Applying Roof Coatings To Extend Roof Life

When any type of roof is nearing the end of its useful life — indicated by the frequent need to repair cracks, leaks, loose, and flaking tiles and slates — you can recondition it with an overall roof coating. The coating should prove effective for about 10 years, after which the roof will require permanent repair by stripping and replacing the covering — or further temporary waterproofing with another overall coating. The advantage of such coatings is that they can be applied without the help of a professional — there is no need to lay hot asphalt, melted from solid blocks on site.

The coatings available cover most types of roof. Bitumen-based emulsions are particularly suitable for slate roofs. Plastic-based treatments can be applied over more or less any type of roof — asbestos, concrete, slates, clay and concrete tiles, metal, asphalt, roofing felt, wood, brick, cement, foamed and expanded plastic and building boards.

Apply a bitumen-based emulsion with a large brush; kneel on planks to prevent damaging the roof

1 Three coats of bitumen-based emulsion, with a reinforcing membrane between the first and second. Will seal a roof

2 Bitumen-based emulsion can also be applied to corrugated roofs; press the reinforcing membrane onto the first coat and apply two more coats

3 Two layers of plastic-based coatings are sufficient for roofs which are not too badly damaged

Bitumen-based emulsions

These have been in use for many years; they consist of three layers of bitumen with a membrane of reinforcing mesh sandwiched between the first and second layers. The mesh gives the treatment greater flexibility, allowing it to take up any slight movement of the roof covering and ensuring slates are held in position.


Remove dust and dirt (and rust in the case of steel roofing) with a wire brush and a knife and sweep the roof to remove the debris. If there is moss or lichen, scrape it off and treat the roof surface with a fungicide solution; allow this to dry before applying the treatment. Cut any blisters in felt roofing and stick the edges back down with some bitumen. Slates and tiles should be pushed back into place and the surface checked to make sure it is structurally sound. Stout roofing felt can be used to replace missing or broken slates; fill smaller gaps with bitumen. Flashings should be removed or bent upwards so the treatment can be applied under them. All internal angles, such as junctions of roof and parapet walls or upstands, should be filled with self-adhesive flashing strips to ensure they are adequately sealed.


Brush an initial coat of liquid bitumen proofing onto the roof; while this is still wet, press reinforcing fabric into its surface so the proofing is forced through the mesh of the fabric or membrane. Cover an area the width of the fabric at a time; subsequent areas of membrane should overlap by 75nun (3in). Brush heavy duty bitumen proofing over the fabric and allow the whole treatment to dry out before applying the final coat of liquid bitumen proofing. The standard finish is black, although red, green, grey or white are available. If the work is to be done during winter, it is advisable to use a solution type in preference to the standard emulsion proofing. The solution products are resistant to rain almost immediately after application and do not need to be stored in frost-free conditions.

Plastic-based coatings

The standard liquid plastic coating is supplied as a water-based paste which is applied with a brush; when dry, it forms a thick elastic membrane which will fill small cracks and will take up any movement in the roof. The coating is supplied in a variety of colours; white is particularly useful for flat roofs since it reflects sunlight, thus helping to reduce expansion and contraction of the roof surfaces. Preparation The roof surface should be prepared as for bitumen -covering. The plastic coating may be applied directly to clean slates and clay ’tiles, but absorbent surfaces such as concrete tiles and old asbestos cement must first be primed with a special sealer supplied by the coating manufacturer. There are also special primers for asphalt, bitumen, pitch, metal and timber roofs.


Brush a thick, even layer of the liquid plastic onto the surface. Most plastic coating compounds do not use reinforcing membranes; special reinforcing tape is supplied to strengthen certain gaps liable to movement, such as the joint between the roof and a parapet wall. Brush plastic coating along the joint, lay the tape over this and apply a second thin coat of plastic.

When coating the roof take care to ensure the gaps between slates and tiles are completely filled. Allow the first coat of plastic to dry; after 24 hours a second coat will complete the job.

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