Building a Steel-Wall Pool – A Complete Build Report
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Subsurface and Base Slab: the Foundation Decides
The most common fundamental mistake happens before the first wall even stands: an inadequately prepared subsurface. The bottom rail must be perfectly level over its entire length. Even a few millimetres of slope will later result in a visibly tilted water line and in permanent wrinkling of the liner that can no longer be corrected.
A concrete slab has proven itself as the foundation. It distributes the load evenly, prevents settlement and provides a clean, level bearing surface. A plain sand bed is tempting because it is quick, but it readily gives way under the point load of the filled wall. A thin levelling or fine-sand layer goes on top of the cured slab so that the bottom rail sits snugly and without voids. Slab dimensions, thickness and reinforcement depend on the pool size and the subsoil – follow the manufacturer’s assembly instructions and, on difficult ground, bring in a specialist contractor.
Erecting the Steel Wall: Avoiding Handling Mistakes
The wall panel is delivered as a coiled steel band and is under tension. Never unroll it on your own: as it unwinds the band can spring back, and the curve can only be guided cleanly into the bottom rail with two people. Kinks in the sheet metal are irreparable – a wall that has once been kinked remains a weak point.
The coating is just as critical. Scratches that occur during erection or from tools become rust spots later on. Do not lay the panel over a sharp-edged surface and protect the edge as you feed it in. Once the wall is closed – depending on the system, via a clamping rail, plug-in profile or bolted joint – check the curve with diagonal and radius measurements. A wall that is out of round or not level can only be corrected now, no longer after the liner has been hung. With oval pools there is the added factor that the straight side walls do not absorb the earth pressure themselves: they absolutely require the supporting walls or support structures specified by the manufacturer, executed exactly according to the assembly instructions – otherwise the structural design is undersized.
Fitting the Floor Fleece and Inner Liner
Before the liner comes the floor protection fleece. It levels out minor unevenness and protects the inner liner from below against puncture by small stones or rough spots. On the wall, an additional wall fleece prevents the sheet-metal structure from pressing through. Do not skimp on the fleece – small stones that work their way in afterwards are one of the most common causes of holes in the liner.
Hang the inner liner (typically 0.6–0.8 mm, depending on the version a beaded or overlap liner) on a warm day. Warm material is elastic and lies with fewer wrinkles; a liner hung cold pulls permanent folds. Roughly align the liner, let in a few centimetres of water and smooth the folds from the centre of the pool outwards before the water level rises further. Folds that have once been flooded stay put.
Installing and Connecting the Built-In Parts
The skimmer and inlet nozzle are only set once a little water has fixed the liner in place. Mark out the cut-outs, drill a pilot hole and cut the liner only once the flange with its seal is fitted – that way nothing shifts. Make sure the sealing surfaces are clean and free of folds; a fold under the flange is the classic leak point.
For the connection to the filter system, solvent-cemented PVC pipework is the durable solution compared with a floating hose. You usually connect the skimmer (suction side) and inlet nozzle (pressure side) to the sand filter via d50 (DN40). Fit a union in each line at the pump and filter for later maintenance, plus a ball valve each, so the pool can be shut off and drained for wintering. Leave the electrical connection of the pump, filter and lighting, as well as the equipotential bonding, to a qualified electrical contractor.
Backfilling a Partially Recessed Pool
If the pool stands partially or fully in the ground, the backfilling is the most safety-critical step. The thin steel wall cannot bear one-sided earth pressure – it only holds as long as the water pressure counteracts it from the inside. Hence the basic rule: always backfill and fill with water in parallel, and the water level inside must always be higher than the backfill material outside.
Fill in layers and compact gently, without working against the wall with heavy equipment. Coarse, angular material does not belong directly against the wall; for partially and fully recessed pools a ring of lean concrete around the wall, which takes up the load, is often recommended. Also bear in mind groundwater and frost: an empty, buried pool can float up when the groundwater level is high. When in doubt, clarify the subsoil, drainage and uplift protection with a specialist contractor.
