Applying the Underlay

With the correct amount of underlay strips cut, you are ready to apply the self-adhesive underlay to the deck.

Start at the gutter edge

Starting from the lowest point of the roof (the gutter/drip edge) lay out the first felt strip in its correct position on the roof. this first strip of Underlay should be laid to overhang the gutter/drip edge by 50mm.

Next roll half of the strip back towards the centre to expose the release paper underneath.

At a point close to the centre of the strip that has been folded back , carefully cut the release paper across the width of the roll with a Stanley knife using a straight edged blade without cutting the Underlay

Peel the paper

• Peel back some of the release paper to expose that part of the underlay which is now ready for sticking to the deck. You will be therefore, working from the centre of the strip towards a roof side edge. (see Fig. 9)
• Gradually peel back a section of the release paper at a time whilst pressing down the self-adhesive side of the Underlay onto the decking, using a rag or soft headed broom to eliminate air bubbles.

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Fig. 9 Applying the Underlay

STEP 2

NB. It is best to use a hooked blade when cutting Coldseal membranes.

The underlay will be laid in strips running parallel with the gutter/drip edge. The first strip of underlay should be cut to half its width along its length. This will allow for staggered joints when applying the Top Sheet. The length of each strip required should provide for covering angle fillets as necessary.

If the length of the roof is longer than 8m roll, allowance should be made for overlaps of 75mm were two ends of roll join (see Fig. 7)

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 Page 9

• Where two ends of strips need to be joined. overlap the ends by 75mm and ensure that all overlaps face the same direction.
•  All joins should be staggered so that no two overlaps appear in the same position on adjacent strips.
• Securely press the Underlay into any angles that are encountered; acute angles can be more easily stuck with pressure from a cloth, soft broom or, if necessary a wallpaper roller or similar.
• Repeat this procedure for other half of the membrane.
• Repeat this procedure for each strip or strips, starting at the centre at the centre of the strip working to one side and then repeating the process to the other side.
• Each additional strip  should overlap each lower strip along its length by 75mm.

• At the edge At open roof edges, dress down the vertical face by 50mm.
• Up the wall. If there is a vertical wall where the highest point of the deck ends, the Underlay will need to go up the wall by 150mm from the finished roof surface. It is usually easier to do this with separate pieces of membrane cut to the required size.

Cover all areas. Finally check that all areas of the decking, kerbs and upstands are covered with Underlay and that any trapped air bubbles have been removed to achieve a smooth surface as possible.

Where there are internal and external corners to be waterproofed, the membrane will need to be cut and positioned to instructions on pages 16 and 17 as required.