In short: A basement wall in contact with the ground is waterproofed from the outside in four stages: expose the wall and make the substrate load-bearing and smooth, prime with Teroson PR Primer M+S, lay the cold self-adhesive Teroson FO KSK bitumen sealing membrane without wrinkles with about 80 mm overlap at each joint, and secure the finished waterproofing with a protective layer before backfilling. Before that comes the most important decision: under DIN 18533-1 the membrane covers classes W1.1-E and W1.2-E – that is, ground moisture and non-pressing water. With pressing water or accumulating seepage water it is, according to the manufacturer, not sufficient.
Before buying material: determine the water exposure
The waterproofing is not determined by the building but by the water that stands against the wall. For the KSK membrane the following applies according to the manufacturer: ground moisture and non-pressing water (W1.1-E and W1.2-E) are covered, and under screeds also the barrier effect against capillary rising damp (W4-E). Not covered are accumulating seepage water and pressing water – for example with cohesive soils without drainage or below the design water level. A system for class W2.1-E is required there, and that belongs in the hands of a specialist designer.
Second point before the first spade goes in: earthworks along the foundation are safety-critical. Slope angles, shoring and the stability of the foundation decide whether the excavation may be carried out as DIY at all. With excavations deeper than about hip height or with doubts about the ground, commission the earthworks. You can then carry out the waterproofing itself quite well yourself.
Which waterproofing principle is right for your case is compared in the guide Waterproofing slurry or bitumen – what goes where?
What you need: shopping list
Basic set (always required)
1. Primer
Teroson PR Primer M+S, 750 ml. Adhesion promoter for mineral and bituminous substrates, substrate-consolidating, applicable down to −10 °C and on substrates with construction moisture.
View primer
2. Waterproofing layer
Teroson FO KSK bitumen sealing membrane, 15 m² per roll at 1 m sheet width, 1.5 mm thick. Radon-tight, EMICODE EC 1 Plus, watertightness 4 bar, tear strength 240 ± 40 N/50 mm.
View sealing membrane
3. Seams and connections
Teroson RB 81 butyl sealing tape, 1.5 mm thick, 40 m roll, in 15 mm and 40 mm width. Adhesive on both sides, self-fusing, −40 °C to +80 °C.
View butyl tapeOptional – depending on the installation situation
- Birtel BIWA-SP bitumen filler 5 kg – when cracks, joints, voids or pipe penetrations have to be closed or a cove has to be formed at the foundation connection. Ready to use, up to 5 mm dry film thickness per pass, approx. 1.3 kg/m² per millimetre.
- Soudal Soudabond Perimeter PU adhesive foam 750 ml – when perimeter insulation boards or insulation and drainage elements are bonded on as the protective layer. According to the manufacturer it also adheres to coated bitumen sheets, approx. 14 m² of basement wall area per can.
- Ottoflex waterproofing slurry 20 kg – mineral variant, according to the product data approved as structural waterproofing on basement exterior walls and retaining walls, exclusively from the positive side. Useful for heavily fissured walls where a sheet does not lie cleanly.
- KSK bitumen sealing sheet 15 m x 1 m – alternative to the Teroson membrane, also self-adhesive, according to the product data applicable down to −5 °C and also on damp substrates, pressure-water-tight up to 5 bar.
You will find all materials of this group collected in the category Basement waterproofing, bitumen & waterproofing slurry.
Tools: Schuller Magic Push HD seam roller 4.5 cm for pressing the overlaps, Schuller Myron painter's brush 180 x 80 mm for dedusting and for spreading the primer, Schuller Terion bitumen brush 170 x 70 mm for bituminous compounds, plus utility knife with spare blades, smoothing trowel, hand brush, safety goggles and solvent-resistant gloves (nitrile).
Why primer, cove and protective layer are non-negotiable
A self-adhesive sheet is only as good as the bond to the substrate. Mineral walls are absorbent and carry a fine layer of dust; without a primer, the membrane sticks to this dust instead of to the concrete. The primer binds the dust, consolidates weakly bound surfaces and has a barrier function against moisture – that is why the manufacturer expressly calls membrane and primer a matched system.
