Thread: fibre glass

Originally Posted by Gags_17

hey guys
i dont normally wonder these parts of the forum but since this is a boat section and some boats are made of fibre glass and im working with fibre glass atm this would be the perfect place for my questions
1. how long should it take to dry?
2. i want it to be really smooth so is there something i can use to help with that before or after sanding?
3. is the a way i can speed up the drying procces?
4. what would you recomend the best way to cut it?
thanks guys

Howdy and welcome,

We are more focussed on wooden boats, but we use fibreglass too.

Often we use it with epoxy resins rather than normal fibreglassing polyester resins because the epoxy sticks to wood much better.
1/ The resin manufacturer is the only source for this information. BTW it is not drying - it is curing - a chemical reaction that links the plastic together. If using polyester you have quite a lot of control by adding more or less catalyst. With epoxy you can change the times with your handling methods as you cannot change the ratios.
2/ It also depends on the type of glass you use. If you use "Chopped Strand Matte" - short lengths in random orientation then the usual way to get it smooth is to use a mould which gives you one good face and then the other side is usually disguised.
The other option is to use woven cloths which are smoother, but you need more layers as it is thinner/lighter.
3/Speak to your materials supplier. and see 1/
You can also use heat, but there are risks of creating air bubbles as any air or vapour in the resin expands.
4/Scissors

Hope this helps. If you give us more information we can be more helpful.

Best wishes
Michael

thanks for the reply mate im using a pretty course matting with ongs strands in it. id say im using the polyester because on the can it ays how much catilyst to add depending on the temp of the day. im making a centre console i alleady made the mold and then put materil over it as a base and then coverd that in the resin then put the fibre glass over that and then aded more resin i hope that the right way to do it. im hoping to get it realy smooth so that i can get a good finish when i paint it probally gloss white, what toher info would be helpfull?

Gags,

I hope that you have a release agent between the wooden former and the resin coat. If you don't, you will have a dog of a time seperating the console from the former because you have effectively created a bonded polyester/glass skin over the former.

In order to get a dead smooth exposed surface, the normal production procedure is use a dead smooth female mold coated with lots of wax and release agent. The mold is generally in at least two pieces flanged and bolted together, so the mould can be dismantled around the finished part to release it.

The sequence then is assemble the mould, wax it to smooth and fill any minor gaps in the part (seperation) lines, coat it with release agent, (more coats is generally better), then apply a resisn gelcoat to the mould. Gelcoat is a variation on resin that is normally opaque, can be pigmented to suit, and can produce a fine surface finish. Once the gelcoat is set, the resin/glass amalgam is layed up inside the gelcoated mould and allowed to cure. For boats etc, other reinforcing such as timber stringers and engine mount beams, ply transom inserts, and even the ply floor, are then glassed into position to stiffen the finished hull before the moulds are dismantled from around the hull.

As you are working a 1 off, and have started with a male mould, your best bet for a smooth finish will be to apply a slightly filled resin (resin thickened with microballons) over your coarse glass layer, sand to get as smouth as possible, then apply a layer of very fine glass cloth as a finish layer, fill that and sand. You can very fine glass cloth (slightly thicker than tissue paper) at f/glass suppliers or model shops (there's one in Lilydale).

If you get to a decent finish stage and find the part is bonded to the blank, any significant force will damage the part before it seperates from the blank. In this instance you might find it better to keep the part and blank as a unit and use it to create a female mould that can generate the part you want, and duplicates later if desired.

Usually polyester resin will set in about 45 minutes, leave it overnight and it should be right. If it isn't, you've done it wrong and it's time to throw it out and start again. (don't try working with 'hot' mixes - that's mixes with extra catalyst - unless you have experience because it can set very fast!)

Chopped strand mat isn't all that good as a finished surface (unless, as has been said above, you have used a female mould and have a gelcoat - even then a layer of surface tissue is good to use before the CSM.

The car stereo guys who make their own custom subwoofer housings usually do a combination of timber formers connected by stockings/grille cloth that gets covered in resin and left to set, then it has mat on top of that, and then the final finish is done with lots of sanding and bog, and sanding, and bog, and did I mention sanding, and bog with a little extra sanding plus more bog? Oh, more sanding is good, too.

thanks for the rplies guys! the mold is set now and i sanded it and boged it then sanded again and bogged bout 3 or 4 times and it is pretty smooth allthough no quite up to what i want it to look like so i think ill get some really fine fibre glass matting as you suggested malb and then jsut put that over the top then sand and bog and sand and bog lol what sand would you reccomend the best for sanding the fibre glass.i learned my leeson realy quick about fibre glass splinters to