An often overlooked area when it comes to winterizing the home is the pointing in brickwork. If water enters any cracks in the mortar and freezes, it will expand and blow out the mortar. In severe cases, it can also damage the brickwork. Replacing old or damaged mortar is known as repointing. People are generally a bit scared about dealing with brickwork since it involves the structure of the building, but as long as a bit of time and patience is used, this is a relatively straightforward job to undertake.
Repairs should be in made in areas where the mortar has been eroded by the weather or has cracked. The damaged mortar will need to be taken out (raked) using a specific tool that fits onto a power drill or angle grinder (imaginatively entitled a mortar raking tool). Once an initial hole has been drilled, the tool allows the user to move along through the mortar to clean it out. As for how much to rake out, if the height of the mortar is ½ inch, you should clear out to a depth of one inch. This is to allow the new mortar to establish itself with the brickwork properly and not simply get washed out.
This job will create a lot of dust, so be prepared before you start to make sure you've covered or removed anything in the vicinity that you do not want to get filthy. Once you've raked out the mortar, the walls should be brushed down to remove as much of the dust as possible.
Brickwork generally consists of brick (or blocks) laid down with mortar between acting as the glue. Mortar is a mix of cement dust and building sand. The mixture of mortar can vary, but a good mix for house walls is five sand to one cement or a 3:1 mixture for retaining walls in which horizontal force is applied to them. A house generally needs to support itself and the roof so the load is vertical. There are some who prefer to use sharp sand rather than building sand for retaining walls, as it can offer a bit more strength.
While it's not a requirement, a plasticizer can be added to make the mortar more elastic and easier to work with. Before cement was around in great quantity, lime was used. Mixed with sand and horsehair to bind it together, it doesn't go hard as cement mortar will. In many cases, the lime mortar has been replaced with cement so it's fairly rare to find, although it can still be added to give mortar a little more flexibility; some claim it allows the property to breathe a bit more.
Before refilling with new mortar, or re-pointing, the surrounding bricks should be made wet so that they don't absorb all the moisture from the mortar too quickly. Once that is done using a jointing tool, the fresh mortar can be applied. Any excess mortar should be brushed off the brickwork.
It should be noted that it's important to not let the mortar dry out too quickly. Working in the hot sun isn't ideal, but if there is no choice, ensure that the brickwork is regularly damped down.
If you have larger cracks that aren't increasing in size but need to be remedied, then you can use a stitching kit to re-stabilize the brickwork. Purchase the kit from a home improvement store or reputable internet vendor. This kit will comprise of five or six metal rods, resin (an adhesive / filler product), and a resin applicator. The resin will either be ready-made or you'll need to add water.
The process involves raking out the horizontal pointing from within 1.5 feet on either side of the crack. You should then have a three-foot length of the wall that will allow for a rod to be inserted. Before inserting the rod, squirt in some suitable resin along the length. Then, insert the rod into the resin. Once hardened, you have to point over the top to fit in with the existing brickwork. The rods should be inserted every 12-18 inches. If the finish requires rerendering or repainting, then this can be done after everything has dried off. Personally, I would give the brickwork five days to harden off properly.
Once it has all dried out, then the final finish to the wall can be applied, if required. This could be render, paint, or cladding.