Pinholes, Air Voids & Grout: What a “Perfect” Polished Concrete Floor Really Looks Like

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Polished concrete is often marketed as a flawless, glass-like surface. In reality, a high-quality polished concrete floor is natural, honest, and unique — and that means small imperfections such as pinholes and air voids are normal.

Understanding what causes them (and what can realistically be achieved) helps set the right expectations before grinding starts.

What Are Pinholes and Air Voids in Polished Concrete?

Pinholes and air voids are small holes or pores that appear in the surface once the concrete is ground and polished.

They are caused by:

• Trapped air in the concrete mix

• Bleed water evaporating during curing

• Cement paste shrinkage

• The original slab finish and workmanship

These voids are often not visible before grinding and only appear once the surface cream is removed.

👉 Important: They are not defects — they are a natural characteristic of concrete.

Why Do Pinholes Appear During Polishing?

Polished concrete is a mechanical process, not a coating.

As grinders remove the top layer of cement paste:

• Air pockets become exposed

• Micro voids open up

• The true structure of the slab is revealed

This is especially common in:

• Power-trowelled slabs

• Slabs poured quickly

• Concrete with high cement content

• Residential slabs not designed for polishing

The more you grind, the more of the slab’s internal character you see.

Can Pinholes Be Fixed?

Short answer: Improved, yes — eliminated completely, no.

Most professional polished concrete systems include a grouting stage, which fills many surface pores.

What grouting does well:

• Reduces the appearance of pinholes

• Creates a tighter, smoother surface

• Improves stain resistance

• Enhances final clarity and gloss

What grouting cannot do:

• Make the slab look like poured resin

• Remove every microscopic void

• Change poor concrete mix design

Multiple grout applications can help, but 100% pore-free concrete does not exist without coatings.

Are Pinholes a Sign of Poor Workmanship?

No — in fact, the opposite is often true.

Pinholes usually indicate that:

• The slab has been properly opened

• The polishing is mechanical, not cosmetic

• No thick coatings are hiding the surface

Floors with zero visible pinholes are often:

• Grind-and-seal systems

• Epoxy or topical coatings

• Burnished surfaces hiding flaws temporarily

These systems can look good initially but typically wear, scratch, or peel over time.

What Does a “High-Quality” Polished Concrete Floor Really Look Like?

A professionally polished concrete floor should have:

• Consistent aggregate exposure (cream, salt & pepper, or stone)

• Even gloss level

• Minimal but natural pinholes

• Visible depth and clarity

• A surface that improves with age, not degrades

Each slab is unique — and that uniqueness is part of the appeal.

How to Set the Right Expectations Before Polishing

If you’re considering polished concrete, ask:

• Was the slab designed for polishing?

• What level of aggregate exposure is achievable?

• Will grouting be included?

• What imperfections should I expect?

A good contractor will explain limitations upfront, not promise perfection.

Final Thoughts

Polished concrete is not about creating a flawless, artificial surface — it’s about revealing the true character of the slab while delivering a durable, low-maintenance floor that lasts decades.

Pinholes and air voids are part of that story.

When understood and managed correctly, they don’t detract from the floor — they prove it’s the real thing.

Thinking About Polished Concrete?

At AusGrind, we focus on mechanical polishing, realistic expectations, and long-term performance — not quick cosmetic fixes.

If you’re planning a polished concrete floor and want honest advice before grinding begins, get in touch.