while still maintaining the vapour permeability required for traditional solid-wall construction.
For projects requiring a stronger breathable mortar without resorting to cement-based products, NHL 3.5 Coarse provides a practical and conservation-friendly solution.
Typical Applications by Use
| Application | Recommended Use |
|---|---|
| Bedding Mortar | Stone and brick masonry |
| Pointing Mortar | Traditional stone and brickwork |
| Base Render Coat | Scratch and float coats |
| External Masonry | Exposed elevations |
| Conservation Work | Heritage and listed buildings |
Installation Overview
1. Surface Preparation
Substrates should be:
- clean,
- stable,
- free from dust,
- and appropriately dampened before application.
2. Mixing
Add approximately 4–5 litres of clean water per bag and mix thoroughly. Allow the mortar to stand briefly before remixing and application.
3. Application
Suitable for:
- bedding,
- pointing,
- masonry repairs,
- and coarse render coats.
4. Protection & Curing
Protect fresh work from:
- frost,
- heavy rain,
- rapid drying,
- and direct sunlight during curing.
5. Storage
Store dry, off the ground, and protected from moisture prior to use.