The cove at the foundation/wall transition solves a different problem: at a sharp internal edge the sheet is pulled over a line and gets wrinkles there or tears open with settlement. A rounded cove distributes this movement. Conversely, sharp external edges must be broken so that the membrane does not run over a ridge.
And the protective layer: under DIN 18533-1 the finished waterproofing must be protected against mechanical damage – dimpled membrane or protection board are usual. Otherwise gravel and stones in the fill material damage the sheet at points during backfilling, and exactly these holes lie unreachable under the soil afterwards. A note on our own range: we do not currently stock dimpled membranes and protection boards – but we do stock the adhesive for the boards and the perimeter insulation.
Step by step: waterproofing a basement wall
Expose the wall and let it dry
Expose the wall down to below the top edge of the foundation, knock off old paint, mortar residues, sinter layers and loose parts and sweep off. The substrate must be load-bearing, level, sufficiently dry, frost-free and free of oil, grease, tar and release agents; preparation follows DIN 18533-2. Check: Run the flat of your hand over the wall – if dust or sand stays on your palm, keep cleaning.
Break edges, form the cove, close defects
Round off external edges, form a cove at the foundation/wall transition, close cracks, joints and voids. BIWA-SP is formulated ready to use for this and is applied cold with a trowel, spatula or smoother – up to 5 mm dry film thickness per pass, thicker build-ups in several passes. Substrate and surroundings must be above +5 °C; the material is solvent-containing and belongs exclusively outdoors, not in closed interior spaces. Check: The cove is continuously rounded, no sharp line shows anywhere; the surface is not more uneven than permitted by DIN 18202.
Prime and let flash off
Clean heavily dusty areas – especially at the lower horizontal connection – beforehand with a scrubbing brush, hand brush or vacuum. Apply Teroson PR Primer M+S with roller or brush; the spray can is sprayed on directly, and the spray head can be turned from horizontal to vertical. Do not spray in closed rooms or in wind, the can should be at least +10 °C, cover adjoining components. Then let it flash off for 20 to 50 minutes, depending on temperature, substrate and humidity. Check: Finger test – the primer film must feel dry. If it is still tacky, it is too early for the membrane.
Set the first sheet at the base
Start at the bottom and work upwards, so that every further sheet overlaps the one beneath and water does not run into the seam. Cut the sheet, set it without wrinkles, pull off the release paper and roll it on from the middle outwards. Application range of the membrane: −5 °C to +35 °C. Check: No air pockets, no wrinkles – a bulge can still be cut open and taped over now, but not later.
Press the joints with about 80 mm overlap
Bond every joint with about 80 mm overlap and press it firmly with the seam roller. These 80 mm come off the roll area: from 15 m² per roll, considerably less remains after deducting overlap and waste at corners. Check: Run a fingernail along the seam edge – nothing may lift.
Secure connections and penetrations
Work pipe penetrations, light wells, basement window bases and the top termination with Teroson RB 81 butyl sealing tape. The tape is adhesive on both sides, self-fusing, plastoelastic and compensates movements of about 5 %; it adheres to metal, plastic, wood, concrete, stone and plaster, prime porous surfaces beforehand. Important temperature difference: The membrane can be laid down to −5 °C, the butyl tape is only applied between +5 °C and +40 °C – below +5 °C the overlap area must be preheated. Check: Tape pressed on with at least 1.5 kp/cm², no bubbles, tape ends overlap.
Apply the protective layer
Set dimpled membrane, protection board or perimeter insulation in front. Insulation, drainage and rigid polystyrene foam boards are set with Soudabond Perimeter from the gun can; according to the manufacturer the adhesive adheres to concrete, coated bitumen sheets and bitumen thick coatings and is enough for about 14 m² of basement wall area per 750 ml can. The order and special features of bonding onto bitumen are described in the instructions Bonding XPS boards onto bitumen. Check: Boards sit without wobbling, no cavity is left open at the base.
Backfill in layers
Backfill only when the waterproofing is completely protected. Avoid point or line loads on the waterproofing and make sure that no water-retaining soil abuts the waterproofing surface directly – with such soils, according to the product data, an area about 50 cm wide in front of it is filled in layers with water-permeable fill material. Check: Every layer compacted, no angular stones directly against the sheet, protective layer still completely present at the top after backfilling.
