FIBREGLASSING
At the outset, I have to say that I am not a fibreglass expert. I learned everything below to make bits for my Locost. The sources of information were books in the library and free literature from suppliers. Everything set out below completely exhausts my knowledge on the subject. If you need to know more, I'm afraid you'll have to ask someone else. But what I can say is that this recipe worked for me - I made all the fibreglass (yellow) bits you see on the car in photographs elsewhere on the site.To make something in fibreglass it is customary to have something to mould it on. It is up to you to decide if you want to start with a negative mould or positive pattern (sometimes called a plug). It is often said that it is quicker to start with a negative mould. I prefer using positive patterns as the pattern looks exactly like what I am going to mould. It does mean that you have an extra stage, ie taking a negative mould from the positive pattern. (Following this ok?)
Whichever way, the actual fibreglassing process below is the same.
Make your mould/pattern out of whatever material suits you - but ensure that it is something that is either non-porous or will take a finish that is non-pourous.
Another word of warning. Don't try to do any fibreglass work much under an ambient tempereture of 15 degrees C - as the resin will take an awful long time to cure (harden) or won't harden at all. Yes, there are ways of overcoming working in lower temperatures - but they only serve to complicate things, and wouldn't you prefer doing something else in the warm!
The Materials you will need are listed below. Get your supplies delivered in bulk from a specialist fibreglass supplier. I have been very pleased with Glassplies in Southport, Lancashire, England (01704 540626) - who will also send you masses of helpful technical information if you ask for it. It takes the form of a lot of closely typed pages but if you spend a couple of nights selecting what you want to know and absorbing it, you won't go far wrong.
The materials you will need are -
Chopped strand mat (CSM) (Glassfibre mat to you and me. It comes in various weights. I used 1oz per sq ft (300 gm psm) and it did just fine.)
Surface tissue
Gelcoat resin (Resin B)
Laminating resin (Resin A) (This is polyester resin. You don't need epoxy resin (unless you are building an aircraft) - it's expensive and overspecified for a roadcar's non-structural parts.)
Release agent (blue PVA) (Don't think of starting without it!)
Split washer roller
Brushes
The process is -
Polishing
A lot is written about applying masses of coats of non-silicone polish to the plug/mould and buffing them between coats. In my experience - forget it. Provided you have a non-pourous surface on your mould and apply the release agent properly the job will separate without applying any polish.
Release Agent
Work in a dust-free atmosphere. If you have used the mould before, make sure all previous PVA has been washed off and the mould is dry.
Apply one coat of blue PVA with a sponge (or spray) (don’t brush as this will leave tramlines)
Ensure complete, smooth, coverage.
Leave in a dust-free atmosphere to dry thoroughly.
If it doesn't look right (streaky or with PVA ponds) when it dries or if an insect sticks to it (they do seem attracted to it!) - wipe it off and start again. This is the easiest stage to sort a poor finish.
Gel Coat (known as Resin B)
Use a gelcoat with some pale grey or white colour in it as an "undercoat" colour for final painting.
Work out how much gel coat to make up - @ a min of 2oz per sq ft (for or a finished thickness of about 0.5mm).
Initial gel coat should be well catalysed (see table below) and the catalyst very well dispersed in the resin.
Resin B gel coat should be spread as thick and even as possible.
Don’t allow it to build up too much in corners and in details.
Allow 3 - 5 hours @ 16°c to part-cure. It will be ready for the next stage when it feels slightly tacky to the finger, but not damp. To check if Resin B gel coat is ready for Resin A, press ball of thumb to surface, especially at the edge of laminate. If the thumb comes away with traces of resin - allow longer until it doesn’t.
Two coats of gel coat allow more scope for smoothing defects without cutting through the gel coat. Apply the second coat after part-cure of the first and using the same method as the first.
Do not laminate on this too soon but do not leave it for days either.
Laying Up
STAGE 1: surface tissue
Cut surface tissue sufficient for one layer.
Only make up enough Resin A at this stage for the surface tissue (see table below).
Paint a liberal coat of Resin A over the gel coat.
Apply the surface tissue and leave to harden.
STAGE 2: glass mat
Cut glass mats (enough for all layers) roughly to shape - allowing 10% overlaps and have these ready for applying - so they are ready for later stages.
At 20°c 10cc per lb = 11 mins gel time (in Glassplies literature -See table C for BIP 864E)
Work out how much Resin A to make up to cover at least one thickness of mat.
Working at higher ambient temperatures means less catalyst therefore less shrinkage. Watch out for pot life - determined by ratio of resin to catalyst and temperature. Once this has been established, larger volumes can be made up to cover larger areas or more layers.
Paint a liberal coat of Resin A over the surface tissue.
Stipple the first layer of mat into the resin with a paint brush - applying more resin. Stipple, don’t brush as this will disturb the fibres.
When the matt is fully wetted, leave it for a short while to allow the matt to take on a translucent appearance – indicating that it is fully wetted out.
At this point, consolidate the first matt with the roller - rolling from the centre out - to remove entrapped air. Ensure all parts are covered. As the matt is compressed, the air will be seen being removed and the resin will change from being milky to almost transparent. Remove any remaining bubbles by dabbing with the brush.
Continue laminating with all the other layers. Laminating should be continuous.
Don’t overlap at the same place each time as this will create a thick build-up.
Removal
Do not try to remove the piece for 36 hours - despite the temptation!
If necessary-
tap thin plastic wedges in the gap
tap the whole thing with a rubber mallet
run warm water in the gap between the mould and the finshed article to soften the PVA.
When/if the piece comes out of the mould - stand back and smile. Relax. Give your pulse time to return to normal. Have a cup of tea, you deserve one.
MIXING RATIOS
|
GEL COAT (RESIN B) |
CSM (RESIN A) |
||
|
Catalyst |
Resin |
Catalyst |
Resin |
|
15cc |
1 lb |
10cc |
1 lb |
|
7.5cc |
8 oz |
5cc |
8 oz |
|
4cc |
4 oz |
2.5cc |
4 oz |
|
2cc |
2 oz |
1.25cc |
2 oz |