Cara Guna Gam Simen

Whether you’re filing in a crack, repairing a section of concrete, or pouring a whole new layer over an existing layer of concrete, getting the new concrete to adhere to the old layer can be difficult if you don’t follow the proper procedures. Start by cleaning the older concrete with a strong acid wash. Then, prepare a bonding slurry to ensure the new concrete adheres to the previous layer. Dampen the existing concrete, apply the bonding slurry, then add your new concrete. 

Part One of Three:

Cleaning the Old Concrete with Acid Wash

1.      Clear the area and sweep the concrete to remove large particles. Pick up any objects, move any furniture, and remove any people or pets from the area so you can clean the concrete. Use a broom to sweep away dirt and debris from the old concrete.^[1]

• If your concrete has cracks or grooves, use the bristles to sweep out and remove as much of the dirt or debris as possible.

2.      Mix 7 parts water to 1 part muriatic acid in a bucket. Muriatic acid is a strong chemical cleaner that will strip away dirt, oil, and debris. The acid will also soften the top layer of the concrete and make it ready to bond with the new concrete. Put on a face mask to avoid inhaling the fumes and pour the water into the bucket first, then add the muriatic acid and give the mixture a gentle stir.^[2]

• For example, if you add 7 cups (1,700 mL) of water, add 1 cup (240 mL) of muriatic acid to the water to create an effective cleaning solution.
• You can find muriatic acid at hardware stores and online

Warning: Muriatic acid can put off noxious fumes. Work in a well-ventilated area when you’re mixing the solution so you don’t breathe in the vapors.

3.      Pour the acid mixture over the old concrete. Pour the mixture directly from the bucket or use a plastic sprinkler can to distribute it over the old concrete. Be sure to cover all of the concrete evenly.^[3]

• If you get some of the mixture on your skin, rinse the affected area under cool water. The acid can cause dryness and a slight burning sensation if you let it sit for too long.
• Wash out the bucket or plastic sprinkler can with clean water when you’re finished applying the acid mixture.

4.      Allow the mixture to sit for 10 minutes. The acid wash should start to foam and may make a hissing sound. This is a normal part of the cleaning process. Allow the mixture to remain on the concrete for about 10 minutes so it can work to lift and remove oil and dirt.^[4]

5.      Wash the old concrete with a pressure washer. Take a pressure washer and use a back and forth sweeping motion to spray and clean the concrete. Work in sections and be sure to clean every bit of the concrete and wash off the acid mixture.^[5]

• You can rent a pressure washer from home improvement stores if you don’t own one.
• If you can’t get a pressure washer, you can use a garden hose to rinse the concrete, but it won’t be as effective at removing oil and grime.
• If you’re rinsing concrete near grass or plants, throw a handful of baking soda on the plants that come into contact the the acid mixture to neutralize it. The acid could kill the grass or plants.^[6]

Part Two of Three:

Mixing a Bonding Slurry

1.      Mix together equal parts water and white glue in a bucket. A bonding slurry will greatly increase the adhesion between pieces or layers of concrete. In a large bucket, add equal parts water and white glue and stir the mixture together.

• For example, if you add 2 cups (470 mL) of water, you need to add 2 cups (470 mL) of white glue into the bucket.
• You can use ordinary crafting glue that you can find at department or art supply stores.

2.      Put on a face mask before you add cement. Breathing in the cement dust can irritate your mucous membranes and cause respiratory problems if you inhale it. Before you add any dry cement mix, put on a face mask to prevent possible inhalation.^[7]

• Make sure the mask fits snugly over your nose and mouth.

3.      Add 2 parts of dry cement mix to 1 part of the water and glue mixture. Once you’ve mixed the glue and water together, add dry cement mix into the bucket at a ratio of 2 to 1. You want the mixture to have a consistency similar to a thick paint.^[8]

• For example, if you’ve mixed together 1⁄2 gallon (1.9 L) of water and glue, you’ll need to add 1 gallon (3.8 L) of cement mix.
• If you add too much concrete, add more water and glue to loosen the paste and make it softer.
• Use portland or mortar cement mix for the most effective bonding slurry.

4.      Stir the mixture in the bucket to create a slurry. Use a wooden spoon or a metal mixing tool to stir the mixture until it’s the right consistency. Stir along the bottom and the edges of the buckets so there aren’t any pockets of dry concrete powder.^[9]

• Add more concrete powder or water if necessary.

5.      Keep the bucket of slurry covered and cool so it lasts longer. The slurry mixture will harden faster than concrete and become unusable once it sets, so don’t allow the slurry to sit for more than 1 hour. Use it soon after you mix it together.^[10]

• Avoid keeping the bucket in the sun or it will harden faster.

Part Three of Three:

Bonding New Concrete to Old Concrete

1.      Wet the old concrete thoroughly. In order for the concrete to adhere together effectively, it cannot be dry. The concrete must be damp so the water permeates into the older concrete to help achieve a strong bond.^[11]

• Don’t soak the concrete or allow standing puddles of water to form or the concrete won’t set.

2.      Mix a new batch of concrete. Use a large bucket and add your water to the concrete mix according to the instructions on the back of the bag. Pour the water slowly and stir the mixture well. Work out any lumps that form to create an even consistency.^[12]

• Keep the concrete mixture nearby so you can apply it when you’re ready.
• Wash the tools you use to mix your concrete after you’re done so the concrete doesn’t harden on them.

3.      Brush a thin layer of the slurry mixture onto the old concrete. Before you add your new concrete, take a large brush and dip it into the bonding slurry. Brush the slurry over the damp concrete to form an even layer. Make sure all of the old concrete has a layer of slurry on top of it before you move on.^[13]

• Use a big paintbrush or any other type of large brush to apply a layer of the slurry.
• Make sure the concrete is damp before you brush the slurry mixture.

4.      Pour the new concrete on top of the old concrete. After you’ve brushed your slurry mixture onto the old concrete, you can apply the new concrete that you mixed. Dump out all of the concrete onto the old concrete and spread it out with a hand trowel or a paver to form an even layer.^[14]

• Make sure you form a layer with a consistent thickness so the concrete dries evenly and doesn’t have any bumps or waves.

5.      Allow the concrete to dry for 12 hours. After you’ve poured the new concrete and formed an even layer, allow it to sit undisturbed so it can set. Drying times can vary depending on the concrete mixture, and the temperature and humidity of the area. To be safe, let the concrete dry overnight or for 12 hours.^[15]