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The content contained in this Good Roofing Guide article is for information purposed only. While every effort is made to ensure this article is accurate at the time of posting, JJ Roofing Supplies would recommend that you always seek to use a professional roofer for completing all roofing related jobs.

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Buying Guides

Finding the Right Roof Coating for the Job

If you’re looking to build or replace a roof, there are several roof coating systems you should be aware of. The three main choices are Glass Reinforced Plastic (GRP), Ethylene Propylene Diene Monomer (EPDM) or Torch-On Felt roofing. Which of these is the best roof sealant for you will depend on your needs and your budget.

GRP Roofing

GRP provides a good looking, long lasting finish, and is one of the best flat roof coatings around. With a lifespan as long as 30 years, a GRP roof is a good investment.

Amongst their other benefits, GRP roofs are the best roof coating if you want to guarantee the roof is completely watertight and durable for the long term.


By far the most attractive of the roof coatings available, GRP can be laid in almost any colour you might want.


A typical GRP roof will be laid down onto 18mm OSB 3 decking. Application is relatively simple, starting with applying GRP trims and fascias. Reinforcement bandage is then applied to all the joints and seams, and a double layer of chopped strand mat is laid over the roof. With the mat in place, roofing resin is then applied, forming the waterproof finish. Some systems use “pre-pigmented” resin, others require a final top coat.


GRP systems start in the region of £70 per square metre, and can run as high as £90.

Browse GRP Products Here

EPDM Roofing

EPDM roofs are another durable and long-lasting option, with a lifespan running as much as 25 years. Usually laid down onto OSB 3 decking, EPDM involves spreading a rubber sheet out over the roof. Smaller roofs can be done in a single sheet with no seams, giving an excellent watertight finish. EPDM roofs are incredibly tough, and can withstand a great deal of wear and tear.


For all their other benefits, EPDM roofs aren’t much to look at. A well-fitted roof will look smart, but in terms of colour you’ve little choice beyond a flat grey.


Application is very simple, and starts with laying out the sheet over the roof and allowing it to relax for about half an hour. You then gently roll back the rubber, exposing the first half of the roof. A special deck adhesive is laid out with a roller, leaving a clear space of about 150mm around the edge of the roof. Whilst the adhesive is still wet, the rubber is gently rolled back over it, and any air bubbles are then brushed out with a large broom. This process is repeated on the other half of the roof. This brings us to the edges, where the rubber sheet is rolled back to expose the area left clear of adhesive earlier. This area is brushed or rolled with a contact adhesive, with the same applied onto the rubber sheet that will cover it. This adhesive is left to dry until tacky, and then the rubber sheet is rolled back over it and pressed gently into place. Air bubbles should then be brushed or rolled out. The final step in fitting an EPDM roof is applying the trim, and then trimming away the excess rubber.


An EPDM roof can be fitted for as little as £60 per square metre, running as high as £80.

Take A Look At Our Range Of EPDM Here

Torch-On Felt

The cheapest option available for a full roof coating is Torch-On Felt. This also has the shortest lifespan of the three options, with many contractors only offering guarantees between 10 and 20 years. That said, a well cared for felt roof may last far longer.


Felt can be found in a range of colours, usually green or grey. A well laid felt roof can look very smart, but a poor job will show.


Torch-on felt has the most complicated application process of the coatings mentioned here, and requires a lot of skill. It’s also a hot process, involving the use of a blowtorch. As such, you should take suitable precautions, keeping the work are clear of flammable debris, and keeping an extinguisher on hand.

A felt roof is usually built up in three layers – a pair of bitumen felt underlays with a mineral felt top layer. The two underlays are placed down perpendicular to the final layer, and all overlaps are staggered, so that no two edges lie on top of each other.

The top layer is rolled out and carefully positioned to check how it will lay on the roof. It’s then rolled back up, taking care to keep it straight. A blowtorch is used to heat the underside of the roll, allowing it to weld to the underlays and the other strips of felt as it is laid down.
If too much heat is applied, the felt won’t stick down, and may catch fire. If too little is applied the joins will be weak, and won’t seal properly.

Well-laid felt will show about 3/8” or roughly 10mm of bitumen flowing out from the overlap. An optional final touch is to scatter loose mineral granules onto the overlaps as they cool, giving a cleaner appearance to the roof.


Felt is the cheapest option of the three discussed here, typically running between £40-50 per square meter.

Browse Our Range of Torch-On Felt Here

Elastomeric Coatings

Another option if you want to touch up a felt roof is using an elastomeric coating – essentially forming a seamless plastic layer over the roof. These coatings don’t just improve the look of the roof – they also have excellent waterproofing characteristics and can increase the lifespan of the roof dramatically. The best elastomeric roof coating can even change the roof’s solar performance, keeping the building much cooler in summer. These are the best coating for your flat roof if you just want to give it a touch-up.


Typically these coatings are available in black, grey or white – though other colours may be available. A well-applied coating will give a crisp, clean look to the roof.


Elastomeric coatings are very easy to apply. The roof is first cleaned, cracks and gaps sealed, and then the coating is simply brushed or rolled on.


Elastomeric coatings run at around £10-20 per square metre.


There are many factors that come into play, but whether you need to give an old roof an new lease of life or you’re exploring your options for a new roof, hopefully the information here will help you to pick the best roof coating for your needs.

  Cost/m2 Lifespan Appearance Options Application
GRP £70-90 30 years Many colours Easy
EPDM £60-80 25 years Grey only Very Easy
Torch On Felt £40-50 15 years Grey or Green Skilled
Elastomeric £10-20 30 years Black, White or Grey Very Easy


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