Permanent insulating forms
Two insulating panels joined by ties form a wall cavity and stay in place. They make the forms quick to assemble and provide insulation, but do not support the pool on their own.
Concrete pools
Permanent insulating forms
How ICF pool walls are built
The blocks form permanent insulating formwork; reinforcement and concrete provide structural strength. Design the slab, walls, penetrations and finish together for a reliable pool.
How the system is built
The four main parts of an ICF pool
Reinforced concrete core
Vertical and horizontal reinforcement, together with properly placed concrete, form the structural wall. The design specifies core thickness, bar layout and concrete cover for the pool and ground conditions.
Base slab and wall connection
The wall must transfer loads into the base slab. Detail starter bars, the construction joint, any waterstop and the wall-to-slab connection before pouring the slab.
Internal finish
Prepare the inner surface and install a watertight finish. Liners and reinforced PVC membranes are common; mineral finishes need a specifically designed, compatible build-up.
Suitable projects
When is ICF a suitable choice?
A suitable project
A rectangular or moderately complex pool, understood ground conditions and a team experienced with the chosen ICF system, reinforcement and controlled concrete placement.
Advantages of the system
The blocks help you set out accurate walls, and the formwork stays in place to insulate both sides. Installation details can be prepared while the wall cavity remains open.
What ICF does not remove from the job
You still need structural design, groundwater control, concrete curing and a complete waterproofing system. Poorly filled areas of the core can remain hidden behind the insulation.
Soil and water
Account for ground conditions and groundwater
Soil and fill
Uneven settlement can damage the slab-to-wall joint or distort paving. The designer uses ground investigation findings to specify base preparation, the slab and structural support.
Groundwater
When the pool is empty, groundwater can exert upward and external pressure. Drainage, pressure relief and draining procedures must be designed for the site; installing a drainpipe alone is not a guarantee.
Outside the wall
Do not backfill against unprotected blocks without the specified protection and drainage layers. Use backfill materials and compaction methods that will not damage the wall or impose excessive lateral loads.
Surface water
Grade paving to drain rain away from the pool and equipment. Water continually running beside the wall can overload otherwise adequate underground drainage.
Concrete placement
Checks before and during the pour
Follow the design and technical documents for the chosen system. This is an inspection checklist for the owner and supervisor, not a DIY structural specification.
- 1Confirm the exact block, concrete core width, compatible ties and maximum permitted concrete lift height.
- 2Check vertical and horizontal reinforcement, laps, slab starters, corners, lintels and reinforcement around large openings.
- 3Brace walls, corners and openings as instructed; check alignment, diagonals, levels and plumb before and during the pour.
- 4Agree the concrete mix, consistency, maximum aggregate size and delivery method with the designer, ICF supplier and contractor.
- 5Pour in controlled lifts, working evenly around the perimeter instead of building excessive pressure at one point.
- 6Consolidate concrete using a method approved for the block system, especially around reinforcement, corners, penetrations and the slab joint.
- 7Record bulging, movement or leaking formwork immediately. Do not continue pouring over a defect that will become hidden.
- 8Keep delivery tickets, placement times, photographs, specified test results and the supervising professional's inspection record.
Penetrations and edges
Check openings and the pool's top edge carefully
Skimmers and return fittings
Confirm the model, elevation and pool finish before cutting blocks. Secure each fitting so pouring cannot move it or leave a void behind its flange.
Lights and service sleeves
Plan cable access, junction boxes and compatibility with the finish. Drilling through the completed core creates another penetration that needs careful detailing.
Pipes in and beside the wall
Pipes must not occupy space required for concrete and reinforcement. Photograph routes, pressure-test before covering and protect them during subsequent work.
Top edge
Detail coping, membrane retention, stone or paving, movement joints and drainage together. Prevent water entering behind the finish or into unprotected insulation.
The water-facing finish
ICF blocks are not a pool lining
Factory-made liner
A replaceable liner made to fit relatively simple shapes. It needs a smooth, clean base, a suitable retaining profile and compatible flanges on every fitting.
Reinforced PVC membrane
Cut and welded on site to suit steps and more complex details. The installer must check the substrate, welds, corners, penetrations and material compatibility.
Tiles or a mineral finish
Applying tile adhesive directly to insulating blocks is not enough. Use a documented supporting and waterproofing system with crack control and compatible finishing products.
Do not combine products just because each is described as waterproof. The base, levelling layer, waterproofing, adhesive, membrane, flanges and seals must form a documented, compatible system with clear installer responsibility.
Construction stages
From design to handover
Coordinate the structure, services and finish before construction; changes later are expensive.
- 1Define the intended use, shape, water levels, steps, cover, safety barrier and equipment area.
- 2Check approvals, buried services, soil, groundwater and surface drainage; complete structural, plumbing and electrical designs.
- 3Excavate and prepare the base, drainage and reinforced slab, with accurately positioned starters and a designed construction joint.
- 4Assemble blocks, reinforcement, corners, openings and penetrations; brace the walls and record the pre-pour inspection.
- 5Place concrete following the system's documented procedure, check wall geometry and cure exposed concrete as specified.
