1. Before Application of Concrete Structure Restoration
Working space shall be clean and tidy with no obstructions. Record the substrate, ambient temperature and relative humidity. Check pot life information on bag or in the product data sheet and allow for climatic conditions e.g. high/low temperatures & humidity. External applications shall be adequately protected. Do not apply recasting mortar in direct sun, windy, humid or rainy conditions, do not apply if there is a risk of frost within 24 hours in unprotected areas. Make sure blow holes are not obstructed and can allow the escape of air.
Calculate the required volume for the application and then using the equation in section 10 of this method statement, calculate the yield of the product. Make sure there is enough material on job site to carry out the work.
2. Reinforcement Corrosion Protection
Where a reinforcement corrosion protection is required, apply material to the whole circumference of the steel reinforcement bar in two layers. Wait until the first layer has dried before applying the second layer. Use a mirror to inspect behind the back of the bars to ensure full coverage. Take care not to splash or apply material on a dry concrete substrate behind the bars.
For small areas use two paint brushes to apply 2 layers and ensure full coverage. For larger areas use hopper gun aim the spray in different directions to ensue coverage behind the back of the bars. The recasting mortar shall only be applied when the reinforcement corrosion protection is hardened.
3. Bonding Primer
Refer to relevant repair mortar product data sheet if a bonding primer is required. If a bonding primer is required, the substrate surface shall be pre-wetted. Bonding primers can be applied by hand (pressing the material firmly into the surface), using a brush or using a hopper gun for larger areas. The repair mortar shall be applied wet on wet to a bonding primer. Ensure the substrate surface is fully covered behind the reinforcement bars. For large applications use only a bonding primer with long open time to take into account the formwork construction.
4. Recasting using a Pourable Repair Mortar
A pourable repair material shall be applied into the prepared opening as soon as possible after mixing. A grout shall be poured into the prepared opening within 15 minutes to optimise the expansion properties of the material. Pot life shall also be taken into consideration, adjusting for climatic conditions, when planning the work duration.
Pour the grout through the “mouth” of the formwork allowing the material to flow to the opposite end. Always maintain sufficient pressure head while pouring. Ensure a process of continuous pouring to avoid air entrapment and prevent the material flow from coming to a stop before the operation is completed. Make sure air displaced by the material can easily escape. Always pour from opposite ends to any air release (blow) holes.
Maintain pouring until material escapes from the air release holes. Allow some material wastage until it is certain all air has been released and there is no air trapped air in the application. Avoid the free fall of the material to prevent segregation of the aggregate (max ~2 cm). Never make an application from two places as it will be difficult to determine if all air has been released, and the entire void has been filled. Do not vibrate the formwork as this will cause segregation and bleeding.
5. Recasting using a Pumpable Repair Mortar
The method of pumping a material must ensure complete filling of the voids, crevices. Pumping equipment shall suit the material and purpose for which they are to be used. Always read the pump manufacturer’s instructions and obtain further guidance if necessary. Pumping shall generally be applied from the bottom of the application to force the air out of the top through controlled air release hole(s). Pumping shall only take place from one position on an application and shall continue until material escapes out of the controlled air release points. Allow some material wastage until it is certain all air has been released and there is no air trapped air in the application.
6. Removal of Formwork
The formwork shall not be removed until sufficient strength has been achieved. This time depends on the material characteristics and climate conditions. As guidance the formwork around a high performance, low shrinkage grout in normal 21°C/55% relative humidity conditions may be removed approximately 12 to 24 hours after application. Formwork shall only be removed with the agreement of the supervising officer or qualified engineer.
7. Curing
Best curing is achieved while the formwork is still in place. As soon as the formwork is removed, protect the still green material from premature drying. Cure with proper curing methods for 3 days or spray with appropriate curing compound once any surface water has evaporated. Curing methods include jute and water, plastic sheets or other suitable membranes.
8. Smoothing / Leveling Mortars
Smoothing mortars can be applied by hand, by hopper gun or by mechanical spray equipment for large areas. Refer to relevant product data sheet for further information. A smoothing coat shall be applied over the whole prepared concrete surface (including repair and non-repaired areas). Any laitance layer on the surface shall be removed and surface pre-wet. Smoothing coats may be hand, using notched trowel, or by spray applied.
Use a toothed trowel to apply the mortar onto the surface in a vertical direction. Hold the trowel at an acute angle to the surface and use different size toothed trowels to regulate the application thickness. Finish surface with damp sponge, wooden or plastic float after material has set. Do not add apply additional water on the surface as this will cause discoloration and cracking.
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