Spalling chimney brick
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Hannah



Joined: 20 May 2011
Posts: 74
Location: Kansas City

PostPosted: Wed Mar 19, 2014 12:25 am    Post subject: Spalling chimney brick Reply with quote

Hi, all! It's been a while since I've been here; having lost my house to the bank a couple of years ago, I haven't had much occasion to visit. Happily, I've been given a chance to live vicariously through my mother's house, as I've recently been able to convince her that the place actually does need some attention. She's willing to put a little money into materials if I do the work.

One thing that has concerned me for several years now is the spalling chimney brick. Much of it has cracked all the way through, and it's coming out in thin slivers perpendicular to the exposed surface, littering the roof with shards. The brick below the roofline that has not been exposed to the elements looks sound, as do the crown, clay flues, and mortar. There is no rain cap, which I suspect might be adding to the problem.

My masonry experience is limited to laying pavers; I certainly wouldn't attempt to rebuild a chimney. The house to which this chimney belongs is a Midwestern 1950s Ranch, and I understand that the quality of the brick used in this type of construction was not always the best. My mother is not willing nor able to shell out $10,000+ to have the chimney rebuilt. I should also add that she does use the fireplace from time to time, gas only.

Is there anything I can do to slow the decay of this brick? What should my priorities be? I've read mixed opinions about sealers, but I couldn't afford much more, and the brick WILL eventually have to be replaced, somehow. As much as I believe in fixing it WELL, and fixing it RIGHT, I hate to ask: how can I buy some time?

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johnleeke
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Joined: 20 Aug 2004
Posts: 3009
Location: Portland, Maine, USA

PostPosted: Sat Mar 22, 2014 9:38 am    Post subject: Reply with quote

Hannah, welcome back!

Moisture is probably the problem, with two sources. The obvious one is rain water. The other is fumes from natural gas, which are mostly water vapor, which condenses into the chimney's masonry when it is cool. The fumes are also acidic, which can also deteriorate the masonry.

One good aspect of burning the gas is that it warms up the chimney, which helps dispel the moisture from the chimney.

If the exterior surface of the chimney is highly fragmented (lots of cracks, nooks & crannies, then a surface water-repellant will be less effective than if the surface is more continuous.

Can you attach some pictures of the chimney? That would help us brainstorm up some options for you.

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Hannah



Joined: 20 May 2011
Posts: 74
Location: Kansas City

PostPosted: Sat Mar 22, 2014 8:35 pm    Post subject: Reply with quote

I'd had no idea that natural gas fumes were acidic--you learn something every day. The chimney coatings I'd been looking at claim to be vapor-permeable, but I don't know how one could prove that. Actually, it looks like the mortar is in worse shape than I remembered. Here are some photos:



Above: West side of the chimney.



Above: East side of the chimney.



Above: Mortar crown and flues.



Above: Close-up of the spalling action.


Sorry the pictures are so huge; I actually reduced their size by more than half. The indestructible Ryobi contractor camera isn't kidding around when it comes to resolution!

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johnleeke
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PostPosted: Sat Mar 22, 2014 9:14 pm    Post subject: Reply with quote

Well, it looks like that last round of repointing (or possibly the original work) was done with hard cement mortar and that has forced the moisture to pass through the bricks, damaging the bricks when it freezes. If they had used a softer lime-rich mortar the moisture would pass through the mortar joint instead, preserving the bricks.

If the flue tiles go all the way down to the gas burning devices the tiles are probably doing a good job of protecting the mass of brick masonry from moisture damage.

OK, what are some low-cost strategies that could nurse this chimney along?

#0: Forget anything you have read or heard about how good water-repellants are.

#1: Safety First: Seriously, don't go up there unless you can be safe. Seriously? Seriously. Be careful to not fall off that roof! And don't drop anything off the roof onto someone down below. Read an article or book on roof top safety and follow the recommendations strictly. If you have a safety harness and been trained in how to use it, do so. Don't work alone. Have a safety spotter person, probably on the ground, to watch out for you and make sure you don't do anything unsafe or foolish. Read an article or book on ladder safety and follow the recommendations strictly.

