Insulating mortars or foam concrete are rewarding solutions for creating cementitious slope layers on flat roofs. They are quick and easy to install. However, it is advisable to look critically at the implementation conditions: too hot weather, frost or heavy rainfall are pernicious for a good final result.
Patrick Vanderstichelen, Technical Training Manager at Tectum Group, has come across more foam concrete or insulating mortars on flat roofs in recent years. "It does involve about 80% of our sites. Sometimes they are even installed in large thicknesses. The cementitious slope layers then not only provide a suitable slope to the water drainage points, but must also contribute to the thermal insulation of the roof. In itself, I have nothing against these insulating slope layers as long as they are placed under the right conditions. That is my main concern and first point of interest when inspecting a roof on which we will be working.
It sometimes happens that the top layer of cementitious slope layers was not neatly smoothed. This makes the surface less level. As a result, there is not only the risk that the primer for the installation of the vapor barrier will not adhere as well, but there is also the danger that the top layer will flake under the influence of sun or frost. For an insulating mortar with incorporated EPS beads, there is a risk that we will scorch the EPS when firing the vapor barrier or that there will be a chemical reaction between the solvents in the primer and the EPS. If the surface is insufficiently flat, it is necessary to apply an additional layer of cement mortar at least 20mm thick to ensure proper adhesion of the vapor barrier," explains Patrick Vanderstichelen.
A second important reason why the top layer of insulating mortar or foam concrete is best finished properly is to avoid moisture buildup in the package. "When precipitation falls in the first two days after placing the mortar or concrete and the top layer is not properly finished, the rainwater soaks into the built-up package. That moisture will never be able to fully evaporate since we typically apply the vapor barrier about 5 to 7 days after placing the slope layer. Rain can further roughen the surface shortly after installation if there is no screening cement layer. And worse, built-up moisture can work its way in over time - even more than a year later. Then the roof waterproofing is always considered first. We then do an on-site check. If in doubt, we may put the roof under water and add dye to the water. Then we know with certainty whether the leak is due to the roof sealing or not. On more than one occasion we have found that the leaking water did not discolor, which indicates that the visible water is indeed residual water," Patrick Vanderstichelen says.
Moisture built up in the roof package can make its way inside even after more than a year.
To avoid possible problems, Patrick advises all site supervisors to drill holes at the lowest level of the upstands at regular intervals so that rainwater can easily flow off the roof in. In addition, urge the installer of this type of mortar to properly strip the top layer so that the cement rises to the top and forms an impermeable layer. But above all, keep an eye on weather conditions and do not have the insulating mortar or foam concrete placed when rain or snow is predicted, and likewise not in excessively high temperatures or risk of frost immediately after placement.
If things go wrong with the top layer despite these precautions, our roofers cannot glue the vapor barrier. "We then have to consider whether to lay the waterproofing loose and put ballast on it afterwards. The question then is whether the supporting structure can handle that extra weight. Another option is still to apply a minimum 20mm thick cement mortar over the existing surface." concludes Patrick Vanderstichelen.
Insulating mortars or foam concrete are rewarding solutions for creating cementitious slope layers on flat roofs. They are quick and easy to install. However, it is advisable to look critically at the implementation conditions: too hot weather, frost or heavy rainfall are pernicious for a good final result.
Patrick Vanderstichelen, Technical Training Manager at Tectum Group, has come across more foam concrete or insulating mortars on flat roofs in recent years. "It does involve about 80% of our sites. Sometimes they are even installed in large thicknesses. The cementitious slope layers then not only provide a suitable slope to the water drainage points, but must also contribute to the thermal insulation of the roof. In itself, I have nothing against these insulating slope layers as long as they are placed under the right conditions. That is my main concern and first point of interest when inspecting a roof on which we will be working.
It sometimes happens that the top layer of cementitious slope layers was not neatly smoothed. This makes the surface less level. As a result, there is not only the risk that the primer for the installation of the vapor barrier will not adhere as well, but there is also the danger that the top layer will flake under the influence of sun or frost. For an insulating mortar with incorporated EPS beads, there is a risk that we will scorch the EPS when firing the vapor barrier or that there will be a chemical reaction between the solvents in the primer and the EPS. If the surface is insufficiently flat, it is necessary to apply an additional layer of cement mortar at least 20mm thick to ensure proper adhesion of the vapor barrier," explains Patrick Vanderstichelen.
A second important reason why the top layer of insulating mortar or foam concrete is best finished properly is to avoid moisture buildup in the package. "When precipitation falls in the first two days after placing the mortar or concrete and the top layer is not properly finished, the rainwater soaks into the built-up package. That moisture will never be able to fully evaporate since we typically apply the vapor barrier about 5 to 7 days after placing the slope layer. Rain can further roughen the surface shortly after installation if there is no screening cement layer. And worse, built-up moisture can work its way in over time - even more than a year later. Then the roof waterproofing is always considered first. We then do an on-site check. If in doubt, we may put the roof under water and add dye to the water. Then we know with certainty whether the leak is due to the roof sealing or not. On more than one occasion we have found that the leaking water did not discolor, which indicates that the visible water is indeed residual water," Patrick Vanderstichelen says.
To avoid possible problems, Patrick advises all site supervisors to drill holes at the lowest level of the upstands at regular intervals so that rainwater can easily flow off the roof in. In addition, urge the installer of this type of mortar to properly strip the top layer so that the cement rises to the top and forms an impermeable layer. But above all, keep an eye on weather conditions and do not have the insulating mortar or foam concrete placed when rain or snow is predicted, and likewise not in excessively high temperatures or risk of frost immediately after placement.
If things go wrong with the top layer despite these precautions, our roofers cannot glue the vapor barrier. "We then have to consider whether to lay the waterproofing loose and put ballast on it afterwards. The question then is whether the supporting structure can handle that extra weight. Another option is still to apply a minimum 20mm thick cement mortar over the existing surface." concludes Patrick Vanderstichelen.
Insulating mortars or foam concrete are rewarding solutions for creating cementitious slope layers on flat roofs. They are quick and easy to install. However, it is advisable to look critically at the implementation conditions: too hot weather, frost or heavy rainfall are pernicious for a good final result.
Patrick Vanderstichelen, Technical Training Manager at Tectum Group, has come across more foam concrete or insulating mortars on flat roofs in recent years. "It does involve about 80% of our sites. Sometimes they are even installed in large thicknesses. The cementitious slope layers then not only provide a suitable slope to the water drainage points, but must also contribute to the thermal insulation of the roof. In itself, I have nothing against these insulating slope layers as long as they are placed under the right conditions. That is my main concern and first point of interest when inspecting a roof on which we will be working.
It sometimes happens that the top layer of cementitious slope layers was not neatly smoothed. This makes the surface less level. As a result, there is not only the risk that the primer for the installation of the vapor barrier will not adhere as well, but there is also the danger that the top layer will flake under the influence of sun or frost. For an insulating mortar with incorporated EPS beads, there is a risk that we will scorch the EPS when firing the vapor barrier or that there will be a chemical reaction between the solvents in the primer and the EPS. If the surface is insufficiently flat, it is necessary to apply an additional layer of cement mortar at least 20mm thick to ensure proper adhesion of the vapor barrier," explains Patrick Vanderstichelen.
Moisture built up in the roof package can make its way inside even after more than a year.
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