Micro Concrete — Practical Guide
Micro concrete (also called microcement, micro-silica concrete in some contexts) is a thin-bedded, high-strength cementitious material used for repair, surfacing and thin overlays. It combines fine aggregates, specialized cements, polymers and admixtures to achieve high bond strength, reduced permeability and good resistance to cracking when used correctly.
Contents
What is micro concrete?
Micro concrete is a cement-based mortar or very fine concrete designed to be applied in thin layers (typically 3–25 mm depending on formulation). It is engineered to achieve good structural repairs and overlays where conventional concrete would be too bulky or heavy.
Composition & typical mix
While formulations vary between manufacturers and project requirements, common components include:
- Ordinary Portland cement (or blended cements)
- Fine aggregates — very fine sand or engineered fillers (particle size typically <1 mm)
- Silica fume or metakaolin (optional) to improve microstructure
- Polymer modifiers (acrylic, styrene-butadiene) to enhance bond and flexibility
- Superplasticizer for flow without excess water
- Corrosion inhibitors or shrinkage-reducing admixtures when required
Example field mix (illustrative): 1 part cement : 0.6–1.2 parts fine filler : 0.03–0.06 part silica fume (if used) with polymer binder 5–10% by weight of cement. Water is added to achieve a trowelable consistency; use superplasticizer to keep water low.
Key properties
- High bond strength to substrate when surface is prepared correctly.
- Low permeability when properly compacted and cured.
- High early strength—many mixes reach significant strength within 1–3 days.
- Thin-bed capability—suitable for <25 mm repairs without heavy formwork.
- Reduced shrinkage with proper admixtures and curing practice.
Common applications
- Patching and resurfacing of slabs, steps and precast units.
- Ramps, screeds and overlays where thin-profile repair is required.
- Bonded overlays on concrete, masonry and some steel substrates (with primer).
- Repair of spalls, honeycombing and small-depth delamination.
Advantages
- Less dead load than conventional concrete — useful for structural repair on beams/slabs.
- Faster return-to-service due to high early strength.
- Good surface finish — can accept polishing or protective coatings.
- Reduced need for heavy formwork for thin repairs.
Site preparation & application
Successful micro concrete repairs depend largely on substrate prep and application method:
- Clean substrate: remove loose material, dust, oil, paints or treatments that impair bond.
- Mechanical key: roughen smooth substrates (grinding or light scarification) to provide mechanical interlock when required.
- Priming: many systems require a cementitious or polymer primer/bond coat applied wet-on-wet.
- Layering: apply in thin lifts; compact each layer and avoid trapping air. Some mixes allow trowel application while others suit pumping or spraying.
- Curing: protect from rapid drying for at least 24–72 hours (polythene, damp curing or curing compounds depending on manufacturer guidance).
Precautions & quality checks
- Follow manufacturer datasheets for mixing ratios and pot life.
- Verify bond with pull-off tests for critical repairs.
- Control temperature during application; extreme heat or cold affects workability and curing.
- Avoid adding excessive water — use superplasticizer instead to adjust workability.
- Check compatibility if applying coatings or sealers after the micro concrete cure.
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