Mistake Catalog from Real-World Builds
The following overview brings together the mistakes we encounter most often in practice – and how to prevent them.
| Assembly mistake | Consequence | How to avoid it |
|---|---|---|
| Subsurface not level | Tilted water line, permanent folds | Level the bottom rail to the millimetre |
| Wall scratched or kinked | Rust, permanent weak point | Erect it with two people, protect the edge |
| Fleece omitted | Holes in the liner from below | Always lay in floor and wall fleece |
| Liner hung cold | Permanent folds | Hang on a warm day, smooth before flooding |
| Backfilling without water counter-pressure | Dented wall | Fill with water in parallel, water higher than soil |
| Coarse backfill material against the wall | Pressure marks, liner damage | Use fine material or lean concrete |
Building a Steel-Wall Pool Step by Step
- Prepare the subsurface and base slab Excavate the ground, compact it and lay a load-bearing, level concrete slab with a thin levelling layer. Slab dimensions and reinforcement as specified by the manufacturer.
- Align the bottom rail and erect the wall Level the bottom rail to the millimetre and lay it out in a true circle. With two people, feed the wall panel into the rail free of tension, without kinking or scratching the sheet metal.
- Close the wall and check the curve Close the wall via a clamping rail, plug-in profile or bolted joint. Check the roundness and level with diagonal and radius measurements and correct them now. With oval pools, set the supporting walls specified by the manufacturer according to the assembly instructions.
- Lay in the fleece and inner liner Lay out the floor protection fleece and, if applicable, fit the wall fleece. Hang the inner liner on a warm day and align it roughly.
- Let in the first water and smooth the folds Let in a few centimetres of water and smooth the folds from the centre of the pool outwards before the water level rises further.
- Cut out and seal the built-in parts Mark out the skimmer and inlet nozzle, fit the flange with its seal and only then cut out the liner free of folds.
- Pipe up the filter system Solvent-cement the suction and pressure line in d50 (DN40) to the sand filter, and fit unions and ball valves for maintenance and overwintering. Electrical connection by a specialist contractor.
- Backfilling for partial installation Backfill in layers only in parallel with filling; always keep the water level inside above the backfill height. Fine material or lean concrete against the wall, compact gently.
Bill of materials
Example – please verify with a specialist. Parts and quantities depend on the installation; sizes shown are examples.
| Component | Size | Art. No. | KLN No. | Qty |
|---|---|---|---|---|
| PVC-U pressure pipe with socket | d50 | 76910 | 51515804 | as needed |
| 90° Elbow, solvent socket (PVC-U) | d50 | 70506 | 51513082 | 4-6 pcs |
| Union Ocean, solvent socket / solvent socket | d50 | 170397 | 51512461 | 2-4 pcs |
| 2-way ball valve M1, solvent socket (PVC-U) | d50 | 128814A | 51511559 | 2 pcs |
| Griffon UNI-100 PVC-U adhesive | – | 20023 | 51512566 | 1 can |
| Griffon cleaner / degreaser | – | 1 can | ||
| Steel-wall pool set | – | – | – | Wall shell, bottom and top rail, connecting profiles per the manufacturer's instructions |
| Sand filter system with pump | – | – | – | Matched to the pool volume and the required circulation rate |
| Floor protection fleece | – | – | – | Under the liner; protects the inner liner against puncture from below |
| Inner liner / pool liner | – | – | – | 0.6-0.8 mm, matched to pool shape and hook-in type (keder/bead) |
FAQ
Is a sand bed enough as a base, or does it have to be a concrete slab?
A load-bearing concrete slab is the safe choice because it distributes the load and prevents settlement. A plain sand bed readily gives way under the weight of the filled wall and leads to tilting.
Can I hang the liner on a cool day?
Better not. Cold liner material is stiff and pulls permanent folds. A warm, sunny day, on which the material lies elastically and with few wrinkles, is ideal.
With a recessed pool, do I really have to fill with water and backfill at the same time?
Yes. The steel wall only withstands one-sided earth pressure with water counter-pressure. The water level inside must always be above the backfill height, otherwise the wall dents in.
What is the best way to connect the skimmer and inlet nozzle?
For durability, best with solvent-cemented PVC pipework in d50 (DN40); unions and ball valves make maintenance and overwintering easier. A floating hose is possible but less durable.
Who must carry out the electrical connection?
Have the connection of the pump, filter and lighting, as well as the equipotential bonding, carried out by a qualified electrical contractor. This is not a DIY job.
This guide provides general technical orientation and does not replace professional planning. Safety-, electrical- and permit-relevant work must be carried out by qualified specialists.
