Roundtower Heritage Trass Coarse is a specialist, ready-mixed lime mortar and render designed for the repair, restoration and conservation of traditional stone and brick masonry. Formulated with lime and natural Trass pozzolan, this coarse-textured mortar combines excellent vapour permeability with low capillary water absorption, making it particularly suitable for older buildings where moisture management is essential.
Developed to work sympathetically with traditional masonry, Roundtower Heritage Trass Coarse provides a breathable alternative to dense cement-based mortars and renders, helping walls release moisture through evaporation while reducing unnecessary restrictions to vapour movement.
Ideal Basecoat for Roundtower SuperTherm Insulating Lime Plaster
One of the key applications of Roundtower Heritage Trass Coarse is as a preparatory basecoat beneath Roundtower SuperTherm Insulating Lime Plaster, particularly on older masonry walls affected by soluble salts.
Traditional stone and brick walls can contain salts resulting from historic moisture ingress, ground moisture or previous building treatments. As moisture evaporates, these salts can crystallise within plaster layers, potentially causing surface deterioration, powdering and loss of adhesion.
Where appropriate following an assessment of the masonry and salt contamination, Roundtower Heritage Trass Coarse can be used as a sacrificial or preparatory lime basecoat before applying Roundtower SuperTherm, helping provide a compatible background for the insulation system.
Its highly breathable formulation also makes it suitable for conservation projects where maintaining the natural moisture movement of traditional masonry is a priority.
Features & Benefits
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Highly vapour permeable – supports moisture evaporation from traditional masonry
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Low capillary water absorption – helps limit liquid water uptake while maintaining breathability
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Suitable for salt-affected masonry – can be considered as a preparatory basecoat where soluble salts are present, subject to project assessment
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Compatible with traditional stone and brick – particularly suited to heritage restoration and conservation work
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Ideal beneath Roundtower SuperTherm – provides a coarse lime-based background for subsequent insulating plaster applications, subject to system compatibility
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Natural Trass pozzolan – contributes to the specialist performance characteristics of the mortar
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Suitable for internal and external applications – where the mortar is appropriate for the substrate and exposure conditions
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Ready-mixed formulation – promotes consistent material proportions and reduces onsite mixing variations
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Coarse aggregate grading – suitable for preparatory coats, backing coats and general lime rendering
Product Specifications
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Product Type: Breathable Lime Mortar & Render
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Binder: Lime with Natural Rhine Trass Pozzolan
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Aggregate: Coarse graded natural sand, up to 5mm
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Application: Internal and External
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Primary Uses: Basecoats, Render Backing Coats, Traditional Masonry Repairs
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Specialist Application: Preparatory coat beneath Roundtower SuperTherm on appropriately assessed salt-affected masonry
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Bag Size: 25kg
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Approximate Yield: 14.5 litres per bag
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Approximate Coverage: 1.5m² per bag at 10mm thickness
Suitable Applications
Roundtower Heritage Trass Coarse is particularly suited to the restoration of older stone cottages, historic brick buildings, period properties and traditional solid masonry walls where breathable materials are required.
It can also form part of a carefully specified internal insulation system using Roundtower SuperTherm Insulating Lime Plaster, helping prepare uneven or salt-affected masonry backgrounds before insulation is applied.
For best results, existing sources of moisture ingress should be identified and addressed before application. Where significant salt contamination is present, the suitability and expected service life of the basecoat should be assessed before installing additional plaster layers.
Roundtower Heritage Trass Coarse offers a practical, conservation-focused solution for traditional masonry repairs and breathable lime plaster systems, combining compatibility with historic building materials and effective moisture management.
