parging a chimney

[julia sobolewska]

The chimney on my roof, which vents gas out of the house has started to lose
quite a bit of its mortar, and as moisture as penetrated some of the bricks,
they are flaking off as well. (I live in Toronto, where summers can get very
warm, and winter very cold!). I have no gas or wood fireplace, the house is
heated by warm forced air, from a gas furnace.

I've been told that it would not be a good solution to parge the exterior of
the chimney and seal it that way, as this would prevent the bricks from
breathing and there could be a gas build-up which could ignite. The chimney
does have a liner.

Does anyone know anything about this?
Thanks!
Julia

[DanG]

I do not agree with the advice you have been given. Parge or
stucco should not affect the situation. Parge and stucco will
breathe just as well as brick.

(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)

Post by julia sobolewska
The chimney on my roof, which vents gas out of the house has
started to lose quite a bit of its mortar, and as moisture as
penetrated some of the bricks, they are flaking off as well. (I
live in Toronto, where summers can get very warm, and winter
very cold!). I have no gas or wood fireplace, the house is
heated by warm forced air, from a gas furnace.
I've been told that it would not be a good solution to parge the
exterior of the chimney and seal it that way, as this would
prevent the bricks from breathing and there could be a gas
build-up which could ignite. The chimney does have a liner.
Does anyone know anything about this?
Thanks!
Julia

[butch burton]

So you have a gas furnace - combustion by products from a gas furnace
includes a lot of water and if there is not a galvanized or stainless
steel pipe inside the flu liner, that water is condensing on the flu
liner and that will destroy a masonry chimney. You need to place a
metal pipe inside this masonry chimney. Then pay a mason to tuck point
your chimney. If it is in really bad shape - the bricks may have to be
pulled down and laid again.

There are surface bonding cements that have all kinds of exotic
materials in them which are waterproof and can be parged over bricks,
blocks and cement but if your bricks are really loose, this is just a
patch that won't last.

[Peter Shepherd]

The standard liner for a gas furnace is aluminum flex, usually $4-500 to
install. You may need a new one in addition to:
- replacing any bricks that have spalled
- relaying any bricks that are loose, often anywhere from the top two
courses down to several [our 4-flue chimney I anticipate paying $400/ft in
height to relay the top 2 1/2 feet)
- repointing [color mortar to match & add bonding agent] where mortar
significantly recessed, ensure that joints are raked to 1/2" deep before
repointing, ususally done with a grinder, unless old soft mortar which can
be raked by hand.

Parging may be okay at grade if mortar mix is either lime(best, as Portland
stops moisture flow too much, so lime safer), or 4/1 sand/N-type mortar,
which is Portland, however a mason friend said that's what he usually uses.
Often you see rising damp just rising above parging & either efflorescing
salts out of brick & mortar, or even spalling old brick if cold climate.
Damp-proofing below grade would lessen that effect.

I wouldn't recommend it on a chimney with acid exhaust gases & temperature
flux, as they should be secure in high winds, with good bond, intact brick
partition between flues if multiple flues, & with masonry or metal cap with
overhang & capillary break to shed water away from brick. If you can't
afford the brickwork in the near-term, I'd just get a new liner & leave it
as is.

Post by julia sobolewska
The chimney on my roof, which vents gas out of the house has started to
lose quite a bit of its mortar, and as moisture as penetrated some of the
bricks, they are flaking off as well. (I live in Toronto, where summers
can get very warm, and winter very cold!). I have no gas or wood
fireplace, the house is heated by warm forced air, from a gas furnace.
I've been told that it would not be a good solution to parge the exterior
of the chimney and seal it that way, as this would prevent the bricks from
breathing and there could be a gas build-up which could ignite. The
chimney does have a liner.
Does anyone know anything about this?
Thanks!
Julia

[Peter Shepherd]

If chimney has lost a lot of mortar, you may also want to wrap it with
chicken wire till rebuilt. Our neighbour's fell down last winter, with no
particular tilt before it fell, just a lot of mortar loss.

Post by Peter Shepherd
The standard liner for a gas furnace is aluminum flex, usually $4-500 to
- replacing any bricks that have spalled
- relaying any bricks that are loose, often anywhere from the top two
courses down to several [our 4-flue chimney I anticipate paying $400/ft in
height to relay the top 2 1/2 feet)
- repointing [color mortar to match & add bonding agent] where mortar
significantly recessed, ensure that joints are raked to 1/2" deep before
repointing, ususally done with a grinder, unless old soft mortar which can
be raked by hand.
Parging may be okay at grade if mortar mix is either lime(best, as
Portland stops moisture flow too much, so lime safer), or 4/1 sand/N-type
mortar, which is Portland, however a mason friend said that's what he
usually uses. Often you see rising damp just rising above parging & either
efflorescing salts out of brick & mortar, or even spalling old brick if
cold climate. Damp-proofing below grade would lessen that effect.
I wouldn't recommend it on a chimney with acid exhaust gases & temperature
flux, as they should be secure in high winds, with good bond, intact brick
partition between flues if multiple flues, & with masonry or metal cap
with overhang & capillary break to shed water away from brick. If you
can't afford the brickwork in the near-term, I'd just get a new liner &
leave it as is.

Post by julia sobolewska
The chimney on my roof, which vents gas out of the house has started to
lose quite a bit of its mortar, and as moisture as penetrated some of the
bricks, they are flaking off as well. (I live in Toronto, where summers
can get very warm, and winter very cold!). I have no gas or wood
fireplace, the house is heated by warm forced air, from a gas furnace.
I've been told that it would not be a good solution to parge the exterior
of the chimney and seal it that way, as this would prevent the bricks
from breathing and there could be a gas build-up which could ignite. The
chimney does have a liner.
Does anyone know anything about this?
Thanks!
Julia