Dry pack mortar is a commonly used material for repairing concrete surfaces that have cracks or holes. This material is particularly effective for repairing holes that are at least as deep as the minimum dimension of the area being repaired. Typically, the holes found on concrete surfaces are cone bolt holes, she bolt holes, or holes created by ties.
However, it’s important to note that dry pack mortar is not suitable for repairing shallow cracks or completely extended holes that go from one side of the concrete to the other. Additionally, it is not appropriate for filling spaces behind reinforcement. In these situations, alternative materials and methods should be used to properly repair the concrete surface.
Steps for Concrete Repair by Dry Pack Mortar
Following are the steps involved in concrete repair work by dry pack method.
- Preparation of Hole Inner Surface
- Preparation of Dry Pack Mortar
- Applying Dry Pack Mortar
- Curing of Dry Pack Repair Area
1. Preparation of Hole Inner Surface
To ensure the proper application of dry pack mortar, it is important to prepare the surface or hole that requires repair beforehand. This preparation involves cleaning, washing, and drying the area to be worked on, as well as removing any damaged pieces of aggregates.
Moreover, in order to achieve a strong bond between the dry pack mortar and the surface, the inner surface of the hole must be rough. If the surface is smooth, it is necessary to roughen it using a tapered reamer or a star drill. This will help to create a surface with better adhesion properties, ensuring that the dry pack mortar adheres firmly to the repaired area.
By taking these steps prior to the application of dry pack mortar, you can ensure that the repaired area is structurally sound and will withstand the test of time. Proper preparation is key to achieving a successful repair that is both durable and reliable.
When preparing the inner surface area of holes to ensure a strong bond with dry pack mortar, there are typically three methods available. These methods are aimed at creating a clean and rough surface on the inside of the hole that will allow the mortar to adhere more effectively.
The first method involves the use of a wire brush. This is a common tool used for cleaning the surface of the hole and removing any loose debris or particles that may be present. The wire brush is typically made of stainless steel and is used to scrub the inside of the hole in a circular motion, which helps to roughen up the surface.
Another method is the use of a chipping hammer. This tool is typically used for breaking up concrete, but can also be used to chip away at the inside of the hole to create a rough surface. The chipping hammer is held at a slight angle to the surface of the hole and is used to break away any loose material. This creates a textured surface that will provide a better grip for the mortar.
The third method is the use of a diamond-tipped drill bit. This method is typically used for creating holes in hard surfaces like concrete or stone, but can also be used to create a rough surface inside the hole. The diamond-tipped drill bit is used to drill into the surface of the hole, creating small indentations and roughing up the surface.
Overall, the goal of these methods is to create a clean and rough surface on the inside of the hole that will allow the dry pack mortar to adhere effectively. By using one of these methods, you can ensure that your dry pack mortar will form a strong bond and provide a stable foundation for any subsequent construction or repair work.
Method – 1
To ensure a strong bond between the inner surface of a hole and the mortar that will be applied, a bonding grout is used. This grout is made up of a mixture of cement and fine sand in a 1:1 ratio. It is important to note that before the bonding grout dries up, dry pack mortar should be applied to the hole. This helps to create a better bond between the mortar and the surface of the hole.
However, it is crucial to ensure that there is no free surface water in the hole before applying the bonding grout. The hole must be completely dry for the grout to be effective. This will help to ensure that the grout adheres well to the surface of the hole and provides a strong base for the mortar to be applied. By following these steps, one can ensure that the mortar will be properly bonded to the surface of the hole, resulting in a strong and durable structure.
Method – 2
To prepare a hole for dry pack, it is important to pre-soak it overnight using wet rags or burlap. After soaking, the hole is left to partially dry or to contain some amount of surface water. This step is necessary to ensure that the dry pack adheres properly to the surface of the hole.
Once the hole has been partially dried or contains some surface water, the next step is to apply dry cement on the surface. This is done by using a small brush to spray the dry cement onto the surface of the hole. The dry cement will absorb any free water and start forming a layer on the surface.
It is important to remove any excess dry cement that is still on the surface of the hole. This is done by using a jet of air to blow away the excess dry cement. Once the excess dry cement has been removed, the dry pack can be applied to the surface of the hole. This process is crucial to ensure that the dry pack sets properly and forms a strong bond with the surface of the hole.
Method – 3
The method of using epoxy bond resins to establish a strong bond between dry pack mortar and a surface is a common practice. To begin, epoxy resin is prepared by mixing it thoroughly and then applied to the desired surface using a brush. It is important to ensure that the concrete temperature is not too high during the application of the epoxy, as this can cause the epoxy to dry out or burn quickly.
One of the significant advantages of using epoxy bond resin is its ability to prevent the hydration of water to the surrounding concrete surface. This means that the surface will remain dry, which is essential for ensuring a robust and long-lasting bond between the dry pack mortar and the surface.
It is crucial to work quickly when using epoxy bond resin because once it has been applied, the dry pack mortar must be immediately added before the epoxy dries out. By doing so, the epoxy will act as an adhesive, securing the dry pack mortar to the surface effectively.
2. Preparation of Dry Pack Mortar
Dry pack mortar is a type of mixture used in construction that is composed of only cement, fine aggregate, and water. Typically, the mixture consists of one part cement and 2.5 parts sand. The fine aggregate used must be able to pass through a No.16 (1.19mm) sieve. To achieve high strength and eliminate excessive shrinkage, a low water content is preferred.
When preparing dry pack mortar, it is important to add water slowly and ensure that the mixture forms a ball when molded in hand. The consistency should not crumble or slump. Due to the high amount of cement present in dry pack mortar, it usually has a dark color that may not match the color of the surrounding concrete. However, if uniform color is desired, white cement can be used instead.
3. Applying Dry Pack Mortar
Dry pack mortar is a type of mortar that should be applied in layers with a maximum compacted thickness of 10 mm for each layer. It is important to apply each layer immediately without any delay, as the layer may harden otherwise. To assist with a strong bond between layers, grooves are provided on the surface after each layer is placed.
The compaction of each layer is obtained by striking the surface with a hardwood stick using a hammer. The hardwood stick used for this purpose is generally 8 to 12 inches long and 1 mm in diameter. During tamping or compacting, the stick is placed at an angle to compact the sides of the hole.
It is worth noting that the use of metal rods or water for ease of compaction is not recommended in the dry pack method. This is because the method relies on the proper use of the hardwood stick for compaction, and the use of other materials may compromise the quality of the mortar.
4. Curing of Dry Pack Repair Area
The repaired area, once the applied mortar has been set, requires water curing for a duration of 14 days. It is crucial that the mortar does not dry out during this period.
Following the 14-day water curing, a curing compound needs to be applied to the surface of the mortar. Two coats of either wax-based or water emulsified resin-based compounds can be used for this purpose.
After the application of the curing compound, it is important to ensure that the repaired area is protected from freezing temperatures for at least 3 days. This will ensure that the curing process is not disrupted and the repaired area can fully set and bond.