Brick decaying

[Nebraska]

I've got some bricks crumbling on a chimney.
I took a day and ran up to our "cabin" to go duck hunting with my son yesterday. It was gorgeous for the first of November and no birds were flying so after breakfast we packed up. It was on to some projects,  stacked some firewood, got on the roof and cleaned gutters etc. While up there  I rembered since it was nice I hadn't put sealer on the chimney this year, it's a thin clear latex  type product  I put on with a little garden sprayer. I don't know if it helps or it just makes me feel better trying. That  chimney was built in the 70's with recycled brick, about 20% are affected... I suppose painting   or adding a stucco covering  might protect it better,  I just don't want recovery badly  as I like the brick.
Is there anyone else who has any experience with this?? Just fishing for ideas.

[Bricklayer51]

I did a lot of these jobs its probley a common brick soft and solid sucks up water and crumbles over time tear down to the flashing rebuild with kiln dry brick problem solved

[Nebraska]

Three flued chimney tearing them out would be a big job,  I don't have a picture handy, but you are right I'm sure.

[Tom King]

I expect they are really old bricks.  They used to stack them in a loose "clump", smear mud over the outside, and leave tunnels along the bottom for fireboxes to keep stuffing wood in for several days.  The ones on the outside never got fired hot enough to vitrify really densely.

Those soft bricks were typically used for fill bricks, and back then, they knew not to use them for an exterior, exposed surface.

The lighter the color, the softer they are.  The darker, the more high fired they were, and the harder they became.  Some in by the firebox would be pure black.  The black ones are called "clinkers", because when you throw them in a pile, they clink almost like metal.  They're about hard as steel too.

Sorry, I don't have an answer about how to preserve  the soft ones exposed to weather.

When we were rebuilding a chimney on an 1828 house, we had a bunch of the same sized bricks in an interior basement wall in that house made from the soft bricks.  I carried them to a brick manufacturer, and they fired them along with a regular run of bricks in a kiln.  They all came out as hard as any other higher fired brick, but the only trouble was that they were exactly all the same color since they were fired to a uniform heat.  They still worked, mixed in with other old ones.

Today's bricks are different colors because they put colored sand on the faces.  Back then, the colors were different because the heat in the clump was so uneven.  You can tell which ones are soft, just by the color.

[farmfromkansas]

The guys who sell used brick don't usually separate the filler brick from the face brick.  But sometimes they do.  Remember a house the brick were not sticking to the mortar, and brick were falling off, and they were the hard face brick.  Another house had all filler brick, and they were crumbling off on the outside.

[Don P]

The clump was actually a "clamp" of bricks, stacked like you said to self make the kiln to fire them, usually right on site. Back then brickmaking was a "wheelbarrow trade", the brickmaker could travel to the jobsite with all his tools and molds right in the wheelbarrow. The softer low fired "salmons" were used for nogging in the frame. It was draftstopping, insulation and plaster backing.

You can take a diamond grinder blade and cut the mortar and then chisel them out and replace them... wear a good respirator, a friend has silicosis from years of masonry work. Find a masonry sealer that contains silane or siloxane in the ingredients, that will bond with the silica and provides good water repellancy but is breathable. Paint or anything that traps water behind it causes those old bricks to spall, popping the hard outer shell off the lower fired core. Pay attention to older painted chimneys as you drive around, usually you'll see a bunch of spalled bricks, kind of the kiss of death.

[Nebraska]

 Thanks for the reply's... I'm going to try to get back up there this Thursday and  I will hop back up on the roof and take a pictures of the chimney.  I will also check the label of the sealant to see what it contains.  I'm guessing these bricks came from something that was torn down in the area.  As the original owner/builder was a local carpenter handyman and he used the house to show different things he could do. Each room has a different ceiling texture/ finish for instance.

[farmfromkansas]

Would a stucco type product bond to the brick and seal it as well?  Might add considerable life to the chimney.

[Tom King]

You can skip to about 5:30 in this video, to see them firing the brick in Colonial Williamsburg.

Firing the Brick Kiln at Colonial Williamsburg - YouTube

Another potential problem with old brick is that they don't play well with Portland cement mortar.  They were laid with Lime Mortar, which is nothing but lime, and sand, before the invention or Portland Cement about the middle of the 19th Century. 

Lime Mortar is softer than the brick.  Portland Cement Mortar is harder than most of them.  When the face of a brick softer than the mortar has absorbed water, and then freezes, it will blow the face off the brick.  Lime Mortar is much more forgiving, but you still have to be careful which bricks you expose to weather.

