Frequently Asked Questions

Why is Sikadur 32 needed for concrete repair and cannot fresh repair mortar be placed directly on the substrate?

Plain cement repair mortar placed directly against prepared concrete without a bonding agent achieves bond only through mechanical interlocking of mortar paste into the substrate surface voids. This mechanical interlock bond is limited to 0.5 to 1.2 MPa pull-off strength — below the 1.5 to 2.0 MPa minimum required by BS EN 1504 for structural concrete repair. In structural repairs (beams, columns, bridge decks) the bond failure at the repair-to-substrate interface produces delamination and repair dropout, wasting the entire repair investment. Sikadur 32 epoxy bonding agent achieves bond through chemical adhesion of the cured epoxy to the concrete mineral surface as well as mechanical interlocking — the combined mechanism delivers 3 MPa pull-off strength, and failures occur by concrete fracture below the bond plane rather than at the interface itself, confirming the bond is stronger than the substrate. For non-structural cosmetic repairs (filling small surface voids, patching depressions in non-loaded areas), Sika Latex SBR bonding slurry may be adequate at lower cost — but for all structural concrete repair, Sikadur 32 is the mandatory bonding agent in the Sika system specification.

What is the correct application timing for Sikadur 32 and repair mortar to achieve the best bond?

The repair mortar must be placed onto the Sikadur 32 bonding agent while the epoxy is in the wet-on-wet (green-tacky) state — after the epoxy has lost its initial liquid flowability and become slightly tacky to the touch, but before it has cured to a hard non-reactive film. At 25 degrees ambient, this window is approximately 1 to 3 hours after Sikadur 32 application. In Indian summer conditions (35 to 40 degrees), the window shortens to 30 to 60 minutes — crews must time the repair sequence carefully. If the Sikadur 32 cures to a hard, glossy film before the repair mortar is placed, the epoxy must be removed by grinding or abrasive blasting and fresh Sikadur 32 applied before proceeding — placing repair mortar over fully cured epoxy produces an inadequate bond similar to unprimed concrete. At each stage of a large repair, apply Sikadur 32 to the area that can be covered with repair mortar within the wet-on-wet window, working in manageable zones rather than priming the full area at once in hot weather.

Is Sikadur 32 compatible with repair mortars from other manufacturers or must it only be used with SikaTop repair products?

Sikadur 32 is primarily specified and tested as part of the Sika complete concrete repair system with SikaTop repair mortars, and Sika provides combined system certification for the Sikadur 32 plus SikaTop system to BS EN 1504 requirements. However, the cured epoxy bonding layer provided by Sikadur 32 is a universal, stable epoxy adhesive surface that is compatible with polymer-modified cementitious repair mortars from other manufacturers — the fresh mortar bonds to the green-tacky epoxy through polymer-to-epoxy adhesion that is independent of the specific repair mortar brand. In practice, on projects where the specifier or contractor sources repair mortars from different suppliers, Sikadur 32 performs reliably as the bonding agent. The recommendation is to confirm with Sika technical if a non-Sika repair mortar is to be placed over Sikadur 32, and to carry out a pull-off adhesion test on a trial area before proceeding with the full repair, to verify that the specific mortar achieves the required minimum bond strength on the Sikadur 32-primed substrate.