This is a problem with an old chimney - the house was built in 1919 and the
chimney is probably that old - don't know for sure.
The mortar has weathered thru in places. What's the best material to use
for patching it up?
"weathered thru in places" sounds like it can be fixed with mortar in
a caulk tube. [see the local borg]
See how much mortar you can rake out with a sharp object. If the
mortar is crumbling, then your best bet is to tear the thing down and
You do not say if this is a brick or stone chimney and what percentage of it
needs repair (re-pointing).
Brick chimney needing lots of work is best handled with a diamond saw on an
angle grinder, to get the old mortar out. It makes a mess, as dust is
flying all over, but it's quick and good. Stone construction is less
regular and more labor intensive. You probably need a new crown/cap as
well, if it's that old.
As to what put back in the place of old mortar - can't answer that. Had
some work done recently, but my crown cracked a few days after it was
replaced. So the formula was not good. Been trying to find out the
sand/cement/etc mix myself that would hold up. The re-pointing is holding
up in my case, but don't know what mix the guy used, as he did it himself.
The crown is more crucial in more ways than one.
Chimney guy coated the mortar around ceramic pipes on my chimney with a
mortar mix which I think contained acrylic binder. As other poster
points out, bricks may need to be repointed. This senior no longer
climbs on his roof but if I were younger could have DIY.
I had "my guy" leave a gap between the "ceramic pipes" (flues) to prvent
cap/crown cracking. He also mixed acrylic binder with water 1:1. This did
not prevent the cap from cracking in only a week.
I can still climb and found what some website claim, that 90% of the
chimneys are fixed with the wrong mortar. Those same sites do not suggest
the RIGHT mortar, just try to sell you stuff to smear on top of bad fix job.
Even contacted one of them for a suggestion on the right way and only answer
I got is to buy the goop.
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