Roundtower NHL 2 is a feebly hydraulic natural lime designed for breathable internal plastering, soft masonry repair, pointing, and sheltered external applications. Manufactured to EN 459-1 standards, NHL 2 offers high vapour permeability, flexibility, workability, and compatibility with softer traditional building materials such as historic brick, soft stone, cob, and lime-built masonry.
Compared to stronger hydraulic limes, NHL 2 develops strength more slowly and remains more flexible and vapour open, making it particularly suitable for conservation work and older solid-wall buildings where moisture movement and substrate compatibility are critical.
Technical Data
| Property | Value |
|---|---|
| Product Type | Natural Hydraulic Lime (NHL 2) |
| Standard | EN 459-1 |
| 28 Day Compressive Strength | Approx. 2.36 MPa |
| 7 Day Compressive Strength | Approx. 0.95 MPa |
| Free Lime Content | Approx. 44.5% |
| Initial Set | Approx. 1245 minutes |
| Vapour Behaviour | Highly vapour permeable |
| Bulk Density | Approx. 0.589 g/cm³ |
| Real Density | Approx. 2.59 g/cm³ |
| Colour | Natural off-white/light buff |
| Packaging | 25kg bags |
Key Benefits
Highly Breathable
NHL 2 is the most vapour open of the hydraulic lime range, allowing moisture vapour to evaporate safely through the wall structure while supporting capillary drying within traditional masonry.
Soft & Flexible
Its lower hydraulic strength allows the mortar to accommodate slight movement and thermal expansion within older buildings without concentrating stress into softer masonry units.
This makes NHL 2 particularly suitable for:
- soft stone,
- handmade brick,
- cob,
- and historic lime-built structures.
High Free Lime Content
The high free lime content improves:
- workability,
- adhesion,
- plasticity,
- and self-healing behaviour
within lime mortars and plasters.
Suitable for Conservation Work
Frequently specified for:
- heritage restoration,
- internal lime plastering,
- repointing,
- and sheltered masonry repairs
where softer breathable mortars are required.
Moisture Compatible
Unlike dense cement mortars, NHL 2 allows moisture to evaporate naturally rather than becoming trapped within the wall structure, helping reduce:
- freeze-thaw damage,
- trapped damp,
- and salt migration.
Excellent Workability
The slower set and high lime content provide extended working times and improved finishing characteristics compared to stronger hydraulic lime grades.
Cement-Free & Natural
Contains no:
- Portland cement,
- waterproofers,
- plasticisers,
- or synthetic additives.
Typical Applications
- Internal lime plastering
- Soft stone pointing
- Heritage masonry repair
- Cob construction
- Sheltered external rendering
- Traditional lime mortars
- Breathable masonry systems
- Historic brickwork repairs
- Conservation projects
Why Use NHL 2?
Traditional buildings manage moisture through vapour diffusion and capillary drying. Dense cement mortars can trap moisture within masonry, increasing the risk of:
- masonry decay,
- trapped damp,
- salt accumulation,
- and freeze-thaw damage.
NHL 2 provides:
- maximum breathability,
- flexibility,
- moisture compatibility,
- and substrate softness
within the hydraulic lime range.
This makes it particularly suitable for:
- delicate historic masonry,
- internal lime plastering,
- and conservation work requiring softer breathable mortars.
Typical Mix Ratios
| Application | Typical Mix Ratio |
|---|---|
| Internal Plastering | 2.5:1 sharp sand : NHL 2 |
| Pointing | 2.5:1 sharp sand : NHL 2 |
| Soft Masonry Bedding | 2.5:1 sharp sand : NHL 2 |
| Sheltered Render | 2.5:1 sharp sand : NHL 2 |
Mixes should always be adjusted depending on:
- substrate strength,
- exposure level,
- aggregate grading,
- and project requirements.
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:
- plastering,
- pointing,
- rendering,
- bedding,
- and masonry repair work.
4. Curing
Fresh lime work should be protected from:
- frost,
- rapid drying,
- direct sunlight,
- and heavy rain
during curing.
5. Storage
Store dry and off the ground. Use within the manufacturer’s recommended shelf life.
