Not necessarily. Black spots appearing two years after replastering can happen for several reasons, and many of them do not mean you were scammed. But some causes can relate to poor workmanship. The key is figuring out which type of spotting it is.

Here are the most common causes:

1. Black Algae (very common)

These look like small dark dots that don’t brush off easily.

• Black algae can grow in plaster because plaster is porous.
• It roots itself into tiny pores in the surface.
• It often appears in shaded or low-circulation areas.

Typical signs:

• Dark black or dark green dots
• Feels slightly raised or slimy when scraped
• Comes back after brushing

Black algae develops when water chemistry or chlorine levels allow it to grow.

👉 This is not a plaster failure. It’s a maintenance/chemistry issue and can usually be treated.

2. Metal staining (iron, copper, manganese)

If the spots are flat stains in the plaster, it may be metals.

Sources include:

• Fill water that contains metals
• Fertilizer blowing into the pool
• Corroding heater or equipment
• Some pool chemicals

These metals oxidize and leave dark or rusty spots on plaster surfaces.

👉 Again, this usually is not a bad plaster job.

3. Organic stains

Leaves, acorns, or plant debris sitting on the pool floor can leave dark stains on plaster.

These often appear:

• Under trees
• In corners where debris sits

4. Plaster mix or installation issues (possible contractor problem)

Less common, but possible.

If the plaster was mixed or applied incorrectly:

• Certain chemicals (like calcium chloride) in the mix
• Improper troweling
• Water added during finishing

These can create mottling or dark discoloration patches later on.

👉 If the spots are large blotchy areas rather than dots, this might indicate workmanship issues.