Frequently Asked Questions

Does SikaFerro 903 need to be applied to reinforcement bars that show only surface rust (Stage 1) without pitting or cross-section loss, or only to bars with severe corrosion?

SikaFerro 903 should be applied to all exposed reinforcement bars regardless of corrosion severity — even bars that appear to show only minor surface rust (Stage 1: discoloration and red-brown staining without visible pits) should be coated with SikaFerro 903 as part of any proper concrete repair sequence. The reason is that the assessment of corrosion severity by visual inspection alone is unreliable — half-cell potential mapping and carbonation depth testing frequently reveal that bars showing only surface rust are already in an active corrosion state with high anodic half-cell potentials, meaning active corrosion will continue after the repair is closed up unless the bar surface is protected. Additionally, the new repair mortar placed over unprotected reinforcement will have a lower pH than the original concrete at the bar interface (due to the absence of original calcium hydroxide), which means that even bars that were passivated in the original concrete can become active at the repaired interface. The only bars that may not require SikaFerro 903 are bars that are fully embedded in concrete that has tested as non-carbonated (phenolphthalein positive, bright purple/pink) and shows no chloride contamination — in all other repair situations, apply SikaFerro 903 to all exposed bar surfaces as standard practice.

Can SikaFerro 903 be used as a standalone waterproof coating on mild steel structural members such as I-beams and plate girders?

No — SikaFerro 903 is formulated and tested for one specific application: coating cleaned reinforcement bars embedded in cementitious repair mortars during structural concrete repair. It is NOT a suitable standalone anti-corrosion coating for exposed structural steel elements such as I-beams, channels, plate girders, hollow sections, or other steel structures exposed to atmosphere, weather, or immersion. The reasons are: SikaFerro 903 is a thin-film, brush-applied cementitious coating with a dry film thickness of approximately 0.5 to 1.0 mm per coat — far below the minimum film thickness required for standalone steel protection (typically 100 to 400 microns DFT for a complete anti-corrosion system); it has no tested performance data for atmospheric corrosion resistance in the steel protection sense (adhesion to steel, barrier properties, cathodic protection); and it is not classified or certified as an anti-corrosion coating system per IS or ISO 12944. For exposed structural steel protection, specify an appropriate multi-coat anti-corrosion paint system from the Sika Sarnacor range or another approved paint system per IS 1477 / ISO 12944.

What is the maximum interval between cleaning the reinforcement and applying SikaFerro 903, and what happens if the bar re-rusts before coating?

The maximum interval between mechanical cleaning of reinforcement to Sa 2.5 standard and application of the first coat of SikaFerro 903 is 4 hours in normal conditions (below 30 degrees C, relative humidity below 70 per cent). In hot, humid North Indian monsoon conditions (July to September in Ghaziabad and Delhi NCR — high humidity, frequent rainfall), steel bars begin to show flash rusting (light orange discoloration) within 1 to 2 hours of cleaning in exposed outdoor conditions. Flash rust that has formed as a very light orange tinge within a few hours of cleaning is acceptable for SikaFerro 903 application — the alkaline cementitious composition will passivate the lightly rusted surface. However, if the bar has been left uncoated overnight or longer and has developed visible red-brown rust deposits (not just flash rust tinge) or has re-rusted at pitting sites, the bar must be cleaned again to Sa 2.5 before SikaFerro 903 application — applying cementitious corrosion primer over re-rusted steel traps active corrosion product under the coating, which will continue corroding and eventually debond the coating from the bar. On monsoon-season repair projects, plan the work sequence so that SikaFerro 903 is applied on the same day as reinforcement cleaning, preferably within 2 hours of cleaning, and cover the repair area with polythene sheeting overnight to prevent rain and humidity exposure.