Take care to provide a suitable, safe means of access to any roof. Remember also, to take care when working near the edges of the roof. If you have any doubts about a safe means of access, consult a professional. Make sure that the roof structure itself is sound and capable of supporting your weight
Examine the overall condition of the flat roof covering. If it has deteriorated significantly over a large part of the total, consider getting a quote for its replacement. Whilst repairs on a serviceable covering are sensible, as it gets towards the end of its useful life, repairing may be uneconomic.
Finding the leak
The first problem can often be locating the source of the fault. You may well be able to see where water is seeping through into the ceiling below, but the point at which the water is getting in may not be immediately above.
Where dampness appears at the ceiling edges, the usual cause is a defective flashing – the sealing strip at the edges.
To find the source, identify the corresponding position on the roof above the damp area. Flat roofs have a slight slope, so the source must either be here or uphill from this point. Examine the surface for cracks, splits or blisters.
If the roof is covered with chippings, sweep these away to enable closer examination. Where the chippings are stuck in the bitumen, apply light heat with a hot air stripper to soften the bitumen and release the chips.
If there are splits, these may be caused by movement in the roof structure, usually as a result of expansion and contraction under the heat of the sun.
Blisters may be caused by moisture penetration or trapped air. They can be squeezed lightly to see if they have any weakness. If they are sound, they are probably best left alone rather than creating more problems.
Various kits containing special tape and adhesive are available for carrying out patch repairs. These should obviously be carried out in dry weather.
Clean the area thoroughly removing chippings and killing off any mould growth with fungicide.
If the surface is split, fill the gap with bitumen compound before patching.
If you have a burst blister, dry it out first with a hot air stripper. In the case of asphalt, you may be able to fill in the hole by spreading the warm asphalt with a stripping knife.
Allow to cool, then prime the surface of the area to be repaired with the special primer supplied.
Cut the tape to length and press firmly down into place.
Make sure the edges are well sealed.
When complete, recover with chippings as before or ‘blind’ with sand to protect the surface.
Felt covered roofs
In the case of felt, carefully make a cross cut in the surface and lift up the flaps to dry it out. Apply bitumen adhesive to the hole before folding back the flaps and pressing down into the adhesive.
This area should then be further protected by coating with the bitumen adhesive and patching with a square of roofing felt a little larger than the damaged area. Once again, make sure this is firmly pressed down and well sealed at the edges.
Whole surface treatment
If you have several repairs looking somewhat unsightly and there are signs that further deterioration is imminent, it may be rejuvenated by treating the whole surface.
Brush off all loose material and treat the surface with a fungicide to kill off any mould growth.
Once cleaned and allowed to dry, apply liquid bitumen – purpose-designed for the job. . Plan your work pattern to avoid being ‘boxed’ in by the wet bitumen. Use an old broom to spread this as it will be a thankless task to try cleaning it out afterwards.
To provide additional strength, lay glass fibre matting. This is pushed down into the bitumen before it dries and should be tamped down so that it is thoroughly coated. To ensure continuity of strength, overlap the glass fibre joins by a couple of inches.
Allow to dry according to the manufacturer’s instructions before applying a second coat of the liquid bitumen. When this is dry, apply a third and final coat but ‘blind’ this with sharp sand before it has fully dried. Spread the sand lightly using a seed sowing action.
Prepare the area as you would for a repair to the flat surface. If there is an angled mortar fillet, carry out any necessary repairs to damaged areas using a mix of sand and cement, having removed any loose sections.
Using a proprietary repair kit, apply the adhesive to the affected area and allow to set in accordance with the instructions on the pack.
Cut tape to length and apply to the area. Smooth down with an old rag ensuring that the edges are well sealed.