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Unread 06-22-2020, 06:49 PM   #1
makethatkerdistick
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repointing chimney

Yet another project I discovered while inspecting my house. Since I'll be getting a new roof soon, I am trying to repoint my brick chimney beforehand. The chimney is structurally sound but has several small holes in the mortar joints, some of which go pretty deep. Rain water is certainly getting in there, accelerating the process of decay. No big leaks at this point, though.

Sorry for the bad picture but it gives you an idea of the shape the mortar is in. Certainly weathered and crumbly in a few places.

My plan is to remove approx. 1/2 to 3/4 in of the existing joint depth. Then use type N masonry mortar to fill it in. The brick is from the late 1960s, and I assume the soft type N would be the right choice to allow for expansion and contraction without compromising the brick. The current joints are recessed by 1/2 in. I plan to make the joints almost flush with the brick, thus being able to get about 1 in worth of material depth embedded.

I know I need to buy a pointing trowel. Not sure whether a regular small manual chisel or perhaps an old worn blade on my oscillating tool will work better with the removal. I have to find out.

The chimney cap is made from sheet metal, covering the entire crown. I am good there and don't need to form a concrete crown.

If you are familiar with this sort of work, is there anything I am overlooking? As always, I tend to overthink new projects but I figured you might have some words of wisdom for me here.
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Unread 06-23-2020, 06:09 AM   #2
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That's some interesting work around the bottom of the chimney there. No leaks, I presume?

I did a few of those with my dad about three decades ago. Actually, I mixed mortar and watched him do it.

I just remember it being very slow and tedious work, with a lot of cleaning on the way. I'd cover the roof around the chimney with a tarp to catch mortar.

Seems like an angle grinder and masonry blade would work a lot faster getting the horizontal joints cleaned out. Probably not for the vertical ones, though.

I'd start at the top and work my way down so's not to spill on my previous work. Keep a good brush handy, and be ready with your jointing tool. That mortar will dry quickly on the summer heat. You could even plan your work to do the west side in the morning and east side in the evening to keep the heat off of you.
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Unread 06-23-2020, 02:59 PM   #3
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The roofers may have to re-flash that chimney so I would wait on the bottom end of it until they are done.

But, like Kevin said, a cordless grinder with a diamond blade, brush out the joints to get them clean, use a grout bag and masonry mud. We used to mix a little bit of dish soap in the mortar to make it flow through the bag better.

Then let it set up just a little bit and use a rat tail dipped in water to strike the joints. Then brush it off with your foxtail hand broom.
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Unread 06-23-2020, 08:29 PM   #4
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Agree with what’s been said. And while some folks have used grout bags, I don’t mix my stuff loose enough to flow through the tip. I’d need Popeye’s forearms to get it to work. For filling the joints, I’d suggest you consider a narrow trowel and use it to shove mortar off your hawk and right into the joints.

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Unread 06-23-2020, 09:47 PM   #5
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If you make it loose enough to flow through a bag, you'll likely have some slump.

We always used a tuck pointer for this job. It's just a handle with a narrow piece of metal about 8-10" long, and maybe 1/4" wide.

A brick trowel full of mud can be held next to the brick, while the tuck pointer pushes enough off the trowel to fill the joint.

If it's hot where you are, you might dampen the joints with a spray bottle to keep the old mortar from drying out the new mortar too quickly.
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Unread 06-23-2020, 10:21 PM   #6
makethatkerdistick
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Thanks for the good tips, guys! I'll do this one on the cheap, so will use one of my bigger trowels as a hawk. The pointing tool and the jointer are only $7 each at Lowe's. Supplies will run me less than $50.

My angle grinder is corded unfortunately, but I'll have to make do with what I got. Spray bottle with water is always a good idea in this heat. I ground out the topmost horizontal joint today. The angle grinder naturally makes a mess but is quick. The oscillating tool works great on vertical joints.

Is re-pointing this in stages a problem? As in creating "cold" joints? Or is that acceptable?

