What is positive-side waterproofing?

Applying the waterproofing layer on the exterior or water-side of the structure so hydrostatic pressure compresses laps against the substrate. New basements with accessible excavation use post-applied PetroGrip SBS or double-layer systems from Petroseal.

When is negative-side waterproofing used?

When external access is impossible (existing occupied basement, tight urban sites) or as temporary control after failure. Cementitious or injection systems may apply; they do not replace a missed external membrane on a high water-table new build.

Can any contractor apply negative-side coating instead of external membrane?

Only where engineering accepts the risk and product data supports negative-side pressure. Many Lahore contractors market internal chemical coatings; consultants should require leak mapping and compatibility with active head pressure before accepting that in place of positive-side design.

positive side

Positive-Side vs Negative-Side Waterproofing (Basements & Tanks)

Where the membrane or coating sits relative to water pressure—and when PetroGrip SBS on the outside beats internal injection or coating remediation.

Petroseal Technical TeamSeptember 202612 min read

Direct answer

Water pressure pushes against waterproofing from the wet side. Positive-side systems sit on that wet side—external wall membrane, raft membrane under slab, tank lining on the water face—so pressure helps seal laps to concrete. Negative-side systems sit on the dry interior; water pushes away from the bond line, which limits long-term reliability under full hydrostatic head unless the product is explicitly rated and the structure is cracked-stabilised.

Petroseal specifies positive-side PetroGrip SBS (and double-layer build-ups) for new basements, rafts, and tanks where excavation or formwork access exists. Negative-side cementitious or injection approaches are discussed only after diagnosis on retrofit work—not as a default substitute for external membrane on greenfield projects.

Comparison

Aspect	Positive-side	Negative-side
Water pressure effect	Presses membrane into substrate/laps	Pushes water toward interface—higher disbond risk
Typical new build	External SBS torch + protection	Not a substitute for external line
Retrofit basement	External if excavatable	Internal coating/injection if access blocked
Petroseal primary products	PetroGrip SBS, waterstops, double-layer specs	Cementitious system page + specialist remediation quote

Positive-side build sequence (new basement)

Prepare concrete: cure, dry, repair defects; verify reglet and upturn heights.
Prime per PetroGrip method; torch or self-adhesive primary SBS ply.
Detail raft-to-wall, penetrations, and construction joints with waterstops.
Install protection board or screed before sharp backfill.
Hold inspection and photograph laps before cover-up.

Contractors such as Unicorn or Roof Power may install positive-side systems using various membrane brands; Petroseal supplies Lahore-manufactured rolls with traceable marking and publishes method guidance on download pages.

Negative-side limits

Active leaks through structural cracks may migrate past internal coatings if movement continues. Negative-side cementitious systems can perform on stable, low-movement structures with controlled head—consult Petroseal’s cementitious system page for scope. High water-table basements without external membrane rarely achieve dry occupancy with interior paint-alone solutions marketed generically in Punjab.

Do not confuse DPC/rising damp treatments (PetroDPC) with full basement negative-side tanking—they address different moisture paths.

Tanks and retaining structures

Water tanks and retaining walls normally receive positive-side membrane or geomembrane on the water face. Petroseal supplies PVC waterstops for joints and HDPE/PVC liners where sheet lining replaces bitumen. Positive-side placement is non-negotiable for primary containment unless a fully engineered alternative is stamped.