When leaks develop in brick walls, chimneys or similar brick structures, they are almost always due to failure of the mortar in the joints, rather than to failure of the bricks themselves (although bricks sometimes crack and flake badly due to poor quality).

As mortar ages, it may crack and crumble, allowing water to enter and furthering the deterioration of nearby mortar joints. This is especially true in climates where temperatures drop below freezing during the winter. Water that has entered freezes and expands on the inside to hasten the cracking and loosening process inside the surrounding joints.

Repairing defective mortar joints as soon as they are noticed is the best way to avoid further deterioration and the possibility of a future major breakdown. The procedure to follow in doing this, which the professional masons call tuck point, is not difficult to master, but it can be time-consuming if there is a great deal to do -- and that is why contractors charge so much for doing this kind of work.

The only tools needed are a wire brush, a cold chisel, a hammer, a small triangular metal pointing trowel and a tool known as a hawk. (A square sheet of metal or plywood with a handle attached to the bottom, a hawk is used to hold the mortary while working.) Metal hawks can be purchased from hardware stores and mason-supply dealers, or a homeowner can make one by nailing a short length of broomstick under the center of a piece of plywood about 12 inches square. Mortar is carried to the work site by heaping a small pile on this piece of plywood, with the length of broomstick serving as a handle for easy carrying.

Mortar-mix cement is used for patching and/or replacing the defective mortar. You can buy this ready-mixed in dry form (just add water) or you can mix your own. If you elect the simpler method of buying it ready-mixed, be sure you get a bag or box specifically labeled mortar mix, or for use in mixing mortar. The typical "patching cement" mix is merely cement and sand, and this will not stand up properly when used for mortar -- the mortar mix has lime added or is mixed with a special mortar cement.

For those who prefer to mix their own, a formula often recommended calls for one part hydrated lime, one part portland cement and six parts fine sand (all parts by volume). An alternate mix that gives similar working qualities is one part mortar cement, (not regular portland cement) and three parts fine sand.

In either case, the dry ingredients should be thoroughly mixed first by using a shovel, hoe or similar tool to turn the pile several times. (If you are using the ready-mixed dry material, empty the whole bag and mix it dry, even if you don't intend to use it all at this time. You can put back what you don't intend to use after mixing, before adding the water.)

Add enough water to bring the mix to a smooth workable consistency, stiff enough to hold its shape when piled on the trowel, yet buttery enough to slide slowly off when the trowel is tipped sideways.

The most tedious and time-consuming part of any tuck-pointing job is raking out or chiping out the old mortar. The tool that works best for this is an old cold chisel or a mason's chisel. The chisel is held edgeways so the corner of the blade can be used to chip or scrape out the old mortar wherever it is cracked or crumbling. The old mortar should be removed from the entire joint to a depth of of at least 1/2 inch, but this must be done carefully to avoid chipping the bricks and loosening them any more.

Start by manually raking the chisel along the joint to remove what comes out easily, then use a hammer to tap the chisel with a series of light blows to chip out the parts that do not come out easily. Wear safety goggles to protect your eyes while doint this, and limit the working area to about 1 square yard at a time. Rake all joints out in this area first, then fill these before going to the next section.

After the old mortar has been chipped out to the depth required, use a wire brush to scrub out all the loose particles and dust. Then use a hose and a stiff brush to scrub the bricks and the joints as clean as practical. When finished, spray all the bricks once again to keep them damp, then mix a batch of mortar cement a previously described.

With the bricks still quite damp, but not dripping water, place a small pile of the mortar cement in the center of the hawk and then walk over to the area being worked upon. If you are working at heights where a ladder is required, try to rig up a working scaffold or platform of some kind. If this is impractical, climb up first with one end of a long rope and then have an assistant send the cement up in a bucket; (you haul it up on the end of the rope after you are in position).

While holding the hawk directly under the joint being filled, use the point of the trowel to pack fresh cement tightly into the open joint. Use plenty of cement since the excess will fall back down and be caught by the hawk, but try to avoid smearing any onto the face of the brick in order to minimize the need for extensive cleaning up afterward. Use the trowel to smooth off each joint approximately flush with the bricks, then move onto the next joint.

As soon as the mortar in the first few joints starts to stiffen, (5 to 10 minutes in most cases,) the face of each joint should be shaped or finished off to match the appearance of the other joints in that wall. In most cases this will mean merely rounding off the surface of the mortary while recesing it slightly -- and one simple way to do this is to rake the surface with the end of a short piece of broomstick or a tool handle of some kind which gives a concave joint.

If a flush joint is required, simply use the back of the trowel to smooth off the face of the mortar; for a V-joint, use the point of the trowel.

As soon as the joints have been raked or finished off, (this process is known as striking), excess mortary should be washed or wiped off the face of the bricks. Use a stiff scrub brush while the cement is still wet; it can be quite a chore once the cement or mortar hardens.

To cure properly, the mortary should be kept damp for at least 24 hours and, on sunny days, this will mean spraying with a fine mist several times the first day. An alternate method is to hang a large sheet of burlap over the area, then soak this burlap with water once or twice a day.