With exposure to the elements, the mortar holding bricks and stone together on an external wall can often start to crumble and fall out. On older properties, the pointing is often a harder mortar than the bonding mortar, once this is dislodged, the softer bonding mortar will become exposed and wear away quite quickly.
This sort of damage occurs over a long period of time, however it is important to repair the pointing as necessary otherwise water will increasingly penetrate and damage the wall.
If the damage is limited to a small area, just that area can be repaired; however the repointed area will often stand out. Generally the whole wall face will have weather in a similar way; therefore the whole wall will need repointing at the same time.
Repointing can be time consuming as it may involve the use of scaffolding or access towers when working above head height, however to achieve a good overall appearance it’s worth the effort.
Work down the wall (this will avoid any debris falling on to areas which have already been repointed), working on about 3 rows of bricks at a time. On soft mortar use a hook or old screwdriver to rack out the old mortar, alternatively use a 'plugging' chisel and club hammer - start by taking out the vertical joints, then work on the horizontal joints. If you clear the horizontal joints first, you will risk chipping into the brick when you come to clear the vertical joints.
Remove the old mortar back to a depth of 8 to 12mm from the front face (at least equal to the width of the joints) - where the old mortar is loose beyond this depth, clean it back until fairly firm mortar is located. Some old brickwork can have very narrow joints in places - where the hook or chisel is too wide, use a masonry saw, or hacksaw blade to remove the mortar.
Don't try to speed up the job by using a disc cutter or angle grinder, it is impossible to keep the disc lined up with the mortar beds and every miss alignment will damage the neighbouring brick.
Make sure that the old mortar is removed from the top, bottom and sides of the bricks so that the new mortar will adhere to them.
Any damaged or loose bricks should be replaced before proceeding with the repointing. When refitting such bricks, make sure that the new mortar bed is well back from the front face so that they can be finished with the new repointing
The usual mortar for repointing is either a 6:1:1 mix of builders sand, hydrated lime and cement or a 3:1 mix of sharp sand and hydrated lime. Measure the amounts carefully so that each batch will set to a consistent colouring.
Don't use a simple sand and cement mix as it will trap water in the wall and any frost will loosen it; also, it sets too quickly and forms weak bonds to the bricks.
Only mix up a small amount of mortar at a time as repointing is time consuming so you won't do a very large area before the mortar will start to go off.
The consistency of the mortar is very important. If it is too wet it is hard to apply and will stain the face of the bricks. It needs to be firm enough to cut it into narrow strips with the trowel and the strips stay in shape. As a test, the mortar should stand up on the trowel without sagging.
Do not attempt to re-point if heavy rain or frost are expected.
Remove all dust and debris from the joints using a large soft brush, and then dampen the joints using either a wetted soft brush or a fine watering spray - you need to damped the existing mortar at the back of the joints as well as the sides of the bricks.
Put a small amount of mortar on a hawk and, using a pointing trowel, flatten the mortar so that it is about as high as the joints between the bricks with a fairly straight edge on one side.
Repoint the bed (horizontal) joints first and then the head (vertical) joints working downwards and sideways. Concentrate on about one square metre of wall at a time.
Flush finishing can be difficult to achieve due to the irregularities of most mass produced bricks. This is achieved by drawing a strip of wood about 12mm wide, 6mm thick and 100mm long along the joints after the mortar has started to go off.
Hollow key - is formed by pulling a suitable curved or round shaped piece of metal (i.e. tube or rod) along the joints. This is probably the easiest finish for a new diyer to achieve.
Weathered finishing throws off rain water and is considered to be fairly durable but it is difficult for a diyer to achieve a good finish.
The joint is made by drawing the blade of a small trowel, tilted slightly inwards at the top, backwards along the joint, the top edge of the trowel being in contact with the underside of the bricks above the joint being struck.
For vertical joints, the edge of the trowel is in contact with one of the side bricks and is inclined by the same amount as the horizontal joint. Keep the direction of the vertical strikes the same all over a wall, otherwise it may look peculiar.
The mortar needs to be racked out to a consistent depth from the face of the wall and then the face of the mortar is pressed back firmly using a metal jointer tool or a piece of wood. A tool known as a 'chariot', which is designed to recess the joint evenly, can also be used.
Generally this finish is not recommended for external brickwork as water will collect in the recess.