Tips for Repairing a Gunite Swimming Pool

A pool and a waterfall.
What You'll Need
Diamond blade
Portland cement
Putty knife
White sand

Gunite is a concrete material used in the construction of swimming pool structures. The benefit to a gunite swimming pool is its resilience and flexibility, allowing for pools of almost any shape. It is also extremely strong and durable. Gunite is just concrete and sand but it is mixed together with water right before it is applied pneumatically as a spray. Gunite pools are relatively easy to build and therefore, are often cheaper than pools made from other materials. They are also conducive to adding amenities like slides and islands and easy to clean because they can be completely drained to replace the water if necessary.

How Do Gunite Pools Crack?

Over time, however, cracks can form because of weather or other damage. Besides cracks, “pop-ups” can also appear. These are hollow spots in the pool's surface. Pool surfaces sometimes chip as well. It is possible to repair this damage yourself.

Gunite is porous and is sealed from the water by a plaster coating. When the water behind the pool permeates the porous material and changes temperature it expands and contracts and cracks can appear.

Also, if the ground around the pool moves over time, it can crack the surface material. The ground can shift due to various factors like freezing and thawing, water table levels, and earthquakes.

If you see a crack, sometimes it is only the surface plaster and that can be repaired with more plaster. Other times the gunite itself has a crack. This also can be repaired.

Step 1 - Clean

A pool.

Make sure the pool is completely dry and, using the broom, sweep any loose dirt away from the area of the crack.

Step 2 - Use a Grinder

Use the grinder with the diamond blade to widen and deepen the crack. Use a low setting on the grinder and place it in the crack to accomplish this. Move the grinder around carefully until the crack is made a few inches deep and wide.

Use the rag to wipe the gunite dust. Wet the area with the hose. This will prevent the gunite from extracting moisture from the cement.

Step 3 - Mix Cement

In the bucket, mix three parts cement and two parts white sand. You can also add an acrylic cement bonding agent if you desire. This can be purchased at any home improvement or pool supply store. Slowly add in one part water until the mixture is pasty but not dripping, like peanut butter.

Step 4 - Caulk

A pool.

Using the putty knife, first line the walls of the crack with the mixture. Alternatively, you can put a bead of caulk and spread it along the length of the crack leaving space to let the cement cover the caulk. You should leave about ¼ inch. Allow the caulk to dry.

Then, fill the crack entirely with the cement, sand, and water mixture. Any excess should be removed. Smooth the top using the trowel.

Step 5 - Plaster

Once this had dried, complete the plaster coat over the surface.