Introduction: Repointing Pre-1920 Brick in a Historic Home.
I live in a house originally built in the 1860's, owned by 10 or twelve folks over the years, and even was a boarding house in the 50's. Over the years, as people got money, they expanded the house. The last major expansion was around 1917, where a kitchen and "mother-in-law" room were added. Sometime after 1898, someone put in two fireplaces, brick - and put some internal brick walls in the house. I know this because I was able to find the patent for the fireplace based on some patent date info moulded into the iron. BTW, they did all the patents once a week, so knowing the date means you have to wade through about 3000 patents. The patent was for a coal-burning fireplace you could put together with a screwdriver. Cast Iron Ikea, as it were. But I digress.
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".
DISCLAIMER:
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
Imagine a Brick. A hard shell on the face contains a softer core. To cut a brick, you just scratch the surface a little, and then strike it and it cracks in a (roughly) neat line. If you placed wight on one side, and had a fulcrum, it would do the same.
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)
Archived version of the park service page: https://web.archive.org/web/20160315154521/http://www.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htm
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.
Step 2: Tools
Buy a hawk. The padded handle and hand pad will allow you to do three times what you can do with a flat board. trust me. your forearm will love you for it. When you are done. clean your tools.
Two trowels. A fat one with a square end, and a thin one roughly the width of the space in your bricks.
a squeegee.
a plastic brush, different sizes and shapes - especially a few stiff ones that can get between the bricks,
cheap paint brushes - the best thing for sweeping out dust and sand.
a steel chisel the width of your spaces in your brick.
water bottles and misters to clean, and then for misting the surface.
Optional - a "reamer" - essentially a nail on a roller for raking/scraping out the brick.
Optional - wood chisel - thinner and lighter for smaller spaces. Also, the handle makes for pretty beveled pointing. I dremmeled off the scooped part to essentially make a very thin small steel chisel.
A mason angle grinder - DANGER! You can seriously damage your brick and bring your house down. I recommend doing a few meters of brick with the chisel, at least 3 or 4 sessions the hard way before you go messing things up with a grinder. NEVER GRIND VERTICALS, you'll cut the faces. Don't make your house fall down. learn to do it the slow way first.
Step 3: Removing Loose Material
Just sweeping out the loose stuff so we can see what it actually holding this building up. gentle! you can accidentally sweep out support for a brick. I've had a few drop out on me.
Step 4: Chisel, Rake, and Remove Slightly Less Loose Material
We're looking to at least have a quarter inch worth of space to add new mortar. Depending on what I have to work with, I at LEAST try to have that much depth. I do have a few spots I leave it there just isn't much support under the brick... but the new mortar has to have a toe-hold in there. unless you are using a hammer, you should be ok. If these were hand-moulded bricks you may want to be extra careful. Mine were made and fired locally around 1900.
You may have to get those brushes out when you're done to make sure you got everything.
poke occasionally, you'll sometimes find a very thin stiff crust with powder behind it.
Again. be careful if your walls are as bad as mine.
Step 5: Finding Voids in the Old Mortar
Sometimes.. you'll poke a thin crust and find a big gaping hole - or just loose powder. Go easy on those "crusts" - they may be all that holds up a section of wall. Use your judgement... get as much as you can without undermining the support. In my case I can get to both sides, and will be replacing everything, eventually.
Step 6: Washing Out the Last of the Loose Bits
wash away the debris. just make sure you don't wash away ALL the support. gently now. I start with a basic "thick" stream, and then get lighter and lighter. working top down to wash out what I can.
Step 7: The Importance of Wetting
The mortar needs water to cure... and if the bricks are too dry, they will suck the water out of the mortar before it has a chance to dry. So you need to dampen the bricks, give them some time (maybe 30 minutes or so) and then may need to dampen them again. you're not trying to soak them - but just make sure that they have enough internal moisture to prevent them from stealing it from the mortar you're going to make.
Step 8: Preparing Mortar and Slaking
MASON WORK + L is the magic phrase. M is the hardest, K softest. "L" is just lime and sand.
Some of the oldest standing structures just use Lime and Sand.. just know that there is some reading and special care you may need to know if working with just "L".
I'm using N, which may be a bit too hard - but it's what I'm using. see http://www.nps.gov/hps/tps/briefs/brief02.htm for lots of info.
Archived: https://web.archive.org/web/20160315154521/http://www.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htm
N is fairly standard. If in doubt, get the test done - ask questions. Get the existing stuff tested.
My ratio is 4:1 with water. It makes it turn out something like thick mashed potatoes.
Slaking is the time it takes for the mortar to be ready to use, the lime has to change form. I was told 7 minutes is sufficient.
If you want to see what is happening mix some pickling lime with water. wait, watch the powder-in-water change into something fluffy-in-water. Google calcium hydroxide / calcium carbonate. learn something new.
So:
1. mix
2. stir for a minute until it is roughly uniform add a little water at this point if you need.. just a little. very little.
3. let sit 7 minutes to slake.
