The resin that needs to be measured and mixed has a limited pot life so preparation is key to save time whilst the mix is ‘live’. The Fibreglass was cut into appropriate sized strips beforehand, the mould or plug surface sufficiently cleaned as well as orientated to receive the Fibreglass and lastly the ambient temperature needs to be correct in order to allow the timely curing of the resin. Fibreglassing I found to be very messy, however careful I was, and so make sure there is plenty of towels or paper to clear up any spills and plenty of disposable gloves available. The work area will need to be well ventilated too due to the resin having a strong vapour.
The temperature was by the far biggest obstacle and I was lucky that I was ready to Fibreglass in the summer, although being on the North coast of Scotland the temperature still struggled to stay above 20 degrees centigrade. I invested in a fan heater to bump up the temperature in the garage to help in the curing (as well as my own comfort). There are other tricks such as mixing the resin warm or warming the surface (plug) prior to laying on the Fibreglass. I suppose you could even warm up the strips of Fibreglass on a radiator prior to laying to help. As I understand it the resin will still cure in the cold, within reason, but will just take much longer. In the end I found no issues although the gel coat layer seemed to remain tacky indefinitely but I think that may have been due to a bad mixture rather than temperature related.
I would recommend reading the resin specification for ideal curing temperatures as it will vary but there are resins on the market that are specifically for cold curing.
I had several mixing pots which were including as part of a fibreglassing kit I bought and these pots were purpose made for the job. These pots are disposed of after each use so make sure there are plenty for the job. I measured the resin in the pot, usually 100 – 200 ml each time and syringed in the specified amount of hardener (2% of resin volume). I then mixed with a mixing stick, trying not to introduce too many air bubbles and ensuring that all the residue on side of the cup was incorporated into the mix. After a good mixing it is ready for the Fibreglassing. Remembering that you want to make sure it’s all mixed in well but also that it does have a limited life so don’t spend too much time being sure.
So once the resin was mixed it was ready to be applied to the surface. I used disposable brushes which can be picked up cheap from any hardware store or online. They don’t need to be high quality brushes as they are only going to be thrown away straight after use and are only used to wet the Fibreglass, not to paint. Only a thin coat of resin mix is needed on the surface as more was applied over the Fibreglass to completely wet the Fibres. I generally left the coat for a couple of minutes so it started to go tacky which was about the time it took me to coat the entire surface so I could go straight back to where I began and start laying on the Fibreglass.
For me the first layer of Fibreglass was about getting a good solid foundation down for the rest of the layers and less about the finish, as the first layer wouldn’t be seen. So I used strand mat to cover the surface making sure to get it in all the finer detailing and around the edges, such as where the dive plane meet the body or around the edges of the coning tower. The brush is used to get the resin from the pot to the surface and then to work in the resin to fully saturate the fibres. The brush is dabbed down and not stroked across the surface as that will only pull on the fibres. It is important to ensure all the fibre has been wetted and is stuck down to the surface, pushing out any air bubble there may be by working from the centre outwards. A paddle roller can be used to help in pushing the air out, although I found it more of a hindrance especially once the resin began to get tacky as it pulled up on the fibres
I repeated the lay-up process until I was satisfied I had enough coverage and layers, that would result in a strong and stiff casing (I think I managed about 4 layers before I ran out). I found it better to mix smaller pots of the resin at a time rather than try to use larger volumes faster, remembering to discard the mixing pot, mixing sticks and brush after each mixture (otherwise clumps in the mixture will form). I also chased perfection on the shape between layers by sanding down and adding filler and then applying the next layer over.
Once happy with the coverage and layer depth it was time to dress up the surface as much as possible with one final top layer of Fibreglass, as bare Fibreglass is not the most attractive or smoothest of finishes.
To ensure a smooth polished surface when using a mould a gel coat layer would be applied to the first layer of Fibreglass, however in this case a plug was used so the surface finish wouldn’t be as smooth and polished. To get as good as I could I used a fine Fibreglass tissue cutting out the strips to fit the shape as close as possible with minimal overlaps. I also used a gel coat to provide a smooth as possible surface as it will fill in the smaller imperfections. It’s worth spending a little extra time on this layer as it will be the one that remains visible, so work slowly from the middle out and work the resin in and the air out.
The mixture ratios vary for a gel resin and somehow I think I got the mix wrong as the gel coat refused to cure, remaining tacky indefinitely, which I managed to remove in the end with warm water. Colour pigments can also be applied to gel coats to give a coloured finish but as I knew I would probably have to work out the kinks after the last layer I chose a clear coat.