Cast-in-place versus precast concrete
Precast is made against a mould. That shows.
Surface quality
Precast units are cast against steel or GRP moulds and come out dense, flat and smooth — usually excellent for vacuum attachment.
Cast-in-place concrete is finished on site: trowelled, floated, broomed or left as struck. Quality varies across a single pour.
Drilling
Precast is often higher strength and more densely reinforced, with reinforcement positioned precisely — which means you can plan around it, but also that hitting it matters more.
In-situ concrete has less predictable aggregate and rebar placement.
Practical approach
On precast, expect good attachment and plan holes against the reinforcement drawings.
On in-situ, expect to prepare the surface more and scan more.
Age
Green concrete is weaker, wetter and holds curing compounds. Both drilling and sealing improve considerably as it matures.
At a glance
| Vacuum sealing | Precast usually excellent; in-situ variable |
|---|---|
| Recommended mode & tooling | Rotary hammer, SDS carbide, hammer ON |
| Limits on this tool | 40 mm max bit diameter, 200 mm max length, 145 mm max depth |
Common mistakes on this material
- Assuming in-situ concrete matches precast surface quality.
- Ignoring reinforcement drawings on precast where they exist.
- Treating green in-situ concrete as mature.