What causes grout to fail prematurely?
There are 4 basic causes of premature grout failure:
- Improper drilling and delivery
It is not uncommon for contractors to drill directly into the crack or too close to the surface. By doing this type of technique, a seal is created that is 1/3 to ½ of the crack depth and water under hydrostatic pressure is still within the concrete element. Very little flexural movement causes leakage to recur.
- Inadequate mixing ratio of water to grout during application
Most contractors are taught by manufactures that pre-wetting the crack prior to urethane grout injection is all that is needed to activate the material. This would likely be the case of the wall was 4 to 6-inches or less in thickness. Wall and floor sections greater than 12-inches would not fit the criteria; however, and a multi-ratio pump for injecting water reactive urethane grouts should be used.
Some contractors prefer to use two small electric pumps – one to inject urethane, one to inject water – and then rotate a few strokes of water to several strokes of grout thinking they are getting good cross-polymerization of water to urethane. While this may seem a viable solution because the first grout that comes to the surface appears to be fully reacted, it is very common to have areas of water deprived urethane grout within the cracks and various defects. When these conditions are subjected to high temperatures in the environment (in excess of 100 to140º Fahrenheit), it is common to see a brown, unreacted urethane resin extrude from the cracks anywhere from 2 months to 2 years after the initial grouting. This urethane resinous material has now contaminated the crack for future injection. Many contractors have found that the only viable way to seal cracks with unreactive grouts is the backside grouting method.
- Excessive wall movement
Excessive movement is most prevalent when the concrete is subject to outdoor temperatures – i.e. exterior tanks, retaining walls, exposed foundations, and similar. Most resins have some degree of flexibility. It is not uncommon that during warm to cold cycles, a 5 mil crack will open to a 10 mil crack. Most resinous grouts, even though they are called flexible, cannot sustain repeated opening and closing of the crack and will fail. Grout adhesion to the substrate may fail during expansion and contraction of the crack if surface contaminants on the grout sidewall are prevalent.
- Chemical attack
Chemical attack is very common in the industrial environment and this type of issue usually takes several years to work its way through the grout matrix. Residue hydrocarbons within water will commonly attack many of the grout formulations. This is exacerbated if chemical attack and thermal expansion/contraction are occurring simultaneously.