[Don P]

That is a cool video. It brought to mind a letter my aunt came across from an ancestor, he was writing home after moving to town for higher schooling. He had taken a boarding room in Williamsburg and described where it was in relation to the kil. He was rooming somewhere right down the road from that brick kiln.

There is a really good Nat'l Park Service preservation brief on repointing mortar, especially with softer historic brick. It goes into more detail on what Tom is talking about but is worth reading;
https://www.nps.gov/tps/how-to-preserve/preservedocs/preservation-briefs/02Preserve-Brief-MortarJoints.pdf

Our most common limestone right here is dolomitic so I take a slight exception to that part, they used what was local. The general rule is the same though, the mortar should be weaker than the masonry or when things need to move the masonry fails which is much harder to repair than the mortar.

Some of the qualities they talk about with lime based mortar vs portland apply to timber work as well. Portland didn't really get here much until the 40's or so. Old log cabins were chinked with lime based mortar. That is breathable. When we started restoring them with portland based mortar chinking it often trapped water and rotted them. The same thing has happened in old European timber frames with exposed timbers and lime renders. Modern isn't always better.

One of the neat things when we burn lime in a lime kiln, the quicklime that comes off is pure alkali, very "hot" lime. It can blind you or scorch your lungs looking for moisture. Slaking it with water makes hydrated "slack" lime, masons lime, but it has several uses in construction. That same slaked lime was the basis of plaster, tempered with gypsum to adjust the cure.

I just boiled up a batch of hominy tonight using pickling lime, which is just the food grade version of the exact same hydrated lime. A Mexican farm hand was describing how they make it and we had the usual word trouble till I listened carefully, he was saying "white powder, cal", I finally realized, duh, calcium, lime.  When exposed to air over time lime mortar reabsorbs CO2 and basically returns to limestone.

Here's the main link to the NPS preservation briefs, more topics if anyone needs it;
Online Publications?Technical Preservation Services, National Park Service

[Tom King]

Limestone is Calcium Carbonate-CaCO3.  It's found in all sorts of things.  Add a little organic matter to it, and you have bone, and sea shells.  One way they used to get lime to make mortar, and plaster from was to burn a pile of shells.  They called the pile of stuff they burned a "Lime Rick".  There are many places now with the name Limerick.

When you burn Limestone, whether the pure rock, or a lime rick, it gives off CO2, much like burning almost anything, and leaves CaO-commonly called Quicklime.  If you remember the Moon landings, they had trouble with Moon dust sticking to everything.  That single molecule of Oxygen wants to bond to almost anything.  The Moon dust is a large percentage of CaO, so that's why it stuck to everything.

To make the quicklime more stable, they "hydrate" it, by soaking it in water.  The chemical reaction is so strong that it makes the water boil.  What you end up with is Hydrated Lime-CaOH.  This is the way they used to make the lime to make mortar, and plaster from.  The Chemistry is really simple.  CaOH in plaster, and mortar will give up the Hydrogen atom readily, when a CO2 molecule happens by.  That's the way it turns back into Limestone, and why it continues to strengthen for centuries.

I used to buy Lime Mortar, and Plaster in bags, but when Virginia Limeworks went out of business, in 2012 if I'm remembering correctly, I started making my own by simply making Lime Putty by screening fresh bags of Hydrated Lime into water.  

The Hydrated Lime you buy is bags is really only partially hydrated to the point that it's easy to handle.  Further hydration by making it into putty allows the molecules to crosslink more, and it becomes even easier to work with in Plaster, and Mortar.

I'll see if I can find a video of burning a Lime Rick.

Building George's House: Lime Rick Burn - YouTube

[Nebraska]

Here's a picture of that chimney and what the bricks are doing. I think are just facade for the block coming through the roof. At least that's what I hope.

 

 

I got up there yesterday and patched in a couple torn  shingles I noticed when I cleaned the gutters. Winter is coming back soon.

[Tom King]

I can't tell much by the pictures.  If you go back up there, take some closeups, including the problem bricks.

[Bricklayer51]

whats that thing in the middle

[Nebraska]

An extra section of chimney  tile added to the top of the flu with angle iron brackets in case the adhesive fails. I didn't care for the big wide open fire place and its poorly sealing damper. So I made the chimney a little taller added a wood burning insert stove and an insulated stainless  chimney liner.  Its  really nice to start a fire and warm the place up and shut my brain off.

[farmfromkansas]

When I was building, the masons always used block for the main part of the chimney, then just laid brick where it could be seen.  See no reason for major concern, a lot of others are in same or worse condition.  Adding a liner and a wood stove insert sure does make a huge difference.  Did you have to remove the damper to hook up the pipe?