Fosroc Exposeal UW
A solvent-free, thixotropic two-part epoxy putty that seals cracks, blow holes and surface defects on concrete that is damp, splash-zone or fully submerged, without dewatering.
What is it?
A two-component, solvent-free epoxy putty based on water-insensitive resins, inert fillers and thixotropic agents, formulated to be worked and cured on wet or underwater concrete.
Where is it used?
Water tanks, reservoirs, canals, dam faces, jetties, dock walls, marine piles and any submerged or continuously damp concrete needing crack and defect sealing.
Why use it?
It lets crews stop leaks and fill defects in place, on wet substrate, without the cost and delay of draining a tank or dewatering a structure.
How is it applied?
Base and hardener are mixed 1:1 by weight to a uniform colour, then pressed firmly into the prepared crack or blow hole by gloved hand or spatula and struck off flush; it holds on vertical and overhead faces and cures underwater.
About Fosroc Exposeal UW
Fosroc Exposeal UW answers a problem every hydraulic and marine contractor knows well: a crack, honeycomb patch or blow hole that needs sealing, but on concrete that cannot be dried out. Draining a service reservoir, dewatering a wet well or cofferdamming a jetty pile is expensive and often impractical, so the repair has to happen on the wet substrate. Exposeal UW is built for exactly that. It is a thixotropic, solvent-free, two-part compound based on water-insensitive epoxy resins, inert fillers and thixotropic agents, engineered to displace surface water, grip damp concrete and cure in submerged conditions without shrinking.\n\nWhat makes it practical on site is its handling. The two parts mix at a simple 1:1 ratio by weight, so there is no cartridge gun or precise metering to fuss over in the water. The putty is non-slump, meaning it stays put on vertical walls and overhead soffits rather than sagging or washing away before it sets. Once cured it forms a hard, chemical-resistant seal firmly bonded to the concrete, capable of taking the water, sewage and mild chemical exposure typical of tanks, sewers and coastal structures. For Delhi NCR and Pan-India projects, Space Arc Engineering supplies Exposeal UW as an authorised Fosroc distributor and applicator, with technical support on substrate prep and detailing.
The technical insight
The core trick is water displacement plus moisture-tolerant cure chemistry. Ordinary epoxies are compromised by a film of water on the substrate, which prevents wetting and adhesion, so the bond fails at the interface. Exposeal UW uses water-insensitive resins and a hardener system that cures in the presence of moisture; as the stiff putty is pressed hard into the crack or void, it physically shoves surface water aside and makes intimate contact with the concrete, then chemically cross-links whether the surroundings are damp or fully immersed. The thixotropic fillers give it a stiff, non-slump body so it stays where it is placed on walls and soffits and is not washed out by the surrounding water before it gains strength. Because the reaction is a solvent-free thermoset with no water in the mix, it cures without shrinkage, so the seal does not pull away from the crack walls as it hardens. The result is a dense, low-permeability plug bonded to damp concrete rather than a coating sitting on a wet, weak boundary layer.
