Once step one has been completed and then you have assessed the mortar in your brick wall you should then proceed to scrape out the horizontal joints to a depth of at least ¾ of an inch (joints wider than ½ an inch have to be deeper: 2½ times the joints width). A carbide-tipped grout saw works very well on the ¼ inch wide butter joints. Try and avoid electric angle grinders, unless you have experience with such a tool, if you don’t they can cause serious damage.
After removing three or four courses of bed-joint mortar, proceed to then start digging out the vertical joints, being careful not to hit the edges of the bricks above or below.
Wash your wall down and whisk away all of the crumbly debris, then check the blade of your tuck-pointing trowel will fit the joint. If the blade is too wide, grind it down. Mist the wall with water until the brick is thoroughly damp and starts to drip; this is a crucial step because any dry materials will suck the moisture out of the new mortar and prevent it from curing properly, you’ll have to wait until the next day before filling in the joints.
Mist the brick again. Then, following the directions on the bag, stir water into the dry mix until it reaches the consistency of peanut butter and clings to an upended towel.
Wait until a film of water forms on the mix after about 15 minutes, stir the water back in. The mortar is now ready to use and remains workable for around 8 hours. If the mix becomes too dry you can re-temper it by adding water.
Scoop a dollop of mortar onto a brick towel, hold it up even with a bed joint and push the mortar against the back of the joint with the tuck-pointing towel. Eliminate voids with a few slicing passes with the towels edge, persist to add more mortar until the joint is filled.
One you’ve finished three or four courses of bed joints, go back and fill the head joints. Finally smooth and compact all the mortar with the towel’s flat face and scare the excess mortar off the brick.
When the mortar is filled, dried and feels firm to touch, get an outdoors brush and brush the mortar diagonally to remove any dry mortar crumbs. The carefully sponge the mortar residue off the brick face. For a few days after use a tarp to protect the joints from the sun, wind or hard rain and give them daily misting.
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How to repair the mortar in a brick wall
If your brick is 50 years old or less then you can repoint it safely with modern cement- based mortar where as if your home was build before the World War II then your mortar is probably a likely mix of lime putty and sand - so when repairing and repointing you should try to match it. Otherwise, over time, the soft old bricks swell and shrinks against the rock-hard mortar, the bond will begin to break and moisture will begin to become trapped within the wall resulting in the brick faces popping off. A restoration mason (like ourselves) can assess old mortar and make a compatible mix.