Caulk-applied, one-component, hydro-swelling mastic for sealing smooth and rough construction joints and pipe penetrations in wet or underwater applications

Product Description

SWELLSEAL® Mastic WA is a one-component, grey, polyurethane-based, elastic, hydro-swelling mastic, supplied in aluminium sausages, for the sealing of expansion joints and around pipe penetrations.

SWELLSEAL® Mastic WA cures and swells in the presence of moisture. Curing time is dependent on temperature and humidity conditions, i.e. curing time will reduce if RH and Celsius degrees are higher. SWELLSEAL® Mastic WA will become firm in 24-36 hours. Performance is not affected by the curing time.

Product Advantages

  • Due to its special formulation, SWELLSEAL® Mastic WA can be applied onto wet surfaces or in underwater applications.
  • Suitable for fresh or salt water applications.
  • Solvent free.
  • SWELLSEAL® Mastic WA adheres to concrete, PVC, HDPE, steel, fibre glass, etc.
  • The excellent filling and adhesion properties of the product provide a first line filling of cracks and voids, even on lightly humid, smooth or rough surfaces.
  • In contact with water SWELLSEAL® Mastic WA will expand to about 200% of it’s original volume.
  • Flexible system, which adapts to the irregular surface of the substrate.
  • Easy application with a standard caulking gun.
  • Durable: will exceed the construction’s life.
  • Good chemical resistance(*).
  • Resistant against petroleum products, mineral and vegetable oils and greases.

(*) For chemical resistance please contact your local GCP representative.

Field of Application

  • Sealing of joints of in-situ cast concrete in wet and underwater applications.
  • Sealing joints between precast segments in wet or underwater applications (e.g. manholes, box culverts, cable ducts and pipes).
  • Sealing of the locks between sheet piles.


SWELLSEAL® Mastic WA is preferably applied onto a dust-free concrete surface. The surface can be rough or smooth, moist or dry. When applying SWELLSEAL® Mastic WA in underwater or very wet applications, be certain to cast the concrete within 6 hours to prevent premature swelling.

Application Method

For 600ml Sausages

  • Put the sausage in the empty tube of the caulking gun and cut 1cm off the top of the sausage. Close the tube and install the nozzle. Cut the nozzles diagonally at the appropriate position.
  • SWELLSEAL® Mastic WA is applied in an uninterrupted band (minimum 10mm wide and high), placed with a caulking gun in the middle of the joint or prefab element (minimum concrete cover is 7cm).
  • In case of fresh concrete, SWELLSEAL® Mastic WA should be covered by at least 7cm of concrete on both sides, in order to avoid cracks from the expansion pressure of swelling SWELLSEAL® Mastic WA.


Pasty during application and rubbery after curing. Colour: grey.

Technical Data / Properties

Solids 100% Test DNC
Viscosity Gel / Paste Test DNC
Density (at 20ºC) Approx. 1.45kg / dm3 DIN 53504
Slump in Vertical Application < 5mm Boeing test
Hand Dry (at 20ºC and 60% rel. humidity) 10h Test DNC
Flash Point > 130ºC Pensky-Martens method
Cured (7 days at 25ºC, 10mm thick)    
Swelling Capacity in Contact with Water Swells to approx. 200% of its original dry volume Test DNC


3mm 40 - 50m
6mm 16 - 20m
8mm 8 - 10m
10mm Approx. 6m


12 per cardboard box
1 pallet = 40 cardboard boxes

Weight per sausage

  • 0.99kg gross
  • 0.99kg gross


Minimum 12 months in a dry place at temperatures between 5°C and 30°C.

See shelf life information on the packaging.


To be ordered separately

  • Caulking gun for sausages 600mL closed tube.
  • Nozzle for caulking gun 600mm closed tube.

Health & Safety

For full information consult the relevant Material Safety Data Sheet.


Release Date: 02/11/18. The information contained in this product data sheet supersedes all previous versions.


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We hope the information here will be helpful. It is based on data and knowledge considered to be true and accurate, and is offered for consideration, investigation and verification by the user, but we do not warrant the results to be obtained. Please read all statements, recommendations, and suggestions in conjunction with our conditions of sale, which apply to all goods supplied by us. No statement, recommendation, or suggestion is intended for any use that would infringe any patent, copyright, or other third party right.

SWELLSEAL is a trademark, which may be registered in the United States and/or other countries, of GCP Applied Technologies, Inc. This trademark list has been compiled using available published information as of the publication date and may not accurately reflect current trademark ownership or status.

© Copyright 2018 GCP Applied Technologies, Inc. All rights reserved.

GCP Applied Technologies Inc., 62 Whittemore Avenue, Cambridge, MA 02140, USA

Printed in Australia GCP PDS 047 07/17

This document is only current as of the last updated date stated below and is valid only for use in Australia. It is important that you always refer to the currently available information at the URL below to provide the most current product information at the time of use. Additional literature such as Contractor Manuals, Technical Bulletins, Detail Drawings and detailing recommendations and other relevant documents are also available on www.gcpat.com.au. Information found on other websites must not be relied upon, as they may not be up-to-date or applicable to the conditions in your location and we do not accept any responsibility for their content. If there are any conflicts or if you need more information, please contact GCP Customer Service.

Last Updated: 2021-02-05