Water Tanks and Pools Waterproofing

What Actually Works and Why Most Fail

Waterproofing a terrace is one thing.
Waterproofing a water tank, sump, or swimming pool is a completely different game.

Why?

Because in most cases, we try to stop water from entering.
Here, the situation is opposite. Water is already inside and continuously trying to come out.

This one difference changes everything.

First Understand This Simple Concept

Positive Side vs Negative Side Waterproofing

Don’t worry about jargon, simple samajh lo:

• Positive side = where water is present
• Negative side = opposite side, where water is trying to come through

Example:

• Tank waterproofing from inside = Positive side
• Basement wall from inside = Negative side

Why this matters:

• Positive side: water pushes coating into surface, better bonding
• Negative side: water tries to push coating off, higher failure risk

Simple rule:
Waterproofing works best when applied on the water side

1. Overhead RCC Water Tanks

Most homes have RCC overhead tanks.

What is required here:

• Water should not leak out
• Water should remain safe for drinking
• Coating should handle continuous water contact

Key things to check:

• Material should be non-toxic
• No smell, no taste
• Surface must be properly cleaned and cured
• Pay attention to joints, corners, and pipe entries

What works best:

Use polymer modified cementitious coating
Example type: MoistureZero, SikaTop, Zentrifix Elastic

Why this works:

• Bonds well with concrete
• Handles water pressure from inside
• Does not peel under constant water load

Application basics:

• Minimum 2 coats
• Apply in cross direction
• Proper curing before filling

Final Test (Very Important)

Don’t just look and assume it’s done.

• Fill tank fully
• Keep for 48 hours
• Check outside walls

No seepage means system is working

2. Underground Sumps and Tanks

This is where most people get confused.

Why it is tricky:

• When tank is full → pressure from inside
• When empty → pressure from outside (groundwater)

So pressure comes from both sides.

What works better here:

Instead of only coating, use integral waterproofing inside concrete

Simple meaning:
Waterproofing is mixed inside concrete itself.

Example: crystalline waterproofing systems ( MC Special DM , Sika Control WDT etc)

Why this is better:

• Works inside concrete
• Blocks water paths permanently
• Cannot peel off
• Can self-seal small cracks

For old leaking tanks:

If you cannot dig from outside:

• Apply crystalline slurry from inside
• Treat joints and cracks separately

This is usually the most practical repair solution in Indian conditions

3. Swimming Pools

Pools are one of the toughest waterproofing areas.

Because they have:

• Continuous water pressure
• Chlorine exposure
• Temperature changes
• Structural movement

Why most pools fail:

• Cracks in structure
• Poor joint treatment
• Wrong waterproofing system
• Wrong grout selection

Important rules:

1. Structure first, coating later

If structure is weak, waterproofing will fail.

2. Joints are critical

Most leakage happens at:

• Floor to wall junction
• Construction joints

3. Chemical resistance matters

Chlorine can damage many coatings

Avoid basic acrylic coatings
Use chemical-resistant systems

Two common systems:

Painted pool

• Epoxy coating
• Seamless finish

Tiled pool

• Waterproofing below tiles
• Use proper pool-grade adhesive and grout ie, Epoxy Grout (Laticrete SP 100 or Vura Epoxy Grout or Buildsmart TGE 100)

Important point:
Sometime Failures are not tiles, but wrong grout selection

4. Rainwater Tanks and Water Features

These are simpler but still need care.

Requirements:

• Non-toxic
• No chemical leaching
• Safe for water storage

What to use:

• Cementitious waterproofing systems

What to avoid:

• Solvent-based coatings unless fully cured

Important rule:

Do not rush filling

• Allow 7 to 14 days curing

The Flood Test

The Only Real Proof

Every waterproofing job must be tested.

How to do:

• Fill structure fully
• Mark water level
• Keep for minimum 48 hours
• Check for drop

One smart trick:

Keep a bucket of water nearby

Compare water loss (to account for evaporation)

Result:

• No drop = success
• Drop = problem needs investigation

Final Understanding

Waterproofing of tanks and pools is not normal waterproofing.

It requires:

• Correct understanding of water pressure
• Right product selection
• Proper joint detailing
• Testing before finishing

Simple Rule to Remember

• Underground tank > integral waterproofing + 1K Acrylic Cement Coating
• Overhead tank > If concrete , Integral + cementitious coating 1k or 2k
• Swimming pool > if concrete integral waterproofing + 2K Acrylic Cement or 2K Crystalline or chemical resistant system
• All cases > testing is compulsory

Final Thought

Don’t select waterproofing based only on brand or price.

Selection should depend on:

• Structure type
• Water pressure condition
• Usage and exposure

One Line Summary

Waterproofing works when you understand water behaviour, not when you just apply a product.