Matting manHow to fibre glass a roof

 

 

 

 

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Choosing the right weight of CSM  fibreglass matting

You may find all sorts of suggestions from fibreglass suppliers of what weight of fibreglass CSM mat to use on your roof. Some don’t say, some say 450g, some 600g or others say double laminate 300g or 450g. In the end it turns into a mines bigger then yours contest devoid of all logic and reason. The simple truth is there taking a guess because they want the best for you but they haven’t seen your roof, it’s size, it’s shape or how well its constructed. Some fiberglass suppliers are just suppliers, and some have a history of fibreglassing roofs and can speak from experience. Here are my suggestions, feel free to use them, ignore them or improve on them.

  •   Small roofs, small garages, porches and bays 450g ( 1.5oz)
  •   Small garage sized roof’s with foot traffic or medium to large roof 600g ( 2oz )
  •   Large roofs i.e. > 50m2 single 600g or possible 450g double laminate
  •   Large roofs i.e. > 100m2 double 450g laminate

These figures are on the assumption the roof is well constructed and in good sound condition, any type of roof covering fitted to a poorly built roof will fail prematurely. If you have a funny shaped roof or a large roof and are concerned about laminate thickness or expansion and contraction please read our Fibreglass FAQ page ( opens in new page )

Aligning the matting and laying the laminate

Have all your matting pre cut and ready to go, roll out a run of fiber glass mat and make sure its square and aligned how you want it. When you know its all OK roll it back up again and store it on the roof so its easily accessible later.

Setting out the matIf your starting at a drip trim, I like to over hang the edge of a drip trim by 10 to 20mm ( 1/2” to 3/4” ) this helps catch any excess resin that may dribble down the face of your trims.

This overhang is easily cut off later with a Stanley knife.

 

Preparation is everything

Prepare your tools ready for use, If its a larger project say over 10m2 and you are new to fibreglassing I would recommend you double up on resin rollers, consolidation rollers and 50mm ( 2″ ) brushes.

If it’s warm weather or the catalyst cures faster than you can work your rollers or brushes can harden on you, this can cause stress or a feeling of panic. If your backup gear is on hand it allows you to carry on without the panic and to adjust your next mix accordingly.

Saftey glassesWear full wrap around safety glasses before touching any resin or catalyst.

 

Never mix more roofing resin than you know you can work with, it’s easy to mix more if you need it, there’s nothing worse than stressing and rushing because you’ve mixed too much resin to work with before it hardens. I recommend 4 or 5 litres at a time if you haven’t done this before.

Laying fiber glass matting is often compared to wallpapering except that you put the paste on the wall, roll out the paper and paint more paste on top of the paper.

Laying the GRP laminate

Roll out and align your pre-cut matting, when the fiberglass matting is in the correct position roll it back up without moving it, so that when you roll it back out into the resin it’s in exactly the right place. Pictured below.

wetting out fiberglass mattingDunk the roller into your resin bucket ( marked internally in litres ) and wet out just over a square meter of roof deck, now roll back the matting half a meter and apply more resin with the roller, once the mat is covered roll back another half a meter and add more resin.

 

If laying 450g fiberglass mat, the correct coverage is about 2 litres per square meter in my opinion ( or just under ). If you follow this advice you should find it to be a smooth operation. Do not skimp on resin, this makes it harder work as you roll backwards and forwards many times trying to spread the resin out, skimping will also increase the chances of pinholes and dry spots. To see the suggested resin ratios for other weight matting see How to Mix Resin and Topcoat

matting deck turning see throughSimply repeat this process and keep going. After a couple of minutes you will notice the matting becoming see through, this is the resin breaking down the binding agent that holds the fibreglass strands together, this is exactly what you are looking for.

 

 

Is there an easier way to laminate fibreglass?

Youtube-Video-thumb2To see how to apply roofing resin the easy way on a small roof like this 4m2 bay roof window,  click the picture for Video link.

Also shows cold cure resin for cold weather situations.

 

Using a consolidating roller

Preferably have a second person on hand to consolidate the matting and resin for you this will allow you to concentrate on laying and wetting out, a second person is not necessary but it helps. Look for bubbles or opaque areas, if you see any consolidate again until there gone. If you see dry patches apply more resin with the roller, if you see pin holes use the consolidating roller and apply resin as necessary.

consolidating and wettingRoll up and down the matting a few times with the consolidating roller taking particular care of any joints or seams.  

My preference is a fin roller because splashes are greatly reduced as the vertical fins do not flick resin as much as a horizontal finned paddle roller.

 

Overlapping fiberglass matting and joints

feather edge matting ready to go overlapsOverlap the matting 50 to 75mm ( 3″ ) , always lay the feathered edge of the matting on top of your last run if possible, this will help the of look of visible edges on the joints when the roof is completed.

This is purely for aesthetics only and does not alter strength.

 

Pulling at fiberglass matIf you haven’t got a feathered edge but you want one, just pull firmly at the edge of the matting and it will break away in your hand.

 

 

Fiberglass matting on top of trims

I like to lay my fiberglass so the matting finishes on top of any raised edge trims like this, again this isn’t necessary but it looks nice. You will need to allow the resin time to break down the binding agent in the fiber glass mat so it goes soft, before rolling it with the edge of your resin roller or using a detail brush to press it down.

Overlapping a fibreglass grp trim raised edgePictured here during the sanding process you can see how the matting sits on top of the trim if you want it to.

 

 

 

Fiberglass matting against upstand or fillet trims

D260 upstand trim fiberglassedTry to allow enough fiberglass matting so it can finish at the top edge of your upstands or D260 Fillet trim, this stops the possibility of driving rain finding a pin hole in a joint between your fiberglass and trim. Covering flashing’s will later hide the join between the matting and the trim.

 

Cleaning tools

Brushes and roller sleeves will obviously have to be disposed of when used but consolidation rollers and roller frames etc. can be cleaned in a shallow tray of acetone ready for re-use.

wipes CaptureDo not clean your hands or skin in acetone as it strips out the oil in you skin and can lead to skin problems. Clean you hands with industrial cleaning wipes instead, some brands are better than others at cleaning resin and topcoat so you may need to experiment.

 

For low cost high quality fibreglass roofing materials – East Coast Fibre Glass Supplies

 

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