Temperatures, waiting times and limits
| Work step | Material | Value from the product data | Check |
|---|---|---|---|
| Priming | Teroson PR Primer M+S | 20–50 min flash-off; applicable down to −10 °C; can at least +10 °C | Finger test: film feels dry |
| Lay the surface | Teroson FO KSK | −5 °C to +35 °C; thickness 1.5 mm; 15 m² per roll | wrinkle-free, rolled on from the middle outwards |
| Press the joints | Teroson FO KSK | approx. 80 mm overlap per joint | Seam edge cannot be lifted |
| Connections | Teroson RB 81 | Application +5 °C to +40 °C; contact pressure at least 1.5 kp/cm² | preheat below +5 °C; no bubbles |
| Cove and cracks | BIWA-SP | from +5 °C; max. 5 mm per pass; approx. 1.3 kg/m² per mm | Cove continuously rounded, no voids |
| Protection boards | Soudabond Perimeter | approx. 14 m² of wall area per 750 ml can | Board sits firmly at once, no cavity |
| Mineral variant | Ottoflex waterproofing slurry | 2–3 passes, max. 5 mm; 1–3 days to dry through; 7 days to set before backfilling | evenly covering, no wet sheen |
The quantity of material for waterproofing slurry and liquid membrane is worked out for you by our waterproofing calculator.
Common mistakes – and how to avoid them
- Wrong exposure class. A W1 membrane does not hold with pressing water. Clarify the water exposure first, then buy material.
- Primer skipped. Without a primer the membrane, according to the manufacturer, does not adhere reliably to mineral substrates – the most common reason for sheets coming away.
- Covered too early. The primer needs 20 to 50 minutes. Anyone who bonds onto the still-tacky film gets a separating layer instead of a bond.
- Sharp edge without a cove. At the internal edge foundation/wall the sheet tears at the first settlement. Form a cove, break external edges.
- Overlap too tight or not pressed. About 80 mm is the dimension; the seam roller is not an accessory but part of the waterproofing.
- Butyl tape applied in the cold. The membrane tolerates −5 °C, the tape does not. Preheat below +5 °C or postpone the work step.
- Backfilled without a protective layer. Gravel perforates the sheet during compaction. The protection is required by DIN 18533-1, not optional.
- Spray primer in wind. The spray mist lands on windows, render and paving and, once dried through, can only be removed mechanically. Cover neighbouring components.
Frequently asked questions on basement waterproofing
Is the KSK membrane enough with pressing water?
No. Teroson FO KSK is approved for ground moisture and non-pressing water (classes W1.1-E and W1.2-E). For accumulating seepage water and pressing water – for example with cohesive soils without drainage or below the design water level – a system for class W2.1-E is required.
Do I really have to prime?
Yes. Mineral substrates are primed; the manufacturer names Teroson PR Primer M+S for this and recommends it particularly on damp substrates and in the cold. Without a primer, according to the product information, the membrane does not adhere reliably.
How much wall area does one roll cover?
One roll contains 15 m² at 1 m sheet width. Of that, about 80 mm overlap per joint and the waste at corners and penetrations come off. With small-sectioned walls, allow a considerable extra.
From what temperature can I work?
The primer is applicable down to −10 °C, the membrane from −5 °C to +35 °C, the butyl sealing tape, by contrast, only from +5 °C to +40 °C; below +5 °C the overlap area is preheated. The bitumen filler BIWA-SP needs substrate and surroundings above +5 °C. The coldest value in the build-up therefore determines the working day.
Do I need a dimpled membrane or protection board?
Yes. Under DIN 18533-1 the finished waterproofing must be protected against mechanical damage, usually with dimpled membrane or protection board. We stock the matching adhesive for insulation, drainage and protection boards, but not the boards themselves at present.
Can I use waterproofing slurry instead of the sheet?
According to the product data, Ottoflex waterproofing slurry is approved as structural waterproofing on basement exterior walls and retaining walls, exclusively from the positive side. It is applied in 2 to 3 passes up to a maximum of 5 mm, must dry through for 1 to 3 days and set for 7 days before backfilling. The procedure is described in the instructions Applying waterproofing slurry.
Questions about the build-up? Give us a call: +49 (0) 2831 - 916 77 03. Baustoffheld, Lindenstrasse 56, 47623 Kevelaer.
