Wednesday, October 8, 2008

Masonry 101

The House of 42 Doors is all brick and it's one of the things I love about it. With the masons here doing work, I thought I'd take up a post by going over bricks and mortar. If you don't care about bricks, go get a cup of coffee and peruse some other blog. If you're curious, go get a cup of coffee and come back. Here's what I've learned and a few photos to illustrate the point.

The bricks were made by the Streator Brick Company. They're still in business, but it appears that they no longer make our type of brick. Hopefully we'll never need to match the brick because I think we'd be out of luck if we had to.

Brick composition has changed over the years. Bricks today are hard, much harder than older bricks used to be. Many older bricks have a hard exterior with a relatively soft interior. This is due to the older firing process. As long as the brick exterior stays in place, the brick should be fine, but bust through that hard exterior and the soft interior will wear away faster than a neocon's deregulation stance during a financial meltdown.

The problem is that during periods of high humidity, water has a nasty tendency to get behind bricks and then during periods of low humidity want to migrate out. If the moisture wicks through the brick, it will make the brick flake away (or spall), especially during winter with the freeze/thaw cycle. Once that happens you expose the soft interior and the brick crumbles. Older bricks can avoid this by having a very soft mortar around the brick. This porous mortar allows water to wick out without going through the brick. The downside is that the mortar will eventually crumble and fall out.

If you've ever seen a white substance on bricks that looks like road salt, it is probably due to something called efflorescence. This is also a problem with bricks and water moisture. Water is coming through the brick and as it travels through, it picks up salts in the brick. Once this mixture gets to the brick exterior, the water evaporates leaving behind the salt residue.

One of the problems in tuckpointing an old building is that a "modern" mason will come in and replace the soft, historic mortar with a modern mortar mixture, which is much harder. If the mortar is harder than the brick, the water will evaporate through the brick, causing spalling and efflorescence. A good mason understands the different types of mortar and how hard they are. They will also understand when they should use modern mortar or historical mortar.

The other tricky bit is that when a mason is going to tuckpoint, he needs to remove all the old loose mortar from the problem areas before filling in with new mortar. This insures that the new mortar will stay in place. This can be done one of two ways, either by hand with a hammer and chisel, or with a grinder. The hammer and chisel method is highly precise and there is almost no chance of damaging the brick. It also takes forever. The grinder is much faster, but if the mason is not careful, it's easy to nick or chip a brick. Once that happens, he's exposed the soft interior and it's possible that brick will deteriorate, just as if it had been victim of bad spalling. Purists insist on hand chiseling, which means they either do it themselves or are filthy rich.

The house originally had black mortar between the bricks. We can still see this on the interior masonry for the fireplace. The problem is that black coloring agent does not stay in the mortar for long. It fades relatively quickly, leaving a gray/buff color mortar. A good mason will take the time to match the color of the mortar he is tuckpointing. Otherwise where he has been will painfully obvious, as the mortar will stand out.

Mortar doesn't just fail because of water migration. Mortar will show failure if the building settles. Mortar can also fail if water drips down onto the brick. In both of these cases "step cracks" develop. Below is a picture of one of my larger step cracks. It may have been caused by settling, but it may also have been from water dripping down from the lintel above onto the wall. From there the water just found it's way down to the ground.

In this next picture it doesn't look like there is a step crack. The holes here are probably from moisture freezing, thawing and pushing mortar out.

The next picture shows a wall that has been tuckpointed, but not cleaned. There's a step crack going from the upper left hand corner to about mid way in the picture, where it split and went both directions.

It's pretty easy to see above where Howie tuckpointed, but Larry and Howie haven't washed the building yet. Once they do that, it will be quite difficult to tell where they have done their work, which is exactly what we want.

The tuckpointing job they are doing is expensive (the bid was $6,000), but if we keep water away from the bricks by keeping the gutters in good shape, there's no reason why this tuckpointing job shouldn't last another 85 years. When compared to the costs of vinyl siding, stucco or paint over an 85 year time frame, I think that's a pretty good investment. And it qualifies for the historic tax credit.


ShoNuff said...

Cool. I'm excited that I get to see it in person soon.

Pusher said...

Have I mentioned lately how very much I love this blog?