Broken Pool Plaster, Calcium Nodules, Plaster Delamination, Pop-Offs

July 4, 2022

Pool Plaster Problems: Calcium Nodules, Delamination & Pop‑Offs — Causes, Signs & Realistic Fixes

Pool plaster problems like calcium nodules, plaster delamination, and pop‑offs occasionally happen in gunite/plaster pools. These issues create rough surfaces, bumps, cracks, and even chunks of plaster that break away. Understanding the causes, signs, and realistic repair options can save you time, money, and frustration.

In this guide, we explain how to tell if your plaster problem is isolated or widespread and what practical steps you can take.

What Are Calcium Nodules?

Calcium nodules are small, hardened mounds that form on pool plaster. They often look like tiny volcanoes or drips on the walls and floor of your pool.

How they form:

Water penetrates voids beneath the plaster.
Calcium hydroxide crystallizes as the water evaporates.
Over time, these deposits push through the plaster, creating bumps or nodules.

Key points:

Nodules are not caused by water chemistry alone.
They often appear alongside plaster delamination or bond failure.
Early detection can prevent minor damage from becoming major problems, if the problem is localized.

What Is Plaster Delamination & Pop‑Offs?

Plaster delamination occurs when the plaster separates from the pool’s shell (gunite or shotcrete).

Pop‑offs are areas of plaster that completely break away, leaving rough holes or sharp edges.

Causes of delamination and pop‑offs:

Voids beneath plaster
Improper surface preparation before replastering
Poor bond coat application
Cracks or shrinkage in the plaster

Signs you have delamination or pop‑offs:

Volcano-like bumps or mounds on the floors and walls of your pool
White splotches on the plaster that look like bird splatter (poop!)
Hollow sound when tapping the plaster
Cracks forming near nodules
Pieces of plaster breaking off

Symptoms: How to Spot Pool Plaster Problems

Early detection is crucial. Watch for:

Bumps or nodules on the plaster surface
Hollow spots when tapping
Cracks or chips around nodules
Rough edges or holes from plaster pop-offs

Pro tip: While UNDERWATER, tap the plaster across multiple areas to check for hollow sounds (water conducts sound well, but you have to be IN THE WATER to hear it). This helps determine if the delamination is localized or widespread.

Causes: Why Pool Plaster Fails

Pool plaster problems usually stem from a combination of factors:

Poor Surface Preparation
- Failing to properly prep the surface prevents proper plaster adhesion.
Voids Beneath Plaster
- Water can penetrate gaps, leading to calcium nodules and weak bonds.
Cracks or Shrinkage
- Natural shrinkage or improper curing creates cracks that can propagate delamination.
Environmental Factors
- Heat (when the pool is drained), or improper water chemistry can accelerate plaster deterioration.

Realistic Fixes for Calcium Nodules & Delamination

Repair strategies depend on how widespread the damage is.

Localized Damage

If nodules appear in a single area, you can chip out the damaged area and patch that spot.
Once patched, nodules in that specific area generally won’t grow back if done correctly.

Widespread Damage

If calcium nodules are present throughout the pool, it’s a sign that delamination is occurring everywhere.
In this scenario, patching individual spots is usually not a long-term solution, because the plaster is separating from the substrate in multiple areas.
The realistic fix for widespread delamination is full resurfacing, depending on severity.

For this reason, when a pool is resurfaced, I strongly suggest the “chipping out” method which removes all existing plaster down to the gunite. Doing so won’t guarantee preventing delamination but it will dramatically decrease your chances of it occurring. There are local plaster companies in our area that chip out and other companies that don’t. If you are replastering, be sure and ask!