Sydney Based + National Delivery
Sydney Based + National Delivery
A damp-proof course is a horizontal barrier within a wall that stops ground moisture rising upward through the masonry. In modern construction it’s typically a physical membrane built into the wall during construction. In older buildings, particularly those built before the 1950s, that membrane is often absent, has deteriorated over time, or has been compromised by subsequent building works.
Heritage masonry in Australia presents this problem regularly. Sandstone, brick and lime mortar construction from the Federation and Victorian eras was built without a DPC, or with materials that have long since lost their effectiveness. Render applied over the years, changes to external ground levels, garden beds built against walls, and floor slab additions can all bridge or bypass whatever DPC originally existed.
When the DPC is absent or no longer functioning, moisture rises through the wall fabric by capillary action. The height it reaches depends on wall porosity, moisture load at the base and evaporation rate at the surface. Left untreated, rising damp causes progressive plaster failure, salt crystallisation, masonry deterioration and ongoing internal damage.
Chemical DPC injection creates a new damp-proof course inside an existing wall without cutting, underpinning or major structural intervention. A reactive silane fluid is injected into a horizontal line of drilled holes at the base of the wall. The fluid distributes through the capillary pore network and chemically bonds to the mineral substrate, forming a continuous water-repellent zone at the injection depth.
That zone functions as the replacement DPC. Moisture attempting to rise through the wall from the ground encounters the treated zone and cannot pass through it. The masonry above the treatment line begins to dry out as evaporation continues from the wall surface.
For heritage buildings and older masonry construction, chemical DPC injection is the standard remedial method precisely because it works within the existing wall fabric. No physical membrane insertion. No saw cutting through heritage brick or stone. The treatment is introduced through drilled holes in the mortar joints, which are subsequently repointed to match the original finish.
Silonexx is compatible with lime mortar substrates, which is relevant for any pre-1950s construction where cement repointing would be inappropriate from a conservation standpoint.
A chemical DPC injection treatment is only as reliable as the barrier it forms. The chemistry is well established. What varies between a treatment that holds and one that doesn’t is almost always installation.
Four factors determine the outcome:
Barrier continuity. The treated zone must be unbroken across the full wall width. Any gap in coverage leaves a pathway for moisture to bypass the treatment. This is why drill spacing, hole depth and product volume per linear metre are specified rather than approximated.
Injection line position. The treatment needs to sit at the correct height relative to floor level and external ground level. Too high and it won’t intercept the full moisture front. Too low and it may be within the saturated zone where the chemistry can’t distribute effectively.
Pore network access. The fluid has to be able to move through the masonry. Dense clay brick, heavy salt crystallisation and wall voids all affect distribution. Pre-injection wall assessment identifies where the installation spec needs to be adjusted.
Product volume. Under-dosing is the most common cause of a discontinuous barrier. The volume required varies by wall thickness, brick density and moisture load. Silonexx supply includes volume guidance by wall type as part of the installation specification.
