Frequently Asked Questions

When is Expocrete EUW the right choice over Renderoc UW for an underwater concrete repair?

Both Expocrete EUW (epoxy mortar) and Renderoc UW (non-washout cementitious mortar) can be applied in submerged and tidal conditions, but the correct selection depends on the structural requirements and the exposure conditions of the repair. Renderoc UW is appropriate for the large majority of underwater concrete patch repairs where the structural requirement is reinstatement of section loss and protection of reinforcement from continued corrosion — the 35 MPa compressive strength and 1.0 MPa bond strength of the cured cementitious mortar are adequate for most structural elements in marine ports, jetties, and coastal structures. Expocrete EUW is appropriate where one or more of the following requirements apply: the compressive strength of the repair must significantly exceed that achievable with cementitious mortars (70 MPa versus 35 MPa); the bond strength requirement is higher than 1.0 MPa (such as in heavily loaded repairs where the repair carries applied stress); the repair is subject to abrasion or impact from water-borne debris, sediment, or hydraulic flow; or the chemical environment contains acids, hydrocarbons, or other chemicals that would degrade a cementitious repair. The higher cost of epoxy mortar versus cementitious mortar is justified in these demanding applications by the significantly superior performance.

How is Expocrete EUW applied by a diver to a vertical underwater pile or pile cap?

Application of Expocrete EUW by a diver to a vertical underwater surface follows a similar process to the bagged placement technique used for Renderoc UW cementitious mortar, but with the specific mixing and timing requirements of an epoxy system. The three components (resin, hardener, and pre-dried aggregate) are mixed on the surface using a low-speed drill mixer until the aggregate is fully coated with the combined epoxy resin and hardener — the pot life at the water temperature must be confirmed before mixing (cold water extends pot life, warm water shortens it). The mixed epoxy mortar is placed into a flexible bag and lowered to the diver, who pushes the mortar from the bag into the prepared repair cavity. The diver must confirm that the repair void is clean and free of silt, biological growth, and loose concrete (preparation must be carried out by water jetting or chipping before the repair epoxy is applied). The epoxy mortar must be held firmly in the cavity against the prepared surface until the initial cure period is complete — typically 30 to 60 minutes depending on water temperature.

What are the limitations of epoxy mortar repairs in permanently submerged conditions and how long do they last?

Epoxy mortars in permanently submerged conditions have excellent long-term durability — the cured epoxy resin matrix is highly resistant to water penetration and chemical attack from seawater and fresh water. The primary limitation of underwater epoxy repairs is not the cured mortar performance but the interface between the epoxy mortar and the concrete substrate: if the substrate preparation was inadequate (incomplete removal of biological fouling, loose concrete, or contamination), the bond may be lower than the specified value and could fail under structural loading or wave impact. Thorough mechanical preparation of the substrate — by underwater high-pressure water jetting, pneumatic chipping, or abrasive blasting — is critical for achieving the bond strength that justifies the selection of epoxy over cementitious. A well-executed Expocrete EUW repair on a properly prepared substrate in a typical marine environment should provide a service life comparable to the surrounding original concrete — 20 to 40 years in protected conditions, or 10 to 20 years in severely exposed tidal and splash zones.