If the clay tiles on your roof are of the Rosemary type 10" x 6"1/2 with 4"
showing, it s not a good idea to paint them with anything. Because of the
fine joint gaps, if any water gets in it wont be able to run out. what
happens is, a line of paint collects at the bottom of the tiles and forms a
ridge and the water cant get out and runs side ways and in. Its alright to
paint theses type of tiles on a 90 deg vertical . If you jet or power wash
the roof start at the top and point the jet end down wards, never point the
jet up or side way, all you will do is flood the roof space.
My advice is simply DON'T power wash a tiled roof (down or upwards) -
especially an old one - unless you are prepared to carry out repairs to it
after, along with drying out the attic.
BTW, the reasons are obvious with the pressures used in these things - a
damn site more than mother nature can throw at the roof in this country!
The contractors use a petrol engine pressure jet which has significantly
higher psi than my Karsher. I'm sure I could angle my jet to avoid water
getting onto the sub layer.
I'm still looking for the paint.
I've spent all my working life on housing maintenance (over 40 years as a
'chippie' and general foreman) and seen all sorts of damage (some hilarious,
some serious and dangerous) caused by the D-I-Y enthusiast following what
'contractors' have done.
If your roof is over 30 years old (and sometimes younger) a man walking on
it - let alone a pressure washer on the loose - can do a fair bit of damage,
especially if not used to working on at height...
My advice - as always in these situations - is if it 'aint broke, don't try
and fix it! Especially if all that you want to do is 'make it look pretty'.
Anyway, best of luck when you do it - and here's a link for a roof coating
that may be of use
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