Spider cracks in a pool's plaster are common and do not always mean structural damage. Plaster cracks as it ages and dries, and repairing it takes some special tools and products. If you want a like-new pool again, patching and repairing the cracks is the most effective way to do so.
Why Pool Plaster Cracks
Pool plaster cracks due to pressure placed on the plaster surface. The shifting of the pool beneath the plaster sometimes causes cracking, especially if gaps between the pool and plaster exist. When the plaster breaks down, expect cracks to form regularly. These hairline cracks are called spider cracks. They extend like a spider web from the center of the gaps in the plaster. The cracks repair with some effort as long as you know how to proceed.
Assessing Cracks and Damage
A big difference exists between spider cracks and large structural pool plaster cracks. The size of the crack indicates the seriousness of the damage. If cracks are deep and wide, the plaster is shifting, which indicates a structural problem. A typical, hairline spider crack is not a problem aside from its aesthetics. Inspect the spider crack closely to determine how deep it is. Tap on the cracked area and listen. If it sounds hollow, it means a gap is present. Once you assess the crack, you know how to repair it.
Patching Spider Cracks
To patch a spider crack without a void underneath it, clean the area with a brush, removing all dirt and grease. Apply a pool patch compound with a trowel or float tool over the cracked area. Pool patch is a mixture of plaster and water. It spreads like plaster and is applied directly over the cracked or damaged area. Another option is to use cement, sand and a bonding agent, which forms a similar patching compound that is applied right over the cracked area with a trowel. Cover the entire cracked area, and let the patch compound dry for several hours.
Filling Voids Under Cracks
If you find a void under your spider cracks, the void requires filling. To begin, chip up the plaster in the void to expose it. Use a chisel and hammer along with a protective pair of goggles to break up all the plaster in the immediate area. Another option is to acid wash the plaster with an acid solution, which strips off a layer of the plaster and is suitable if your pool has many voids and pockets. Always wear protective equipment when acid washing your pool, and handle the solution with care. Once exposed, fill the voids with new plaster by spreading it over the area with a trowel. In essence, you are replastering the area to fill in voids and create a solid plaster layer.