The soil around your swimming pool is not actually solid, it's composed of organic and mineral particles. The gaps around these particles in the soil are often filled with
ground water that comes from rain, nearby natural springs, rivers, lakes, or other sources. This ground water exerts hydrostatic pressure.
When your fiberglass pool was constructed a protective layer of pea gravel or sand was filled in around the outside of the fiberglass shell. This layer, just like the surrounding soil, is porous and allows ground water into the spaces between the gravel.
The hydrostatic pressure of the ground water pushes against the shell of your swimming pool. The weight of the water within the swimming pool pushes back against the ground water and keeps the pool shell from becoming buoyant and rising up. It’s VERY important to NEVER take ANY water out of your fiberglass pool! Even when winterizing the pool it should stay full of water. If for any reason your pool needs to have water taken out make sure you hire a professional who is licensed and insured and knowledgeable.
Not all pool companies have this knowledge and experience. A fiberglass pool is designed to be full of water at all times.
Hydrostatic pressure is the force exerted by or existing within a liquid at rest with respect to adjacent bodies. Hydrostatic pressure is what creates buoyancy... it’s what allows something to float.
In this illustration you can see that hydrostatic pressure makes the boat buoyant.
When water is removed from the pool the weight that was holding the pool shell down is gone and the force of the hydrostatic pressure of the ground water pushes against it. Even a few inches of water being removed, if below the water table, will cause pressure to increase on the shell and damage is inevitable.
In some instances the pressure on the pool shell will cause it to bulge out of shape and crack.
At the same time the surrounding backfill collapses into the void that had been occupied by the pool shell. Once the backfill falls in, the shell is locked into place and
misshapen to the point that repairs are required.
Any damaged pool can be saved! You don’t need to replace it. Find a reputable pool company that has the knowledge and experience needed for complex repairs. An unqualified pool company can cause further damage. Be sure to ask for references. If you’re unable to find a qualified pool company in your area give us a call.
We work throughout the United States using our unique experience, techniques, and products to fix any pool in need of help!