Question 1

What is piling injection?

Accepted Answer

Piling injection involves forcing resin into voids or defects within deep concrete foundation piles. Piles can suffer from 'necking' (narrowing) or soil inclusions during casting. By drilling down the length of the pile or using integrated pipework, we inject high-strength grout or resin to fill these voids, restoring the load-bearing capacity of the pile without the massive cost of installing replacement piles. In more detail: cast-in-place piles (bored and CFA piles) are concreted blind, deep in the ground, and defects are common. Besides necking and soil inclusions, piles can contain honeycombing and voids from poor tremie placement or segregation, and cold joints or cracks from installation, ground movement or load. Defects are usually found by integrity testing (low-strain sonic or pulse-echo tests on most piles, and cross-hole sonic logging through pre-installed access tubes on larger bored piles) or by excavating and exposing the pile. Once a piling or structural engineer has confirmed that repair, rather than a replacement or additional pile, is acceptable, the method depends on where the defect sits. Defects near the head are exposed by excavating around the pile, broken out and reinstated, and any cracks injected. Deeper defects are reached by coring down the shaft, or through the sonic logging tubes, to the defective zone; loose material is flushed out with water or air, and the void is pressure-grouted with cementitious grout or injected with low-viscosity structural epoxy until refusal, after which coring or re-testing confirms the result. Where the problem is water rather than capacity, for example water tracking through a secant or contiguous piled basement wall or through the joint between pile cap and slab, hydrophilic polyurethane resin is injected to stop the leak, often from inside the basement without excavation. Injection repair is normally far quicker and cheaper than a replacement pile, which can require new pile caps or transfer beams, but it is only appropriate where the engineer is satisfied the repaired pile will carry its design load.

Question 2

How do you treat exposed rebar in damaged concrete?

Accepted Answer

Treating exposed rebar is the most critical step in concrete repair, and done properly it follows a five-stage protocol. First, we break out the concrete around the bar — typically 15-20mm behind it — because corrosion always extends further than the visible damage. Second, the steel is cleaned back to bright metal (Sa 2.5 standard) by grit blasting or mechanical wire brushing to remove every trace of rust; painting over corrosion simply traps it. Third, where the bar has lost more than around 10% of its cross-section, a structural engineer must assess whether supplementary reinforcement is needed. Fourth, the cleaned steel is coated with a zinc-rich passivation primer (such as Sika MonoTop-910 N) that protects it against future corrosion — this is the step DIY repairs almost always miss, and the reason they fail within a couple of years. Finally, the section is reinstated with a polymer-modified structural repair mortar compliant with BS EN 1504-3, compacted around the bar so no voids remain. If you only need a short-term hold, sealing exposed rebar with a rust converter and cementitious fairing coat can slow corrosion, but it is not a repair: once rebar is exposed and rusting, the expansion of the steel (up to seven times its original volume) will keep cracking the surrounding concrete until the corroded material is removed and the bar is properly passivated and re-covered.

Question 3

What is crack bridging?

Accepted Answer

Crack bridging refers to the ability of a coating or resin to span across a crack and remain intact even if the crack widens or moves due to thermal expansion or structural settling. 'Static' crack repair materials (like epoxy) will snap if the crack moves. 'Dynamic' crack bridging materials (like flexible PU resins or elastomeric coatings) stretch to accommodate the movement, maintaining the waterproof seal. Selecting the right elasticity is vital for long-term success.

Question 4

What is 'feather-edging' and why avoid it?

Accepted Answer

Feather-edging is the practice of troweling a repair mortar out to a super-thin layer (a feather edge) to blend it with the surrounding surface. This is bad practice in structural repair because the thin edge dries too fast, cracks, and delaminates. We always saw-cut the edges of a repair area to a minimum depth (e.g., 10mm) to provide a square shoulder that the repair material can butt against for a durable bond.

Question 5

What is a 'Form and Pour' repair?

Accepted Answer

Form and pour is a technique used for large volume concrete repairs. Instead of hand-applying mortar in layers, we build a shutter (formwork) around the damaged area and pour a flowable micro-concrete into the void. This ensures complete compaction and bond without the risk of layering (cold joints). It is ideal for vertical columns or soffit repairs where hand application would be slow and difficult.

What is piling injection?