Roundtower NHL 2

Roundtower NHL 2Roundtower 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

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

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

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.