22/11/2018
Avoid installation issues this Winter!
Apart from making sure that the temperatures on site are going to allow for the exotherm of any reaction to fully take place - the main issue is dew point - the temperature at which the moisture vapour in the air becomes moisture droplets.
Given we are talking about the condensation of moisture from within the air the actual dew point revolves around the relationship between temperature (substrate and ambient) and relative humidity. The two factors combine to to give a calculable temperature at which the dew forms, the dew point.
Calculation of Dew-Points for Application of Coatings
Air Temperature Dew point temperature °C with a relative air humidity of
| +°C | 40% | 50% | 60% | 70% | 80% | 90% |
| 25 | 10.5 | 13.9 | 16.7 | 19.1 | 21.3 | 23.2 |
| 24 | 9.6 | 12.9 | 15.8 | 18.2 | 20.3 | 22.3 |
| 23 | 8.7 | 12.0 | 14.8 | 17.2 | 19.4 | 21.3 |
| 22 | 7.8 | 11.1 | 13.9 | 16.3 | 18.4 | 20.3 |
| 21 | 6.9 | 10.2 | 12.9 | 15.3 | 17.4 | 19.3 |
| 20 | 6.0 | 9.3 | 12.0 | 14.4 | 16.4 | 18.3 |
| 19 | 5.1 | 8.3 | 11.1 | 13.4 | 15.5 | 17.3 |
| 18 | 4.2 | 7.4 | 10.1 | 12.5 | 14.5 | 16.3 |
| 17 | 3.3 | 6.5 | 9.2 | 11.5 | 13.5 | 15.3 |
| 16 | 2.4 | 5.6 | 8.2 | 10.5 | 12.6 | 14.4 |
| 15 | 1.5 | 4.7 | 7.3 | 9.6 | 11.6 | 13.4 |
| 14 | 0.6 | 3.7 | 6.4 | 8.6 | 10.6 | 12.4 |
| 13 | -0.1 | 2.8 | 5.5 | 7.7 | 9.6 | 11.4 |
| 12 | -1.0 | 1.9 | 4.5 | 6.7 | 8.7 | 10.4 |
| 11 | -1.8 | 1.0 | 3.5 | 5.8 | 7.7 | 9.4 |
| 10 | -2.6 | 0.1 | 2.6 | 4.8 | (6.7*) | 8.4 |
| 9 | -3.4 | -1.0 | 1.6 | 3.8 | 5.8 | 7.5 |
| 8 | -4.4 | -1.5 | 0.7 | 2.9 | 4.8 | 6.5 |
| 7 | -5.0 | -2.4 | -0.2 | 1.9 | 3.8 | 5.5 |
| 6 | -5.8 | -3.2 | -1.0 | 0.9 | 2.8 | 4.5 |
| 5 | -6.7 | -4.0 | -1.9 | 0.0 | 1.8 | 3.5 |
(*) Example With an air temperature of +10°C (+50°F) and 80% relative humidity, dewing starts when the structure / substrate temperature is as low as +6.7°C (+44°F). If the contact thermometer shows a value only slightly above the dew-point temperature or below it, application of coatings should not be carried out.
The following procedure is to be adopted for dew-point control:
- Attach contact thermometer to the structure (wait 15 minutes before reading the temperature so that thermometer can settle down to final temperature).
- Read air temperature.
- Read relative humidity of the air.
- Look up dew-point temperature in chart (at point of intersection between air temperature and relative humidity).
- Read object temperature on contact thermometer. If this is approximately 3°C (5 - 6°F) above the dew-point in the chart, then there is no objection to going ahead with the coating application. However, if the temperature of the structure is close to the dew-point or even below it, then work should be halted or not start due to the risk of condensation.
This is important especially in the case of resin floors because of their sensitivity to the presence of moisture during their cure phase. Failure to take into account the dew point can lead to a blooming of the resin which in usually manifests as an unsightly white stain across the floor. This doesn't affect the durability or mechanical performance of the floor but clearly has an aesthetic impact. However, other more serious effects might be noted, especially at the priming stage, in terms of poor adhesion, cracking and blistering.
To avoid this issue it's important to measure the both the rH and and temperatures on site to ensure floors are laid in conditions at least 3 deg C above the dew point. It is also important to consider the likely effects of falling night time temperatures might have on the dew point especially if the job site is not heated overnight.