# FlexBond Thinset chimney repair



## Steampiper (Apr 12, 2006)

I have a few loose bricks on the top of my chimney and lots of crumbling stucco on the sides. I was thinking I could use FlexBond Thinset to "glue" these bricks back and repair any cracks and then scrape off the loose stucco and re-stucco the sides. It appears to have been repaired poorly in the past and I want to fix it once-and-
for-all. I have some extra FlexBond Thinset and it seems to be
stronger and more water resistant than mortar.
Is there any problem using Thinset for this application? Will stucco stick to the old brick and block without a scratch coat? If not, can I use Thinset as a scratch coat?

Thanks,
Bill


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## tkle (Apr 15, 2006)

Thinset has no body to it and isn't a direct replacement for mortar.The aggegate in the mortar also gives it strength.If you're trying to stick the brick to the old mortar with thinset,shave the brick off a strong eigth of an inch to allow for the thickness of the thinset.The best way if it can be done without further damage ,is to chisel off the old mortar and use new mortar.Spec mix works well.Thinseting over the brick directly before browncoating should increase the bond,however this is probably overkill and will increase the total thickness possibly making it harder to blend in to the old stucco.Thinset in itself isn't rough enough to make a good scratch coat.


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## Steampiper (Apr 12, 2006)

*Thank you*



tkle said:


> Thinset has no body to it and isn't a direct replacement for mortar.The aggegate in the mortar also gives it strength.If you're trying to stick the brick to the old mortar with thinset,shave the brick off a strong eigth of an inch to allow for the thickness of the thinset.The best way if it can be done without further damage ,is to chisel off the old mortar and use new mortar.Spec mix works well.Thinseting over the brick directly before browncoating should increase the bond,however this is probably overkill and will increase the total thickness possibly making it harder to blend in to the old stucco.Thinset in itself isn't rough enough to make a good scratch coat.


Thank you for the info. Is there anything I could seal the chimney with, after I repair it, that will stop the frost damage? Or do I just make sure there are no cracks for water to get in?


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## denick (Feb 13, 2006)

We repair quite a few chimneys every year here in CT and I would ask you Why are the bricks loose and the stucco crumbling? 

Is this a stucco chimney? Or is it a brick chimney that someone stucco'd?

What is the construction of the top 1' of the chimney?

Nick


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## Tscarborough (Feb 25, 2006)

Pictures or diagrams? I can't visualize what you are saying.


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## Steampiper (Apr 12, 2006)

*Bad Chimney*



denick said:


> We repair quite a few chimneys every year here in CT and I would ask you Why are the bricks loose and the stucco crumbling?
> 
> Is this a stucco chimney? Or is it a brick chimney that someone stucco'd?
> 
> ...


Denick,
I don't know why the thing is crumbling. It is 50 years old and I don't think the previous owner even looked at it. The whole house is a money pit. 
It is a cement block chimney with 6"or 8" clay flue inside and 2 rows of decorative red bricks on top with stucco coating only the block. This is the chimney for my natural gas heater and hot water heater.


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## denick (Feb 13, 2006)

Steam,

You need to start with the top of the chimney. What you have said points to water in the chimney. The top of your chimney needs to be solid, waterproof and able to shed water away from the lower chimney. The stucco on block is OK but it needs to terminate at the top to something solid that over hangs it and sheds the water.

If you can post a picture we could look at the construction. 

Nick


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## Tscarborough (Feb 25, 2006)

The chimney flaunching is generally the problem. Most masons, in lieu of adequate detailing, simply lay a sheet of lath across the top and put a sloping mud base up to the flue liner. This is guaranteed to leak and have a short life. Here is a detail of a good way to do it, though there are others:

http://www.maconline.org/tech/construction/chimney/chimney.html


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## Steampiper (Apr 12, 2006)

*That's the problem!*

You guy's confirmed what I suspected. The chimney is poorly constructed. It's top is just a mortar wash up against the flue with gaps and cracks all over. I'll have to pour a proper cap as shown on that website.

Thank you for your time.


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## RobertExpr (Feb 27, 2009)

*Using the Ceramic Flue Sealant (CFS)*

I Recommend you to apply several layers of Thermocrete CFS to be sprayed inside. The coating seals all small holes and cracks, and strengthens the chimney.  is a very important issue for all of us since it may waste our time and money a a lot. I think olivertwistchimneysweeping.com can give us the better view. I found there some useful things.
Regards,
Robert.


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