Why do I Need a Reflective Coating on my Flat Roof?
Flat Roofs and UV Rays
Flat roofs, by there very nature, have a surface which faces the sun all the time. The UV (Ultra Violet) rays from the sun can oxidise (combines some of the chemical elements in the flat roof covering with oxygen) the flat roof surface covering.
When oxidisation occures it can withdraw some of the plasticisers from the covering which will eventually make it brittle and prone to cracking as it will have lost much of it’s flexibility.
This is why a 3-layer felt roof covering is only guaranteed for 10 years and why you will pretty much always see cracked felt on a flat roof, especially where the felt is asked to change direction as it does when it turns up at the sides of the roof over a timber arris trails or firring piece. An arris rail stops water from going over the sides of a flat roof, directing it to the gutters instead.
Expansion and Contraction
The main structure of the flat roof is usually timber. Sometimes it can be metal. The top covering is usually a bitumen or Acrylic polymer coating. The UK weather is entirely unpredictable with zero degrees one minute and high temperatures the next.
This leads to expansion and contraction in all materials and as they all have a different rate, or coefficient of expansion (IE they all increase or decrease, in greater or lesser amounts, in size, volume or area according to the given temperature) and when two different materials are moving in different directions at different rates, something has to give.
Because of the loss of expansion in an older felt roof as explained above, it is usually the felt that splits, so protecting the surface with a solar reflector of some kind is a good move.
Why is Rezistal Solar Reflective Paint Better Than Flat Roof Chippings?
Flat roof chippings (usually Limestone or a light coloured granite or spar chipping) are usually about half and inch (12.5mm) in size. They are not round, but irregular and can have sharp edges.
The shape of the chippings mean they can actually sit well next to each other, a little like jig-saw pieces in small areas of the roof and, given that chippings should not be used ona roof with over 10 degrees of slope, the tesselation of the stones can slow down the flow of water to the gutter.
This means moss can grow on the roof which, in turn, gathers more water. When this water expands (ice) and contracts, as everything else does on the roof, more damage can be doe to the felt. The more moss, the more water, the more damage.
Also, putting anything with a sharp edge on top of a bitumen surface is really not the best idea unless it can be guaranteed that there will be no foot, or any other kind. With children’s (and adults!) footballs nd throwing games it is inevitable that someone, somewhere, will end up walking across a flat roof at some time.
The sharp edges of the chippings can dig into the roof covering and you have a weak spot, if not a leak.
A third, but very important reason for using the Rizistal Solar Reflective paint rather than chippings on a flat roof, is that the wind and driving rain we are so used to over here will push the chippings down any slope, no matter how minor, and the chippings (as any flat roof owner will testify) will end up in the gutter.
This blocks the gutter at best. At worst it will clog up the downpipe causing water to push out of the joints and soak into brickwork causing joint failure, damp and potentially mould.
You will see many many garages with green mould on the walls near downpipes and much of the time, despite looking for other, plumbing related reasons, the problem is caused by chippings which should be on the roof!
Why is Rizistal’s Solar Reflective Covering so Good? – The Onsite Test
We had recently completes a large flat roof in two sections. One section was covered in the Rizistal High Build Bitumen covering while the other sections was covered in their Acrylic Polymer Roof Repair Coating. When both sections of the roof were complete, it was time to protect them. We chose the solar reflector because every Rizistal product we had used thus far was absolutely excellent.
Mixing was quite hard but that is a testament to the viscosity of the liquid. The video will show the various colour changes the solar reflector goes through but ultimately, when it has been applied to the roof, and the air has got to it, it turns from black, to gold, to silver. I’m sure there are excellent chemical reasons why it does that, but really, I don’t care…..It works!
Once mixed, application was just so easy. Using a 3 inch brush to "cut in" round the arris rails and the front, we used the really strong Rizistal Roller and handle together with their paint scuttle and simply painted it on just like emulsioning a wall, but a lot thicker.
The coverage was incredible at 1.5 sq m per litre and with only 12-hours between coats (most bitumen products require a curing time of minimum 24 hours) it was a joy to put on the 2nd coat as it was even easier.
How Rizistal’s Solar Reflector Helps with Waterproofing
Solar reflective paint is also a bitumen and rubber based paint. It contains aluminium flakes which give it the reflective quality but primarily it is another waterproof coating for your flat roof. It has fibres within the mix which allow for greater strength in it’s flexibility and it will even bridge small cracks possibly missed by the main roof covering. It really is great stuff.
DIY Doctor Opinion on the Solar Reflective Covering from Rizistal
Quite simply, why would you want to use anything else!! This is not just a paint. The embedded fibres help with waterproofing the roof, it is so easy to apply, it mixes well and you can actually feel the quality of the covering while you are mixing. We were very very peased with it as we have been with all Rizistal’s products.