In a basement the water sometimes comes not from the wall but from under your feet: through cracks in the floor concrete, at the corners where wall meets slab, at column bases. Instead of breaking out the slab and waterproofing it again, we drill the concrete on a grid and inject acrylate gel beneath it. The gel forms a layer under the slab, on the side the water comes from.
Foundation and under-slab gel injection is a method applied without breaking out the slab, where water comes from underneath the basement floor. The floor finish is removed, the slab is drilled right through on a 30–50 cm staggered grid, and Dryvatec G101 acrylate gel is injected through the packers at low pressure. Under the slab, the gel combines with the fill and soil and aims to stop the water before it reaches the concrete. At the wall-to-slab junction the packers are placed closer together. Afterwards the holes are filled with R101 and N102 Crystal 2K can optionally be applied to the surface.
In buildings where the groundwater table is high, on a slope, or close to old stream beds, the basement slab is in constant contact with water. The waterproofing placed under the slab during construction either does not exist, or has opened at the junctions, at column bases and at the foot of the walls. Water finds the weakest places in the concrete: hairline cracks, pour joints, the corner where wall meets slab and service penetrations.
The conventional solution here is to break out the slab and lay new waterproofing and new concrete underneath. In a building in use, that means weeks of dust, noise and loss of use; keeping the connection to the wall intact during the breaking-out is another headache. Coatings applied to the surface stop the water inside the concrete, so the slab stays wet from below.
Under-slab gel injection opens a path between the two. Gel injected through holes drilled right through the slab spreads under the concrete, combines with the fill and water there and cures. The aim is to stop the water on the underside of the slab, that is, on the positive side. It is the horizontal version of the curtain injection we use on basement walls.
Not all the wetness on a basement floor comes from below. At the survey we first separate condensation, pipe leaks and water coming from the wall.
Water rises through cracks in the slab, pour joints or pores, and ponds in wet periods.
The line where wall meets slab, the column bases and the corners are where water gets in most often. Here the wall and the floor are dealt with together.
In areas on a slope, a stream bed or a high water table, the underside of the slab is in constant contact with water.
The basement is in use, with machinery or racking in place, and breaking out and new concrete would take weeks. The work is done section by section and from inside.
If the wetness comes from condensation or a pipe leak, injection is unnecessary. If the water pressure is very high, or the slab is thin and weak, a structural assessment comes first.
The first drawing is a vertical section of the slab, the second is the packer plan seen from above. The drawing is not to scale and shows the logic of the application.
The basement floor concrete. The finish and screed are removed and the holes pass right through the slab.
30–50 cm staggered grid; closer at the wall base and corners.
A gel layer on the underside of the concrete that combines with the fill and soil. The thickness is illustrative.
The wall-to-slab corner is the most critical line; where needed it is dealt with together with curtain injection.
The sequence we follow on site. Same materials and same logic as curtain injection; the difference is that the surface we work through is horizontal.
The floor finish and screed are lifted down to bare concrete. Wet zones, cracks and the wall-to-slab junction are marked. The reinforcement and services are scanned and the slab thickness measured. If water is running under pressure, E101 Pur In is used first.
A 30–50 cm staggered grid is marked over the wet area and around it. Holes are drilled right through the slab, deep enough to reach the fill beneath, cleaned out, and the packers are tightened. At the wall base and corners the spacing is reduced.
The reaction time is measured in a trial cup. G101 gel is injected at 1 : 1 with the two-component pump, at the lowest pressure. When gel appears at the neighbouring packer, we move on to the next. The slab surface is watched continuously for lifting or cracks opening.
The gel cures within minutes. Points that stay wet are marked and, where needed, completed with intermediate holes. The checks are written in the site record.
The packers are removed and the holes are filled with R101 Repair Mortar.
Optionally, N102 Crystal 2K crystalline waterproofing is applied to the concrete surface. The screed and floor finish can then follow.
