Laitance Removal Grinding Sequence

Q: Can I remove laitance with 80, 120 or 200 grit?

No. Higher-grit diamonds like 80, 120 or 200 grit only refine the surface and glide over the weak laitance layer. They do not cut through the 1–3 mm of laitance, so the weak surface remains in place.

Q: Will 30/40 grit expose aggregate?

Used correctly, 30/40 grit removes approximately 1–2 mm of the surface to expose strong cement paste, not stone. The aim is paste exposure, not decorative aggregate exposure.

Q: Can I stop at 200 grit for a matte finish?

Yes. Following a 30/40, 60/80, 120 and 200 grit sequence will leave a very smooth, natural matte finish without needing to enter a full polishing sequence.

Q: Do powerfloated floors require grinding?

Yes. Powerfloated floors develop a dense but weak surface cream, or laitance, which must be removed mechanically so that DPMs, screeds, adhesives and coatings can bond properly.

Q: Should I test moisture after grinding?

Yes. Grinding removes the weak surface layer but does not remove moisture from the slab. A moisture test should always be carried out before applying DPMs, screeds, resin coatings or sealers to avoid blistering and adhesion failure.

Nov 20, 2025 | Blogs, Grinding Grit Sequence, Laitance Removal

Laitance Removal: Why It’s Essential & The Correct Grinding Grit Sequence (UK Guide)

What Is Laitance?

Laitance is the weak, powdery surface layer that forms on new concrete due to excess water, over-trowelling, powerfloating or poor curing conditions.
It often looks smooth or shiny, especially on powerfloated floors, but beneath the appearance it is a fragile, low-strength layer only 1–3 mm thick.

If coatings, DPMs, screeds, adhesives or sealers are applied over laitance, early failure is guaranteed.

Why Laitance Must Be Removed

Every major manufacturer (Sika, Ardex, Mapei, Flowcrete, Weber) requires mechanical laitance removal.

If it is not removed, you risk:

Resin delamination
Screed cracking
DPMs not bonding
Vinyl or LVT lifting
Blotchy sealing
Moisture blistering
Dusting returning within months

Mechanical grinding or shot blasting is the only correct preparation method.

Why High-Grit Diamonds Cannot Remove Laitance

Higher grit diamonds (80–200 grit) cannot remove laitance because they:

Refine rather than cut
Glide over the weak cream layer
Smear fine cement paste
Polish the laitance instead of removing it
Do not penetrate the 1–3 mm weak layer

High grits do NOT remove laitance — even with extended grinding time.
Only coarse metal-bond diamonds can cut through it.

Correct Grinding Sequence for Laitance Removal

Before selecting grits, choose the correct diamond bond hardness:

Soft-bond for hard/powerfloated concrete
Medium-bond for general slabs
Hard-bond for soft or weak concrete

Once bond selection is correct, follow this grit sequence.

View all metal-bond diamond tooling here →
https://www.pwm-sales.co.uk/products/surface-preparation/diamond-grinding/

1. 30/40 Grit Metal-Bond Diamonds – Minimum Required

This is the essential first pass.

It:

Cuts through the laitance layer
Removes only 1–2 mm
Exposes strong cement paste
Prevents unwanted aggregate exposure

The goal is paste exposure, not decorative stone exposure.

2. 60/80 Grit – Refinement Stage

After laitance removal, this pass:

Smooths 30/40 scratches
Levels the slab
Begins restoring natural tone
Prepares the slab for finer smoothing

3. 120 Grit – Fine Smoothing

120 grit creates:

Clean, uniform matte finish
Strong mechanical key for coatings
Even absorbency
Smooth walking finish

Suitable for densifiers, sealers, DPMs and resin systems.

4. 200 Grit (Optional) – Very Smooth Matte Finish

Provides:

Very smooth matte appearance
Natural, non-gloss finish
No shine
No exposed aggregate

Ideal end-point when customers want a matte concrete finish without polishing.

Moisture After Grinding

Grinding does not remove moisture.
Perform a moisture test before applying:

DPM
Screeds
Resin coatings
Sealers

This prevents blistering, pinholing and adhesion failure.

Dust Control & Compliance

UK law (HSE) requires M-Class or H-Class extraction for silica dust.

Recommended extractors:

Always use shrouds and appropriate PPE.

HAVS Considerations

Check vibration levels (m/s²) when selecting grinders to stay within daily HAVS trigger time limits.

Particularly relevant for:

Handheld grinders
Long grinding durations
110 V site environments

Recommended Machines for Laitance Removal

Small to Medium Floors

Medium to Large Floors

Sabre G500 Concrete Floor Grinder / Polisher

Industrial / High Output

Finish Appearance After the Correct Sequence

After the full sequence (30/40 → 60/80 → 120 → 200 grit), the concrete will be:

Smooth
Uniform
Matte finish
No shine
No exposed aggregate
No laitance layer
Strong and bond-ready

Frequently Asked Questions

Can I remove laitance with 80, 120 or 200 grit?
No. These grits refine but do not cut the weak laitance layer.

Will 30/40 grit expose aggregate?
No — it removes only 1–2 mm and exposes cement paste, not stone.

Can I stop at 200 grit for a matte finish?
Yes. This gives a smooth matte finish without polishing.

Do powerfloated floors require grinding?
Yes — the cream layer must be removed for coatings to bond.

Should I test moisture after grinding?
Yes — always perform moisture testing before applying DPM or coatings.

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