Otterbein NHL 3.5 is a premium Natural Hydraulic Lime manufactured in Germany from carefully selected natural limestone deposits and produced to EN 459-1 standards. Designed for breathable masonry, rendering, pointing, and conservation work, it offers an effective balance between strength, flexibility, vapour permeability, and durability.
As a moderately hydraulic lime, Otterbein NHL 3.5 develops greater weather resistance and strength than NHL 2 while remaining significantly more breathable and flexible than cement-based mortars. This makes it particularly suitable for traditional solid-wall buildings, external lime rendering, stone masonry, and conservation projects where long-term moisture management and compatibility with historic materials are essential.
Technical Data
| Property | Value |
|---|---|
| Product Type | Natural Hydraulic Lime (NHL 3.5) |
| Standard | EN 459-1 |
| 28 Day Compressive Strength | Approx. 4.8 MPa |
| 6 Month Compressive Strength | Approx. 8.5 MPa |
| 12 Month Compressive Strength | Approx. 10.5 MPa |
| Free Lime Content | Approx. 32% |
| Bulk Density | Approx. 0.55 kg/dm³ |
| Vapour Behaviour | Vapour permeable & breathable |
| Sulphate Resistance | High |
| Colour | Natural light buff |
| Packaging | 25kg bags |
.
Key Benefits
Breathable & Vapour Open
Otterbein NHL 3.5 allows moisture vapour to diffuse safely through masonry, helping reduce trapped damp and moisture accumulation within traditional solid-wall buildings.
Balanced Strength & Flexibility
Provides greater durability and weather resistance than NHL 2 while remaining softer and more flexible than cement mortars. This balance makes it particularly suitable for:
- external rendering,
- pointing,
- bedding masonry,
- and breathable solid-wall construction.
High Workability
The lime offers:
- strong water retention,
- high plasticity,
- excellent adhesion,
- and smooth finishing characteristics,
making it particularly workable for traditional lime mortars and renders.
Suitable for Conservation Work
Its vapour permeability and lower stiffness make it highly compatible with:
- historic masonry,
- soft stone,
- traditional brickwork,
- and lime-built structures.
Sulphate Resistant
Naturally resistant to sulphate attack and free from damaging cement additives often associated with masonry deterioration.
Long-Term Strength Gain
Like traditional hydraulic limes, Otterbein NHL 3.5 continues strengthening gradually over time through ongoing hydraulic set and carbonation.
Cement-Free & Natural
Contains no:
- Portland cement,
- synthetic waterproofers,
- gypsum,
- or plasticisers.
Typical Applications
- External lime rendering
- Lime harling
- Pointing & repointing
- Bedding mortars
- Stone masonry
- Breathable solid-wall construction
- Heritage restoration
- Traditional lime plaster systems
- General masonry repair
Why Use Otterbein NHL 3.5?
Traditional masonry buildings rely on vapour diffusion and capillary drying to regulate moisture naturally. Dense cement mortars can trap moisture within walls, increasing the risk of:
- trapped damp,
- salt migration,
- freeze-thaw damage,
- and masonry decay.
Otterbein NHL 3.5 provides a balance between:
- breathability,
- durability,
- flexibility,
- and weather resistance.
This makes it particularly suitable for:
- exposed external work,
- traditional stone buildings,
- breathable masonry systems,
- and conservation-compatible 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 |
| General Lime Mortar | 2.5:1 aggregate : NHL 3.5 |
Mixes should always be adjusted depending on:
- exposure level,
- masonry type,
- aggregate grading,
- and substrate strength.
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:
- rendering,
- plastering,
- pointing,
- bedding,
- and masonry work.
4. Curing
Fresh lime work should be protected from:
- frost,
- rapid drying,
- strong sunlight,
- heavy rain,
- and excessive wind
during curing.
5. Storage
Store dry and off the ground within the manufacturer’s recommended storage period.
