The sauna floor should be hard, waterproof, and warm.
Hard, because we like a hard, solid floor. A sauna floor made of 8mm plywood, elevation Styrofoam and set on beams spaced every, say, a meter, is a recipe for disaster. Such a floor will last at most a few months of use, after which it will probably start to bend.
Waterproof, because in the sauna we often use water to pour it over the stones on the stove. It may happen that the water does not have time to evaporate from the heat of the stones, and some of it lands on the sauna floor. In this case, the floor should prevent the water from seeping downward. It is best if there is a point drain in the floor, and the floor itself is at a slight slope, so that the water can drain freely.
Warm, as this is one of the partitions separating the sauna from the outside world. In a typical garden sauna, the floor is responsible for about 10% of the heat loss. In the long term, proper insulation of the sauna floor is simply economical - it will pay for itself especially quickly if you have an electric stove.
Answering the basic question: how to build a sauna floor, we have prepared 2 answers, one way for an indoor sauna (in a building) and the other for an outdoor sauna ( freestanding).
Indoor sauna floor
If the sauna is located in the house, such as in the basement or bathroom, then the matter is simple. Ceramic tiles - the classics. On the market we have a lot of types, sizes, colors and textures of ceramic tiles, so the only problem here will be to choose one that will match the interior design. Tiles are naturally waterproof and resistant to abrasion. Of course, the floor in the basement or bathroom should be isolated from the ground, just like in the rest of the building.
Example of floor layers in an indoor sauna:
- Ceramic tiles
- Flexible tile adhesive
- Waterproof primer.
- Primary floor, such as poured concrete.
Floor in an outdoor sauna
If the sauna is located in the garden, as a freestanding building, then we need to think of everything. The sauna floor on the structural frame should be insulated with mineral wool. As a structural 'base', OSB can be used. OSB these days should be certified as having no formaldehyde emissions, so make sure your OSB has this certification. In our sauna Tuula, we additionally gave a cement chipboard.
For the OSB board, we can make a thin layer screed of suitable concrete. We used a product from Kerakoll GeoLite. It is ideal for such applications, because it has a special admixture of mineral fibers that strengthen the thin layer of the laid floor.
Kerakoll GeoLite product
The thickness of the screed can range from about 10mm to 40mm. To make the floor waterproof, you still need to apply a layer of special resin for floors. It is applied with an ordinary paint roller.
Example of floor layers in a garden sauna:
- Epoxy resin for the floor ( applied with a roller)
- Thin layer concrete screed such as Kerakoll GeoLite
- Waterproof primer
- OSB 12mm x 2 laid crosswise ( We used an additional layer of cement particle board, instead of additional OSB)
- Thermal insulation - 100mm mineral wool
- Frame construction