DPC Injection in Brickwork

Why Brick Type Matters

Brick type, age, and manufacturing method directly affect porosity, absorption rate, and injection behaviour. Understanding the brickwork is critical to selecting drilling method, spacing, and dosage.

Brick Identification by Era (Australia)

Brick Type / Era	Typical Characteristics	Injection Behaviour	Practical Notes
Sandstock / Hand-moulded (Pre-WWII)	Irregular size, rough face, variable density, soft mortar common	High uptake	Readily accepts injection. Control volume to avoid over-loss. Check mortar condition.
Early Machine-Made (1920s–1930s)	More uniform, still relatively porous	High–Moderate	Generally predictable. Direct brick injection usually suitable.
Post-War Solid Pressed (1940s–1950s)	Uniform, solid, moderate–high density	Moderate	Consistent drilling and spacing required. Typically reliable uptake.
Modern Extruded / Wire-Cut (1960s+)	Very uniform, often harder, frogs or perforations common	Low–Moderate	Slower uptake. Hole placement and depth critical. Allow time for distribution.

Early to Pre-WWII Bricks

Common types:

Sandstock bricks (including Sydney sandstock)
Hand-moulded or clamp-fired bricks

Characteristics:

Irregular shape and size
Higher porosity
Variable density
Mortar often softer than the brick

Injection notes:

Readily accepts injection
Volume control important to avoid over-loss
Mortar condition should be checked carefully

Early Machine-Made Bricks (1920s–1930s)

Common types:

Early machine-pressed clay bricks
Transition bricks between hand-moulded and post-war pressed bricks

Characteristics:

More uniform than sandstock bricks
Still relatively porous compared to later bricks
Variable firing quality

Injection notes:

Generally accepts injection reliably
Direct brick injection usually suitable
Uptake is typically predictable but still requires volume control

Post-War Solid Bricks (1940s–1950s)

Common types:

Solid, machine-pressed clay bricks

Characteristics:

More uniform than earlier bricks
Moderate to high density
Generally solid with fewer voids

Injection notes:

Typically suitable for direct brick injection
Consistent drilling and spacing required
Usually predictable uptake

Modern Extruded Bricks (1960s onwards)

Common types:

Wire-cut / extruded bricks

Characteristics:

Uniform size and shape
Often harder and brittle (crack easily)
May contain perforations or frogs

Injection notes:

Hole placement and depth critical
Perforations can influence distribution
Injection is best in the mortar above the target brick.

It is advised to drill mortar above brick and fill the brick extrusions from the top with Silonexx. Injection fluid can drain from extrusions when injected to the centre (side) of the brick.

Mortar Considerations

In some masonry, particularly sandstone construction or brittle brickwork, mortar injection may be preferred over direct brick injection.

Mortar must be:

Sound
Continuous
Free from severe deterioration

Repointing may be required before injection.

Pointing after injection is complete and/or rendering may bridge the new dampcourse layer causing water to bypass the injection dampcourse.

Mortar condition plays a significant role in post-injection performance. In walls with salt-laden or hygroscopic mortars, moisture retention and ongoing salt crystallisation can continue above the injected DPC even when the barrier itself has formed correctly.

Where salt contamination is present, removal of salt-affected mortar and plaster is recommended to prevent continued deterioration and misleading signs of dampness after treatment.

Key Takeaway

There is no single injection approach that suits all brickwork.

Correct identification of brick type and era allows drilling, spacing, and dosage to be adjusted to achieve full saturation and a continuous damp-proof course.

Related Technical Pages

Drilling Pattern & Hole Spacing →

Installation Method Overview →

Common Failure Modes →

Brick Classification by absorbtion Behaviour

Classification	Typical Indicators	Injection Considerations
Soft Bricks	High porosity, rapid absorption, often older masonry	Monitor saturation closely. Control volume to avoid excessive loss.
Hard Bricks	Dense structure, low porosity, slower uptake	May require tighter spacing or longer saturation time.
Brittle Bricks	Cracking during drilling, often poorly fired or aged	Reduce drill pressure. Consider mortar injection if damage occurs.

Explore the Silonexx chemical DPC injection fluid specification and supply options.