Expert: Dwain Gregory - 7/4/2006

Question
Dwain - I intend to make the repairs myself. Do you recommend a specific mortar? Will firebrick mortqar also work to repair the face of deteriorated firebrick? Thanks.
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Followup To

Question -
I recently had my chimney cleaned and the tradesman pointed out that some of the bricks in the back of the firebox are cracked and the face of several have spalled. He suggested that the cause of the problem is that rain comes down the chimney and wets the bricks and they crack when we have a fire. He suggested two actions: put a birdcage cover on the chimney to keep out the rain and repair the cracks and bricks with a product he referred to as "goop". I have installed the chimney hat, but would like your opinion regarding the repair. Is this the correct way to repair the bricks and what product is best?

The problem is primarily on the back face. The cracks are vertical, about 1/16 inch across (some may extend to almost 1/8 inch.) They start along the mortar joint and travel through the bricks. The cracks end before they reach the damper assembly. Also, several of the bricks have erroded areas. The corners have cracked off several bricks and about 1/2 inch of the face is eroded on a few. Help!

The fireplace is about 25 years old. We have fires infrequently, but more this last year. We live in Albuquerque, NM where pine and juniper are the primary woods available. Winters are cold but dry, average precipitation about 9 inches per year.


Answer -
Hello John,
Yes Sir ,that will crack Firebrick.At the start of the fireplace season,start a small fire first for a few hours,or even the first night.This should cure the brick out enough to start a good fire after it's been fixed.It doesn't even have to be actual rain water getting to the brick, just heavy moisture in the air is enough sometime.
 I'm not familiar with "goop"
It's probably a composite material like epoxy.This sounds like it should work.It would be iether this or type"s" mortar.
If I can be of any help just let me know,Dwain

Answer
Hello John,
So your going to do it yourself.Let me suggest a tool.A 4 1/2 inch grinder,but with a diamond masonry blade on it.Use this to cut out the joints, when you replace the brick.If a brick has a crack,cut down the crack,say about 3/8 of an inch and pack it full of mortar with a 1/4 inch pointing tool.
I have never tried to reface a brick with mortar and fireclay.I don't see why it wont work.All I can say is give it a try.
I would use type "s" mortar,and a little fire clay, mixed.
Like I said,if I can be of any help don't hesitate to let me know.   Dwain