A great general-purpose, pre-mixed lime mortar, suitable for building, pointing and rendering.
This mortar is a mix of coarse (5mm down), yellow flint sand and mature lime putty, which dries to a buff/beige finish.
Applications
- Building
- Pointing
- Render and plaster base coats
Instructions for Rendering
Dubbing out the wall involves levelling it to a relatively flat surface by filling pockets, voids, or missing mortar with a stiff mix designed for durability. Ideally, dubbing should be completed as a separate process before applying scratch or float coats, ensuring a proper bond for subsequent coats.
Once the wall is prepared, apply the first undercoat at a thickness of 10-12mm. This layer should be scratched with a cross-hatch pattern no deeper than one-third of the render's depth; avoid using the typical waved scratch pattern common in modern sand and cement renders, as it is not suitable for this material type.
Allow this coat to cure for at least 7 to 14 days, keeping it damp with mist sprays and protecting it from direct sunlight and drying winds, preferably using damp Hessian sheeting.
The float coat should then be applied at a thickness of 8-10mm, ensuring it does not exceed the scratch coat’s depth. To control suction, mist spray the surface before application if needed. Finish the surface with a ruled-off plane, then use a wooden or plastic float to compress the render, creating a smooth finish. For lime renders, use a stiffer mix than sand and cement at floating time to minimise dragging. Once stiffer, the surface can be sponged to achieve a smoother final coat.
While the float coat can be left as a finish, CLM28, made with coarse sand, often produces a rough surface, making a finer topcoat preferable for a smoother appearance. For topcoats, prepare the surface with a devil float or key it appropriately.
When building with mortar, use a consistency suitable for the masonry units—stiffer for stonework, but still workable.
For pointing, maintain a mortar consistency that allows efficient application while minimising the risk of drying shrinkage caused by excess moisture.
Throughout the process, avoid rapid drying by monitoring work conditions and using control measures such as mist spraying, Hessian, or polythene sheeting to ensure optimal curing and adhesion.
Coverage (Render)
- Coverage for render at 12.5mm thickness: 1 m² per 25 kg, equivalent to 40 m² per tonne.
- Mortar requirements per tonne include brickwork pointing for 100 m², bedding for 20 m², and stonework pointing for 40 m².
- These coverage figures are approximate; uneven surfaces or irregular joint sizes may affect actual consumption.
- Renders are generally easier to estimate than bedding mortars, particularly for stonework.
Avoiding The Pitfalls
CLM28 is composed of lime putty, a Non-Hydraulic Lime that sets by absorbing atmospheric carbon dioxide in the presence of moisture. This setting process varies with climate, behaving differently across seasons based on ambient temperatures. Work should never be carried out in freezing conditions or if temperatures are expected to drop below 5°C during application or until the mortar has fully hardened, which, for non-hydraulic mortars, can take months rather than weeks.
Protective coverings should remain in place as long as necessary. Maintain a consistent drying rate and prevent strong drafts in the work area, especially where windows are removed or doors are open. Heating should be carefully controlled to avoid forcing the mortar to dry too quickly.
Typically, lime mortar dries more slowly in winter than in summer, so proper precautions are essential; it must not be allowed to dry out prematurely. Forced drying using excessive heat should be avoided. If heating is needed to maintain a suitable working temperature, propane heaters are recommended because they generate both heat and moisture simultaneously. Always monitor and regulate the temperature appropriately.
The CLM Range
- CLM28F - Ready-mixed fibred coarse lime mortar.
- CLM35 - Ready-mixed fine lime mortar (3mm and down) for tighter pointing and fine render coats.
- CLM66 - Ready-mixed Superfine top coat plaster for internal use.
Delivery
Due to the weight and fragile nature of the tubs, we ship them only on pallets, regardless of order quantity. As a result, delivery charges reflect that cost.
To calculate delivery charges to your location, add the items you are looking to order to the cart, go to the cart, enter your postcode, and click the "Calculate Delivery Cost" button.
Safety & Liability Notice
- Lime mortar is alkaline and can cause skin burns, eye injuries, and respiratory irritation.
- Avoid contact with skin and eyes, and do not inhale dust.
- Wear appropriate protective gear, including gloves, eye protection, and a mask.
- Ensure proper ventilation and keep the product out of reach of children.
By purchasing this product, the user agrees to handle, store, and dispose of it safely. The manufacturer and supplier are not responsible for any injury, loss, or damage resulting from misuse or failure to follow safety instructions and regulations.
Please read all Safety Data Sheets (SDS) before using this product.
Downloads
- Ready Mixed Coarse Lime Mortar - (CLM28) Data Sheet
- Ready Mixed Coarse Lime Mortar - (CLM28) Safety Data Sheet
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