Fosroc Renderoc Plug
A single-component, chloride-free plugging mortar that arrests pressurised water leaks in roughly a minute, straight against a running flow.
What is it?
A ready-blended, rapid-setting cementitious mortar (BS EN 1504-3 Class R1) that stiffens in about one minute to physically stop active water ingress.
Where is it used?
Basements, tunnel and shaft linings, sewage chambers, tie-bolt holes, water tanks and any concrete or masonry structure with a live leak.
Why use it?
It grabs and sets under hydrostatic pressure, so a leak can be sealed without diverting or dewatering the flow first.
How is it applied?
Chase out the leak, mix one part clean water to three parts powder, then hand-press or trowel the stiff mortar into the opening and hold until set.
About Fosroc Renderoc Plug
Water finding its way through a construction joint, a tie-bolt sleeve or a hairline crack in a basement raft is one of the most stubborn problems on any waterproofing job. You cannot brush a coating over a spot that is actively weeping, and you rarely have the luxury of dewatering the structure first. Fosroc Renderoc Plug is built for exactly that moment. It is a pre-bagged blend of cements, graded aggregates, special fillers and set-controlling additives that needs nothing but clean water on site. Once mixed, it goes from a stiff paste to a load-bearing plug in roughly sixty seconds, gripping the sides of the chase and shutting off the flow while the pressure is still on.
Because the formulation is chloride-free and low-exotherm, it can be pressed hard into a repair without the risk of corroding embedded steel or cracking from the heat of a fast reaction. Space Arc Engineering supplies Renderoc Plug as an authorised Fosroc distributor and applicator across Delhi NCR and Pan-India, and we treat it as the first move in a leak-repair sequence rather than the whole answer. Arrest the flow with Renderoc Plug, let the structure dry, then come back with a permanent membrane or an injection resin. Used that way it saves hours of frustration and keeps the rest of the waterproofing system on schedule.
The technical insight
The trick behind Renderoc Plug is a carefully accelerated cement chemistry. The blend uses rapid-hydrating cements with additives that push the initial set to around one minute at 20 C, so hydration products lock the mortar into place faster than water can wash it out. As it sets it develops a slight positive volume change that wedges the plug against the walls of the chase, converting the incoming water pressure into a self-sealing clamping force instead of a wash-out failure. Setting is exothermic by nature, but the mix is engineered for low heat output, which is why it can be built up in thicker sections without the thermal cracking that would otherwise open a fresh path for water. The set is temperature-sensitive in a predictable way: warm water accelerates it in cold weather down to 1 C, and cool water in the shade slows it in heat above 35 C, giving the applicator a usable working window in Indian site conditions.
Where it is used
- Emergency stopping of pressurised water leaks through basement and retaining walls
- Sealing seepage at construction joints, cold joints and honeycombed concrete
- Plugging weeping tie-bolt holes and form-tie sleeves before they are grouted
- Arresting active leaks in concrete-segment and brick tunnel linings
- First-step leak arrest in sewage systems, below-ground access chambers and pipes
- Temporary water-stop repairs in tanks, reservoirs and pump wells
- Fixing and pointing where a fast grab is needed on damp substrates
- Preparing a dry, sealed surface ahead of membrane or resin-injection repair
Key advantages
- Stops live, pressurised leaks in about a minute, often without dewatering
- Single component – only clean water is added, so site batching errors are avoided
- Chloride-free formulation is safe against embedded reinforcement
- Low exotherm minimises thermal cracking, allowing thicker build-ups
- Bonds strongly to concrete, masonry and brick substrates
- Works on horizontal, vertical and overhead surfaces
- Conforms to BS EN 1504-3 Class R1 for concrete repair
- A companion grade (Renderoc Plug 20) is BS6920 / WRAS approved for potable-water structures
Limitations & considerations
- Very short working time (roughly 60-90 seconds) – only tiny batches can be mixed and placed at once
- It is a leak-arrest product, not a structural repair mortar or a standalone waterproofing membrane
- Minimum applied thickness is 15 mm; feather-edges are not permitted and will fail
- Set and strength gain slow markedly in cold weather and accelerate in heat, so water temperature must be managed
- The standard grade is not certified for potable-water contact – specify Renderoc Plug 20 for tanks carrying drinking water
- A permanent coating or injection system is still needed once the leak is dry
Selection & best practice
Cut the leaking area back to at least 15 mm and give it a mechanical key; for a crack, chase it out to roughly 20 mm square and undercut the groove so the plug cannot be pushed out. Remove all loose material, dust and laitance. Mix only what one pair of hands can place in a minute – one part clean water to three parts powder by volume, worked to a stiff consistency in a bucket. Press or trowel the mortar firmly into the opening and, if water is running, hold it in place by hand until the initial set is felt. Build thicker repairs up in layers rather than one deep pour. In cold conditions use warm water up to 20 C; above 35 C store the material in shade and mix with cooler water. Once the plug is set and the substrate has dried, overband with a cementitious membrane such as Fosroc Brushbond or inject the joint with Nitofill UR63 for a durable finish.
Specifications
| Product type | Single-component rapid-set cementitious water-stopping mortar |
| Standard compliance | BS EN 1504-3, Class R1 (repair principle 3.1) |
| Initial set time | Approximately 1 minute at 20 C (standard grade) |
| Compressive strength | >10 MPa at 1 hour; ~23 MPa at 28 days (Renderoc Plug 1) |
| Bond strength (pull-off) | >0.8 MPa at 28 days |
| Mixing ratio | 1 part clean water : 3 parts powder, by volume |
| Minimum applied thickness | 15 mm (no feather-edges) |
| Chloride ion content | <0.05% (chloride-free), Class A1 non-combustible |
| Application temperature | 1 C to 35 C substrate/air (adjust water temperature accordingly) |
Industry use cases
Basement & Below-Grade Waterproofing
Arrests weeping construction joints and tie-bolt holes in raft slabs and retaining walls so the permanent membrane can be applied on a dry surface.
Tunnels & Metro
Seals active leaks in concrete-segment and brick linings under groundwater pressure as the first step before resin injection.
Water & Sewage Infrastructure
Plugs seepage in access chambers, pump wells and pipes; the Plug 20 grade is used where potable-water contact requires BS6920 approval.
Industrial & Commercial Structures
Stops leaks in lift pits, water tanks and effluent sumps quickly, minimising downtime on running facilities.
Repair & Rehabilitation Contractors
A dependable emergency item to carry on site for unexpected live leaks during any concrete-repair or waterproofing package.
Frequently asked questions
How fast does Renderoc Plug actually set?
Can it stop water that is already flowing?
Is Renderoc Plug a complete waterproofing solution on its own?
What is the difference between Renderoc Plug 1 and Renderoc Plug 20?
Will it corrode the reinforcement in the concrete?
How much water do I mix with the powder?
How we position Fosroc Renderoc Plug
Renderoc Plug is the emergency leak-stopper that opens a waterproofing repair, not the finish. Within the Fosroc family, pair it with Renderoc Plug 20 when a job needs a longer working time or potable-water approval, follow it with Nitofill UR63 single-component PU resin for injecting cracks and joints once the plug is in, and protect the dried, sealed surface with a Fosroc Brushbond cementitious membrane or a Nitoproof coating. For structural section rebuilding rather than leak arrest, move to the Renderoc repair-mortar range. Where clients standardise on other brands we stock, comparable crystalline and acrylic waterproofing systems from Dr. Fixit and Sika sit alongside these Fosroc products in our catalogue, so the specification can be matched to the site rather than the shelf.
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Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.