4. have a beverage, you're probably a little thirsty after all that prep work... the heavy lifting is about to start,
ONLY MAKE ENOUGH THAT YOU CAN USE SAFELY IN 30-40 minutes! Adding water later is bad.
There's chemical reactions going on here - so if you can't use it in 30-40 minutes, then you're just wasting it. if you run out, make more and have another beverage.
Step 9: Filling in the Spaces - the Thin Trowel and the Thick Trowel
Remember, you only have about a half hour to do this, so start small and work your way up. I can do 4 really deep rows of bricks, about 2 meters long in about a half an hour. At first? maybe only a half a meter of one row. After 30 minutes things start hardening up, and adding water WILL NOT WORK - it's not drying, it is chemically hardening. Adding water would just break the bonds down, and you'll have it crumble. You'll just have to make a new batch after 30 minutes or so.
Thin trowel is for horizontals, thick for verticals.
My Workflow:
1. Scoop three big scoops with thick trowel onto the center of my hawk.
2. "slice off" a long "lift" of mortar to the edge of the hawk.
3. push the hawk up (but not ONTO) the edge of the crack.
4. push the mortar into the back of the hole, tapering on the end so it's thinner on the back where I'm going to add more.
5. slice off another block
6. #4 and #5 till I run out.
7. scoop more as needed.
8. at the end of the row, take the fat trowel and do the verticals
9. push some mortar into the vertical
10. angle/wedge the mortar in.. scrape off. repeat until I can't get any more in... takes a while, since you can only put a little in at a time
10b. push the trowel in here and there to make sure you didn't leave a big pocket of air. while the mortar is wet, you can tell when you missed something.
11. finish verticals for that row.
11b. scrape off excess with trowel back onto your hawk, mix in with the stuff there to be used.
12. next "lift" or horizontal row of bricks. Scoop, slice, push, slice, push... scraaaaape.
13. next set of verticals.
14. shoulders burn. feel the burn. you can do it. drink lots of water.
15. done.
Don't be tempted to do all the horizontals THEN the verticals, because the verticals will then be wet when you go to do your pointing... and you won't want to do them. Just do them at the end of each row.
Step 10: Squeegee Off the Excess
At a 45 degree angle, squeegee off the excess... just don't accidentally rake out your fresh mortar!
Step 11: Brush Off the Brick.
With the big brush, just like the squeegee... then the little "toothbrush" to clean the brick faces more carefully.
Step 12: Rest, Then the Actual Pointing.
Let it sit until it reaches something called "thumbprint" hard. if you push with your thumb it moves, but doesn't stick to your thumb. What you are doing it tapping it in and making a thin hard layer on the surface.
place the dowel or handle on the mortar. tap and move, tap and move, tap and move... do the vrticals as well.
If it gets dirty, the mortar is still too wet and needs to wait another 15 minutes or so.
The pointing looks pretty, creates a durable surface, and also helps shed water if it gets wet.
If your brick has an existing pattern (raised, etc) you may need to find special tools and instructions. This is in my basement, so I'm going for pretty + functional with minimal fuss.
Step 13: More Rest, and a Final Wetting.
After a few hours, mist the surface to slow the drying, and ensure the proper chemical processes involved.
Just mist it. If you wet it, you may erode your work.
Step 14: Clean Your Tools!
I don't have running water nearby, so here's what I do:
1. brush off the tools that have mortar on them.
2. scrape trowels off with the other trowel
3. wet the tools.
4. brush again
5. air dry - keep them off the ground (notice mine are at least up on some extra bricks)
That just leaves a little haze.
If you have a hose, then you can really rinse and dry them. Take care of your tools and they'll take care of you.
You may also need to dremel your chisels every 10 sessions or so to keep them sharp. That mortar can really dull them. You'l notice a difference.
Step 15: Done.
In my house, with some severe problems, I wait at least 3 days to a week before doing more work on the same section. I don't do more than 3 or 4 lifts (rows) on long sections, or 7 lifts if the section is very short (like this one) and I know there are other supporting bricks in the area. So, if you want to get more done, find an area of unrelated load to the last area and continue there.
On healthy brick, this isn't a problem, but in my house, I have found large sections completely lacking support. So making sure I don't remove too much is a big issue.
Just remember:
- Mortar ISN'T GLUE, it is a PILLOW for the bricks - it flexes.
- Mortar must be as permeable as (or more than) the brick, or you just trap water in the wall.
- Mortar sticks best to damp brick (which doesn't suck up water from the mortar).
- Mortar should be softer than the brick, and softer/same softness as existing mortar
- Mortar has to slake for 5-7 minutes before using.
- Don't make more than you can use in 30-45 minutes... it hardens by chemical reaction not dryness. adding extra water to hardening mortar will cause it to fail. I use premix, and do 4 parts mortar to something like 1-1.25 parts water.
- Keep the mortar bags off the floor, and dry, the investment isn't the $8 a bag, it's your back lifting an 80 lb block off the floor.
