Where to look for the cause of the damp
- Ventilation Hold a slip of paper by the extract grille with the door closed. If it does not move, air is not flowing.
- Joints Look at the joints in the corners and around the bath, shower and sink. Black, cracked or detached joints let water get under the tiles.
- Tiles Tap the tiles by the shower. A hollow sound and loose tiles can mean there is water under them.
- External wall and corners If the mould is by an external wall or in a ceiling corner, the cause can also be in the building's structures.
In series buildings, damp problems are also mentioned in lists of typical problems: for the 602 series, possible damp penetration and checking corners for mould are mentioned; for the 464 series, waterproofing problems and poor ventilation on the lower floors. Check in your own apartment whether this applies to you.
Sources: apollo.lv on series projects in Riga; nopo.lv on apartment building series. Checked 11.11.2026.
Ventilation: what the rules say
The kitchens, toilets, bathrooms and shower rooms of residential buildings are ventilated through natural extract ducts (LBN 231-15, paragraph 90.²). On a shared ventilation system, the air ducts of the kitchen and sanitary rooms may only be connected each to its own duct.
The Fire Safety Regulations currently in force require natural ventilation ducts to be cleaned and inspected at least once every 10 years, and in rooms with gas appliances at least once every five years. In an apartment building, connecting a mechanical ventilation unit to a natural ventilation duct is prohibited if the room has a gas hob or another gas appliance and there is no constant air exchange.
The ventilation duct is part of the building's engineering systems, so ask the building manager about its cleaning and inspection. If the duct is blocked, the mould will come back even after a new renovation.
Sources: Cabinet Regulation No. 310, LBN 231-15, paragraphs 85.4 and 90.²; Cabinet Regulation No. 238, sub-paragraphs 80.1, 80.2 and 89.10 (will cease to be in force on 02.01.2027). Checked 11.11.2026.
Waterproofing under tiles
If water gets under the tiles, the tiles usually have to be removed, the substrate dried and new waterproofing applied. The manufacturer's requirements show why this work cannot be done over the top:
- Ceresit CL 51 is intended for waterproofing walls and floors before tiling in wet rooms, including on heated floors.
- The manufacturer recommends at least two coats so that the dry layer is 0.5 mm.
- Waterproofing tape is worked into the wall and floor joints and edges, collars are used for pipes and drains, and corner pieces for corners.
- The substrate must be dry, load-bearing, stable and clean; crumbling surfaces are primed.
Source: Ceresit CL 51 technical data sheet LV, 11/2025 (Henkel). Checked 11.11.2026.
Joints: silicone and grout
In the Ceresit CM 17 technical data sheet, the manufacturer requires joints in corners, at the floor and at plumbing fixtures to be filled with silicone, not grout. Hard grout cracks in these places, and water goes through the crack.
For Ceresit CE 40 grout, water exposure is allowed after 24 hours, it reaches full strength after 5 days, and for the first 5 days it is washed only with clean water. If the mould is only in the joints and the tiles hold, regrouting tile joints may be enough.
Sources: Ceresit CM 17 technical data sheet 10/2026; Ceresit CE 40 technical data sheet 05/2026. Checked 11.11.2026.
Treating mould and renovation
Treating the room for mould and renovation are two separate jobs. For treating the room against mould, see dezinfekcijariga.lv. Renovation removes the cause: the joints, waterproofing, tiles and finish.
| What you see | Possible solution |
|---|---|
| Mould only in silicone joints | Replacing the joints |
| Mould in the grout, tiles hold | Regrouting |
| Tiles move, damp underneath | Removing the tiles, waterproofing, tiling |
| Mould on the ceiling and on the walls above the tiles | Checking the ventilation, then skimming and painting |
How much bathroom renovation costs after mould
| Work | Price |
|---|---|
| Demolition of old tiles | from €9/m² |
| Waterproofing in a bathroom | from €6/m² |
| Tiling | from €24/m² |
| Floor drain installation | from €100 per drain |
| Bathroom renovation (all the work) | from €3,000 |
Example: tiling 18 m² × €24 = from €432, waterproofing 5 m² × €6 = from €30 and floor drain installation from €100, a total of from €562. These are only these three jobs; a whole bathroom renovation is from €3,000. Prices are for labour. Materials are calculated separately in the estimate.
The price is affected by the area of the bathroom, whether the old tiles have to be removed and whether the pipes are changed. An exact estimate can be made after seeing the apartment.
What can go wrong
- The mould is painted over with ordinary paint, and after a couple of months it appears again.
- New tiles are laid over old ones without finding out whether there is damp under them.
- The joints in corners and around the bath are filled with grout instead of silicone.
- A finish or a cupboard is put in front of the ventilation grille.
Sources
- 602 series: possible damp penetration, check corners for mould checked 11 November 2026
- 464 series: waterproofing problems, poor ventilation on the lower floors checked 11 November 2026
- Bathrooms are ventilated through natural extract ducts; each into its own duct checked 11 November 2026
- Cleaning and inspection of ventilation ducts; mechanical unit next to gas checked 11 November 2026
- CL 51: use, two coats for a 0.5 mm dry layer, tape, collars, base checked 11 November 2026
- Silicone in corners and at plumbing fixtures checked 11 November 2026
- CE 40: water exposure 24 h, full strength 5 days checked 11 November 2026