#2: Moisture: Prevent moisture from getting into the mass of the masonry. At the flue tops and crown, use a flexible sealant like Sonolastic NP1 to seal up the joints around the flues and cracks in the mortar crown and where the crown meets the top surface of the bricks.

#3: Fix the bricks: Remove any loose pieces of brick and fill the major voids with a soft lime and sand mortar. For better appearance you could add some red pigment to match the surrounding brick. No need to fill the minor shallow spalls along the edges of the bricks.

#4. Monitor: Every other year check the chimney for further deterioration, take photos and compare with past photos.

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Hannah



Joined: 20 May 2011
Posts: 74
Location: Kansas City

PostPosted: Sun Mar 23, 2014 6:38 pm    Post subject: Reply with quote

Thank you, John! I'll forget all about coatings and concentrate on sealing up the mortar crown and patching the missing chunks with soft lime mortar.

I think that the hard cement mortar is the original work--on the west side of the chimney where there is a brick missing, you can see a cylinder of the same kind of mortar that would have been encapsulated by the brick that is now gone (a three-hole brick, perhaps?)

Should I look into constructing a rain cap that puts a roof over top of this whole apparatus? I have a friend who can help me with welding, and the materials don't look too expensive. Or should sealing the cracks in the mortar crown suffice to keep rainwater out?

I don't own a harness, but I try to exercise caution and good common sense on any roof. I crouch to keep my center of gravity low, crab-walk up and down the grades, and I never climb unless someone knows I'm up there and is keeping an eye out for me. I go up by way of a sturdy, trusty stepladder placed on the back deck (six steps and you're up). That said, the roof isn't very steep. I've been monkeying around that particular roof since I used to take cordless phone calls up there as a teenager, ha ha!

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Hannah



Joined: 20 May 2011
Posts: 74
Location: Kansas City

PostPosted: Sun May 11, 2014 5:51 pm    Post subject: Impasse Reply with quote

Well, over a month has passed and we're getting into those hot days on which you wouldn't want to walk on a shingled roof--I have looked everywhere for soft lime and sand mortar, all the local mom-n'-pops and even the big box stores. No one has soft lime and sand mortar or has even the foggiest idea what I'm talking about. In much the same way DAP has taken over retail window putty selections (now no one carries whiting locally, either), Quickcrete has completely taken over all the mortar selections. I have yet to find a formula that does not contain Portland cement.

So--I have sand. I have lime. I have water. And I have a question for the wise gurus who preserve the arcane knowledge: in what proportions do I mix them to produce soft lime and sand mortar?

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johnleeke
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PostPosted: Mon May 12, 2014 10:00 am    Post subject: Reply with quote

First test out some small batches. 3 sand to 1 lime, 4 sand to 1 lime, 5 sand to 1 lime, 6 sand to 1 lime. The reason you have to test is that sand can vary a lot.

1 part equals 1/4 cup, measured leveled.

Mix the dry sand and lime first. Then mix in the water adding just a thimble full at at a time. This is so you don't add too much water. Mix for five minutes with each thimble full. Keep track of the number of thimble fulls. Stop when it looks like mortar. It should be dry looking but wet enough to stay in a clump when you squeeze it in your fist. Soupy & runny is too much water--start over.

The second mix you'll know how may thimble-fulls to add.

Take your mixed batch and form a pancake 1/2" thick, pack it into a round shape with no splits around the edges. Work on a non-porous surface like sheet metal. Label the pancakes for mix proportions. Let the pancakes set up and begin cure in a shady open place, not in the sun. This may take several or many days, even a few weeks.

Observe if there are any cracks developing in the pancakes. If there are no cracks you can use that mix. If there are cracks there is probably not enough sand. Of the mixes that don't crack take up the pancake and break it with your fingers. Crumbling into many fragments is not so good. A clean single break is better. Use the mix that seems strongest.

Since this is a straight lime mortar it will be very white. If you want to match the color of the existing mortar you can add dry pigment colors. Do more test mix pancakes to get the color you want. Judge the color on the broken surface of the cured pancake.

Well, this should get you started. Post your results here. Please post photos of your mixing, testing, and results.

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