Welding Single Ply Roofing Membranes - Application Guidelines

Hot Air Welding

All joints in the Monarplan single ply roofing system are hot air welded. It is recommended that automatic welders are used for all field joints. Manual hand held welders should be used for details and inaccessible areas only.

The figures below act as a guideline (at standard conditions 20 °C, relative humidity of 60%):

  • Automatic welding machine: Air temperature 480 °C Traction 2m/min
  • Manual hot air welder: Air temperature 360 °C.

Welding temperatures will vary dependant upon the weather conditions of the day. To check the correct welding settings have been achieved, hold the nozzle approximately 10-20mm above the surface of the membrane. If the single ply membrane finish turns ‘shiny’, the correct temperature has been achieved.

Welding operation – automatic welders

automatic welding tool for forming welds to single ply roofsPosition the automatic hot air welding machine with the pressure wheel approximately 3mm over the weld edge to ensure a sealed edge.

Lift the overlapping membrane sheet and insert the blower nozzle between the overlap. Immediately begin moving the machine along the lap to prevent scorching of the membrane. At the end of the run, remove the nozzle first and then stop the machine’s forward motion.

When the automatic welder moves over an insulation plate, insulation step off, lap crossover, etc., these areas should immediately be handrolled to ensure a complete weld.

Welding operation - hand welder

hand held welding tool for single ply roofing membranesUse a hand-held welder and silicone covered roller to complete welds and details where the automatic welder is inappropriate.

When the parameters are adjusted correctly, a fine bead of molten (mostly dark) material of the sheet’s underside becomes visible outside the upper membranes edge. When welding, there is a certain development of smoke and the surface of the lower sheet turns shiny – brilliant when heated correctly. A change of colour or the formation of ashes on the nozzle or the welding zone indicates that the welding temperature is too high.

When there is a risk of wrinkles or sliding of strips and sheets, it is advisable to provisionally stitch (spot weld or pre-weld) the two sheets every 20 – 30 cm.

The weld must have a minimum width of 40mm. This avoids a local peak of peel forces under wind uplift at isolated areas where there are sudden changes of width.

Welding - working conditions

For hot air welding there is no general limit for working at lower temperatures. It is crucial that the sheet can be rolled out without wrinkles and the temperature difference between the single ply membrane and the hot air does not become too great (this leads to wrinkles outside the welding zone).

When stored in a warm or heatable location the material should have a temperature of at least +5°C – 15°C (ideally 10). When the waterproofing is installed roll by roll, work can proceed at very low temperatures – general conditions for welding apply – i.e. welding parameters and tests.


Wrinkles, capillaries and fish-mouths are to be avoided. When these deficiencies occur they shall be repaired immediately.

Seam sealant

The use of sealant to seal cut edges is not required. Monarplan’s unique anti-wick reinforcement eliminates the need of such action.


Complete all roofing work and flashing each day to prevent water from getting under completed roof sections. Any areas where water has penetrated the completed roof must have any moisture and wet insulation removed.
Temporary sealing of the edge of the single ply roofing membrane is the responsibility of the contractor. The tie-off must be higher than the drain, and slope to the drain.

Video demonstrating use of tools and welding techniques

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