Painting a flat roof from Promain

When painting a flat roof in order to provide waterproofing, preparation of the roof and an understanding of the practical application of the liquid product and related items is critical.

Where to begin

One of the first steps Promain advises is to ensure the roof is clean and free from any contamination.  The use of GS36 concentrate or ready to use GS37 fungicidal wash is recommended, allow this product to dry in before painting.

Dacfill Hz Roof Paint
Dacfill Hz Roof Paint

Fungicidal wash destroys the root of organic growth. Therefore it will prevent the re-growth of algae and moss under the new paint membrane. This is important to stop peeling and de-lamination.  Loose chippings and degraded asphalt should be removed and repaired with cementitious mortar.  Roofing felt should be inspected, and either replaced or repaired.  Blisters can be cut open and re-bonded flat on to the surface underneath.

Long life expectancy

For paint systems which offer 20-25 years life expectancy, a range of primers may need to be applied.  This will depend on the substrate. The Thortex GP830 Primer has excellent adhesion to a wide variety of surfaces, but for clean metal and fibreglass, the Urethane Primer MC 135 will need to be applied.  Metal surfaces showing signs of rust will need to be primed with MCU125 as it offers corrosion protection.  Wooden surfaces are best primed with FB856.  The different primers have different drying times and will need to be applied at different stages during the project prior to the first coat of 661 is applied.  If you need confirmation on the most suitable primer, consult Promain UK Limited on 01462 421333.

For the 3M Scotchkote Polytech 661/662 system, the following products and methods are required.

One of the fundamental requirements for a long life waterproofing system is to create a seamless membrane across the entire roof, avoiding the edge of the paint from exposure to running water.  If the edge of the paint is exposed, water can gradually creep under the paint over a period of time. This can then cause the waterproofing membrane to fail.  Edge protection can be achieved by painting up and over a lip. Alternatively if you are painting several inches up a parapet wall, chasing in-between a brick course and re-pointing, or painting under a strip of flashing.  Quite often, there will be a crack or gap which needs reinforcing.

Detailing work

To ensure any movement is bridged to prevent splitting the cured paint, a ‘pop joint’ can be created in order to spread the tension over a wider area.  This is done by applying 3M 1900 duct tape over the crack or gap, applying the liquid roofing material over this, into which the 050 premier reinforcement mat is embedded.

Where dissimilar substrates meet, further detailing work is required.  For example, a vertical ventilation pipe protruding vertically through the roof will need 050 premier reinforcement mat around the base of the shaft, of at least 100mm across horizontal and up the vertical.  Cut a length of this fibreglass matting with slits half way in, along one side. This will allow the fibreglass to be shaped around the base.  A suitable size of fibreglass with a ‘star cut’ hole in the middle offers double reinforcement in the opposing direction.  This fibreglass is embedded within the liquid roofing product. Again, paint up the vertical to a point where the edge of the paint is not exposed to running water.

Main Body of The Roof

For the main body of the roof, the stronger heavier 055 Premier plus reinforcement mat is embedded within the first coat of polytech 661 Embedment coat and allowed to dry.  Next day apply the second coat of 661 to increase the thickness.  On the final day, apply the Polytech 662 UV stable coating, which is available in light, medium or dark grey.

The number of coats applied will differ depending on what product, system and lifespan is required. 

Dacfill HZ is an economical two component water based acrylic, which is easy to apply by DIY’ers and contractors.  To ensure both components are thoroughly mixed, use a paddle mixer on a low speed drill for best results.  Pour the paint into a paint scuttle which allows easier loading of a wide roller which otherwise would not fit into the tin.

Flat Roofs

When painting a flat roof, in order to provide waterproofing preparation, Rustoleum reinforcement membrane is used within the first coat which is applied at a rate of 1.5kg per m2.  The second coat of HZ can be applied at a minimum 1kg per m2.  This system when applied correctly is expected to last up to 10 years.

For specialised applications where solar reflectivity is required, for example cold stores, converted barns used as offices etc.  Dac Hydro Alu can be applied over the Dacfill HZ in order to reflect unwanted heat absorption into the roof during the summer months.  This can be applied either as a waterproofing coating or as an aesthetical layer.

Keep an eye on the weather reports

Check the weather reports.  Some emergency patch repair products such as Rustoleum Fillcoat Fibres or 3M Scotchkote Poly-Tech AW654 can be applied even when it is raining, but they will only provide a temporary solution.  You will need to avoid conditions where rain fall is imminent for long term waterproofing solutions.  Conversely, ensure the surface is not too hot! Applying products in a ‘heat wave’ (although very rare in the UK), can cause paints to dry up and become difficult to apply.

Paints and primers need to remain in a liquid state long enough to create a good bond to the surface.  Products will dry more effectively where there is a light breeze or air movement.

Ensure you have measured the roof and have purchased sufficient quantity and don’t forget to allow for wastage.  We can help calculate the amount of product required and therefore the cost for the project you are working on.

Products offered range from an emergency patch repair, to a multi-layered 20-25 year system.  We are happy to offer guidance and support on selecting and applying the most suitable system for your needs.