Hydraulic plugs: rapid-setting compounds for stopping leaks

What a hydraulic plug is

A hydraulic plug is a dry mix based on rapid-setting cement that is mixed with water and pressed into the point of an active leak. Within seconds or minutes the mass hardens right in the flow and shuts it off. Many products also expand or swell slightly and press against the walls of the cavity from the inside: KÖSTER Waterstop, for example, expands by about 0.5 % by volume. All these materials have the same job — to stop the water so that the main waterproofing can be carried out.

The plug is held in place by the shape of the cut-out cavity, by its expansion and by its bond to wet concrete. It is a rigid material: it closes a point or a short length, but it does not make the whole structure watertight and does not tolerate crack movement. That is why a hydraulic plug is the first step of a repair, not its end.

Where they are used

  • concentrated leaks through cracks, honeycombing and construction or cold joints in basements, pits, lift shafts and manholes;
  • pipe and cable penetrations, form tie holes, manhole ring joints and sewer pipe sockets;
  • tunnel linings, collectors, underground chambers and shafts where water comes in continuously;
  • temporary drainage openings that are left during waterproofing work and closed last;
  • substrate preparation before penetrating and cementitious waterproofing: the main coat is applied only once all running water has been stopped.

If water comes through a large area, through many small defects or through a moving crack, a plug will not stop it — this calls for injection waterproofing. Construction and movement joints that leak along their entire length are dealt with by dedicated details — see the “Joint waterproofing” section.

How to choose a product

Setting time

The stronger the flow, the faster the mix must set, otherwise it is washed out before it hardens. The fastest products in the catalogue start to harden after about 30 seconds — PENEPLUG, Remmers WP RH rapid, KÖSTER Waterstop and the Turkish-made version of Fosroc Renderoc Plug. Sika MonoTop-108 Water Plug hardens in 60–80 seconds at +20 °C, MC-Fast SM sets 60–120 seconds after water is added, and Xypex Patch’n Plug reaches its initial set in 1.5 to 4 minutes. Ceresit CX 5 hardens in about 5 minutes: it is primarily an assembly cement, which its data sheet also allows for the temporary sealing of spot leaks. Slower products are more convenient for long chases, faster ones for a jet of water under pressure.

Pressure and inflow

A plug resists high pressure only in a correctly cut-out cavity. With a heavy inflow, the water is diverted first: a hose or pipe is fixed at the wettest point, the crack is sealed around it, and the remaining hole is closed last. This is what the Xypex, Schomburg FIX-20-T and Kryton data sheets prescribe, while Remmers recommends drainage tubes.

Compatibility with the main system

It is better to take the hydraulic plug from the same system as the main waterproofing: the manufacturer describes the whole sequence of work for its own materials. PENEPLUG is followed by PENETRON and PENECRETE MORTAR, Krystol Plug by Krystol Repair Grout and the Krystol T1 coating, and Xypex Patch’n Plug by Dry-Pac mix and Xypex Concentrate — more on such systems in the “Penetrating waterproofing” section. Around a KÖSTER Waterstop repair, the data sheet recommends KÖSTER NB 1 Grey slurry over a radius of at least 40 cm, and around MC-Fast SM — MC-Proof 101 HS.

Working conditions

Most data sheets allow work at substrate and air temperatures from +5 to +25…+30 °C. In cold weather the mixing water is warmed and in hot weather it is cooled; Schomburg limits the temperature of the powder itself to +23 °C. In the Uzbek summer the material is stored in the shade — Fosroc requires this once it is hotter than +35 °C — and mixed in small portions.

Documents

Some products are marked to EN 1504-3, the European standard for repair mortars used in structural and non-structural repair of concrete; the data sheets in the catalogue show classes R1, R2 and R3. For a hydraulic plug the strength class is secondary: setting speed and performance on a wet substrate matter more. For drinking water tanks, hygiene documents are checked — foreign approvals, such as NSF 61 for Xypex Patch’n Plug, do not replace the documents recognised in the country of use.

Preparing the leak

  • Source. The leak is opened up to sound concrete and the crack is traced along its whole length: if only the visible wet spot is sealed, the water will come out next to it — the Kryton instruction warns about this explicitly.
  • Cavity shape. The shape is set by the material’s data sheet, but the principle is the same: the cavity must not narrow towards the bottom, and the Sika, Fosroc and Xypex data sheets do not allow a V-shaped cut. The data sheets call for a dovetail (Lamposilex, Schomburg FIX-20-T), an undercut (Xypex, Fosroc), a wedge or cone widening inwards (Remmers, ISOMAT) or a rectangular chase deeper than it is wide (Kryton).
  • Dimensions. The minimum dimensions in the data sheets range from 2 cm deep for Lamposilex, MC-Fast SM and KÖSTER Waterstop and 20 × 20 mm for the Sika and Fosroc products to 3 × 3 cm for Remmers, 25 × 37 mm for Xypex and 25 × 40 mm for Kryton.
  • Cleaning. Loose concrete, old plaster, paint and dirt are removed, the cavity is flushed with water, and dry edges are wetted.

