For architects, engineers and design managers: decisions made at design stage can materially influence how well a car park slab resists deterioration over its service life.
A new multi-level car park opens. The slabs are clean, the line marking is crisp, and nobody gives the concrete a second thought.
Ten years on, there’s dust on the lower decks, rust staining under the ramps and a drip landing on cars one level down. By then the talk is of repair budgets and closed bays.
The damage didn’t start when it became visible. It started on day one, inside the concrete.
- MORE FOR LATER: Protecting the Concrete in Car Parks?
Why new car park slabs deteriorate out of sight
The threats arrive with every vehicle.
Moisture and contaminants
Tyres carry in water, oil and road grime, plus salt on coastal sites. Water draws those contaminants into the concrete’s pores and towards the reinforcing steel. Corroding steel expands, cracking the concrete from the inside.
Exhaust fumes and carbonation
Carbonation is a slow reaction between carbon dioxide and concrete that strips the steel of its natural protection. Exhaust-filled decks and soffits are prime candidates.
Traffic wear
Turning tyres and constant loads wear the surface, causing dusting and thinning the cover over the steel. Topical sealers wear off too, and are rarely re-applied on schedule.
None of this shows up at handover.
One critical factor the designer can influence is the movement of moisture and contaminants through the concrete.
 |
| New multi-level car park floor slab protected with a penetrating hydrogel treatment – John Gorton Hospital campus |
Treat the porosity, not the surface
Penetrating hydrogel treatments are sprayed on, soak in and form a silica gel that fills the pores. Because the treatment works within the concrete rather than forming a topical film, the protection is not exposed to traffic wear in the same way as a surface coating. Key treatments include
CONQOR SEAL – suits internal decks and soffits. It hardens the surface, controls dusting and immobilises moisture to resist carbonation from traffic fumes. It leaves no film, so it’s line-marking compatible and won’t add tyre squeal.
CONQOR PROTECT – ideal for slabs facing more moisture and contaminants, such as ramps and exposed edges. It combines sealing, hardening and waterproofing, locking up internal moisture so contaminants can’t do their damage. Independent laboratory testing conducted by Cement Australia found CONQOR PROTECT delivered curing performance equivalent to seven-day water curing across the tested parameters, including chloride resistance.
Fully exposed top decks usually need a complete deck waterproofing system as well.
- TECHNOLOGY BEHIND THE PRODUCTS: What is Colloidal Silica?
In practice
John Gorton Campus, Canberra.
A new 5,001–10,000 m² multi-level car park at the University of Canberra, built in 2024–25. The floor slabs were protected with penetrating hydrogel treatments, including a moisture barrier option on the top level.
 |
Ports of Auckland, New Zealand.
A 33,000 m² car park completed in 2024 on Bledisloe Wharf, beside seawater. Lower decks were sealed and hardened against wear and carbonation, and the top deck fully waterproofed.
 |
Bristol Airport UK
A new multi-storey car park whose 14,530 m² top deck was waterproofed through a wet, snowy winter in 2024–25, without a membrane. The treatment ran alongside the pour schedule, minimising scheduling delay.
 |
| Download the Bristol Airport car park case study here. |
Questions worth asking at design stage
- What design life is the slab expected to reach, and what does the maintenance plan assume about re-sealing?
- Which decks, ramps and edges face salt, moisture or weather, and is their protection specified differently?
- Can curing and protection be combined into one step to save programme time?
Talk to us before the slab specification is locked in
If you’re designing a new multi-level or basement car park, we can help match the right treatment to each deck, ramp and soffit. Request a durability review or explore our car park solutions.
For related learning, try our on-demand webinar “Concrete – Waterproofing – Durability“.
