We used on a flat roof bitumen mastic to plug a hole we then painted with a water proof roofing paint.
White flat roof stones.
Your roofing merchants can supply the stones.
2 to break up the rain into fine mists and keep the noise level down.
A wear surface of finely crushed stone granules is usually applied to the top layer of hot tar to protect the built up roof assembly from uv.
Flat roofs usually come with a 10 to 20 year warranty but can last 25 years if you build the roofs right and maintain them using commonsense rules.
But as said the stones help the roof from bubbling etc from the sun.
There are different types and weights of gravel used on flat roofs for these purposes.
Gravel is used on flat roofs for two reasons.
Built up roofs or burs also called a tar and gravel roof is a well established and popular style of flat roof that is made up of alternating layers of roofing felt or fiberglass and asphalt that is applied with heat which combine to make a long lasting sturdy roofing system.
To protect the underlying layer of roofing materials as is the case with built up roofs burs.
3 to protect the roofing felt from perishing and heat melting the bitumen.
Gravel to protect built up.
To weigh down or secure the roofing material as is the case with single ply flat roofs.
All three types of flat roofing cost 250 to 350 per square 100 square feet but prices vary according to region and size of the roof.
Built up roof bur the traditional hot tar and gravel.
Of course flat roofs are not flat but have a very slight roof pitch of between 1 4 to 1 2 per foot.