How the plug is placed

  1. Mixing. The mix is prepared in a small portion — enough for one plug — strictly in the proportion given in the data sheet: the amount of water determines the setting time. A mix that has started to stiffen is not thinned with water. Remmers, Schomburg and Penetron also allow application as a dry powder.
  2. Shaping. The mass is kneaded in a gloved hand and shaped into a cone or wedge. Most data sheets say to wait until it starts to stiffen and warm up, whereas Kryton and Remmers say to place it straight away.
  3. Placing. The plug is pressed into the cavity in one movement and held firmly until it hardens — from 30 seconds for PENEPLUG and 45–60 seconds for the Turkish-made Sika products to 1–2 minutes for MC-Fast SM and KÖSTER Waterstop. A plug that has started to harden is not moved.
  4. Sequence on a long crack. This too is set by the data sheet: Xypex works from the point of least inflow to the point of greatest inflow, Kryton from one end of the crack to the other, and Sika closes a large area from the edges towards the centre.
  5. Plug volume. The plug must not fill the whole cavity: with Kryton it fills no more than a third of the chase, and the rest is the system’s repair mortar. Excess material is trimmed off immediately after setting.
  6. Curing. The area is kept damp: for SikaTop-591 Seal for 15 minutes, on dry absorbent substrates for 30 minutes; waterproofing over the Turkish-made Sika products is applied after 15 minutes.

Once the water has been stopped, the chase is filled with repair mortar and the surface is covered with the main waterproofing. If there are many leaks or it is unclear where the water is coming from, the work starts with a survey carried out by our engineering centre: we will identify the cause, the sequence of work and the make-up of the system.

Safety

Hydraulic plugs contain cement: the mixed material is alkaline and warms up noticeably as it hardens. Work is carried out wearing protective gloves and goggles, without breathing in the dust; if the mix gets into the eyes, they are rinsed with water at once and medical advice is sought. Other measures follow the safety data sheet of the specific product.

Common mistakes

  • The hydraulic plug is treated as finished waterproofing — the water finds a way round the plug.
  • A V-shaped cut or one that narrows towards the bottom — the pressure pushes the plug out.
  • A whole bucket is mixed instead of a portion for one plug: the mix sets in the container, and the data sheets forbid thinning it with water.
  • Only the visible leak point is sealed while the rest of the crack is left — the water moves to the adjacent section.
  • A plug in a moving crack or a movement joint — the first movement of the structure tears it out.
  • The plug is placed on gypsum plaster or mixed with gypsum — the Schomburg and Remmers data sheets forbid this.

See also: waterproofing — overview, cementitious waterproofing, concrete repair.

Materials in the catalogue

  • SikaTop-591 Seal — Sika — expanding rapid-setting mortar for stopping active leaks and sealing pipe penetrations.
  • SikaTop-596 Seal — Sika — ultra-rapid cementitious water plug for emergency leak stopping, also suited to cold weather.
  • Sika MonoTop-108 Water Plug — Sika — rapid-setting cement mortar for instantly plugging leaks in concrete and masonry.
  • Fosroc Renderoc Plug — Fosroc — rapid-setting cementitious plugging mortar for emergency water stopping in tunnels and chambers.
  • PENEPLUG — Penetron — rapid-setting crystalline water plug for stopping active leaks, including under water.
  • Krystol Plug — Kryton — rapid-setting hydraulic cement for stopping flowing water in concrete cracks and joints.
  • MC-Fast SM — MC-Bauchemie — fast-setting swelling plugging mortar for permanent sealing of leaks and pipe inlets.
  • Schomburg FIX-20-T — Schomburg — rapid-setting swellable mortar for sealing water-bearing holes and cracks in concrete.
  • Remmers WP RH rapid — Remmers — quick-setting plugging mortar for leaks and water inrushes, setting in about 30 seconds.
  • Ceresit CX 5 — Henkel (Ceresit) — rapid-hardening assembly cement for anchoring and temporary sealing of spot leaks.
  • KÖSTER Waterstop — KÖSTER — expanding fast-curing plugging mortar for sealing leaks, including pressurised water.
  • ISOMAT AQUAFIX — ISOMAT — rapid-setting cement for instant plugging of local leaks and quick anchoring.
  • Xypex Patch’n Plug — Xypex — fast-setting hydraulic cement with crystalline chemistry: initial set in 1.5–4 minutes.
  • Lamposilex — Mapei — ultra-rapid hydraulic binder for stopping leaks under pressure, initial set in about 1.5 minutes.
  • Peneplug — Penetron — rapid-setting plug mortar for instantly stopping pressurised leaks in concrete.
  • Waterplug — Penetron — fast plug mortar for stopping pressurised leaks, sets in about three minutes.

Frequently asked questions

Can a hydraulic plug be used without subsequent waterproofing?

No. The plug closes a specific point, but the concrete around it remains permeable, and the water looks for a new path. Once the leak has been stopped, the chase is filled with the system’s repair mortar and the surface is protected with a penetrating or cementitious product.

How does a hydraulic plug differ from injection?

A hydraulic plug is pressed into a cut-out cavity at the surface and closes the leak right where the water comes out. An injection material is pumped through packers into the body of the structure — this is how cracks are sealed through their full depth, as well as moving cracks and leaks over an area. The two are often combined: a heavy flow is first stopped with a plug or foam, and permanent sealing follows.

Does a hydraulic plug work under water and under pressure?

Many products in the catalogue also harden under water — this is stated explicitly in the data sheets for PENEPLUG, Krystol Plug and Schomburg FIX-20-T, and KÖSTER Waterstop is also designed for cracks carrying water under pressure. At high pressure the water is first diverted through a hose, and the hole it leaves is closed last.

How much material is needed?

Consumption is calculated from the volume of the cavities: in the catalogue data sheets it is about 1.6–2 kg of dry mix per litre of volume filled. For cracks, Kryton gives a guide by length — about 30–42 m of chase per 25 kg pail of Krystol Plug. We will calculate the quantity for your project from a description of the leaks and the chase dimensions.

We will select a hydraulic plug and a waterproofing system for your project and calculate the quantities and supply — call us or message us on WhatsApp/Telegram: +998 94 094 52 27.