Can You Put a Fiberglass Pool Over a Concrete Pool?
An old concrete pool can be cracked, stained or simply out of date, and a fiberglass pool looks like the easy fix. The answer depends on what “over” means.
Short answer: Generally, no. A prefabricated fiberglass shell is not set on top of or inside an intact concrete pool. The real options are coating the concrete with fiberglass, which keeps it a concrete pool, or removing the concrete pool and installing a shell in the excavation.
What does “fiberglass over concrete” actually mean?
Two very different jobs share this name.
| Option | What it is | What you end up with |
|---|---|---|
| Fiberglass coating (resurfacing) | A fiberglass finish applied to the existing concrete surface | A concrete pool with a new surface |
| Fiberglass shell | A pool built off-site and set into an excavation | A fiberglass pool, installed after the old concrete pool is dealt with |
Latham describes its shells as built off-site and delivered ready to install. Its renovation page describes homeowners with concrete or gunite pools removing the old concrete and replacing it with a new fiberglass shell. That is the path our pool removal and replacement service covers.
Why can’t a shell sit inside or on top of a concrete pool?
A shell is designed around the ground it sits in, not around a rigid structure. Latham’s installation guides (the Astoria and Corinthian 12 guides, for example) point to four problems.
- It needs a prepared bed. The guides describe an excavation dug very close to the shell’s size, with as little disturbance as possible to the soil that supports it. The shell then rests on a compacted bed of clean stone or sand and conforms to that bed under the weight of the water. A concrete floor does not compact or conform.
- The fit is close. Latham notes that an oversized hole needs extra backfill and can lead to settling or bulging. An old pool’s shape and depth will not necessarily match any given shell.
- Water needs a way out. The guides say water should always drain away from the pool and call for a sump pipe or daylight drain so groundwater can be checked and managed. A solid concrete floor and walls work against that.
- The warranty depends on the method. Latham’s warranty excludes failure caused by improper installation, which it defines as not following local building codes, industry standards, Latham’s owner’s manual and Latham’s approved installation procedures.
Can you put a smaller fiberglass pool inside the old one?
This is the version some search summaries describe. The gap between the two pools would have to be filled, and the shell would sit on whatever lies beneath it. Latham’s guide warns that blindly adding fill under a shell can do more harm than good, and says a properly prepared hole should not need large voids filled. The Latham installation guides we reviewed do not describe setting a shell inside an existing pool.
What happens to the concrete when a shell goes in?
The old pool is demolished or broken up and the excavation is prepared for the shell. Latham says that, depending on the condition of the old pool, it may need to be removed completely. How much comes out is a call for the contractor and the local building office.
Demolition rules are set locally, including how the old pool is handled before the excavation is filled. Your building office can tell you what applies. This is work for a qualified contractor with the right equipment and permits, not a homeowner project. Our guides to partial vs. full pool removal and to replacing a concrete, gunite or vinyl pool with fiberglass go through the options and the sequence.
Do you need a permit or an engineer?
Latham says you will likely need a building permit whether you install a new pool or remove or renovate an existing one, and that rules vary by municipality. It also says unstable soil may need to be built up before a pool is set. If soil or groundwater is a question on your lot, ask the contractor whether an engineer should weigh in. Follow the pool maker’s written installation instructions throughout.
What if I want to keep the concrete pool?
Then the decision is about the surface, not the structure. A fiberglass coating is one finish option for concrete. A pool resurfacing professional can explain the options and what they involve. It is a different job from installing a shell. If you are still weighing the two pool types, see our fiberglass vs concrete comparison.
How do you decide?
A site visit answers what a web page cannot: the condition of the concrete, equipment access, soil, groundwater and local permit rules. Whoever you talk to, ask these questions:
- How will the old pool be handled, and what will be left in the ground?
- How will drainage and groundwater be addressed?
- Who applies for the permits?
- Will the installation follow the pool maker’s written procedures?
If you decide on a new pool, our full installation service covers the project from excavation to a finished pool.
Last reviewed October 2026 by Calm Water Pools.
Related guides
- How to replace a concrete, gunite or vinyl pool with fiberglass
- Partial vs full pool removal
- Fiberglass vs concrete pools
- Fiberglass pool shell vs concrete pool: which is actually better?
- Fiberglass pools FAQ
Planning a fiberglass pool in Maryland, D.C., Northern Virginia or West Virginia? Request a consultation or call 240-372-4440.