Spray-On Concrete Wall Preparation

Clean the Wall

• The wall needs to be clean prior to any application of concrete because dirt or debris interferes with the bonding process. A pressure washer is useful if the existing surface is durable, but a garden hose is fine for more sensitive or softer surfaces. Scrub any stubborn dirt or stains with a scrubbing sponge or scrub brush and a mild detergent to ensure the wall is completely clean before continuing. Rinse the wall again after using detergent to eliminate any remaining residue. Allow the wall to fully dry.

Repair Broken Sections

• Any existing damage to the wall will still be there after spray-on concrete is added, so it is better to repair any damage prior to concrete application to prevent structural problems in the future. The method for this depends on what surface the concrete is applied to. Construction patches are available for nearly any kind of surface. Woody putty fills in damage to wooden walls, while Portland cement fills in breaks in concrete or brick. Follow all instructions for whatever patching materials you choose for best results. Smooth the repair so it is even with the wall around it, and let it dry fully before adding concrete.

Fill Cracks

• Cracks are often the result of moisture infiltration. Even small cracks are likely to get worse if they are not repaired prior to adding the spray-on concrete. Crack-filling syringes help seal cracks efficiently by injecting crack filler directly into the open space caused by the split. Epoxy is often useful for this, but the crack must be completely dry for the epoxy to bond appropriately. Give the crack repairs at least several hours to dry before applying spray-on concrete. If the crack sealer you use recommends a longer drying time, follow those instructions so the crack doesn't reopen after the spray-on concrete is applied.

Prepare the Concrete Mixture

• The concrete needs proper preparation before you can spray it onto a wall. If you use the dry method, the dry cement requires premixing with lime, sand or any other materials you're using with it. The mixture is then added into the sprayer, and an air compressor forces it out to the wall with a stream of water. The concrete then mixes together as it is applied. Wet application requires that water be pre-added to the dry cement, giving you greater control over the consistency and thickness of the concrete. The mixture then needs regular stirring to prevent it from hardening prior to wall application.