Frequently Asked Questions

How is Sika FerroGard 901 applied to a bridge pier concrete face and how many coats are needed for the product to reach 40 mm concrete cover depth?

Sika FerroGard 901 application to a bridge pier concrete face is a multi-coat, timed process that requires patience to allow each coat to absorb before the next is applied. The standard application protocol for Sika FerroGard 901 involves 3 to 4 coats applied over 3 to 4 consecutive days: Day 1 — First coat: apply Sika FerroGard 901 by brush (for best penetration — brush application works the liquid into the surface pore) or roller to the clean, dry (no surface water) concrete face at 0.2 to 0.25 litres per m2. Allow to absorb for minimum 12 hours. Day 2 — Second coat: apply the second coat at 0.2 litres per m2. Allow to absorb for minimum 12 hours. Day 3 — Third coat: apply the third coat at 0.2 litres per m2. For a design concrete cover of 40 mm, the cumulative three-coat application is typically adequate to drive the amino-alcohol molecules to the reinforcement level in normal-density OPC concrete — confirmed by Sika data showing penetration depths above 40 mm after 3 to 4 coats application and 28 days migration time. For higher concrete cover (50 to 60 mm) or very dense, low-permeability concrete, a 4th coat and additional waiting time is recommended. After Sika FerroGard 901 application is complete, allow 24 hours and then apply Sikagard 550 W Elastic or other surface protection coating as the outer layer of the dual protection system.

Can Sika FerroGard 901 be used as the only repair and protection measure on a heavily carbonated RC building frame without removing the carbonated concrete?

Sika FerroGard 901 alone is NOT a complete repair and protection system for a heavily carbonated RC building frame and should not be specified as the only remedial measure. The limitations are: Sika FerroGard 901 is a migrating corrosion inhibitor — it reduces the corrosion rate of reinforcement already at risk but does not remove the carbonated concrete that has caused depassivation, does not restore the alkaline environment around the reinforcement (pH below 9 in carbonated concrete is insufficient to passivate steel), and does not replace the structural concrete cover that has spalled. EN 1504 recognises this limitation and classifies MCI treatment under Principle 11 (corrosion control) rather than Principle 3 (concrete restoration) or Principle 4 (structural strengthening). The correct treatment for a heavily carbonated RC building frame with active reinforcement corrosion (visible rust staining, spalling, cracking) is a combined EN 1504 repair sequence: Step 1 — Remove carbonated concrete to at least 15 to 25 mm behind the reinforcement. Step 2 — Clean reinforcement and apply SikaFerro 903 or Sika Monotop 910 N corrosion protection. Step 3 — Apply SikaTop 122 Plus or Sika Monotop 612 polymer repair mortar to restore cover profile. Step 4 — Apply Sika FerroGard 901 to the whole structure face including repaired areas to protect the surrounding concrete that is at pre-threshold chloride or early carbonation stages. Step 5 — Apply Sikagard 550 W Elastic surface coating as outer protection. Sika FerroGard 901 is an important part of this full system — but it supplements, not replaces, structural repair of already-damaged sections.

What is the effectiveness of Sika FerroGard 901 in arresting chloride-induced corrosion in a car park deck at 30 mm concrete cover and 0.5 per cent chloride by cement weight?

A car park deck with 30 mm cover and 0.5 per cent chloride by cement weight at the reinforcement level is in an active corrosion state (the critical chloride threshold for depassivation of reinforcement in concrete is approximately 0.3 to 0.4 per cent by weight of cement in most Indian concrete). At 0.5 per cent chloride, active corrosion of the reinforcement is likely already occurring or imminent. Sika FerroGard 901 applied in 3 to 4 coats at this stage will penetrate to the 30 mm cover depth (within its documented effective penetration range of 40 to 75 mm) and the amino-alcohol inhibitor will: Reduce the corrosion rate by adsorbing onto the steel surface and forming a barrier film that inhibits both anodic and cathodic corrosion reactions, without fully stopping corrosion at 0.5 per cent chloride. Laboratory testing of amino-alcohol MCI products in chloride-contaminated concrete shows corrosion rate reduction of 30 to 60 per cent compared to untreated control samples at similar chloride levels — a significant benefit that extends the service life of the structure without concrete breakout. However, at 0.5 per cent chloride, FerroGard 901 alone will not fully arrest corrosion — to fully arrest active corrosion at this contamination level, combined treatment is needed: full-system electrochemical chloride extraction (ECE) to remove chlorides from the concrete, or selective concrete breakout of the most chloride-contaminated zones combined with FerroGard 901 treatment of the surrounding concrete. Contact Space Arc Engineering for a full assessment of the most cost-effective rehabilitation approach for your car park.