Case 1

Remedial

Re-paint

Where only very fine cracks are present, re-painting of the surface may be adequate to close and conceal the cracks. Surface should be repaired by removing existing paint coat and sanding. If there is a large area of inadequate adhesion, the entire surface should be scraped and sanded. Make sure the surface is dry and clean enough for new application of coating. Remember to prime surface with a quality latex or oil primer. Apply a masonry sealer and allow it to dry completely. Lastly, re-paint the surface.

Remove crazing

For slightly wider cracks, they should be filled up with repair mortar before repainting the surface. Removing of the crazing can be done by carefully grinding the surface i.e. mechanical cleaning. Following that, the surface should be treated using skim coat.

Remove cracking – Use of concrete impregnation

The American concrete institute (ACI) defines polymer-impregnated concrete as a hydrated portland cement concrete that has been impregnated with a monomer that is subsequently followed by in-situ polymerization. The purpose of the impregantion is to fill any voids and small cracks that occurred during the curing of the concrete structure.  Polymer impregnation works on the principle of impregnating a low viscosity monomer into the voids and micro cracks of a pre-dried hardened concrete and subsequently polymerizing the monomer in-situ to increase the strength and durability of concrete. It also helps to protect the concrete structure against water penetration, especially capillary rising dampness[6].

Application procedures

The following are the steps for impregnation using thermal catalytic monomer polymerization, through the injection method, that can be applied to basement walls and floors:

• Remove the paint and drill holes at a suitable grid distance and to a depth to be decided by the engineer for the installation of injection ports.
• Ensure that the substrate is clean and free of dust and loose particles.
• Dry the concrete uniformly with spot lights maintained at a surface temperature of about 80 degree Celsius for a minimum 5 hours as shown in Figure 1.
• Allow the concrete to cool to about 40 degree Celsius.
• Seal all existing cracks using epoxy mortar immediately and apply a special epoxy coating system on the substrate to hole the monomer to be impregnated.
• Install injection ports using epoxy mortar.
• Allow the epoxy to dry for minimum of 3 days.
• Fix the impregnation equipment comprising of injection hoses, a pressure port and an air compressor (Figure 2) and them impregnate the concrete under incremental pressures to be decided by the engineer.
• Although this is an effective method, it is seldom applied to basement repairs in Singapore. The reason being that the cost of impregnation is much higher than conventional injection methods due to consumption of energy by the heating element as well as the need to purchase patented polymer systems. The repair also needs to be done by well-trained specialists because the required level of workmanship needs to be high so as to ensure a successful repair.