The Constructor

How to make Salt Finish Concrete Surface

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Salt finish concrete surface is obtained by inserting coarse rock salt crystals using rollers on the freshly placed concrete surface and washing it off with streams of water after the concrete is set. This procedure gives a rough subtle texture and skid resistance to plain or coloured concrete. Salt finish surface is a decorative method just as broom finish concrete.

Fig 1: Salt Finish concrete drive way.

In this article we study about the work procedure to obtain salt finish concrete surface.

Procedures of Salt Finish Concrete Surface

The concrete path construction must be properly facilitated by the contractor in charge, in order to obtain the desired quality, finish and durability. The quality of workmanship and the materials used for the construction decides the performance and aesthetics of the concrete path.

A proper concrete driveway construction implements the following requirements.

  1. Proper Subgrade Preparation
  2. Placement of Reinforcement
  3. Concrete Placement
  4. Proper Finishing of Concrete Driveways
  5. Inserting Salt Crystals
  6. Cleaning of Salt
  7. Applying of sealant and Curing

1. Proper Subgrade Preparation

The subgrade must be prepared to ensure uniformity in the soil composition as well as the compaction. Achieving this requirement helps to provide adequate support to the loads coming over the concrete path. The process of compaction can be performed by rammers or vibratory compactors.

This helps achieve:

  1. Even slab thickness
  2. Prevention of cracks in slabs
  3. Achieving uniform slab thickness

2. Placement of Framework and Reinforcement

To hold the concrete at once place and to obtain the proper desired shape  of the concrete, framework is provided at the sides of the concrete path. the depth of the framework is as the depth of the concrete.

In order to increase the structural capacity of the concrete, reinforced concrete can be employed. The reinforcement can be placed in concrete either in the form of a wire mesh or in a grid pattern. In order to correctly locate the reinforcement at the center of the concrete, blocks can be placed under the rebars for support.

3. Concrete Placement

The structural capacity of the concrete is greatly influenced by the thickness implemented. The minimum thickness recommended for a concrete path is 4 inches. An increase from 4 to 5 inches  increases the structural capacity by 50% which is decided based on the specifications and requirements of the path.

Fig 2: Placing of concrete.

Additional thickness by 1 to 2 inches are provided at the edges of the concrete path. As the edges are mostly subjected to heavy loading.

4. Proper Finishing of Concrete Driveways

All the above mentioned procedure is same of all type of driveways and pathways construction. To achieve salt finish concrete surface, further steps are of most important.

Fig 3: Levelling of concrete surface

Special care must be taken in the finishing process of the concrete  as most of the work goes wrong due to overworking on the surface or due to the operations performed over bleeding water on the surface.

Fig 4: Smooth finishing of surface using bull float.

The following steps are followed in the finishing of concrete driveways:

  1. Uniform surface is achieved by striking off excess concrete with a screed.
  2. By means of a magnesium bull float or a wood, the concrete is floated. This helps to prevent the accumulation of bleeding water.
  3. Concrete is gives a even surface with the help of hand floating tool.
  4. With the help of screed and cement, the concrete surface is given a very fine smooth finish using bull float.

5. Inserting Salt Crystals

This is important step of the whole procedure, where utmost care must be taken while doing this procedure. The placed concrete must be left out to dry for a certain time.

To check if the concrete is ready to be inserted with salt grains, press a finger into the concrete to test its readiness for salting. The finger should depress the concrete about 1/4 inch, and no concrete paste should stick to your finger.

Fig 5: Applying of salt grains on the freshly finished concrete surface.

Scatter the rock salt onto the concrete surface, taking care to get even distribution. Use more salt for a highly pitted surface. Typical application rates range from 3 to 12 pounds per 100 square feet.

Press the salt into the concrete using a trowel or roller. The salt crystals should have half their diameter remaining above the surface. Allow it to dry for at least 24 hours and clean off the loose surface salt particle with the help of broom.

6. Cleaning or Removing of Salt Grains

The salts does not dissolve in the concrete due to less amount of water in the concrete. Rinse the surface with a power washer or with water while scrubbing with a brush. The removal of salts is also done using pressure washer for easy removal.

Fig 6: Post cleaning surface.

The water dissolves the salt, leaving a series of irregular dimples where the salt crystals had been. This texture or the concrete surface is known as Salt Finish Concrete Surface.

7. Applying of Sealant

Clean the area you want to seal using the stiff push broom. Make sure to remove as much dirt and debris as possible.

Dip the roller into the sealant and spread evenly onto the concrete. The sealant may appear milky when you first apply it. It will dry clear and glossy. Spread an even coat across all of the concrete, trying not to overlap too much. Apply a second coat after allowing the first to dry for at least 2 hours.

Fig 7: Application of sealant on the finished surface

Points to Remember

  1. For the best effects, use salt crystals 1/8 to 3/8 inch in size and press them into the surface to a depth about half of their diameter. Avoid producing indents larger than 1/4 inch, because they can be a hazard for people wearing pointy-heeled shoes.
  2. To achieve the most distinct salt imprint, give the concrete a smooth finish before applying the salt particles.
  3. The amount of salt to apply will depend on the degree of pattern desired. For a light pattern, start at a rate of about 3 pounds per 100 square feet. Add more salt-up to about 12 pounds per square foot-to achieve heavier textures, similar to travertine. The most important thing is to distribute the salt evenly across the surface, so make sure you have access to the entire slab.
  4. Start working the salt crystals into the concrete at the right time-usually when the concrete is just beginning to set. A good test is to press your finger into the surface. The concrete is at the right stiffness when the imprint depth is about 1/4 inch.
  5. When washing the salt away, remove all traces to prevent surface discoloration, especially if the concrete is integrally colored.
  6. Don't apply a sealer until the concrete surface and the small recesses left behind by the salt dry out completely.

Read More: Methods of Finishing Hardened Concrete Surface

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