"William Joones" wrote in message
om...
No making good needed with a diamond corer. They break out very cleanly.
Well worth the price difference. Especially useful when the outside is
not
easily accessible.
e.g. boiler flue for a 2nd floor flat.

I guess from this that you have installed a boiler flue in a 2nd floor
flat? I have a really similar problem - I want to put a vent pipe
though my kitchen wall (2nd floor flat) for a cooker hood extractor.
I'm happy to hire a diamond core drill to make the hole - but have no
idea how to put a cap over the vent pipe on the outside of the wall.

If I dont, I guess that water has a entry point into the render on the
outside of the wall - which doesnt seem like a good idea.

Any ideas?
The combi flues have a cunning rubber seal for the outside.
You push it through the hole from the inside then pull it back so the
flexible rim seals against the wall. The hole has to be the exact size
specified by the manufacturer, in my case this was 117mm which a size that
easy to hire.
Look at any recent combi install and you'll probably see this.

I've seen a couple of "pro" installs where the gap was sealed from the
inside with filler foam.
Looked messy as the excess couldn't be cut off and it degraded in sunlight.