Concrete cracks caused by spalling will follow a specific repair specification treating both steel and concrete.Concrete cracks not caused by rusted rebar will be repaired using a fibre reinforced polymer modified repair mortar.
Cracks caused by spalling will follow very specific repair regime, treating steel and concrete alike to achieve structural Strength while repairing the area.
When repairing concrete cracks it is important to establish the cause. For example if the cause is water ingress into the substrate causing Spalling, the waterproofing issue needs to be addressed before the concrete repair takes place.
Hairline cracks are less than 0.5mm. These are prepared according to the manufacturers specification and treated with a fibre re-inforced waterproofing compound.
Cracks from 0.5mm to 1mm are raked open and treated with a non acrylic based filler or as per Hairline cracks. Cracks from 1mm to 5mm with no loose plaster are ground open to a depth of 5mm and repaired using a latex modified mortar.
Cracks with loose plaster either side will be chopped out a minimum of 75mm per side and re-inforced with a reinforcing fibre Mesh, providing that the thickness of plaster allows this. If the crack continues into the brickworkand is wider than 5mm, a structural epoxy is used to strengthen the cracked area before applying the latex modified plaster repair as per above
Movement joints main function is to allow for expansion and contraction. In this case the polyurethane is usually over coated with fibre re-inforced acrylic, followed by the specified paint system. It is critical that the correct depth to width ratios are maintained to ensure the longevity of joint.
When the reinforcing steel within a concrete structure rusts it expands. This expansion causes the surrounding plaster and concrete to crack. The above paragraphs deal with the crack repairs.
All loose concrete and plaster must be hacked away to expose steel enough to allow the proper cleaning of rebar.
If the Ph level of the concrete has dropped to an unacceptable level, the surrounding concrete must be treated with a migratory corrosion inhibitor to prevent a anodic and cathodic corrosion which is prevalent under these conditions.
The steel is now ready for treatment. Here caution must be taken not to use products that are bond breakers, otherwise the new repair mortar will not bond to the steel thus giving no strength to the repair.
The concrete area can now be repaired using a fibre reinforced polymer modified repair mortar