Published: November 4, 2026 | Last Updated: November 4, 2026
SEO Title Tag: Halotherapy Salt Room Specification for Spas | Hezhen Meta Description: Four room types are sold under one name. Typical temperature, humidity and salt grade for each, plus the fixings, air changes and claims that decide whether it works.
In European and North American wellness projects, "salt room" describes at least four different buildings. A halotherapy room is a climate-controlled chamber with an aerosol generator. A salt sauna is a hot room lined in salt. A salt wall is a feature finish inside a wet spa. A residential salt wall is a decorative partition in a dry interior. They share a material and almost nothing else. Most disappointing installations are not badly built; they are one of these four sold as another. This guide sets out the typical conditions for each, the grade that suits it, and the details a specification must carry.
Four Room Types, One Name
The halotherapy room is the most specified and the most misunderstood. It is a dry, temperate room — typically 18–24 °C and 40–60% relative humidity — in which a halogenerator grinds pharmaceutical-grade salt into an aerosol and delivers it for a session of around 45–60 minutes. The salt on the walls is a surface, not the treatment. The treatment is the air.
The salt sauna is the opposite proposition: a hot room, typically 65–85 °C at bench level, with very low humidity, in which salt replaces timber as the lining. Salt performs well here precisely because the air is dry. It is also the room where a badly detailed lining becomes a maintenance item, because heat drives thermal movement and the cooling-down phase brings people, water and wet towels.
The salt wall inside a pool hall is the highest-risk of the four: the room is humid by design, and the salt is asked to survive an environment that sits above its deliquescence point for hours at a time. It can work, but only as an assembly with vapour control and a ventilated cavity.
The residential wall is the simplest, because the interior is conditioned and dry — and the type most often sold without a drawing, which is why it produces the most small complaints: staining behind the wall, rusted screws, salt dust beneath.
Typical Conditions by Room Type
The values below are typical ranges taken from published wellness-facility practice and equipment documentation. They are a starting point for a project specification, not test data for a specific product.
| Room type | Temperature | Relative humidity | Salt's job | Principal risk |
|---|---|---|---|---|
| Halotherapy room | 18–24 °C | 40–60% | Surface and light | Aerosol control, not salt |
| Salt sauna | 65–85 °C | below 20% | Lining and thermal mass | Thermal movement, cooling phase |
| Salt wall in wet spa | 26–32 °C | 60–90% | Feature finish | Condensation above 75% RH |
| Residential salt wall | 20–24 °C | 30–55% | Decoration and light | Untreated substrate, mild steel fixings |
Read the third row against the first. A salt wall in a pool hall is asked to operate in air that, at the upper end of that humidity range, is at the point where sodium chloride begins to absorb water. That is not a defect in the salt; it is a design condition that has to be answered.
Salt Grade Follows the Job
Wall salt and aerosol salt are different products and should never be substituted. Wall bricks are typically 95–98% NaCl, cut or pressed to a nominal thickness of 2–2.5 cm, and judged on colour consistency, dimensional tolerance, absence of propagating cracks and, for backlit panels, translucency — white and pale pink transmit light best, deep red the least. Aerosol generators take a much purer halite grit, commonly 99% or higher, screened to a narrow particle range — typically 2–5 mm — because the grinder has to produce a consistent aerosol from it. Putting wall-grade salt into a generator clogs it; putting generator grit on a wall wastes money.
Air Is the Part That Is Not Architecture
A halotherapy room cannot be made by heating a salt room or by putting a salt wall in a small space. The aerosol has to be generated, distributed and removed on a defined schedule, which means dedicated exhaust and a return path that does not push salt dust into the rest of the building. Typical installations specify an aerosol concentration in the low single-digit milligrams per cubic metre and a particle size of a few micrometres, with the exact figures set by the equipment supplier and its protocol.
The architectural consequence: salt surfaces should not sit in the path of supply air. A diffuser aimed at a salt wall deposits aerosol where it crystallises, not in the breathing zone.
Fixings, Light and the Ceiling
Three details account for most maintenance calls. Fixings: chlorides attack galvanised steel and 304 stainless; A4 / 316 is the minimum, and nothing galvanised should be anywhere in the assembly. Lighting: a warm white strip in the 2700–3000 K range behind the bricks is the effect clients are buying, but the strip lives in a chloride atmosphere, so it should be sealed and IP-rated with the driver mounted outside the salt cavity. Ceiling: salt is heavy and brittle, and ceiling panels are where it falls. Mechanical retention, not adhesive alone, is the only defensible detail.
Salt also moves: linear expansion is roughly 40 × 10⁻⁶ per K, several times that of concrete, so joints must allow movement while a mechanical backing carries the load.
Claims, Compliance and the Line to Hold
Two compliance points decide how the room can be marketed. First, halotherapy claims: in the EU a device marketed for treating a condition can fall under medical device regulation, in the US under FDA rules for medical claims. An amenity described as supporting relaxation sits outside that; one that promises to treat asthma does not. The specification should say "wellness amenity" and let the operator's jurisdiction decide the rest.
Second, reaction to fire: salt is an inherently non-combustible mineral, a genuine advantage in a commercial interior, but the classification belongs to the tested product and assembly — ask for the report.
One claim worth dropping entirely is negative ion emission. Measured output from salt surfaces is negligible, and a specifier who asks for evidence will not be satisfied by a brochure. The room sells on light, texture and the aerosol protocol; it does not need the ion story.
Specification Checklist
- Room type stated explicitly, with target temperature and relative humidity
- Salt grade and thickness by surface: wall, ceiling, bench, feature
- Vapour control layer position and continuity where the room adjoins a wet area
- Cavity: ventilated or drained, and how
- Fixing schedule: A4 / 316 stainless, spacing, mechanical backing
- Movement joints and edge gaps
- Lighting: colour temperature, IP rating, driver location
- Aerosol equipment, distribution and exhaust, with the supplier's protocol
- Cleaning method written into handover: dry brush and vacuum, no wet washing
- Reaction-to-fire report for the product and assembly
Frequently Asked Questions
1. What thickness should salt bricks be for a commercial spa? 2–2.5 cm for wall linings; 2.5 cm or more for sauna linings and backlit panels that must span; thicker blocks where the wall should read as masonry.
2. How is a salt wall cleaned? Dry. Soft brush and vacuum. Water dissolves the face and drives salt into the joints, and acidic descalers attack both the salt and the fixings.
3. Does salt need a sealer? A sealer slows moisture pickup but changes appearance and light transmission, and has to be maintained. Most projects are better served by controlling the room condition than by coating the salt.
Next Step
Send the room type, floor area, ceiling height, substrate, adjacent spaces and target temperature and humidity. The Hezhen technical team will confirm grade and thickness per surface, advise on fixings, joints and vapour control, and supply samples with colour and dimensional data so the finish can be approved before ordering.
