How do I know if my concrete needs repair or full replacement?

Test by sounding (tap with a hammer) — hollow sound indicates delamination. Visual spalling with rebar visible needs repair. Structural cracking (through-cracks in load-bearing elements) requires engineering assessment. Deterioration under 30% of a structural element can usually be repaired — more than that needs structural review.

Why does concrete spall around rebar?

Water reaches the rebar through cracks or carbonation. Steel corrodes and expands — rust is 3-4 times the volume of the original steel. This expansion fractures the concrete from inside. Visible rust staining on concrete surface means rebar has already started corroding inside.

Can I just patch the spalled area with cement?

Plain cement mortar will fall off. It has poor adhesion to old concrete and no bond strength. You need: (1) bonding agent (SBR-50) to create adhesion, (2) polymer-modified mortar (RM40) for strength and durability, (3) rebar treatment to stop re-corrosion under the patch.

How long does a proper concrete repair last?

A correctly executed repair — removed all deteriorated concrete, treated rebar, SBR-50 bond coat, RM40 repair mortar, protective topcoat — lasts 15–20 years. A poor repair (cement slurry over dirty surface, no rebar treatment) fails within 2–3 years and leaves the problem worse.

What is carbonation and can Hardex products stop it?

Carbonation is the reaction between atmospheric CO2 and concrete that reduces the pH of concrete below 11.5 — the threshold at which rebar's passive oxide layer breaks down and corrosion begins. HARDSEAL AC200 anti-carbonation coating applied to concrete facades blocks CO2 ingress and stops carbonation progression.

Concrete Repair & Structural Rehabilitation

The Problem: Bad Repairs Make It Worse

Concrete Repair Done Wrong Accelerates Failure

A cement slap over a rusty rebar doesn't fix anything. Within 2 years: the patch falls off, the rust has spread further along the bar, and you have a bigger repair. The cost of doing it wrong is always greater than doing it right the first time.

What Causes Structural Concrete Deterioration

Rebar corrosion — The most common failure mode. Corrosion products expand to 3–4× the volume of original steel. This expansion stress cracks and spalls the concrete cover.
Carbonation — CO2 in air reacts with concrete to form calcium carbonate, reducing pH. Below pH 11.5, the passive protection on rebar breaks down. Corrosion starts invisibly.
Chloride penetration — Salt from sea air or deicing agents penetrates concrete and destroys rebar passivation. Aggressive in coastal India.
Honeycombing & voids — Poor concrete placement leaves air pockets. Water infiltrates, rebar corrodes, structure deteriorates from inside out.

The Repair System — 5 Steps, No Shortcuts

Every step exists for a reason. Skip rebar treatment and the corrosion spreads under the patch. Skip bonding agent and the patch falls off. The system only works as a system.

FASTFIX Structural Repair System

Step 1 — BREAK OUT
Remove all delaminated concrete · Go 25mm behind rebar · No loose material
Product: Hammer/chisel/breaker (mechanical)

↓

Step 2 — REBAR TREATMENT
RR100 rust remover (4 hrs) → CP200 corrosion inhibitor coat
Critical: Skip this and corrosion restarts under the patch

↓

Step 3 — SBR-50 BONDING AGENT
Apply while tacky · Bonds old concrete to new repair mortar
Without this: repair mortar adhesion fails within months

↓

Step 4 — FASTFIX RM40 REPAIR MORTAR
Polymer-modified structural mortar · Max 30mm per layer · Compact thoroughly
Matches concrete strength · No shrinkage

↓

Step 5 — PROTECTIVE TOPCOAT
HARDPROOF COOLCOAT or HARDSEAL AC200 over full repaired area
Blocks future water and CO2 ingress · Prevents recurrence

Method	FASTFIX System	Cement Patch	Epoxy Filler
Rebar treatment included	✓ Yes	✗ No	✗ No
Bonding agent	✓ SBR-50	✗ None	Partial
Structural strength	✓ Matches concrete	Weak (no polymer)	✓ Yes
Patch life	15–20 years	2–3 years	10–15 years
Stops re-corrosion	✓ Yes (CP200)	✗ No	✗ No
Cost per m²	₹800–1,500	₹200–400	₹1,500–2,500

Product Specifications

FASTFIX RM40 — Structural Repair Mortar

1.8–2.0

kg/m² per mm thickness

30

mm max per layer

25+

MPa compressive strength

Zero

shrinkage formulation

Critical: Apply only on bonding agent (SBR-50) while still tacky. Maximum 30mm per layer — deeper repairs require multiple layers with 24 hrs between. Do not add water beyond specified ratio.

