We've been steadily working on the place for 10 years or so as money permits. In the last few years, while trying to get a contractor to level the floors, I discovered that the brick in the basement is in serious need of repointing. The cost to hire someone, about $100 or more per square meter. Area needing help? all of it. I could buy a new house for the total cost. They say you have to do an "overhaul" every hundred years or so. .. well, other than occasional patch jobs by previous owners - I'm having to do it. by hand. every few days. 'Cause I think it would collapse if I tried to do it all at once.
BUT, I discover, you can't just throw any old concrete mix in there - historic brick is SOFTER than modern brick... so just squeezing in some hydraulic cement with a caulk gun is a great way to destroy your house.
I talk to this guy, that guy, the guy who does restoration who comes to look at it, the intertubes, everywhere. It's very simple but comes down to a few simple things.
- Mortar doesn't dry, it cures - a chemical process that requires moisture.
- Brick is hard on the outside and soft inside, so minimizing damage to the face is a must.
- Mortar isn't glue, it's a pillow for the bricks.
Since I had to piece a lot of this together on my own, I decided to make an instructable about it.
Don't say "tuckpointing" - that's the final step that is the decorative part. the functial thing you are doing is "repointing".
I don't have building codes to follow in my area, and your area may be different. I'm kind of on my own here regardless, and I accept the consequences of my actions. Your area may require permits, codes, even specifically certified people. Use them, they know what the hell they are doing. If your house falls down, you have been warned, and you are solely responsible.
Step 1: A little Background on Brick and Mortar
Now imagine your wall, a bunch of bricks with mortar in between - and possibly several tons of pressure leaning on the wall. You decide to use an angle grinder to rake out the old mortar, and then fill in new mortar. You deeply scratch a few bricks. The wind blows, the house pushes down on the wall, and ... *CRACK* - the bricks "spall" (the face pops off) or crack, and the wall is now in worse shape than before.
Begin slowly, like this Instructable, and clear and rake (there are simple tools) by hand until you feel more comfortable with what you are doing.
Now. You might think the mortar is like a glue holding the bricks in place - but it isn't... well, before 1920 or so it wasn't. After 1920, it's all super-tough hydraulic cement that doesn't move and is watertight. Before? Your wall is like self-healing limestone... if tiny cracks appear, the mortar will actually seep Calcium minerals into the crack and become even stronger. That mortar can actually flex! Those minerals are transported by water. If your mortar isn't permeable (being lime based), then that water will go into the brick - which will damage the brick (again, *CRACK*). New house? totally different rules unless it was made with a lime mortar.
So the mortar is like a somewhat movable cushion for the bricks - it absorbs stress, it flexes, it wicks moisture around the bricks that do all the lifting. If you suddenly add a section of harder mortar? That stiffer section might crack out the softer sections nearby. Mortar less permeable than the brick? Water travels through the brick.
So, how do you know? Chemical tests can tell you the exact proportions and components of your mortar and brick. These might be expensive - but you'll be sure. A simpler test that gets you in the ballpark? Take a solid piece of mortar and drop it on a poured concrete floor. *TINK* - harder, more portland cement *THUD* - more lime.
You can actually compare small amounts of each type in the hardness spectrum to compare how they sound. But honestly, you're investing in this house - get the chemical analysis done.
Also, see http://www.oldlouisville.com/circa1900/brick-structures.htm
Learn the types of Mortar: http://www.cement.org/masonry/cc_mortar_types.asp
A great resource: http://www.nps.gov/hps/tps/briefs/brief02.htm (Park service, who know a thing or two)
I'm using Type N, since I'm working in a load bearing part of the house. N is normally for above grade exterior, and is probably a little too hard/impermeable - but these walls don't have soil against them - so there is opportunity for them the breathe on both sides.