It's in the 30's today in Northern Ohio and I want to repoint the mortar at
the top of my firebox (natural fireplace) where the damper frame meets the
fire brick. My concern is the temperature; it's pretty cold inside there. I
made a strofoam air block that works like a charm so the hearth isn't really
exposed to the room air. The fireplace is also below ground level so that
first three feet of dirt outside which is probably colder than hell is right
against my fireplace chimney transferring that cold to the firebrick and
into the hearth. Will this type of weather affect the ability of the mortar
to set up properly?
As long as it doesn't get below freezing for the first week or so
you'll be fine. If there's some doubt, stick an electric space heater
in the fireplace.
First fire is a low and slow one so you don't cook the mortar.
You know that buried masonry is a huge heat sink. It probably
wouldn't be too difficult (at least for me!) to partially insulate the
exterior of the chimney. Buried rigid insulation, either extending
down vertically or extending out horizontally, would help. Something
Got it. I had to dig that area up for a water problem a numbe of years ago
and fortunately did put styrofoam on the bricks below grade. At the time, I
thought I was protecting the tar coating from earth and rocks more than
insulating it. Somethings we just luck out. :-)
I finished my tuck pointing and immediatley reduced the cold temperature in
that hearth. It seams the cement around the damper assembly deteriorated
(from heat and probably water that attacked it over the years) and was
letting cold air stream in. I replaced the top 3 - 4 feet of the chimney two
years ago and sprayed the bricks with a water repelant made for the purpose.
I still get a little water dripping down the inside of the chimney but I
think most of that is from rain that gets blown into the chimney. Nothing
nearly like I used to get. I'll examine the joints agin next Spring. Some
were tuck pointed with a silocone base cement compound made for brinks.
Thanks for the help.
Not common? The chimney bricks run all the way to the footer that is about
four feet below grade but I remember taring them. Come to think of it...
perhaps those bricks are atop concrete blocks and stop just under the ground
surface. I'm gonna' double check. I take it bricks to the footer would be
Consider that brick is usually very porus, and repeated freeze/thaw
cycles will not be healthy. Also brick is usually so rough that frost
will tend to do a lot of pushing on it too.
Around here (Northern New England) you'd see cement to above grade for
The above assumes that the brick is not plastered on the outside,
however. That would help...
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