Cause: Failure of the cement paste to consolidate and fill the voids between the more coarse aggregates.
Possible concrete repair solutions:
Functional/aesthetic concrete only:
- Chip by hand to remove any loose material
- SSD (saturated, surface dry). This is the process of saturating the concrete substrate to receive a topping or patch with water to prevent the rapid absorption of the new materials moisture, which could cause shrinkage and loss of strength. Following saturation, the substrate is blown-off with clean air, or vacuumed so the surface is dry.
- Scrub coat
- Float-in a polymer modified, architectural finishing mortar.
- Finish with a sponge float.
- Cure and seal.
Structural concrete: If the extent of the honeycombing reaches to the reinforcing steel or beyond, it must be treated as a structural repair.
- Saw-cut perimeter of patch to minimum ½” deep. This step serves several purposes, with respect to repair area durability. It contributes to proper patch geometry (a patch that is irregular in shape and depth will cure and shrink irregularly). A square shoulder also provides a straight line between new and existing materials that is easier to anchor, bond, and seal, as well as being more damage resistant.
- Chip out the unsound material to a minimum depth of ½” beyond the rebar. This step is part of the diverse topic of surface preparation. Mechanically profiling the contact surfaces of a repair area to a fractured aggregate profile greatly increases the total bond surface area and provides mechanical interlock between the new and existing. This is especially important with coatings, toppings and overlays that are not anchored like a patch would be. For this reason the International Concrete Repair Institute (ICRI) established industry accepted standards for surface preparation, and product manufacturers will specify requirements based on those standards (below).
- Prep rebar if corroded.
- Saturate prepped surfaces with water (SSD)
- Apply a bond-scrub-coat: scrubbing the repair material into the profiled surface of the substrate using a stiff brush or gloved hand. This forces the repair material into intimate contact with the substrate promoting 100% bond and mechanical interlock between the new and existing. Note: This process is sometimes referred to in error as a “bond-slurry-coat”. This is misleading, and implies that the scrub material be of fluid consistency. This often results in far too much water being used in the scrub material, resulting in a weak mix, counter-productive to the intent. The scrub material should use the same amount of water or less than the patch material.
- Patch with a polymer modified, fiber-reinforced structural mortar.
- Cure and seal.