The marble is a skin, not a tub
First thing to be clear about: a 20-millimetre marble slab does not hold 700 litres of water by itself. The structure is a 25-millimetre glass-reinforced concrete shell that we cast in Tabanan first, complete with 40 millimetres of polyurethane and all the pipework. Marble is bonded to that shell with two-part epoxy mortar that stays flexible at 2 degrees. Ordinary cement-based adhesive goes hard and brittle at that temperature and releases slab by slab in the second wet season, which is exactly how most failed stone tubs fail.
Because the stone is only a skin, 20 millimetres is enough and the weight stays sensible. A 400-litre marble-clad tub is 245 kilograms empty, only 35 kilograms more than the same tub in terrazzo, which is often what makes it possible on an upper floor where solid stone would not be.
Book-matching: cutting one block into a mirror
Two slabs sawn consecutively from the same block have nearly identical veining. Flip one and the pair forms a mirror image, which is what book-matching means. On a tub we use it on the two long faces so the veins meet along the centreline of the floor and read as one continuous piece from above. That requires a single block to cover the entire tub, so slabs are ordered as one group and you approve a photograph of the sawn block before any cutting starts. This is why the lead time is three to four weeks rather than two, and why a marble tub cannot be ordered at short notice.
Honed rather than polished, and it is not a matter of taste
Honed, wet friction coefficient0.42
Polished, wet friction coefficient0.21
Safe threshold for a wet floor0.40
Marble water absorption0.2-0.6 per cent
Mohs hardness3, marked by metal and grit
Acid resistancepoor, reacts below pH 6
Safe working temperature-5 to 60 °C
Polished marble is glass when it is wet. A wet friction coefficient of 0.21 is barely half the accepted threshold for a wet floor, and an ice bath is a place people climb into on wet feet while their breathing is still ragged. We decline to polish the inside of a tub, including when a client asks for it. The outside faces can be polished if you want them to be; the interior and the rim are always honed.
Why chlorine is banned in this tub
A trichloroisocyanurate tablet dissolves into a solution of roughly pH 2.8. Under a tablet lying on the floor of a tub that figure persists for hours and the marble loses its finish overnight, leaving a dull ring that cannot be polished out without re-honing the entire face. Even normally chlorinated water at 3 ppm slowly etches the surface over long contact times. So the mandatory specification is ozone plus ultraviolet, with pH held between 7.2 and 7.8. The equipment is listed under ice bath accessories and the numbers are on the pricing page.
Four stones we work with
| Origin | Character | Water absorption | Note |
|---|
| Tulungagung, East Java | warm cream, fine veining | 0.4 per cent | easiest to find one large block |
| Makassar, South Sulawesi | blue-grey, decisive veining | 0.3 per cent | harder stone, crisper mitres |
| Carrara, imported | white with thin grey veins | 0.2 per cent | most expensive, 4-8 week block wait |
| Ujung Pandang black | black with white veining | 0.5 per cent | high contrast, shows limescale |
Mitred corners at 45 degrees, and why not a lap joint
Two slabs meeting at a corner can be lapped, where one slab covers the thickness of the other, or mitred at 45 degrees so the thickness disappears and the vein carries across the corner. On marble we always mitre, because the sawn edge of marble is paler than its face and a 20-millimetre pale line down every corner destroys the entire vein selection. The price of that is precision: a mitre has to close within 0.3 millimetres over a metre and a half, and a slab that misses cannot be corrected, only replaced. We soften the arris by 1.5 millimetres with a hand diamond pad and fill the void behind the corner completely with epoxy, because a hollow mitre chips on first contact.
When marble is the wrong choiceDo not put marble in a gym, a rental studio, or any tub used by more than about eight people a day: sanitation without chlorine demands daily discipline, and a calcite surface goes dull within two years of heavy traffic. Do not install it outdoors uncovered either — city rain runs at pH 5.2 to 5.8, enough to open the pores over a few seasons. For a luxury stone look that tolerates everything, the granite ice bath answers the same brief without the chemistry.
Price, and what moves it within the range
A marble-clad tub runs Rp 82-135 million for 300 to 700 litres. What pushes a quote to the top of the range is not volume but the block: imported marble with consistent veining can add Rp 14 million over Tulungagung for the same size, and full four-sided book-matching wastes about 35 per cent of the material as offcuts. The chiller follows volume as always — 2 HP for 400 litres in hot lowland, 4 HP for 700. Run yours through the chiller calculator, and if the tub is going into a spa you are still designing, read custom wellness areas before committing to a layout.
Does marble crack at 3 degrees?
No. Marble is stable far below freezing; what breaks stone is water freezing inside its pores, and our water never goes below 3 degrees. What does need care is the adhesive, which is why we use an epoxy mortar that stays flexible at low temperature.
What if the surface gets etched by something acidic?
The affected face is re-honed with 400 then 800-grit diamond pads and resealed. For the floor of a tub that is about Rp 2.8 million and a day's work. If the damage reaches a mitred corner, slab replacement is far more expensive.
How often does it need resealing?
Every twelve months for a tub in daily use, eighteen for occasional use. The impregnating silane sealer penetrates 2-3 millimetres and forms no film, so the surface still feels like stone rather than plastic.
Can marble be combined with a timber or steel rim?
Yes, and we do it often. A 40-millimetre 316 stainless rim protects the most vulnerable part of the stone, its top edge. Teak works too, but timber and stone move differently and the joint between them needs a flexible sealant rather than epoxy.
How long does a marble tub last?
The cladding runs past twenty years with correct sanitation and regular sealing. What ages first is the epoxy in the mitred joints, and that can be raked out and refilled in a day every six to eight years — normally during a scheduled service visit.
