Sydney Based + National Delivery
Sydney Based + National Delivery
A damp-proof course is a horizontal barrier within a wall that prevents ground moisture rising through the masonry. In buildings constructed before the mid-twentieth century, that barrier is often absent, degraded or compromised by subsequent works. Chemical DPC injection is the established method for creating a new barrier inside an existing wall without physical intervention into the wall structure.
A reactive silane fluid is introduced into the wall through a horizontal line of drilled holes at mortar joint level. The fluid distributes through the capillary pore network and chemically bonds to the mineral substrate, forming a continuous hydrophobic zone at the injection depth. That zone functions as the replacement damp-proof course.
For heritage buildings, older brick construction and any situation where saw-cutting or physical membrane insertion is not practical, chemical injection is the technically appropriate solution. It works within the existing fabric of the wall.
Moisture rises in masonry through capillary suction. Water is drawn upward through the interconnected pore network in brick and mortar by surface tension forces acting within the pore structure. The finer the pores, the stronger the capillary pull — which is why dense clay brick and lime mortar, common in older Australian construction, can draw moisture surprisingly high into a wall.
The height rising damp reaches in a wall is determined by the balance between capillary suction pulling moisture upward and evaporation driving it out through the wall surface. In a wall that’s rendering or painted, evaporation is reduced and moisture rises higher. In a wall carrying significant salt load, crystallisation within the pores compounds the damage.
Chemical DPC injection addresses the mechanism directly. The treated zone renders the capillary pathways within the masonry hydrophobic — water can no longer be drawn through them by surface tension. Moisture attempting to rise from the ground encounters the treated plane and stops.
The barrier formation follows a sequential process after injection. The fluid moves laterally and vertically through the pore network under injection pressure, distributing through the masonry across the full wall width. As the fluid contacts moisture within the wall, the reactive silane chemistry undergoes hydrolysis — a moisture-triggered chemical reaction that activates the bonding process.
The hydrolysed silane then condenses onto the mineral surfaces within the pore structure, forming covalent bonds with the silica in the masonry. This is a permanent chemical change in the substrate. The treated pore surfaces become inherently water repellent at the molecular level. The masonry doesn’t carry a treatment — it is chemically altered.
The treated zone remains vapour permeable. The pore structure itself is not blocked or sealed — the chemistry lines the pore walls rather than filling the pores. The wall continues to breathe after treatment, which is particularly important in heritage masonry where vapour permeability is a conservation requirement.
This is Tri-Phase Molecular Technology™ — capillary penetration, moisture-activated reaction, permanent mineral integration.
Penetration depth and lateral distribution vary by substrate. Understanding these variables is what separates a correctly specified installation from one that produces a discontinuous barrier.
Wall material and pore structure. Dense clay brick has finer pores than modern commercial brick and can be slower to absorb fluid. Lime mortar joints typically have higher porosity than the brick units themselves and often provide the primary distribution pathway in older construction. Knowing which substrate is driving distribution changes the injection approach.
Moisture and salt load. Active moisture within the wall is necessary for the chemical reaction — that’s by design. However, very high moisture levels or heavy salt crystallisation within the pore structure can impede initial fluid distribution. Pre-injection assessment identifies walls where this is likely to be a factor.
Internal wall construction. Rubble-filled walls, cavity construction and walls with internal voids all affect how the fluid distributes. Fluid under injection pressure will find pathways through irregular geometry that passive diffusion systems cannot reach, but void distribution still needs to be understood before drilling starts.
Drill depth and spacing. Holes that don’t reach the masonry core, or that are spaced too far apart, leave untreated zones in the barrier plane. Drill pattern is specified per wall type in the Silonexx installation specification — it’s not a one-size approach.
Both fluid and cream systems use silane chemistry. The difference is in how the product gets into the wall and how far it travels.
Fluid injection uses pressure to drive a low-viscosity product through the pore network rapidly and at depth. Distribution is fast, penetration is deep and product movement through the wall is visible at adjacent holes during the injection process. That real-time confirmation is meaningful when the contractor is carrying warranty responsibility for the outcome.
Cream systems rely on slow passive diffusion from the drill hole into the surrounding masonry. For uniform single-skin modern brick where the absorption rate is consistent and predictable, cream works. For older construction, irregular masonry, thick walls or any substrate where distribution needs to be confirmed rather than assumed, fluid injection is the more reliable choice.
A chemical DPC that isn’t continuous across the full wall width isn’t a DPC. Moisture will find the untreated pathway and continue rising. The treatment may look complete from the outside and still fail to resolve the problem.
Continuity requires four things to be right simultaneously: correct injection depth, even fluid distribution across the wall thickness, adequate product volume per linear metre and a drill pattern matched to the wall construction. Get one of those wrong and the barrier has a gap.
This is why the Silonexx installation specification exists as a document rather than a set of rough guidelines. The Capillary Saturation Zone™ standard defines what a correctly completed treatment looks like — full saturation across the wall width at injection depth, confirmed by product behaviour at adjacent holes before the injection sequence is closed out.
A treatment completed to that standard is warrantable. One that isn’t, isn’t.