Here’s a secret most people don’t know about concrete floors: it’s not the polish, the sealer, or the fancy machines that decide how good the finish looks. It’s the prep.
Yep, surface preparation is the unsung hero of great concrete flooring. Whether you’re after polished concrete, a grind and seal, or a specialist flake system, how the slab is prepped can mean the difference between a durable, glossy masterpiece and a peeling, patchy disaster.
At NZ Grinders, we’ve learned (often the hard way) that rushing the prep stage is a recipe for regret. So if you’re a builder, architect, or homeowner planning a concrete floor, let us explain why this part of the process deserves just as much love as the finish.
What Do We Mean by Surface Prep?
Before we polish, seal, or coat a slab, we have to make sure it’s in the right condition. Surface preparation includes:
- Removing glues, paints, and contaminants
- Flattening high spots and grinding off imperfections
- Opening up the surface to accept densifiers or sealers
- Profiling the concrete to the correct texture (CSP rating)
- Filling cracks or repairing damage in the slab
It’s not glamorous. There’s dust (even with extraction), noise, and lots of checking and re-checking. But this work lays the foundation for everything that follows.
Bad Prep = Bad Finish (And No, We Can’t “Polish It Out”)
Let’s say someone skips the prep—or does it half-heartedly. What could go wrong?
- Coatings fail – Sealers or epoxy systems can delaminate or bubble if the surface isn’t properly cleaned and profiled.
- Uneven polish – High and low spots lead to inconsistent stone exposure and burn marks.
- Stains and residues remain – Old adhesives, oils, or curing compounds can bleed through a new finish.
- Cracks get worse – Small cracks that aren’t treated correctly can open up again, even under a polished surface.
- Dirt gets sealed in – You’d be amazed how many jobs we’ve had to fix where dust was sealed under a clear coat.
Clients sometimes ask, “Can’t you just polish it more to fix it?” Unfortunately, no. Once a coating fails or a flaw shows through, it usually needs to be ground back and started again—which costs more in time, money, and good moods.
Every Finish Needs a Different Prep
There’s no one-size-fits-all when it comes to prep. At NZ Grinders, we match the surface preparation method to the final system and use case.
- Polished Concrete – We start with a coarser diamond to level the floor, then refine up through the grits. We check hardness, apply densifier, and inspect the surface between each pass.
- Grind and Seal – We ensure the slab is clean, dry, and free of contaminants. Then we achieve the correct CSP profile (usually CSP-2 to CSP-3) for optimal sealer adhesion.
- Flake Floors – For garages or commercial spaces, we often go to CSP-3 or higher, especially if moisture or oil contamination is suspected. We also moisture-test before applying anything.
- Glue Removal Projects – When someone’s ripped up old vinyl or carpet and wants a fresh finish, glue residue has to be fully removed—often requiring aggressive grinding or chemical cleaning.
Different slabs, environments, and finishes call for different levels of prep. And knowing which one is right? That’s what separates the cowboys from the craftsmen.
We Know What to Look For Before We Even Plug In the Grinder
Before we fire up a single machine, our team inspects the site for:
- Curing compounds (inhibits sealer/epoxy bond)
- Paint overspray or construction debris
- Moisture issues (can cause bubbling or white haze)
- Inconsistent finishing (which affects final exposure)
- Poor-quality patches or past repairs
We’ve seen slabs poured in the rain, slabs poured too hot, slabs that were “burned” by over-trowelling… we’ve even had to prep over slab graffiti. (No judgment. But maybe don’t do that again.)
Builders and Architects: Involve Us Early
The best surface prep happens when we’re brought in early. Why? Because we can advise on what we know works.
Too often, we’re called in after the fact and have to deal with issues that could’ve been avoided. Getting it right at the pour stage can save thousands in rework.
Trust the Grinders Who Respect the Prep
At NZ Grinders, we don’t cut corners. We grind them. (Well, not literally—corners are the hardest part.)
We invest in top-of-the-line gear, from planetary grinders to HEPA vacuums, and we train our crew to spot the problems before they become expensive do-overs. Whether we’re prepping for a garage flake floor or a high-gloss polished concrete masterpiece, we treat the prep like it’s the most important step—because it is.
For project-specific advice or information, give us a call:
📍 North Island – Glen: 021-434-199
📍 South Island – Mike: 027-281-8815
📧 Or email Ian, our sales manager, through our Contact Page.
Let’s prep your floor right the first time—so it stays looking good for years to come.