Fibreglass Matting

This section looks at fibreglass matting (CSM or Chopped Strand Mat), understanding the different weights and how to prepare before starting to fibreglass a roof surface.


Choosing the Correct Weight

Fibreglass Matting is available in various different weights, however for standard fibreglass roofs 450gm and 600gm per m² are the best choices.

There's all kinds of conflicting suggestions on just how many layers and what weight of fibreglass to use on your roof. Some people say it’s 1 layer of 450gm or 600gm while others say it’s 2 layers of 300gm, 450gm, 600gm or a combination of the two, as you can understand the waters get muddied and it all becomes very confusing.

And while people will always have different opinions, heres our own answer on the subject, the fibreglass layer is the first line of protection and having more of it on your roof is certainly not a disadvantage, we recommend you never use 300gm fibreglass matting on a roof and use only 450gm on roofs of up to 10 square metres with no foot traffic, for everything else you can use 1 layer of 600gm or two layers of 450gm depending on the use.

Pre-cut the matting

You will need to need to pre-cut the fibreglass into lengths across the roof parallel to the drip trim, start by rolling out the fibreglass overlapping by at least 50mm. Choose the best place to finish laminating the roof, always best to work toward the ladder, you don’t want to be stuck in the corner of your roof with no escape.

When this is done roll up the lengths and keep them in their position just in case their might be a different size or shape from one length of fibreglass to the next. Next job is to sweep the roof, you need to make sure the roof is as clean as possible before you start.