Lime Mortar Mix
Technical Lime Based Solutions
The Guide to Traditional Pointing & Building
Getting your lime mortar mix right is the single most critical step in preserving and restoring historic masonry. Whether you are repointing a Victorian terrace, consolidating a medieval flint wall, or building a sustainable modern eco-home, the mortar must work in harmony with the building fabric.
Using the correct lime mortar ensures your walls remain breathable, flexible, and protected from the damaging effects of trapped moisture.
Why Traditional Lime Mortar Outperforms Cement
For decades, the construction industry defaulted to Portland cement. However, using cement on solid-wall properties or traditional timber frames is a costly mistake.
Traditional lime mortar acts as a sacrificial layer. It is designed to be softer and more porous than the surrounding brick or stone. This provides three vital structural advantages:
Essential Breathability: Cement seals masonry joints, trapping moisture inside the wall and forcing it to escape through the face of the bricks (causing spalling) or internally (causing damp). Lime mortar naturally regulates moisture, allowing water vapour to safely evaporate.
Accommodating Movement: Older buildings shift and settle with seasonal changes. Traditional lime mortar is flexible enough to accommodate this micro-movement, whereas rigid cement will crack and pull the face off the masonry.
Self-Healing Properties: Thanks to the natural carbonation process, fine hairline cracks in lime mortar can often “autogenous heal” as moisture carries free lime into the voids, sealing them over time.
Understanding Lime Mortar Mix Ratios
When mixing your own mortar on-site using Natural Hydraulic Lime (NHL), getting the binder-to-aggregate ratio correct is essential. As a general rule, a 1:3 ratio (one part lime to three parts sand) is the traditional baseline, but this must be adjusted based on the strength of the lime and the exposure of the wall.
Here is a quick reference guide to standard NHL mortar mixing ratios:
| Lime Type | Standard Mix Ratio (Lime : Sand) | Best Suited For |
|---|---|---|
| NHL 2 (Feebly Hydraulic) | 1 : 3 | Internal plastering, soft internal masonry, and highly permeable historic fabric (e.g., cob, soft red bricks). |
| NHL 3.5 (Moderately Hydraulic) | 1 : 2.5 or 1 : 3 | General-purpose external building, pointing, and rendering on standard brickwork and blockwork. |
| NHL 5 (Eminently Hydraulic) | 1 : 2 or 1 : 2.5 | Severe exposure areas, chimneys, copings, below damp-proof courses (DPC), and dense, impermeable masonry (e.g., granite). |
The Smart Alternative: Dry Ready Mix Lime Mortar
Site-mixing traditional lime mortar requires careful sourcing of well-graded sharp sand, precise measuring, and a thorough understanding of curing times. For many projects, the variability of site-mixing is a risk you do not need to take.
Our Dry Ready Mix Lime Mortars, such as PureLime Mortar and the EcoMortar range, take the guesswork out of the process.
By pre-blending high-quality lime binders with expertly graded aggregates in controlled factory conditions, our ready-mixes offer:
Guaranteed Consistency: Exactly the same strength, texture, and colour in every single bag.
Speed on Site: Simply add clean water and mix—drastically reducing labour time and material waste.
Tailored Solutions: Specifically formulated mixes for pointing, building, and rendering across all historic and modern substrates.
If you are a contractor looking to expand into heritage work, or a homeowner wanting to confidently repoint your own property, join us at our Live Heritage Site Training Courses. Held at a 16th-century barn, our practical, hands-on sessions will teach you how to properly mix, apply, and cure traditional lime mortars and plasters in real-world conditions.
Anglia Lime are a official supplier of Saint-Asiter Products, Saint-Astier® is the only producer of Pure Natural Hydraulic Limes providing high quality constant performance and expertise for conservation and renovation buildings.
Our Specialist Product Range Delivered to London
Pure Natural Hydraulic Limes
The ultimate choice for consistent performance. We stock the complete range of official Saint-Astier® NHL 2, NHL 3.5, and NHL 5 binders. Perfect for custom on-site blending, offering exceptional workability and variable strength grades suited to everything from internal plastering to highly exposed external masonry.
Dry Ready-Mix Lime Mortars
Save time and guarantee mix consistency on site. Our best-selling Dry Ready Mix line includes Thermalime basecoats , Finelime topcoats , and specialised Purelime Mortar systems. Just add water for a highly consistent, professional finish every time.
Insulating Lime Systems
Upgrade the energy efficiency of solid-wall properties without compromising their historic fabric. Our Novaskin® breathable thermal plaster and insulating render lines offer incredible thermal upgrades while protecting your building from structural dampness.