Wednesday, November 21, 2012

Flashing and Slating

22 Nov 2012: With all this rain we have had recently, it's urgent to get the building more waterproof and I have been fixing up a permanent lead flashing. There is a 10mm groove in the wall for it to slot into. Real lead (as opposed to self adhesive Flashband) is very heavy and if you try to push it into the groove at one end it falls out of the other, and if you try to push it in the middle, it falls out of the ends. The answer was to cut it into 1 metre lengths and then each was perfectly easy to handle.

Initially, the flashing stays in place using temporary wedges made of slate, then permanent small wedges of lead have to be pushed into the groove and hammered deeply in so that they hold the flashing firmly.  I had exactly the right amount of lead for the job, so I was reluctant to cut it into sections and lose some in the overlap, and even more reluctant to cut some off the end to make little wedges - which are tightly rolled up pieces of flashing. I have to use lead not aluminium because of long term electrolytic corrosion of two different metals adjacent. 
While the lead is held in by wedges, the groove is filled with mastic sealant specially for beadwork - durable and weatherproof. However, it will take about three of these cylinders to fully fill such a long groove, so the flashing is held in with a first fix of lots of dabs of mastic, and more will be added soon. I got Douglas, one of my tall building students to come and help with the slating, and although it was raining lightly all day and very windy and cold, we got plenty of battens up. 
The battens are at 250mm intervals, screwed firmly into the OSBoard.We got started with the slating, but starting wall slating is very tedious - the first few courses are all cut-slates and are covered by later ones. Getting started with the disc-rivets is also difficult, but once we get to full size slates, it gets quicker. 

I continued late into the evening (by flashlight) and got at high as I could do until I ran out of battens and completely out of 30mm self drilling screws.

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