The application dimensions are specific to this method; the material values come from the Dryvatec G101 technical data sheet.
| Item | Value |
|---|---|
| Packer grid | 30–50 cm staggered; close at the wall base |
| Hole depth | Right through the slab, reaching the fill beneath |
| Pressure | Lowest possible; slab surface monitored |
| Pre-scan | Reinforcement, services, slab thickness |
| Property | Value |
|---|---|
| Viscosity | 5–30 mPa·s, close to water |
| Crack width it can enter | 0.05 mm – 4 mm |
| Mixing | Two mixes, 1 : 1 by volume, with a two-component pump |
| Reaction (gel) time | About 35 seconds to 24 minutes, set by the G202 ratio |
| Pump pressure | 5–100 bar; always start at the lowest workable pressure |
| Minimum application temperature | +2 °C |
| Density / pH | 1.15–1.20 g/cm³ / 6–7.5 |
| Flammability | Non-flammable; water-based |
| G202 ratio | Gel time |
|---|---|
| 0.15% | ≈ 11 minutes |
| 0.5% | ≈ 3.5 minutes |
| 1% | ≈ 1.7 minutes |
| 2% | ≈ 1 minute |
| 4% | ≈ 35 seconds |
| Mix | Liquid | Where |
|---|---|---|
| A — Standard | 20 kg water | Static cracks, porous concrete, the body of a stone wall |
| B — Fully flexible | 20 kg G102 | Moving cracks and expansion joints |
| C — Semi-flexible | 10 kg G102 + 10 kg water | Cases in between; chosen after a trial on site |
Reaction times are laboratory values. On site, cold water lengthens them and hot weather shortens them, so every job starts with a cup test. The G201 / G202 catalyst is part of the four-component system.
A job in the basement of a building, in an area where water was coming through the floor concrete. The floor finish has been lifted and packers fitted in a grid in the slab; in the second photo gel is being injected with the two-component pump. The photos are from our own site.
The method does not repair the old waterproofing under the slab; it puts a gel layer in its place. In some areas extra injection may be needed over time.
Injecting liquid under a slab can lift it if done wrongly. That is why we work at the lowest pressure and watch the surface.
If there is a pipe leak or condensation, injection is wasted. We separate the source of the water first.
If there is settlement, heave or a structural crack in the slab, a structural assessment comes first.
Acrylate gel is not a single method; how it is applied depends on where the water comes from. The highlighted row is the subject of this page.
| What you see | The right application |
|---|---|
| A large part of a buried RC basement wall is wet; water comes through cracks and cold joints | Curtain injection behind the wall (D-06) |
| Water comes in through the joint between two blocks; the old sealant or tape has failed | Expansion joint gel injection (D-07) |
| Water and salts come through the body of a rubble stone or masonry wall; the outside face cannot be reached | Stone wall body injection (D-08) |
| Water rises from under the slab, through cracks and joints in the floor concrete | Under-slab and foundation gel injection (this page) |
| The lower part of a brick or stone wall is damp, there is no water pressure, paint and plaster blister from the bottom | Not gel: D101 DampStop rising damp injection |
| A single crack or service penetration leaks at one spot | Crack injection (PU or acrylate gel) |
In under-slab injection we use the same Dryvatec system as in curtain injection. All the products are from our own brand.
Because we make the material ourselves, whatever we run into on site goes straight back into the formula and the application instructions. The section drawing and steps on this page are part of the Dryvatec application detail set.
The core material of the system. A four-component acrylate gel almost as thin as water (5–30 mPa·s); it gets into hairline cracks down to 0.05 mm wide and stays flexible once cured.
Product page
An acrylic polymer that makes the gel more flexible and improves its bond to concrete. In moving cracks and joints it replaces some or all of the water in the mix.
Product page
Polyurethane injection that stops water flowing under pressure. If there is an active leak it goes in before the gel; pumping gel while water is still running just washes the material away.
Product page
Repair mortar that closes the holes after the packers come out, as well as opened joints and broken surfaces.
Product page
A two-component crystalline waterproofing applied to the inside face. Optional after injection, as a second line of protection and a clean finished surface.
Product pageOur YouTube channel has real site footage of our injection work.
We work with teams based in Istanbul and Izmir; one of our under-slab jobs was in Ankara. Depending on the size of the project we work across Turkey.
From our Maltepe office to every district on the European and Asian sides.
From our Konak office to every district of Izmir and the wider Aegean.
For basement walls buried in the ground: a gel barrier behind the wall, with no excavation.
Application detailThe moving joint between two blocks sealed from inside with flexible gel, both within the joint and behind it.
Application detailIn rubble stone and masonry walls, a water-stopping layer formed inside the wall with gel through the mortar joints.
Application detailSend us photos of the floor and the base of the walls through the survey request form, or give us a call. Let us work out together whether the water is coming from below, from the wall or from a pipe.
