A plinth in the context of building construction serves as a crucial protective feature at the base of exterior walls. It’s usually a line of cement-based mortar designed to deflect splashing rainwater away from the wall, thereby reducing the potential for water absorption and subsequent damage.

The Traditional Role of Plinths

Traditionally, plinths have been employed to combat the detrimental effects of rainwater splash-back on the integrity and longevity of building walls. By diverting rainwater, they assist in maintaining a dry zone at the lower sections of the exterior walls which is essential for preventing dampness, mould growth, and other moisture-related issues.

The Bell Shape Cast Debate

Some surveyors advocate for a bell shape cast cut off the wall above the last course of bricks. This design is touted to throw water off the exposed layer of bricks more effectively. However, there’s yet to be substantial evidence supporting the benefits of this approach. One of the primary concerns associated with this design is the slight thermal imbalance it introduces at the base of the wall. This imbalance could potentially increase the risk of condensation, a precursor to various moisture-related problems.

The Chemical Alternative

An alternative solution to the bell shape cast is the application of an absorption-reducing chemical up to the first five or so courses of bricks. This chemical treatment could provide a similar level of protection against rainwater splash-back without altering the thermal balance at the base of the wall.

Factors Influencing Splash-Back Height

The extent of rainwater splash-back is significantly influenced by the surface upon which raindrops land. Rainwater can bounce off hard stone floors to about 1 metre, while the splash-back height is considerably less from shingles, earth, or grass. Understanding these dynamics is vital for designing effective plinths or alternative protective measures.

Weighing the Options

When considering the implementation of plinths or alternative measures, it’s imperative to weigh the benefits against potential drawbacks. While the bell shape cast may offer an aesthetic appeal and a traditional method of water deflection, the risk of thermal imbalance and subsequent condensation should not be overlooked. On the other hand, chemical treatments offer a modern, less intrusive means of achieving similar protection against rainwater splash-back.


The debate surrounding the design and implementation of plinths underscores the need for a balanced approach. It’s essential to consider not only the immediate benefits of water deflection but also the long-term implications on thermal balance and moisture management. As such, exploring alternative solutions such as chemical treatments, while also considering the surface type around the building, may provide a more nuanced and effective approach to managing rainwater splash-back and preserving the integrity of exterior walls.

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