Frequently Asked Questions

What is the minimum repair depth for Sika Fastfix and how should deep repairs be built up in layers?

Sika Fastfix can be applied in a single layer from a minimum depth of approximately 10 mm up to a maximum of 50 mm per layer. For repairs shallower than 10 mm, the material layer is too thin to develop adequate tensile strength to remain bonded and may curl or delaminate — for repairs shallower than 10 mm, a scratch coat of Sika Fastfix slurry applied to the substrate first, followed immediately by the mortar repair while the slurry is still wet, can achieve repairs from 5 mm depth. For repairs deeper than 50 mm, Sika Fastfix must be built up in multiple layers. Due to the very rapid set time, the first layer must be allowed to set and gain strength (minimum 30 minutes at 25 degrees C) before the next layer is placed on top. Roughen the surface of the first set layer with a wire brush or angle grinder before placing the subsequent layer to ensure mechanical bond between layers. The substrate preparation for Sika Fastfix repairs is the same as for any cementitious repair mortar: saw cut the perimeter of the repair to a minimum depth of 10 mm to avoid feather edges; break out all delaminated, cracked, or contaminated concrete to sound concrete; clean the substrate by sandblasting, grinding, or high-pressure water jetting to remove all laitance, oil, grease, and curing compound; pre-wet the concrete substrate with clean water until uniformly damp (saturated surface dry condition) to prevent the substrate from drawing water out of the Sika Fastfix mix too rapidly — which would prevent proper hydration and reduce strength development. Work in small batches given the rapid set time — mix only as much Sika Fastfix as can be placed and finished within 8 to 10 minutes at 25 degrees C.

Can Sika Fastfix be used for structural concrete repairs and does it need reinforcement for large or deep structural patches?

Sika Fastfix achieves compressive strengths above 40 MPa at 28 days, which is comparable to or exceeds the strength of the original concrete in most Indian construction (IS 456 M25 to M35 grade concrete). This high compressive strength and the rapid strength gain (above 25 MPa within 3 to 4 hours) make Sika Fastfix suitable for structural repair applications including repair of load-bearing columns, beams, slabs, and bridge deck elements. However, compressive strength alone does not determine structural adequacy of a repair — the following factors must be assessed for each structural repair: Bond to substrate: the repair must be fully bonded to the surrounding concrete to transfer load. Correct substrate preparation (saw cutting, breaking out, cleaning, SSD condition) is mandatory for structural repairs. For deep structural patches on beams or columns, a Sika bonding agent (such as Sika Monotop 910 N) should be applied to the prepared substrate before Sika Fastfix to maximise bond. Reinforcement: for structural repairs deeper than approximately 75 mm, or in areas where the original concrete was reinforced, exposed rebar must be prepared (derusted by sandblasting or grinding to Sa 2.5 standard) and coated with a zinc-rich primer such as Sika Monotop 910 N before Sika Fastfix is placed. Additional reinforcement bars (stitch bars anchored into sound surrounding concrete) may be specified by the structural engineer for large patch repairs. Dimensional compatibility: Sika Fastfix has a coefficient of thermal expansion similar to concrete, which ensures good long-term compatibility and minimises differential movement at the repair interface under thermal cycling.