I can't wait to get the metal roof. I am so sick of those crappy shingles. Good thing is I don't have to be careful right now with making a mess.
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Unread 06-24-2020, 07:12 AM   #7
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I'll point out that those flashing strips are likely to be bent into the bed joints between courses. Would be pretty tough to re-flash, I think.
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Unread 06-24-2020, 02:21 PM   #8
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Quote:
Originally Posted by toolguy
and while some folks have used grout bags, i don’t mix my stuff loose enough to flow through the tip. I’d need popeye’s forearms to get it to work.
Quote:
Originally Posted by kman
if you make it loose enough to flow through a bag, you'll likely have some slump.


Quote:
Originally Posted by tigermountaintile
we used to mix a little bit of dish soap in the mortar to make it flow through the bag better.
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Unread 06-24-2020, 03:16 PM   #9
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Sigh. I decided to take off the top four layers of brick as I found the mortar in that area sufficiently degraded to almost sand. Part of the problem was the slight corbelling at the top which permitted water to enter and seep in.

The inside of the chimney doesn't have a segmented clay flue but a second set of bricks (standard red) that form its flue.

I plan to rebuild the layers I took off without the corbelling to reduce water penetration. Do you think it would be alright to completely fill the gap between the inner bricks (forming the flue) and the outer bricks (forming the chimney facade) for added monolithic stability? Should I use mortar in this area or perhaps even a concrete mix?

I will reinstall the metal cap but nonetheless will shape a crown inside the perimeter of said metal cap to completely cover up the bricks. Just some extra insurance should adverse weather drive rain in sideways and under the metal cap.

We will not be using the chimney to burn wood, that much is certain (in fact, we never have for the past eight years that we've owned the house). When money allows, I plan on installing a gas insert with a stainless steel flue liner inside the chimney. Thus, the chimney will remain mostly because it's too cumbersome to completely remove and because it's part of the overall aesthetics of the house (if such a category applies to a 1960s house).
And yes, I probably leave those lower joints alone for now so that the flashing of the new roof can be completed first before I do anything there.
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Unread 06-24-2020, 08:24 PM   #10
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Wolfgang, my old mason (who built several fireplaces and chimneys on my behalf) always told me you could not fill that gap between flue pipe and masonry facade. I don't recall the reason, but he said that was very important. You might wanna research that a bit.

And since you've taken off part of your chimney, your code compliance jurisdiction is very likely to want you should have pulled a permit and gotten inspections on that work. No longer a repair in their eyes.

And early on you said you were planning to use Type N mortar for your re-pointing. I would recommend you use at least Type S.

And since you're having a new roof installed, you might wanna consider building a cricket behind that chimney.

My opinion; worth price charged.
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Unread 06-25-2020, 05:21 PM   #11
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Thanks, CX. I think I'll give my city a call to check.
The separation between flue and exterior is to ensure the independent ability of the flue to expand and contract, I think. Hence, they ought to be separate. I might just keep them like that. However, as you see from the smoke traces on the exterior brick's inside, there must have been small voids in the interior flue. That means I would have to completely rebuild this chimney to obtain its original function without leakage. Or, and this will be my choice, I will eventually install a stainless steel liner inside the flue, thus using the original flue merely as a conduit. Since the chimney is structurally sound (except for the top), I'll re-point it and will probably rebuild the layers I took off, this time without the corbel. When the time comes for the flue liner, then I'll have to replace the current cap with one that permits the stainless steel vent to exit.

I looked into mortars for re-pointing, and the overwhelming consensus is that type N is the best. See for instance here:
http://www.bedrockorlando.com/mortar...h-do-you-need/

Now, I think this has to do with its better ability to dry due to slightly less portland. Or so I gathered. For historic brick, even weaker lime mortars are used because they permit the water to escape. When modern mortars are used on this sort of old brick, the water is driven out through the brick, leading to spalling and other damage. My brick is modern, fired at higher temperature. Still, since it's no spring chicken, I opt for the type N.

Anyway, that's what I gathered so far to the best of my knowledge (or so imagine). Lots of good brick masonry videos on youtube, unsurprisingly from a lot of British masons.

And yes, a cricket behind the chimney is on my mind!
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