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Classicbond EPDM Training – Part 4

Applying a cover patch

A cover patch is a small piece of EPDM used to cover a small join between two EPDM sheets or to add an additional level of protection against water ingress for an overlapping join between two EPDM sheets.  Identify the particular point of potential weakness and use that as a centre point.

As we are going to be using the 150mm Cover Strip to make the cover patch, we will be ensuring that this centre point has 75mm (3") of the patch in all directions for the water to try and work its way along.  This should be more than sufficient to ensure a flat roof that is watertight for at least a generation.

First, fold the piece of cover strip in half lengthwise and then from one end fold it over again to make a small 75mm (3") square.  These will form one end of the cover patch.

Trim the bleed of the pressure sensitive seam tape backing and cut the corners of the same end into gentle, constant radius curves.  This curve makes it much more difficult to lift up even a corner of the cover patch as, rather than having all the stress on a single point, the pressure is distributed along the entire length of the curve.

Once the 2 corners are cut, refold the cover patch to make the cross point easily visible and match this point up with the centre point identified earlier.

When the cover patch is in position, use the end of a pen or pencil, or the handle of a paintbrush to lightly mark the curved edge of the cover patch and then, as we have done previously, mark an additional 5mm past this line to account for the required Primer bleed.

Again, use only a small amount of primer on a scourer to apply it to the marked area and to work it well into the surface.

Once the primer is applied, don't forget to allow it to "gas off" and dry to avoid bubbles ruining the neatness of your EPDM flat roof.

Place the curved edge of the cover patch in position with a visible bleed and, like before, use a flat hand to sweep from side to side, pressing the cover patch firmly into place and pushing any bubbles out at the same time.  Work the cover patch towards the upstand and as you approach it, fold it flat on the base and use the tips of your finger on the reverse, pressure sensitive seam tape side, to tap the cover patch right into the corner.

If you attempt to join both surfaces and then  press the patch into the corner, the elasticity of the patch will slowly pull it away from the corner, creating a "tent" and an easy way for water to reach the join that you were attempting to seal.

Once you have worked the edge of the folded cover patch into the corner, you can now press it onto the upstand and finish it off by using the metal roller and then the back of a paint brush or pen to firmly press the surfaces together and form an unmovable bond.  Once this is complete, you can trim off any remaining EPDM with a sharp knife.

In this picture you can clearly see the bleed visible on both a cover strip (right) and the cover patch (left).

The extra bleed from the pressure sensitive seam tape backing (pointed at by the pen) isn't visible on the cover patch as this should be trimmed off when you trim the corners into a curve.

With the bleed in place, water cascades from the cover strip, to the seam tape to the primer and then to the EPDM giving multiple layers of natural protection from water ingress and removing any gaps for the water to work itself under.

 

Next time, we will be going through the procedures for sealing either and inside or an outside corner with the ClassicBond EPDM system.

Published at: 22-01-2015

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