How to repoint your homes walls
As time goes by and the weather launches its onslaughts on a wall, the pointing between bricks begin to disintegrate. This might even happen to new walls, depending on the quality of the work done on it.
What is repointing?
Pointing refers to the mortar used in the joints between bricks to give it a nice finish. As the cement ages, driving rain penetrates it and makes it more porous. When the water gets caught behind the pointing and freezes, it expands and eventually the mortar gets worked out.
Before Portland Cement became popular, lime was used for pointing and it worked perfectly. It is permeable to water, but expands with the surrounding brick and ensures that no water gets caught inside the wall.
Modern cement is so hard that it can't expand and shrink with the surrounding brick, which opens the way for water to seep in and get behind the pointing. At the same time water also gets behind the outer fire-skin of the brick and also forces that out when it freezes, leaving a softer inner brick, exposed to the elements. When that happens, more water gets in and when that freezes it will cause the wall to crack. Eventually, if left for a few decades, the wall will disintegrate.
Only fixing an affected part of the wall will make it stand out, unless you can find the exact match for the mortar previously used. There are experts who will go to great lengths to find a match for the existing pointing. They may also, in the case of lime pointing, send a sample away for analyses to determine the contents of the existing mortar and to find the exact match for it. You won't see a difference afterwards.
How to repoint a wall
Rather hire scaffolding or an access tower if part of the wall is out of reach. It is definitely not advisable to work from a ladder. The first thing to do is to clean out the old mortar, starting from the top and working downwards. You can work on as many rows at a time as would be comfortably accessible and workable with the bolster or chisel.
If the old mortar is soft, an old screwdriver can be used to rake it out. A special tool, called a joint raker can be used on harder mortars and would cause the least damage, but if you have it on hand, a plugging chisel or small bolster will suffice. You should remove mortar to a depth of about 15mm, or till all loose mortar is removed. Brush all debris away.
Start with the vertical joints first and then the horizontal ones, because it's easier to chip into the upper or lower side of the brick when the vertical joints are done afterwards. Some people use an angle grinder or disc cutter, but it is almost impossible to have complete control over it and to not damage bricks in the process.
On a nice sunny day, wet the whole working area and make sure the joints are fully saturated. Plant sprayers can be used for this. This is to ensure that the mortar bonds properly and doesn't dry out too quickly and crack.
With a normal mix of 6:1:1 of builders sand/hydrated lime/cement or a mix of 3:1 sharp sand/hydrated lime - if you are going to use lime - you can start preparing the first batch. A simple sand/cement mix is not advisable, because it sets too quickly and forms weak bonds to the bricks and allows water to be trapped in the wall, which is what damaged the mortar in the first place.
Because of the laborious nature of the task, prepare small batches of about half a bucket at a time, but make sure the measurements are exactly the same to ensure a consistent mortar colour. The consistency of the mortar is just as important. It has to be firm enough to stand up on a trowel or hawk without sagging. If it seems to be too dry, keep working it until it becomes flexible.
Put some on a hawk and flatten it with a pointing trowel to the same thickness as the joints. Start with the horizontal joints and then the vertical ones and work downwards. Repeat this with only enough mortar for a one square metre section at a time. With the hawk slightly facing you, chop off a strip of mortar about the width of the pointing, scoop it up with the edge of the trowel and force it against the damp upper brick into the joint.
Repeat this until the joint is filled. After each section is finished you can then work on the finish, whether it be flushed pointing, hollow or concave key (the easiest), strap (usually only used on stone), weather struck or recessed key. The hollow key can be achieved by pulling a piece of round tube along the joints. Clean up before the mortar gets too dry.
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