Repairing Chimney and Wall Junctions
Mortar, which seals the weatherproof junctions between a wall and chimney, frequently cannot absorb the natural movement in a structure and cracks. This is often met in older homes.
It may, however, be necessary to replace an ancient fillet. You can use lead, zinc, or felt, or remake in mortar.
Zinc is cheaper than lead and is ‘dressed’ similarly. You need a dresser, which is a special tool made of boxwood or hornbeam.
Any adjacentoutlet should be temporarily blocked off so that old mortar does not block up the stormwater drainage system.
If you are remaking the mortar fillet, apply a 1:4 mortar mixture, with a PVA additive, using a wooden float. Make a fairly stiff mix and when the mortar has dried, cross-hatch the surface with a trowel or scratcher, to provide a scratch coat for a finish coat.
Allow the mortar to go off for about a day and then apply a finish coat of about 15mm thick, with the wood float. Finally, polish this to a fine finish with a steel float.
Make sure that you maintain an even slope so that rainwater cannot collect and percolate through any point into the home.
Soakers are a flashing which go under tiles and are often covered with a sloped mortar fillet. Both the mortar and the material, frequently zinc, may have deteriorated.
Again, an aluminium bituminous-backed strip may assist to put right the trouble, but if water is percolating through surrounding roofing, usually in older property slates, you may have to chip away the fillet and replace the soakers.
Sometimes soakers may be in long strips, which are cut into the wall and located beneath slates and tiles, or just in small sections. A damaged section can be lifted up, once surrounding tiles or slates are removed and cut out with metal shears. A new piece can be inserted and lapped over the old by some 150mm.
Zinc must first be dressed to replace worn or damaged soakers. The joints between bricks should be raked out to about a depth of 25mm. Zinc, 305mm wide, should be cut laid on a board and dressed to provide a 20mm strip at right angles. This angled section fits into the mortar gap of the original flashing.
Establish the angle of slope, using a woodworking, adjustable bevel. Turn the strip of zinc over and lay it on a thicker board. Hammer it down, working progressively outwards from the centre, until it matches the angle of the bevel; constantly check this.
Once it is moulded to shape, dash water into the gap between brickwork to assist mortar adhesion and insert the new soaker or flashing. Provide a 150mm overlap at joints. ,
Fold in small wedges of zinc at each end and then gently adjust the flashing to the slope of the roof. Fill the joint with a 1:4 mortar mix with a little PVA added. Trim off surplus mortar with a small trowel.
When working on sloping roofs always work from a crawling board and scaffolding. A scaffolding tower can be used in most cases for primary access.
Damaged slates or tiles may have to be replaced and surrounding brickwork re-pointed where necessary.
10. November 2011 by admin
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