Chimney Repair: Chimney Flashing, Bricks and Repointing
Before carrying out any repairs to chimneys or to the roofs of houses make sure that any ladders used to gain access to upper parts of exteriors are firmly secured. All ladders used should be of a sensible length, to project at least 12 in. above the guttering, allowing them to be placed at a reasonable angle to ensure safety. The main ladder should be secured to the fascia board at the top, by using a large-eye and length of stout cord.
Access to the roofing surfaces or chimneys is then gained by a shorter ladder or pair of steps, which is placed to lodge firmly against the part of the main ladder that projects over the edge of the roof. The foot of the steps or short ladder should be firmly lashed to the main ladder. The best way of transporting tools or materials for repairs to roof surfaces is by means of a bucket and a length of stout cord. When carrying out repairs to roofs every care should be taken to prevent tools and materials from sliding down sloping surfaces.
The work of repairing or replacing a chimney-pot is usually a job which requires the attention of a professional builder. It should however be possible for the handyman to fit a cowl or other patent device to a chimney-pot without professional assistance, and instructions for fitting these attachments arc provided by the manufacturers.
Renewing a Chimney Capping:
Chimney capping is also known as ‘flaunching’. This is a sloping layer of cement which prevents water penetrating the topmost bricks of the chimney-stack. The capping is exposed to varying weather conditions and it may in time crack or decay, in which case it should be repaired or replaced. Examine the capping and remove any loose sections; any parts of the capping that are still tightly fixed to the bricks may be left in position. The new capping material is a mixture of one part Portland cement to three parts sand, mixed with water. The capping material should be used within 30 minutes of mixing it, and the handyman should prepare the old surface before knocking up the material.
The tops of the uppermost bricks of the chimney-stack should be brushed with a wire brush to remove any loose surface particles, then thoroughly wetted. The surface to which the capping is applied should again be wetted before the new capping material is laid in position. The sand and cement mixture may be raised to working level with a bucket and rope.
The tool used for capping is a medium-sized trowel, together with a hawk will be found useful for transferring the cement mixture from the bucket to the working position. Tap the new capping well in place with the side of the trowel and finish by smoothing the surface No that it slopes downwards to the outer edge. Any cement mixture on the bricks should be removed with a stiff brush before it dries. After laying the new capping it should be covered with a wet sack, which should be left in place for three or four days after the job is done.
Replacing Damaged Chimney Bricks:
Any broken or crumbling bricks in a chimney-stack should be replaced with new ones. The replacement bricks should first be tested for porosity as explained on Damp Walls: How to Treat and Repair Them. The old brick is removed by scraping out the mortar in the joints with the tang of a file. A narrow cold chisel should be used to pierce one of the joints at a corner of the brick to permit the entry of a saw blade. If the job is a small one, an old blade may be used to cut through the remaining layer of old mortar round the brick. With the damaged brick removed all the old mortar should be chopped and scraped from the cavity with a trowel, the sides should be swept clean and thoroughly wetted. The replacement brick should also be wetted by soaking it in a bucket of water.
The mortar used for replacing the brick is the same as the mixture for renewing the cupping. The inside of the cavity should be wetted and then ‘buttered’ with mortar spread with a trowel. The surface of the mortar should slope downwards I tom inside to outside. With this done the new brick should be tapped firmly In position until the face is flush with the remaining bricks in the stack, and any gaps in the joints should be filled level with the mortar. Clean off any mortar adhering to the surrounding brickwork before leaving the job.
Repointing a Chimney-stack:
The term ‘pointing’ is descriptive of the facing of joints between bricks with a material that is harder and more waterproof than the mortar used for building. A suitable repainting mortar consists of one part Portland cement and one part sand, mixed with sufficient water to give the mass plasticity. If too much water is added the material will be found unmanageable. The mortar should be freshly mixed just before the repointing is done. Before mixing the mortar the old joints should be well raked out to a depth of at least 1 in. A special raking tool may be used, but the handyman will find the tang of an old file quite suitable for this job. After raking the joints they should be vigorously brushed with a stiff brush and thoroughly wetted. The repointing should be done by tackling a small area at a time, and before each area is repointed the joints should again be wetted. A hawk will be required for holding the pointing mortar, and the tool for the job is a small pointing trowel. The only other tool required is a straight edge — a thin piece of straight wood.
There is quite a knack to transferring the pointing material from the hawk to the joint. A small amount of mortar should be placed on the hawk, and this should be patted smooth and level with the trowel. The hawk should be held close against the brickwork, a section of the mortar chopped out with the trowel, and this section rammed well into the raked joint.
There should be no void between the new mortar and the old. The upright joints between the bricks should be filled first. The horizontal joints should then be filled and care should be taken not to smother the brickwork with mortar. The mortar should be pressed well home and smoothed to shape with the edge of the trowel. The surplus mortar at the bottom edge of the joint is then trimmed off with an old kitchen knife, using a straight edge to guide the knife.
Flashings are inserted in brickwork at the base of chimneys, and over doorways and windows, which are not protected by the eaves. The objects of flashings in a chimney is to prevent damp entering the house, and the flashings over windows and doorways prevent water dripping from upper edges of window and door apertures. The shape of the flashings may vary according to the nature of the structure and the flashing material may be of lead or zinc. Of these, zinc is the most common material for over window flashings; most chimneys are flashed with lead. With the passage of time zinc will decay, and this is to some extent due to the lime content of the mortar. When flashings decay it will be necessary to renew them to prevent rain-water and melted snow seeping into the main structure. The flashings in chimneys are renewed by raking out the joint and removing the old flashing material, which in most cases will have a zig-zag shape as illustrated in here:
Only one side of the chimney-stack should be dealt with at a time, the flashing removed, a new one cut to shape and inserted, and the joint sealed with fresh mortar and allowed to set before the other sides are dealt with. In addition to the bottom of the chimney lead flashings, supplementary zinc flashings may be inserted between the courses of the stack (see image 2 above). It is usually these which decay most. Lead flashings withstand the passage of time, although they may bulge away from the face of the stack, particularly if the wedges have loosened. The wedges are rolled strips of lead hammered into the joint where the top edges of the flashings are inserted.
Sections should be hammered flat with a piece of wood held over the lead. Tighten any loose wedges and repoint the joint. The replacement zinc, or lead, flashing is obtainable from local builders’ merchants, and is cut to shape with a pair of tin snips. This tool is illustrated above. The replacement mortar is best made from sand and cement, and lime should not be used. With the joint cleanly raked out and all the old pieces of the flashing removed, the space between the bricks should be brushed to remove all loose particles — the joint surfaces and surrounding brickwork thoroughly wetted with water. The new mortar is made by mixing one part cement to three parts sand, and this should be mixed to a very stiff paste with just sufficient water added to make the mass plastic.
It is advisable to use a waterproof cement for the mortar, or ordinary cement may be used if it is mixed with a waterproofing compound.
Mortar is then trowelled into the space between the bricks, the flashing inserted, with the inside edges turned upwards, and more mortar is inserted to fill the gap between the top of the flashing and the bricks above it. The lower edge of the flashing is bent to fit into tiles, or at the lower edge of the chimney-stack (Image 2). Any damaged or decayed flashing over windows and doors is removed and replaced in the same way as chimney flashings, and when the new flashing is inserted it should be bent upwards in the middle, as illustrated in Image 2 above, to provide a run-away for rain-water. If the handyman is the least bit doubtful about his ability to renew flashing, he should leave the job alone and call in a expert.