Where it is used
- Sealing static or non-moving cracks in submerged and splash-zone concrete
- Filling blow holes, honeycombing and surface pitting on damp or underwater faces
- Plugging minor active seepage points in water-retaining structures
- Sealing around pipe penetrations and fixings in wet walls without dewatering
- Making good defects on canal linings, dam faces and spillways
- Local repair of jetty piles, dock walls and marine sub-structures below the waterline
- Filling and smoothing minor surface irregularities ahead of underwater coating or lining
- Point sealing in wet wells, sumps, sewers and treatment-plant tankage
Key advantages
- Applies and cures on damp, splash-zone or fully submerged concrete, so no dewatering is needed
- Solvent-free, two-part formulation with a simple 1:1 mix ratio by weight for reliable field mixing
- Non-slump body stays in place on vertical walls and overhead soffits without sagging or washing out
- Displaces surface water and bonds strongly to damp concrete
- Cures without shrinkage, so the seal stays tight against the crack or void walls
- Chemically resistant once cured, suiting water, sewage and mild-chemical exposure
- Hand- or spatula-applied with no specialist gun or pumping equipment
- Supplied and technically supported Pan-India through Space Arc as an authorised Fosroc distributor
Limitations & considerations
- Suited to static, non-moving cracks and defects, not to expansion joints or cyclically moving cracks that need a flexible sealant
- A defect-sealing and gap-filling putty, not a structural underwater repair mortar for large-volume reprofiling or load-bearing patches
- Effective on strong, sound concrete; loose, friable or contaminated substrate must be cut back to a solid base first
- Not a substitute for a full waterproofing membrane or tanking system across broad wet areas
- Potable-water contact must be confirmed against BIS and the relevant state drinking-water authority requirements before use
- Working and cure behaviour vary with water and substrate temperature, which needs allowing for in cold or fast-flowing conditions
Selection & best practice
Get the substrate right first: cut back loose, weak or laitance-covered concrete to a sound, strong base and clean out the crack or blow hole of silt, algae and debris, working underwater as needed. Mix only what can be placed in the working time, blending base and hardener 1:1 by weight until the colour is uniform with no streaks. Press the putty hard into the opening so it displaces trapped water and keys into the profile, then strike it off flush and firm it against the crack walls. On vertical and overhead work, take advantage of the non-slump body but still support deep fills in lifts. Keep the repair undisturbed while it cures, and avoid using Exposeal UW where the crack is genuinely moving. For larger-scale underwater reprofiling or structural patch repair, step up to Fosroc Expocrete EUW rather than over-filling with putty. Confirm potable-water suitability before use in drinking-water assets, and always work to the current Fosroc technical data sheet for the batch supplied.
Specifications
| Product type | Two-component, solvent-free epoxy putty for underwater and damp-surface repair |
| Base chemistry | Water-insensitive epoxy resins with inert fillers and thixotropic agents |
| Consistency | Thixotropic, non-slump putty (suitable for vertical and overhead application) |
| Mix ratio | 1:1 base to hardener, by weight |
| Cure conditions | Cures on damp and fully submerged concrete, without shrinkage |
| Primary function | Sealing static cracks, blow holes and minor surface defects; minor grouting |
| Chemical resistance | Resistant to water, sewage and mild chemicals once cured |
| Suitable substrates | Sound damp, splash-zone or submerged concrete and masonry |
Industry use cases
Water & Wastewater
Sealing cracks, blow holes and pipe-penetration gaps in service reservoirs, sumps, wet wells and treatment tanks without draining them down.
Marine & Ports
Local repair of jetty piles, dock walls and quay structures below the waterline, cutting the need for cofferdams on minor defects.
Dams & Irrigation
Making good surface defects and static cracks on dam faces, spillways and canal linings while the structure stays in service.
Industrial & Sewerage
Point-sealing seepage and defects in effluent tanks, sewers and process pits exposed to mild-chemical and sewage conditions.
Building Basements & Tanks
Sealing damp construction defects and minor seepage in underground water tanks and basement retaining walls where the face cannot be dried.
Frequently asked questions
Can Exposeal UW really be applied underwater?
How do I mix it on site?
Will it stay put on a vertical or overhead surface?
Can I use it on a moving or expansion joint?
When should I choose Expocrete EUW instead?
Is it safe for drinking-water tanks?
How we position Fosroc Exposeal UW
Exposeal UW sits in Fosroc’s underwater and damp-surface repair family as the go-to putty for sealing static cracks, blow holes and minor defects in place. When the job grows into rebuilding or reprofiling a larger volume of submerged concrete, or a load-bearing patch, move up to Fosroc Expocrete EUW, the three-component underwater epoxy repair mortar. For general above-water concrete repair, Fosroc’s Renderoc mortar range and Nitomortar epoxy mortars apply, while cementitious tanking and negative-side waterproofing across broad wet areas is better handled by the Fosroc Brushbond and Nitoproof systems rather than a spot putty. Where a crack is genuinely moving, specify a flexible joint sealant, from Fosroc’s Nitoseal / Colpor sealant range, or an equivalent Dr. Fixit or Sika PU/polysulphide sealant we also stock, instead of a rigid epoxy. Space Arc supplies all of these Pan-India and can advise on the right combination for a given structure.
Related Sealants & Joint Treatment products
Source Fosroc Exposeal UW for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.