Monday, October 31, 2011

Replacing Bricks and Pointing

Strangely, I'm feeling a Pink Floyd moment coming on...

Actually, this weekend was a chance to REALLY get my brain around the mortar, pointing up, and historically appropriate mortar thing.

See, we had some deteriorating bricks on the un-painted side of the house and we were thinking that we needed to get on the worst of those bricks. You can see one of the ones I left un-done this weekend below.

Why did I leave that poor "water damaged" brick when I was right there working on two others? Well, I'll tell you why. Those bricks are TOUGH. I mean, HARD. SOUND. You'd think that a spalled brick such as that would have been soft and crumbly. You'd be wrong. There was damned little wrong with the bricks that they built this house from.

So what was with those deteriorated brick? Mortar. HARD mortar. HARD to chisel out.

Mortar used to be sacrificial. That is, it was meant to to fail before the brick does. Mortar is easy to replace. Brick is not so easy to replace. An old brick home is designed to aspirate an water that gets in. BUT water, brick, and mortar expand and contract at different rates as we go through freeze-thaw-freeze-thaw cycles.

So what happened, as far as I can tell, is that some time long ago, maybe 40, 50, or even 60 years ago, someone did a bunch of brick work and really packed the mortar in around these bricks. And they used very hard mortar. As a result, when the brick got moist and then froze, there wasn't any place for it to expand to, and so the front of the brick cracked and then crumbled.

That's the bad news. The good news is that a lot of those bricks look bad but are just fine--very hard and sound. Of course, if I care about how they look, then I've got a very tough task ahead of me if they are all as sound as these three were. I spent 4 hours cutting out 3 bricks and replacing them. I hit my hand with a brick hammer at least 2 dozen times. I can bring in a hammer drill, and I will, I suppose, but this task is not the cake-walk I expected.

In any case, onward. So we don't have this problem again in the future, I made doubly sure that my mortar was soft enough. I came to the conclusion that my prior mix was still way too hard for what I want to do. The trick is to use less than 20% portland vs. your portland+lime mix. Here's what I used:

1 Part Type N Mortar
2 1/2 Parts Lime
5 Parts Sand
Dye to taste

Why dye? Well, lime and Type N are both rather grey. This doesn't look much like the existing mortar and is thus unaesthetic. A little bit of putty colored concrete dye really makes the mortar almost invisible and if you use sand that is close to what is already there, it completes the illusion.

So, here's the step by step.

To replace bricks

1) chisel out as much mortar as you can,
2) using a small or even pointed chisel, break the brick and pry out pieces.
3) chisel out any remaining mortar and make sure the cavity is clean and sound.
4) size the cavity vs. the replacement brick. All bricks are not the same size.
5) either spray the brick with water or use a wetter mortar mix--those bricks suck up water.
6) don't over-pack the cavity with mortar. You want to seal the brick in, but you don't really want mortar between the inside and the outside course of bricks. It's Ok to leave a pretty good air pocket behind the mortar and the brick.
7) smooth the mortar with a pointing trowel. If you need to, you can lightly spray the mortar with water to create a neat finish.
8)After the mortar sets for a bit, come back with a brush and a spray bottle and knock off any excess mortar on the face of the brick.

The tools I used were a standard triangular trowel, a pointing trowel, and a rectangular trowel. The latter was best for mixing mortar in the bucket. The pointing trowel was great for getting into the gap between the bricks and for pushing mortar off the triangular trowel and into the wall.

One last tip: if you are pointing, start someplace that's hard to see. You'll be messier when you start, and will get better as you go.

1 comment:

Anonymous said...

Thanks. Have a whole section of 'bad' brick. Thought that it was the brick alone.