By: Michael Frech
As October comes to a close and the temperatures begin to drop, temperature limits for materials involved in exterior restoration need to be considered. While product specifications define temperature limits, there is often discussion about how to aextend the seasona and complete projects before the end of the year.
In certain cases, it makes sense for the Owner to allow or request that the work continue through the cold weather. In these cases, Sullivan Engineering has had success with electrical and non-electrical thermal blankets. These blankets can be fastened to the wall and keep the area beneath the blanket at acceptable temperatures for curing. They eliminate the need for a specially constructed enclosure and provide even and constant heat.
It is our past experience that the use of non-electrical thermal blankets will keep the area protected by the blanket 8a to 12a warmer than the surrounding unprotected areas. Of course, there are many environmental factors that effect the temperature variations including, sun exposure during the day, elevation of the work performed, wind conditions, etc. Additionally, the work that is being protected effects the temperature variation based on the amount of heat generated during curing.
During the unusually brutal winter of 2014, Sullivan Engineering monitored a 5-story brick replacement project that utilized an electric curing blanket (approx. 6a x 10a) manufactured by Powerblanket. The building elevation was accessed by supported (pipe) scaffolding. This scaffold was enclosed with insulated tarps and heated with fuel-powered heaters during work hours. At the end of the work day, the newly installed masonry was covered with the heated blankets through the overnight hours. The building supervisor checked on the project hourly to ensure that the electricity was still on and that the blankets were providing heat.
A thermometer that records the high and low temperatures was utilized to monitor the actual temperatures on the project. One thermometer was placed on the supported scaffold, away from the wall, to record the outside overnight temperature. Simultaneously, thermometers were placed under each blanket on the wall. These thermometers were placed near the bottom edge of the blanket where it is most difficult to maintain an acceptable temperature.
The thermometers revealed that the wall consistently remained 30a above the outside temperatures, even during the coldest nights when temperatures plummeted into the mid teens. This discovery was only made after the blankets were left on over several weekends to insure proper cure time. As a precaution, work was suspended anytime the outside temperatures were forecasted to be below 25a . Overall the project was a success with the testing, including a Windsor pin test indicating that the mortar achieved the desired hardness. In addition, the wall was monitored through the summer in order to identify any areas showing signs of deterioration. To date, the wall has shown no visible signs of any compromised installation.
This experiment furthered our understanding that the proper implementation and documentation of the supplemental heat process is of paramount importance. The following are some of the necessary steps to successfully use temporary heat during a project:
- A meeting with all parties (owner, design professional and contractor) must be held to present the procedures that will be utilized and the chain of command in decision making. This meeting must include the field foreman as he will be responsible for compliance to the procedures.
- Daily communication (including weekends) between the field foreman and all other parties is mandatory. This will provide real time temperature information so that informed decisions can be made about future installation. This includes daily documentation of the thermometers/temperatures.
- Agreed upon actions if required temperatures are not maintained. This includes the necessary testing or replacement of the area in question and who is responsible for the cost of this testing/replacement.