FASTFIX CP200 — Corrosion Inhibitor Coat

0.20–0.30

kg/m² of rebar surface

12

hours cure before mortar

Apply to

all exposed steel

Creates

passive protective layer

Cost Breakdown — 10 m² Spalled Column Face (50mm average depth)

Material Costs

RR100 Rust remover + CP200 corrosion inhibitor₹2,000–3,000

SBR-50 Bonding Agent (10 m² × 0.13 kg)₹400–500

RM40 Repair Mortar (10 m² × 50mm = ~100 kg)₹6,000–8,000

COOLCOAT Protective Topcoat (10 m²)₹1,500–2,000

Total — Materials₹9,900–13,500

₹990–1,350/m² materials. Labour adds 30–50%.

Compare to column demolition and reconstruction: ₹15,000–25,000/m². Repair typically saves 60–70% vs replacement when done correctly.

Repair Workflow

Day 1

Assessment & Break Out

Sound entire surface — identify all delaminated zones. Break out all compromised concrete to solid substrate, going 25mm behind rebar. Expose all rusted steel.

⏱ Scope-dependent · Don't leave any loose concrete

Day 1–2

Rebar Treatment

Wire brush all exposed rebar to bright metal (St 3). Apply RR100 rust remover — leave 4 hours. Apply CP200 corrosion inhibitor coat. Allow 12 hours before mortar.

⏱ 2–3 hrs application · 12 hrs cure

Day 2

SBR-50 Bond Coat

Wet substrate. Apply SBR-50 bonding agent by brush to concrete and treated rebar. Do not allow to dry fully before applying mortar — must be tacky.

⏱ 1 hr · Apply mortar while tacky

Day 2–4

RM40 Repair Mortar

Pack mortar in layers max 30mm. Compact each layer thoroughly — no voids. Multiple layers for deep repairs — allow 24 hrs between. Build to original profile.

⏱ 24 hrs per 30mm layer · Cure 7 days total

Day 9+

✓ Protective Topcoat

Apply COOLCOAT or AC200 over entire repaired area plus 200mm beyond. Seals surface against future water and CO2 ingress. Repair complete.

Total: 9–12 days for structural repair

Frequently Asked Questions

How do I know if a crack is structural or cosmetic?

Cosmetic cracks are surface-only, hairline (less than 0.2mm), and don't pass through the element. Structural cracks are wider, through-going, and often diagonal (shear). If a crack is in a beam, column, or slab and you're unsure — get a structural engineer to assess before repair. Wrong repair on a structural crack can be dangerous.

Can I fill cracks with epoxy injection instead of repair mortar?

Yes — for structural cracks where load transfer is needed, epoxy injection (HARDPOXY INJ200) restores monolithic concrete. Use repair mortar (RM40) for volume replacements (spalling). Use epoxy injection for hairline to 10mm cracks where structural continuity is the goal.

My building is 30 years old. Is concrete repair worth it or should I demolish?

Assessment is the first step — not assumption. A structural engineer can determine residual life. In most cases, buildings with rebar corrosion damage can be repaired and protected for 20+ more years at 30–50% the cost of demolition and reconstruction. Repair is almost always worth assessing first.

How do I stop concrete columns from rusting again after repair?

Three layers of protection: (1) CP200 on the rebar creates a passive protective coating on the steel. (2) RM40 repair mortar is polymer-modified — lower permeability than original concrete. (3) HARDSEAL AC200 anti-carbonation topcoat blocks CO2 from reaching concrete. All three together stop re-corrosion for 15–20 years.

Concrete Repair & Rehabilitation