Decorative concrete: grinding and professional finishes (polished, satin, raw)

Decorative concrete transforms a raw material into a finished surface in its own right. Walls, ceilings, floors: the current architectural trend integrates exposed concrete as an aesthetic element in commercial, residential and public projects. For grinding professionals, this high-value market demands tooling capable of producing homogeneous, repeatable finishes that meet architects’ expectations.

What are the main decorative concrete finishes?

Raw concrete (formwork concrete)

Raw concrete retains the marks of its formwork: board imprints, air bubbles, a slight laitance veil. The finish consists of homogenising the appearance without transforming it. A light grind at grit 60 to 120 is sufficient to remove surface laitance and even out the colour.

The appeal of raw concrete lies in its authenticity. The architect is looking for traces of the construction process. Grinding must be delicate: pressing too hard exposes the aggregates and destroys the intended effect.

Satin concrete

Satin offers a smooth feel and a matt to very slightly glossy appearance. It is the most requested finish for interior residential and commercial spaces. The abrasive progression runs from grit 60 to grit 400, with visual inspection between each pass.

Satin is less forgiving of irregularities than raw. Surface flatness and grinding consistency are critical. This is the finish where the difference between a suitable tool and a generic one is most visible.

Polished concrete (mirror)

Mirror polish is the most demanding finish. The surface reflects light like a mirror, revealing the slightest imperfection. The abrasive progression runs from grit 30 to grit 3000, in 8 to 10 successive passes. On floor surfaces, this progression is typically carried out with a single head concrete grinder fitted with the appropriate disc size.

Each pass removes the scratches from the previous one. Skipping a step (for example jumping from grit 200 to grit 800) leaves micro-scratches visible in the reflection. Progression discipline is absolute.

Tadelakt concrete

Tadelakt is a lime-based plastering technique applied over a concrete substrate, polished with a pebble and treated with black soap. Although it is a plaster rather than concrete grinding per se, the concrete substrate preparation is identical: the surface must be clean, rough (grit 30 to 60) and free of laitance to ensure plaster adhesion.

How do you choose the right grit progression?

What is the fundamental rule of grit progression?

The fundamental rule of grit progression is never to skip more than a factor of 2 between successive grits, from grit 30 for roughing to grit 3000 for mirror polish. A coarse grit (30) removes significant material and leaves deep scratches. A fine grit (3000) removes very little material and produces a mirror surface.

The golden rule: never skip more than a factor of 2 between successive grits. The recommended progression is:

Roughing: 30, 60 Refinement: 120, 200, 400 Polishing: 800, 1500, 3000

Which grit should you start with?

The first grit depends on the initial surface condition:

• New formwork surface with laitance: start at grit 60
• Old surface with defects or excess material: start at grit 30
• Previously ground surface to rework: start at the grit just below the existing finish

Diamond or resin: which abrasive for which stage?

Diamond suits coarse grinding stages (grits 30 to 120) on hard concrete, while resin discs handle fine grits (200 to 3000) to produce the final gloss.

Resin: used for fine grits (200 to 3000). Resin discs are more flexible and follow the micro-relief of the surface. They produce the final gloss.

The Mygale: the tool for decorative wall concrete

Why use a trolley?

Decorative grinding on wall surfaces presents a fundamental mechanical problem: the operator must keep an even movement while holding the tool at arm’s length. After 2 hours, fatigue alters pressure, which translates into visible finish variations.

The Mygale gantry is self-supporting on 4 wheels and is not fixed to the wall. Its built-in balancer reduces the effort of carrying the machine: the operator guides the movement without bearing the weight.

Technical specifications for tender documents

For architects and project managers writing specifications, here are the relevant technical specifications of the Mygale + Petit Potam system:

• Motor power: 1,600 W (Petit Potam)
• Vibrations: 0.35 m/s² at the handle (Petit Potam, value from its manual)
• Noise level: 59 dB(A) under load (Petit Potam, value from its manual)
• Pad diameter: 165 mm
• Sealing: IP65
• Extraction: compatible with class M/H vacuum (IU33 Longopac recommended)

Which Mygale configuration suits your site?

The equipment is chosen by site type: Mygale for new builds with large volumes, Petit Potam for renovation work with restricted access, and Fouine XB165 for high ceilings above 3 m.

Renovation, restricted access: Petit Potam with 165 mm pad. The compact size enables work in corners and recesses inaccessible to the trolley.

High ceilings (over 3 m): Fouine XB165 on the Gazelle trolley. Working height reaches 3.5 m, and 4 m with the extension arm.

How do you prepare concrete before staining or varnishing?

Post-grinding cleaning

After the final grinding pass, the surface must be thoroughly dedusted. Concrete microparticles lodged in the pores can prevent surface treatment adhesion. A class M/H vacuum with appropriate extraction flow is essential.

What checks are needed before applying a surface treatment?

Three checks before applying stain or varnish:

1. Absorption test: place a few drops of water on the surface. If the water is absorbed within 30 seconds, porosity is sufficient for treatment. If the water beads, the surface is too closed (grit too fine or contamination).

2. Raking light visual check: an LED lamp placed at 15 degrees to the surface reveals defects invisible under diffuse lighting. Residual scratches, overlaps and flatness variations appear clearly.

3. Moisture measurement: the concrete must be dry (residual moisture below 4%) before applying an impregnant or varnish. A pin or microwave moisture meter gives a reliable reading.

Quotation and site scheduling

How long does decorative concrete grinding take?

For medium-hardness concrete (30 to 40 MPa), grinding times per square metre are:

These times include disc changes and intermediate checks. They are based on a suitable tool (Mygale or equivalent). With an unsuitable tool or manual grinding, multiply by 2 to 3.

What does decorative grinding cost in a tender?

The cost of decorative grinding breaks down as:

• Labour: 60 to 70% of total cost
• Abrasive consumables: 20 to 25%
• Tool depreciation: 10 to 15%

On a 200 m² wall project in satin finish, allow 4 to 5 working days for one operator equipped with a Mygale trolley. The same project with a manual or unsuitable tool takes 10 to 15 days.

Architect approach: integrating decorative concrete into the project

Specifications for tender documents

Architects specifying decorative concrete should include in the technical specifications:

• The expected finish type (raw, satin, polished, with visual references)
• The final grinding grit
• Flatness tolerances (typically 2 mm under a 2 m straightedge)
• Expected gloss levels (measured by glossmeter, in GU)
• The surface treatment (impregnant, varnish, wax)

Samples and approval

Before starting grinding on the full surface, producing a 1 to 2 m² sample is essential. This sample must be approved by the architect before proceeding. It serves as the reference for acceptance inspection.

To size your decorative grinding tooling requirements, use the Sept Tools configurator or view the Mygale product page. For personalised advice, contact our team.

Sept Tools products

Equipment featured in this article

Mygale

Self-supporting rolling gantry, reduces carrying effort at the wall

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Fouine XB165

1600 W ceiling grinder for large concrete surfaces

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Petit Potam

Compact wall grinder for restricted access areas

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IU33 Longopac

Class M/H vacuum, concrete dust capture at source

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