Cavity and monolithic block walling explained

Using clay block walling is an alternative to concrete blocks, providing high strength and thermal efficiency, and less time needed to achieve a water-tight shell. Porotherm precision-engineered blocks are suitable for multiple wall types, including inner and outer leaves of cavity walls, internal partition walls, and monolithic external walls.

What’s the difference between cavity and monolithic blockwork?

Cavity 

A cavity walling system in which two walls are built with a layer of insulation in-between. The wall on the outside is called the external leaf, while the wall on the inside is the inner leaf. 

Traditionally, the inner leaf is constructed with concrete blockwork and the external leaf is constructed with facing bricks. However, Porotherm clay blocks can be used to create the inner leaf instead of concrete, offering timesaving and sustainability benefits. Porotherm can also be used for both the inner and external leaf, in a double skin system, then finished with render or alternative facade options.

Cavity walling incorporates thermal insulation and helps reduce moisture getting inside, as well as reducing the weight on the foundation.

Learn more about Porotherm cavity blocks.

Monolithic

Mono means ‘one’ and this typing of walling uses a single leaf for external walls. Porotherm monolithic blocks can provide excellent airtightness and thermal performance when plastered. The Monolithic system offers a thicker block of high thermal efficiency so that only one leaf is required instead of the inner and external leaves used in a cavity system. Blocks can be finished with a render, brick slips or a cladding system.

The main benefit of a monolithic clay block construction is removing a variety of components while still delivering excellent thermal insulation.   

Learn more about Porotherm monolithic blocks.

What are the benefits of clay blocks?

Whether your project uses a cavity or monolithic design, choosing a clay block as opposed to the traditional concrete block has multiple benefits.

Porotherm blocks use a thin joint mortar system. Although the first course of blocks requires a full bed of mortar (10mm) to obtain levels, all subsequent courses only require 1mm of mortar, laid with an easy-to-use mortar roller. The vertical joints require no mortar by using a tongue and groove interlock system, making laying the block easier, with less cement used. The correct amount of bagged dry mix mortar can be mixed in close proximity to working areas, making for a cleaner site, and is simple to mix by adding water. This also means reduced water usage across the whole built, saving up to 90% compared to concrete blocks for a monolithic build, and up to 95% water saved for a cavity construction. 

Porotherm blocks are class A1 fire resistant. This is a walling system comprising of blocks with low moisture content with 1mm mortar joints containing minimal water. This means that buildings can achieve equilibrium moisture content quicker and thereby achieve thermal values a lot sooner that traditional builds This also reduces snagging, as there is a limited transfer of moisture from the masonry to other building components.

Furthermore, with precision-engineered clay blocks and fast setting thin joint mortar you can achieve storey height (3m) within a day, depending on the complexity of design and the geographical location regarding exposure. For cavity walls up to two storeys, weathertight construction can be achieved before the external leaf is built, allowing for parallel internal and external work, to save time across the project.