Choosing a Breathable Paint
Choosing a paint for a traditional building involves more than selecting a colour.
The coating also becomes part of the wall build-up and can influence how easily moisture vapour moves through the finished surface.
For lime plaster, lime render and many traditional solid masonry walls, a paint with low vapour resistance can help preserve the drying characteristics of the underlying construction.
The correct coating should still be selected according to the substrate, existing paint, internal or external location and required appearance.
What Does Breathable Paint Mean?
“Breathable” is commonly used to describe coatings that offer relatively little resistance to water-vapour diffusion.
A useful technical measure is the Sd-value, or equivalent air-layer thickness. In general, a lower Sd-value indicates less resistance to vapour movement.
However, paint breathability should not be treated as a cure for damp.
Penetrating rain, defective gutters, high external ground levels, plumbing leaks, salts and condensation should be investigated separately where moisture problems are present.
Limewash
Limewash is one of the most traditional decorative and protective finishes for lime plaster, lime render and suitable mineral masonry.
It produces the characteristic soft, matt and subtly varied appearance associated with historic and vernacular buildings.
Limewash remains exceptionally vapour open and can be used internally and externally on appropriate backgrounds.
It should also be understood as a maintainable, sacrificial finish. Weathering and gradual changes in appearance are normal characteristics rather than necessarily signs of product failure.
Roundtower Lime Paint
Roundtower Lime Paint offers another lime-based option where increased opacity and a more consistent painted appearance are preferred.
It can be used internally and externally on compatible backgrounds and retains the mineral appearance and high vapour permeability associated with lime-based coatings.
It can be particularly useful where the character of lime is desired but a more conventional painted finish is preferred to traditional limewash.
Beeck Mineral Silicate Paints
Beeck produces specialist mineral silicate coatings for internal and external applications.
Unlike a conventional purely film-forming decorative coating, compatible silicate systems can chemically interact with suitable mineral backgrounds through silicification.
Roundtower's range includes Beeck Maxil Pro for internal applications and Beeck Renosil for external façade applications, together with primers and preparation products used within the respective systems.
These products provide very low vapour resistance while offering the durability and finish expected from a modern architectural coating.
Internal Breathable Paints
Internal coatings need to combine vapour permeability with practical considerations such as opacity, appearance and resistance to everyday use.
Limewash and Roundtower Lime Paint can be suitable for compatible traditional backgrounds.
For projects requiring greater washability and durability, Beeck Maxil Pro provides a highly vapour-permeable mineral interior coating with a matt finish and high resistance to wet scrubbing.
The correct preparation depends on the existing substrate.
External Breathable Paints
External coatings have additional requirements because they are directly exposed to rain, UV radiation and changing weather conditions.
Traditional limewash remains a valid external finish where its appearance and maintenance cycle are appropriate.
Where greater resistance to weathering and lower liquid-water absorption are required, a suitable mineral silicate coating such as Beeck Renosil may be considered.
The underlying render or masonry must still be sound and appropriately prepared before decoration.
Can Breathable Paint Go Over Existing Paint?
Sometimes.
The answer depends on both the new coating and the existing surface.
Traditional limewash generally requires a suitably porous and compatible mineral background.
Modern silicate systems can be more flexible. Selected Beeck coatings and primers are specifically designed for properly prepared existing surfaces including certain sound emulsion, synthetic-resin and gypsum-based backgrounds.
Existing paint should therefore be assessed for adhesion, stability, absorbency and compatibility rather than applying a blanket rule that every previous coating must always be removed.
Painting New Lime Plaster
New lime plaster or render should be sufficiently cured before decoration.
The required period depends on the lime system, coat thickness, environmental conditions and selected paint.
Applying a finish too early can interfere with drying and may contribute to inconsistent appearance or coating problems.
The instructions for both the plaster and paint system should therefore be considered before decoration begins.
Primers & Surface Preparation
Mineral paints rely on appropriate substrate preparation.
Products such as Beeck Fixative, Quartz Filler and Etching Fluid perform specific functions within selected Beeck systems.
Fixative may be used to regulate suitable absorbent mineral surfaces, while Quartz Filler can provide a mineral intermediate coat where minor surface irregularities or hairline defects require levelling.
Etching products should only be used on substrates for which they are specifically recommended.
Breathable Paint & Damp Walls
A breathable coating can help ensure that the decorative finish does not create an unnecessarily high resistance to drying.
It does not, however, remove the source of moisture.
Where walls are persistently damp, investigate possible causes such as rain penetration, failed pointing, defective gutters, inappropriate external coatings, plumbing problems, high ground levels or internal condensation before relying on paint selection alone.
Lime Paint vs Silicate Paint
Both can provide highly vapour-open finishes, but they behave differently.
Lime-based paints offer a particularly traditional mineral appearance and compatibility with suitable lime backgrounds.
Silicate paints can provide greater durability, colour consistency and resistance to abrasion or external weathering, depending on the particular product.
The most suitable system depends on the building, substrate, required appearance and maintenance expectations rather than one technology being universally better.
Frequently Asked Questions
What is a breathable paint?
A breathable paint is a coating with relatively low resistance to water-vapour diffusion, allowing the underlying construction to retain a greater ability to dry through the finished surface.
What paint should I use over lime plaster?
Compatible limewash, lime paint and suitable mineral silicate paints can all be considered.
The choice depends on whether the plaster is internal or external, its condition and the required appearance and durability.
Can I paint over gypsum plaster?
Selected mineral paints can be used on correctly prepared gypsum plaster.
For example, Beeck Maxil Pro can be used on appropriate gypsum backgrounds when the manufacturer's preparation requirements are followed.
Do I need to remove emulsion paint first?
Not always.
It depends on the new coating and the condition of the existing paint.
Traditional limewash generally needs a suitable porous mineral background, while selected mineral renovation systems can be applied over sound existing coatings after appropriate preparation.
Will breathable paint stop damp?
No.
Breathable paint can avoid unnecessarily restricting drying through the decorated surface, but the underlying source of excessive moisture should still be identified and corrected.
Is limewash suitable outside?
Yes.
Limewash has a long history as an external coating for compatible lime renders and masonry, although it should be expected to weather and require periodic maintenance.
What is the difference between internal and external mineral paint?
External paints are formulated to cope with additional exposure to rain, UV radiation and weathering.
The appropriate internal or external product should always be used rather than assuming all mineral paints are interchangeable.
Can Roundtower help me choose the right paint?
Yes.
Roundtower Lime can help identify an appropriate lime or mineral paint system based on the existing substrate, previous coatings, exposure and required finish.
Need Help Choosing a Breathable Paint?
If you are unsure whether to use limewash, Roundtower Lime Paint, Beeck Maxil Pro, Beeck Renosil or another mineral coating system, contact Roundtower Lime with details of your wall construction and existing surface.
Our technical team can help identify an appropriate paint, primer and preparation system for the application.
