Coring, Precast Cutting and Grind and Seal Floors, Kingsgrove NSW

The job

Infinity Constructions built a new development of warehouse units on The Crescent in Kingsgrove, a precast concrete building with ground floor units, mezzanines, corridors and a car park. Perfect Concrete Care was Infinity's concrete care contractor on the job, from the first cores in February 2023 to the last crack repairs in March 2024.

The work changed as the building went up. First it was coring and cutting through the precast walls and slabs for doorways and services. Then, as the units were finished, it was grinding and sealing the floors unit by unit, and at the end crack injection in the car park.

What the work involved

• Cutting doorway openings into precast wall panels with demo and ring saws, including openings 2400 by 1070 mm, and trimming panels before and after they were lifted
• Core drilling through walls and slabs for fire, air conditioning, plumbing and stormwater services, from small cores up to 375 mm diameter, worked stage by stage as each area was marked out
• Stitch coring openings for groups of services, and large diameter cores with the rig fixed to the wall, worked from elevating work platforms where needed
• Grinding the floors of the warehouse units, corridors and common areas back to an even surface, then sealing them, unit by unit, from July to October 2023
• Scanning before coring where the client wanted reinforcement, post tensioned cables or services located first
• Crack injection and floor repairs in the car park and common areas in early 2024

What made it hard

The coring came in stages as each trade got to its part of the building. Every penetration had to wait for its set out, and the holes were spread across the whole site, one or two in one place and a run of them somewhere else, so the crew moved a lot and spent time waiting for marks.

The floor work was a big run of units, each one ground and sealed in turn while other trades were finishing around them. Power on site was not always steady, so the crew brought in its own generators to keep the grinders running, and some units had to wait until they were dry enough to seal.

How it was done

Doorways in the precast were marked out, cut with demo and ring saws and taken out in sections, then the edges were cleaned up. Cores were drilled wet with the slurry vacuumed as the crew went, with the rig fixed to the wall for the larger horizontal cores.

Each unit floor was ground back with a planetary grinder on dust extraction, cleaned and sealed, and taped off to cure before the next trade came back in. Units that were wet or not ready were left and picked up again when they were, so every floor was sealed on a dry, clean surface.

Lessons learned on this job

Every job teaches the crew something. These are the ones from Kingsgrove that we take onto every staged building job.

What worked

• One contractor for every stage. Coring, cutting, grinding, sealing and crack repair from the same crew meant one set of people who knew the building
• Our own generators on site. When site power was not steady, running the grinders and drills off our own generators kept the work going
• Only seal a dry floor. Leaving units that were wet and coming back later gave every floor a proper bond instead of a patchy finish
• Tape off and cure. Taping off each sealed unit until it had cured kept traffic off the finish while other trades were still on site

What was difficult

• Waiting for set out. Cores spread across a big site lose time when the marks are not there yet, so penetrations are best released in batches
• Many small visits. One or two cores at a time in different places means a lot of set up and pack up for little drilling
• Sealing around the programme. Grinding and sealing unit by unit only works if the units are handed over clean, dry and empty
• Heavy precast. Cutting doorways in thick precast panels is slow, and the offcuts need planning to get out safely

How it went

Across more than a year on site, from February 2023 to March 2024, the precast was cut and cored for the doorways and services, the unit, corridor and common area floors were ground and sealed, and the car park cracks were injected and repaired.

If you have something similar

Builders on precast warehouse and industrial unit jobs need coring and cutting through the build and a grind and seal floor at the end. Have a look at our concrete grinding, polishing and sealing Sydney, concrete core drilling Sydney and crack injection Sydney pages, or get in touch.