A Guide to Roof Coatings

A Guide to Roof Coatings

Roof coatings are essentially for the refurbishment of flat and tiled roofs. Tired looking roofs can renovated with various types of coatings. They are not designed to repair serious defects.

Flat roofs, if your roof has a leak because of a defective flashing, or serious cracks in the felt or asphalt or if the roof decking (the boarding that supports the waterproof covering) has deflected or is rotten waterproof coatings are not the answer. You will need to get a specialist to look and advise on the best solution. Look at our articles on flat roofing, Tiled roofing & Maintenance for further advice.

You need special types of coating for roofs

There are many types coatings available that are made specific to the type of surface you want to treat. Make sure you get the correct one.

Back in the day all coatings were bitumen based solutions designed to be applied to roofs. Bitumen based solutions are still available today, most however do not offer any ability to deal with the continual thermal movement of the roofs they are applied to.

Modern coatings can either be Acrylic or polyurethane based some have added glass fibres to provide additional tensile strength.

They are available in many colours to choose from- Remember Lighter colours will deflect sunlight and keep the roof at a more stable temperature. A black flat roof early on a Summers day may have a temperature of only a few degrees. Within a few hours the temperature of the roof may have risen to 50 deg. As with all materials the thermal expansion in these conditions is massive. Continual expansion causes cracking in the roofing membrane. The more light you can reflect the more stable your roof covering will be.

Some roof coatings, mostly the acrylic ones are designed so they can be applied in damp conditions. I would recommend in all cases that the roof you are going to treat is clean and dry before applying.
Below is a list of how to prepare a flat roof. Best done during the summer months.

Roofs can quite often become dirty so coat them to avoid this

Roof coatings create a barrier so moss and algae will not grow.

Flat Roofs

  • Some flat roofs have stone chippings applied over the waterproof coating these need to be removed. In some cases chippings will have been stuck down using a bitumen mastic solution, if this is the case they will be a nightmare to remove. The best method is using a garden spade with a small width blade 4-6 inches is best. The roof needs to be as cold as possible, do this very early in the morning before the sun has risen, it’s the best time & be prepared for a good work out
  • Next job is to repair any obvious defects if it’s an Asphalt Roof by Gently heating and ironing back into place or otherwise using a torch on roofing felt. This is not an impossible task for the DIY enthusiast. However you will need a good quality gas blow torch. If you are not comfortable or competent using this type of equipment then get someone who is
  • Cleaning the roof. Wash the roof using a hose and brush and leave to dry
  • Apply the coating using a roller or brush as per the manufacturer’s recommendation
An example of a well coated roof

An example of a well coated roof

Asbestos roofs

Asbestos roofs are constructed using corrugated sheets of made from cement and asbestos fibres. These roof sheets are very fragile even when new after time they become even weaker.


Do not EVER walk on asbestos roofs, always use timber planks commonly known as duck runs. They should be placed so the planks are supported on the structure that is under the roof sheets.
Otherwise the procedure is similar but a primer is often recommended to act as a bonding agent before the coating is applied. Specialist coatings are available designed specifically for Asbestos roofs.
Asbestos roofs attract the growth of moss so you will need to power wash the roof to remove all the deposits prior to treatment.

Tiled roof coatings

Now becoming increasingly popular. Most roofs have Tiles that are made from Concrete. After approx 20 years they start to look tired as the dye colouring eventually fades. Moss, lichen and algae growth is also a common problem. The fine root structure penetrates into the tiles and helps to retain moisture. When moisture freezes it expands and can cause spalling or cracking of the tile.

Roof power wash

Power washing is the best way to clean the surface before coating however make sure its fully dry before application.

Correct procedure for applying a roof coating to a tiled roof

The correct procedure is documented in the bullet points below:

  • Make sure you have a suitable safe platform to work from. Specialist companies will use operatives that are trained to work using safety harnesses this avoids the cost of Scaffolding
  • Cover Patios, Paths, Decking and planted areas using PVC tarpaulin sheets. Cap off or plug the downpipes to avoid blocking
  • Power-wash the complete roof- this will also remove any loose mortar that was used to bed the ridge, hip & verge tiles. Remember to wash out all the gutters. Any splashing of debris to windows or walls is best washed of at this time before it dries
  • Replace any broken tiles and repair any mortar removed by the washing down. • Redress or renew any defective metal flashings
  • Apply a fungicide to the whole roof area to kill any root systems that remain
  • Apply 2 coats of a specialist coating by high pressure spray application. Use a brush for cutting in at the edges- best to be done on a windless day
  • Reconnect the down pipes
  • Many companies will offer an insurance backed guarantee for up to 10 years