Mould will only tend to grow when the air in your conservatory is too cold and wet, and condensation has occurred.
Mould will only grow on organic material, meaning that it will only grow on the blinds if they are dirty.
If your conservatory shows signs of excessive condensation (which is normal when a conservatory is new and it is drying out) then keep your windows and blinds clean, but address the fact that your conservatory has insufficient ventilation and heating immediately.
Mould will only grow when the air in your conservatory is too cold and wet (referred to as Relative Humidity or ‘RH’) and condensation has occurred. It is a sure sign that your conservatory has inadequate heating and ventilation, most commonly localised to “cold spots” where there are concealed gaps or a small leak that is seeping in.
Mould only tends to occur in the presence of condensation. Condensation occurs when the RH is too high for the air temperature – the excess water condenses on to the nearest surface that is at or below the dew point temperature, for those conditions, which is commonly the glass of a conservatory.
For example, a typical winter evening could easily find that your conservatory has an air temperature of 16°C with a RH of 70% – with these conditions, by the time the air temperature reaches just 11°C the air would have a RH of 100% (saturation) and water droplets (condensation) will appear on walls, windows, floors and even furniture.
Mould requires the RH to exceed 70% for some time before it will start growing. General human comfort level is estimated between 30-60% RH within a temperature range of 18-25°C.
Mould takes the appearance of small black (most common), grey, or green spots on the wall or other surfaces. Mould is most commonly seen around window reveals, on external walls and at high level in external corners.
How to avoid condensation and mould
Improve ventilation so that the air circulates by drawing in fresh air from outside and expelling moist air from in your conservatory. This is most effectively created by ensuring you have adequate cross-ventilation and trickle vents. Without adequate ventilation, no other measures will cure the problem.
Avoid still air pockets and make sure that any unventilated areas are avoided: pay particular attention to corners, behind furniture that is close to an external wall or window, and ensure that you keep blinds and curtains open for a good portion of the day.
Check the conservatory for cold spots using a RF temperature probe. The joints between windows and at the eaves in a conservatory often have gaps that are concealed by 1mm thick UPVC trims, which are a common cause of cold.
Check your conservatory and house for leaks, particularly guttering and rainwater pipes as this can cause water to seep into your conservatory through the walls, or through tiny joints.
While it is good practice to leave windows open for an hour a day, just enough to encourage air circulation, do not leave them wide open for hours when the temperature is cold, as this will just add to the problem.
Conservatories are very poorly insulated compared to your home and do not meet the requirements of Part P of the Building Regulations in respect of heat loss (which is why they are currently exempt) so they are very much at risk of condensation.
Ensure that your conservatory is kept at a stable temperature that does not get too low. Consider background heating (e.g. underfloor heating) that is left on a thermostat to keep the air temperature above 15°C even at night. Your conservatory will be at its coldest around 3.00-5.00am.
What about conservatory blinds?
As we have seen, mould only grows in the presence of water, but it also requires organic material on which to live. The fabrics on most blinds are completely man-made (except pinoleum) which means that mould will only thrive on the fabric if it is dirty. The solution is therefore to keep your blinds clean at all times and not to allow condensation to occur.