We undertake tanking on projects of any size, from house construction to major infrastructure projects.

New Zealand’s leading underground waterproof tanking applicator

We are licensed applicators for many membrane manufacturers. We undertake tanking on projects of any size, from house construction to major infrastructure projects. This includes: 

  • Foundations 
  • Underfloor 
  • Lift pits
  • Basements 
  • Retaining walls 

With extensive underground construction and remediation expertise, our skilled team is equipped to handle the unique challenges of tunnel environments. Using high-quality tunnel membranes and advanced installation techniques, Sansom ensures effective waterproofing and tunnel protection. 

Sansom addresses a range of issues commonly found in basements. Our team specialises in diagnosing and resolving water ingress, dampness, and structural damage. With a thorough understanding of basement construction and advanced remediation techniques, We implement effective, ensuring that basements are restored to a safe, dry, and structurally sound condition. 

With a proactive approach to maintenance and a commitment to industry standards, Sansom conducts regular inspections, implements preventive measures, and carries out necessary repairs to ensure the optimal condition and functionality of tunnels. 

The Newton 500 is a maintainable basement waterproofing solution, ideal for both new construction and renovation projects. This solution consists of four elements: 

  • Cavity drain membranes 
  • Drainage systems 
  • Pumps
  • Control Systems 

Adheres to the New Zealand standards for waterproofing. 

Find out more.

Waterproof tanking at Sansom

Waterproof tanking is more than just a service; it’s an investment in the longevity and integrity of any structure.  

Sansom has been the leader in underground waterproofing in New Zealand since the early 1990s and sits at the core of what we do. 

Our specialised approach goes beyond just shielding surfaces; we thoroughly evaluate a structure to identify potential weak points and customise our solutions accordingly.  

Having worked across some of New Zealand’s most significant infrastructure and construction projects, we bring unparalleled expertise and experience to every tanking project. With a comprehensive knowledge of the potential risks associated with tanking failures, we ensure to engineer proactive, robust solutions that prevent these problems before they even begin to emerge. 

Our tanking division comprises three teams; Our bentonite team uses clay to seal and waterproof effectively. The PVC/VHDPE team works with tough materials to resist high pressure and harsh conditions. Lastly, our bitumen and specialist membranes team handles a variety of other membranes. 

why sansom


With 48 years in the industry, our waterproof tanking service delivers unmatched expertise gained from working on some of New Zealand’s most significant projects, ensuring your project benefits from our extensive and proven experience.


At Sansom, we value honesty and openness in all our interactions. We keep you fully informed about your tanking project’s progress. We are dedicated to building trust through clear, consistent communication, ensuring you’re never left in the dark about your project’s status.


Taking a future-focused approach, we deliver more than just immediate results. We offer enduring waterproofing solutions designed to ensure the longevity of structures. Our meticulous methods, careful material selection, and rigorous quality checks guarantee a resilient tanking solution that resists the test of time.

What Our Clients Say…

Roofing Client

‘Your diligence, attention to detail, very helpful communication, and very pleasant manner make you an amazing person to deal with. A true gentleman too.’

Chris Hunter

Managing Director - NZ Strong

We write this letter in gratitude for the combined efforts Sansom Ltd provided in the completion of the Hobsonville Data Centre.

Concrete Remediation Client

“Many thanks to the Sansom team members responsible for the efficiency and professionalism shown in undertaking the concrete remedial works, with the high quality of workmanship also being greatly appreciated by the Church.”

Alain Venuto

Site Manager, Naylor Love

Sansom is a company that has truly exceeded my expectations with their outstanding performance and exceptional workmanship.


Phillip Helleur - AJ Spicer

Hawkins are pleased to be able to provide this testimonial for Sansom for their excellent work at the Totara Haumaru Northshore Hospital project for Health NZ Waitemata.

Tanking membrane products

Affiliates and Alliances

  • Allnex Membranes G.C.P + Allnex Resins + Liquid Membranes
  • Allco Casali, Bitumen Membranes, HydrotechMM6125,
  •  JM TPO
  • Ardex Membranes Bitumen Membranes + Liquid Membranes
  • Nuralite Membranes Nuraply + G.C.P + Liquid Membranes
  • Sika Membranes PVC, TPO, Bentonite Membranes + Liquid Membranes
  • Viking Membranes Bitumen Membranes + Liquid Membranes
  • Xypex Membranes Cementation Membranes
  • NEWTON SYSTEMS System 500 Membranes