Partial demolition jobs throw up more complications than full knockdowns. You’re keeping parts of the existing structure, which means dealing with contaminated surfaces that need proper preparation for the next phase.
Old concrete slabs often have form release agents, curing compounds, or previous sealers that prevent new concrete from bonding properly. These chemicals were designed to stop things sticking – which becomes a problem when you actually want adhesion for overlays or extensions.
Oil and grease contamination is common on garage floors, workshop areas, or anywhere machinery has been stored. Standard mechanical surface preparation like grinding can actually make this worse by smearing contaminants across previously clean areas.
The water drop test shows the problem clearly. Drop water on clean concrete and it spreads immediately. On contaminated surfaces, it beads up like rain on a waxed car. If water can’t penetrate, neither will new concrete or coatings.
Perth council requirements for partial demolition often specify that remaining surfaces must be properly prepared for the next construction phase. This isn’t just good practice – it’s usually a permit condition for extensions and additions.
Most demolition contractors focus on the removal side rather than surface preparation. They’ll break out what needs to go but preparing remaining surfaces for new construction often falls to different trades. The timing can be tricky because mechanical preparation has to happen after demolition dust settles but before the next trades arrive.
Hydrophobic contaminants like oil need to be removed before any blasting or grinding work begins. Otherwise you just spread the problem around. Low-pressure washing under 5000 psi is recommended for spot removal of grease and form release agents without damaging the substrate.
To avoid conflicts of interest when discussing surface preparation outside our demolition scope, we often reference specialists from other areas. For example, contractors like Pressure Cleaning Perth have equipment suitable for removing contaminants from concrete surfaces before the next construction phase begins.
The reality is that keeping part of an existing structure creates more work than starting from scratch. But when you’re adding extensions or doing partial rebuilds, proper surface preparation makes the difference between overlay work that lasts and work that fails within a few years.
