2 chimneys side by side, crumbling.


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Old 08-11-12, 11:41 AM
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2 chimneys side by side, crumbling.

I participated in building these 2 chimneys in my (then new construction) home, the chimneys were completed in 1986 and all building inspections passed in that day.
  • We used 16x20 block, mortared side by side (for 16x40 overall dimensions);
  • One flue for woodstove, other flue for oil burning furnace;
  • We lined these blocks with flue tiles (red color, almost terra cotta like, visible aggregates when cut with masonry saw);
  • Flue tile joints were cemented with a product referred to as 'fire clay' (that is not a brand name, just the nickname);
  • We bought this 'fire clay' from a company (a masonry block manufacturer and masonry distributor) in plain 5 lb bags, so I have no brand names to offer;
  • This 'fire clay' was very different from standard masonry cement: when wet, it was definitely clay like, no grit or granules.

I haven't been back to that outfit recently, but the last time I went about 5 months after building the chimney, they told me the 'fire clay' was no longer available.

These chimney blocks were set with common masonry cement, with an added 15% more portland cement. No real knowledge of why we added the portland, just that we added it 'for more strength', I was acting as I was instructed to do by the (former) general contractor I worked with. He is since deceased.

Issue today:
The exposed blocks have suffered greatly over the years, freeze/thaw issues. The top of the chimney blocks were originally given a common, handmade mortar cap, about 3" up the sides of the flue tiles, sloped for water run-off. This held up well. The water has run down the chimney block (initially bare, then bonded) and it seeped in, froze when the temperature dropped, the rest is the 'to be expected' spalling damage which we did not forsee. The blocks below the lead flashing are fine and will be used as the base for repairs.

Partial mitigation:
About 2000 or so, we added a layer of a block bonding product, it was cement based (not acrylic) and is glass fiber reinforced (I can see the glass fibers today).

I'm hoping to simply 'rebuild in kind', following original techniques and materials. This time, I plan on adding a huge metal chimney cap (chimneys never had covering over the openings before) and I will add the bonding material immediately, as opposed to waiting 14 years as I did on the original structure.

I believe I will also reduce the overall height by 2 blocks, as I have tremendous draft as it is. I sweep my own chimney, have never found any cement matter in the sweepings, I believe the jointing of the flue tiles will be adequate as is.

Question: Is there a trade name or manufacturer for this 'fire clay', or, was I being duped? If I can locate it, should I use it?

Any other observations?
 
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Old 08-13-12, 03:51 PM
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I haven't followed your description completely - but please look at this "good practice" spec, and tell us how your installation varies from it.

Fire clay liners are usually mortered with a refractory morter, of which fireclay is typically one ingredient. Is there an air space beween the liners and the chimney?
 
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Old 08-14-12, 04:56 AM
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By memory only

By memory only, yes there is air space between tile and block. Also by memory only, I do not clearly recall using any other ingredients with the fire clay, but we most likely added it to the standard mortar mix.
I dont see a link to a "good practice" spec, but I'd like to read it.
 
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Old 08-14-12, 06:55 AM
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