Corrugated galvanised iron roofs fail at the overlaps, the fasteners and the rust line — not across the middle of the sheet. We treat all three, then coat the whole roof so it stops corroding from the top down.
Before · rusted, unsealedAfter · sealed and coated
Sheet fastener, drag to compare
G.I. sheet waterproofing in Karachi
What actually happens when a corrugated G.I. roof gets treated
G.I. sheet waterproofing in Karachi is less about the sheet itself and more about where it joins — corrugated galvanised iron almost never fails across the open span, it fails at the overlaps, the screw and J-bolt fasteners, and the rust line creeping out from a cut edge. Zem Chemicals treats all three in sequence: rust removal and conversion on every affected area, every overlap and fastener resealed with reinforced tape, then a full-surface coating that also turns the roof reflective — the same finish behind our roof heat proofing service, which is why warehouse clients routinely get both done in one visit. The largest G.I. job on record is 28,000 sq.ft at Pakistan Rice Complex in S.I.T.E. 2, handed over in 22 working days — see more completed G.I. sheet waterproofing jobs or send us your roof's covered area for a written quotation.
The problem
Where G.I. roofs actually leak
Sheet overlaps that have lifted and no longer shed water
Screw and J-bolt penetrations where the washer has perished
Rust creeping out from cut edges and fastener holes
Ridge and valley junctions that were never properly sealed
Condensation dripping onto stock even when it has not rained
The treatment
The treatment we apply
Rust removal and conversion treatment on every affected area
Every overlap and fastener sealed with reinforced tape and coating
Ridge, valley and edge junctions detailed before the field coat
Full-surface coating applied to seal the sheet against water
Reflective finish so the warehouse interior runs cooler as well
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
Sheet condition audit
We assess corrosion level sheet by sheet and flag anything that needs replacing rather than coating.
Preparation
Rust treatment
Scaling, cleaning and rust conversion, with safe access arranged for the crew.
Detailing
Seams and fasteners
Overlaps, screws and junctions sealed with reinforced fabric or Fibermesh before the field coat.
Application
Full-surface coating
Coating applied across the whole roof to seal it against water.
Questions we get asked
G.I. sheet waterproofing — the practical answers
Can badly rusted sheets be saved?
Often yes, if the sheet still has structural section left. Where corrosion has gone through, we tell you which sheets need replacing before we coat — we will not coat over a sheet that is finished.
Does the factory have to shut down?
No. We work from above and schedule around your shifts. Most warehouse jobs run with operations continuing underneath.
How long did a large job take?
28,000 sq.ft of warehouse roof at Pakistan Rice Complex, S.I.T.E. 2, was completed in 22 working days.
Does it help with heat?
Yes. G.I. sheets radiate heat straight down into the shed. The reflective finish measurably drops interior temperature.
