Water tank waterproofing, safe with drinking water
Overhead and underground concrete tanks develop seepage at construction joints and hairline cracks well before the structure itself is at risk. We seal the tank from the inside with a coating rated safe for potable water once cured.
What actually happens when a concrete tank gets waterproofed
Water tank waterproofing in Karachi deals with two risks at once — structural seepage at the wall-to-floor construction joint, and water quality, since anything applied inside a tank eventually touches what people drink. Zem Chemicals drains and cleans the tank first, cuts and tapes every construction joint and crack, then applies a potable-safe polymerised cementitious primer and two coats, detailing internal corners and pipe penetrations separately before refilling and holding the tank for a flood check. Underground tanks are treated through the existing access point with no excavation needed, and the same below-grade cementitious approach carries over to our basement and foundation waterproofing work. Typical tanks are back in service in 3–8 working days — see completed water tank projects or send us your tank's details for a written quotation.
The problem
Where tanks actually leak
Seepage at the wall-to-floor construction joint
Damp patches on the external tank wall or the ceiling below it
Hairline cracks that widen after the first monsoon
Visible water loss between fill cycles
Discoloured or off-taste water from a compromised internal surface
The treatment
The treatment we apply
Tank drained and the internal surface cleaned before anything is applied
Construction joints and cracks cut, packed and taped
Potable-safe polymerised cementitious primer, then two coats
Internal corners and pipe penetrations detailed separately
Tank refilled and held for a flood/leak check before handover
How the job runs
Four stages, in this order, every time
Skipping a stage is how a waterproofing job fails in year two. This sequence is not negotiable on our sites.
Survey
Drain and inspect
Tank drained and every joint, crack and pipe penetration inspected before we quote a system.
Preparation
Joint and crack treatment
Every construction joint and crack cut, cleaned, packed and taped.
Application
Primer + 2 coats
Potable-safe cementitious system applied and allowed to cure fully before refilling.
Handover
Refill and leak check
Tank refilled and held to confirm the seal before we sign off.
Questions we get asked
Water tank waterproofing — the practical answers
Is the coating safe once the tank is refilled?
Yes — once fully cured, the system is rated safe for contact with potable water. We hold the correct cure time before the tank goes back into service.
How long is the tank out of service?
Typically 3–8 working days depending on tank size and cure time between coats — we confirm the exact window on survey.
Underground tanks — do you need to excavate?
No. We work from inside the tank through the existing access point; excavation is not required for this treatment.
Does this stop existing water loss immediately?
The seal takes effect once the coating has cured and the tank is refilled — we explain the exact timeline for your tank before work starts.
