How To Apply Torch-On Underlays

Torch-On Underlay Application Instructions

In this article we will breakdown the application process of how to apply torch-on underlays. But firstly, what is a torch-on underlay? A torch-on underlay is a roofing membrane that has been manufactured to be used as part of a BUR roofing system and its application can be used within a refurbishment or a new build development.

See the step-by-step application process below:

Step 1: Prepare the substrate.

Ensure the substrate surface is clean and tidy and free of debris.

Make sure the deck is dry, and then apply quick-drying primer.

Step 2: Application

Roll the underlay and cut to the required lengths.

Line up the membrane so that there is a 75mm side and head.

Position the underlay again to the centre from both ends.

Step 3: Applying the underlay

Direct the flame to the underlay at the point where the underlay forms a V to the substrate. Move the torch across the width of the roll as this will release the fusible film allowing a free flow of bitumen. As the membrane is pressure rolled out, you should be able to see a bleed of bitumen at both salvage edges – a bitumen bleed of 4/6mm must be achieved. Do not to over torch the underlay, this can cause footprints and marking.

Torch-on Application

Step 4: Application of detailing

Several details can be formed using the Underlay. When detailing check for any risk of flame areas and if a risk of flame is found a Self-Adhesive Underlay must be applied.

Step 5: Locate the capsheet

The Capsheet must be stagged to the underlay.

Step 6: Apply the Capsheet

Follow the same instructions for applying the underlay.

You should see a 4/6mm bleed of bitumen on both side and headlaps.

Step 7: Application of detailing:

Several details can be formed using the Capsheet. At detailing check for any risk of flame areas and if risk of flame is found a Self-Adhesive Underlay must be applied.

Below are some Wonderbuilds roofing underlays which are applied using the torch-on process:

WONDERBUILDS 2.5KG T -20C SBS FILM UNDERLAY

WONDERBUILDS 3KG T -20C FILM SBS UNDERLAY

WONDERBUILDS 2.5KG T -20C SBS SAND UNDERLAY

WONDERBUILDS 3KG T SAND SBS UNDERLAY

Below is a roofing system that includes the Wonderbuilds Self-Adhesive Vapour Control Layer (SA VB 600). This system has a 25 Year Guarantee and is safe to torch. It also includes a BROOF (t4) capsheet and underlay.

The Wonderbuilds Film/Film Underlays and Film/Sand Underlays are waterproofing membranes with glass-fibre reinforcement. They are coated with SBS modified bitumen, which makes them high-quality. What sets these underlays apart is that they have high tensile strength and low melting points. These underlays should be used within built-up roofing systems.

Wonderbuilds offers a flat roofing system where the torch-on application method is used to apply the underlays. This system has 15 years guarantee.