- 6Inspect the core using appropriate methods, test pipework, complete external protection and backfill carefully in specified stages.
- 7Prepare the inner surface, install the complete lining system and coping, and separate surrounding paving with the designed movement joints.
- 8Install and test equipment, fill in a controlled manner, commission the system and hand over drawings and instructions.
If something goes wrong
What to check first
A wall has bulged
Possible causes include overly fast or uneven pouring, inadequate bracing or unsuitable concrete. Stop the pour, assess stability and agree repairs before continuing.
A void is suspected
Do not inject foam blindly into a hollow-sounding or defective area. A qualified professional must specify inspection and repair based on its position, reinforcement and structural role.
Dampness at the slab-to-wall joint
First establish whether the moisture comes from the pool, external water or condensation. Check penetrations, pipework, the construction joint and drainage. Do not install a new lining before finding the cause.
An uneven internal surface
Inaccurate block assembly or pressure during pouring can cause unevenness. A membrane needs a smooth base without sharp transitions. Use levelling materials compatible with the system.
Cracked paving
Do not rigidly connect paving to the pool structure without a designed detail. Check the base, drainage and movement joints before cosmetically filling a crack.
Damaged external insulation
Repair it according to the system instructions and restore the protective layer before backfilling. Heavy compaction directly beside the wall can cause damage.
Choosing a contractor
What the quote should include
Compare the same scope and inspection requirements. The lowest quote may leave work out, with the difference appearing later as extras.
- 1The ICF system name and technical documents, core thickness and compatible components.
- 2Approved designs for the slab, walls, reinforcement, joints, penetrations, drainage, plumbing and electrics.
- 3Concrete specification, placement method, bracing, inspection stages, responsible personnel and work records.
- 4The complete build-up from ground to water, including external protection, backfill, surface preparation and lining.
- 5Pipe tests, acceptance tolerances for wall geometry and surfaces, concealed-work records and as-built drawings.
- 6Clear exclusions, system warranties, responsibility where trades meet and a procedure for additional work.
Use and maintenance
Regular inspection points
Regularly check the lining, water level, penetrations, coping, paving movement joints, surface drainage and equipment area. Photograph changes and keep a service record. Do not empty the pool without checking groundwater conditions and lining instructions.
Include construction, equipment and finishes in the budget
Include design, excavation and soil removal, base preparation, slab, blocks and bracing, reinforcement, concrete and pumping, drainage, penetrations and pipes, external protection, backfill, internal preparation, lining, coping, paving, equipment, electrics, tests and commissioning. Allow a reasonable contingency for ground conditions that could not be established beforehand, but do not accept an unclear quote under the heading of unforeseen costs.
Related guides
Plan the next stages of your project
Concrete pools
Compare ICF with cast and sprayed reinforced concrete pool construction.
Learn moreLiner pools
Understand liners and reinforced membranes as finishes, not supporting structures.
Learn moreSite preparation
Check access, soil, groundwater and drainage before excavation.
Learn morePlumbing and electrical work
Plan penetrations, pipes, equipment space and electrics before enclosing the walls.
Learn moreCosts and budget
Compare complete quotes, not just block prices.
Learn moreInstallation mistakes
Know which work must be inspected before it is covered.
Learn moreFAQ
ICF pools: common questions
Are ISO blocks and ICF the same?
ICF is the recognised term for permanent insulating forms filled with reinforced concrete. ISO block is a marketing term used in some markets, but it is not a precise specification. Ask for the manufacturer, core width, technical manual and complete designed system.
Is an ICF pool a concrete pool?
Yes. In a correctly built ICF pool, the reinforced concrete core is the structural wall. The blocks provide permanent formwork and insulation; a liner, membrane or another finish forms the water-facing surface.
Can I build an ICF pool myself?
An owner may organise some non-structural tasks, but structural design, reinforcement, concrete placement, groundwater, penetrations and electrics need qualified input. Easy-to-stack blocks do not remove the need for design, supervision and trained installers.
Must the slab and walls be poured together?
Not necessarily. Many systems use separate slab and wall pours, but the construction joint, reinforcement starters and sealing must be designed. What matters is proper load transfer and water control, not simply describing the pool as monolithic.
Which finish is most practical?
Liners and reinforced PVC membranes are common because the watertight layer can accommodate small substrate tolerances. Tiles need a purpose-designed, compatible build-up. Choose for the pool shape, installer expertise, water chemistry and future refurbishment plans.
Does the insulation greatly reduce heating costs?
Insulation reduces heat loss through walls, especially into cold ground, but the uncovered water surface can still lose substantial heat. A cover, wind exposure, temperature and usage pattern may have a greater effect on energy use.
When can the pool be backfilled?
Only once the concrete has reached the specified condition, the wall has the required support or filling arrangement, and external protection and drainage are complete. The designer must specify materials and backfilling stages for the chosen system.
Can an ICF pool be left empty?
Not without assessing the conditions. Groundwater can affect any in-ground shell. Have a professional familiar with the site and lining system specify draining, pressure relief and drainage procedures.