Vacuum-formed over a CNC mould, not folded from sheet
An 8-millimetre cast acrylic sheet is heated flat to 165 degrees and then pulled down onto a solid timber mould cut on a CNC router. One pull produces the entire inner form — the seat, the 12-degree backrest, the foot recess — with no joint anywhere on the wet side. Acrylic thins as it stretches, from 8 millimetres on the flats to roughly 5 in the deepest corner, and that thinning is exactly why the back has to be reinforced properly rather than decoratively.
The backing is five plies of woven fibreglass in isophthalic resin, six millimetres in total, plus three marine-plywood ribs beneath the base. We use isophthalic resin although it costs about 40 per cent more than standard orthophthalic, because the cheap one takes on water through micro-pores and produces coin-sized blisters between acrylic and glass inside three years.
The weight numbers that decide whether you are allowed
| 400-litre body | Empty | Filled | Load per m² of footprint |
|---|
| Acrylic | 48 kg | 462 kg | about 340 kg/m² |
| 316 stainless | 96 kg | 526 kg | about 390 kg/m² |
| Teak with liner | 165 kg | 590 kg | about 410 kg/m² |
| Terrazzo | 210 kg | 640 kg | about 465 kg/m² |
Apartment balconies in Indonesia are generally designed for a live load of 250 kilograms per square metre, and no 400-litre ice bath of any material comes in under that figure. What saves the installation is how the load is spread: an aluminium box-section frame carries the weight to the two nearest supported edges of the slab rather than into the middle of the span. Before we accept an apartment order we ask building management for the structural drawing, and we have declined sites more than once because it never arrived.
The honest weaknesses of acrylic
Surface hardnessabout 3 on the Mohs scale, a metal zip will mark it
Never usescouring powder, wire wool, acetone, thinners
Safe cleaningpH-neutral liquid soap and a microfibre cloth
Light scratchespolish out with 2,000-grit compound
Direct sunslight yellowing after 4-6 years
Safe surface temperature-20 to 70 °C
Realistic life6-8 years under a roof
Cast acrylic is not stone and we do not pretend otherwise. Swimsuit zips and rings do leave marks. The difference is that a mark in acrylic polishes out in half an hour with fine compound, and we leave a polishing kit with every tub rather than selling you one later.
The condenser is the real apartment problem, not the tub
A shaded 400-litre balcony tub in Jakarta needs 2 HP. That unit draws 1,850 watts and rejects roughly 4.5 kilowatts of heat into the air around it. Stand it on a glazed-in balcony and it breathes its own exhaust: capacity falls by up to 30 per cent, your water stops at around 9 degrees, and the compressor never switches off. The fixes are undramatic — face the discharge outward with at least 60 centimetres to the balustrade, or move the unit to the service balcony and run insulated hose. We measure this at survey, and the chiller calculator has a setting for enclosed spaces.
When acrylic is the wrong choiceDo not specify acrylic for an unshaded garden, for a gym with dozens of users a day, or for a clinic using strong disinfectant daily. Ultraviolet, stiff brushes and repeated chemicals turn eight years into three. For duty like that a 316 stainless ice bath or terrazzo is far cheaper over a decade even at twice the purchase price.
Price, and getting it to the twenty-third floor
Acrylic bodies from 250 to 500 litres run Rp 26-36 million including insulation, the ACP outer skin, the lid, pump and cartridge. Delivery into an apartment is quoted separately when the building requires the goods lift at set hours or a work permit — usually Rp 900,000 to Rp 2.4 million including lift and corridor protection. Everything else is on the pricing page, and what the crew does on the day is set out under installation and cold test.
How we check whether your balcony can take it
- Ask building management for the design live load of the balcony slab, normally written as 250 kilograms per square metre, and the direction the slab spans.
- Measure the span and find the supported edges. A load near a support matters far less than the same load mid-span, and moving the tub 60 centimetres sometimes changes the answer from no to yes.
- Work out the real footprint. A filled acrylic tub of 462 kilograms on a 1.36 square metre frame gives 340 kilograms per square metre, still above 250, which is why the spreader frame is extended to land on the two nearest edges.
- Get written consent from building management. We do not install in an apartment without it, including when the owner insists.
The second question that always arrives in a tower is where 400 litres go on a water change. A balcony floor drain is typically 50 millimetres and takes about 40 litres a minute, so a full drain-down is a ten-minute job and is best not done during a downpour. We fit a one-inch drain valve and a directable hose rather than letting the tub overflow across the floor towards your neighbour.
Is acrylic strong enough for a 100-kilogram adult?
Easily. The load is carried by the fibreglass back and the ribs beneath it; the acrylic is only the surface the water touches. Every body is tested with a static 180-kilogram load on the seat for an hour before it ships.
Can a deep scratch be repaired?
Anything to about 0.3 millimetres deep sands out with 1,500-grit wet paper and polishes away. Deeper than that needs acrylic resin filling and usually stays faintly visible. A crack through the sheet cannot be patched convincingly and we replace the body.
Are colours other than white available?
White, light grey and matt black. Black makes the water read darker but shows limescale more clearly, so on hard mains water we suggest light grey.
How long does it last on a covered terrace?
Six to eight years before the surface dulls enough to want a full polish. The body and insulation are usually still sound after that; what ages is the look, not the structure.
Can I take it with me when I move apartment?
That is the main argument for this shell. Two people lift the 48-kilogram body, the chiller hoses come off on quick couplings, and reinstallation in the new place takes about three hours. We budget roughly Rp 1.8 million for a move within the same city.
