Fiberglass Shell Werplaats IDC

I'm a student at the West-Flanders High School (HOWEST). I study industrial product design and for one of our projects we have to make a tutorial for the first year students about how to make a fiberglass shell.

The first year students have to make a scale model of a chair and we make a tutorial of a prototype technique which enables them to make the scale model. We made a simplified fiberglass shell because the method remains the same regardless of the shape of the chair.

Clothing:
- safety glasses
- plastic gloves
- dirty clothes (overall)

Material:
- fiberglass mat (thick fibers)
- fiberglass fleece (thin fibers)
- polyurethane foam
- polyester resin & MEKP (hardener)
- polyester putty (paste) & hardener
- plastic cup (to throw away after use)
- paper towels
- cardboard

Tools:
- a ruler
- a pen
- sandpaper (P80, P180, P800)
- a brush (to throw away after use)
- wooden stick (scrap wood)

For cutting the polyurethane foam you'll need a band saw or a handsaw. Mark the outlines of the shape you want to make on the foam and cut out the block.

Now mark the side view on one of the planes of the foam block and the same for the front view of your desired shape. Next cut the shapes out of the foam block.

TIP: it is always a good idea to mark your centrelines. This will make your life easier and it allows you to draw the lines more precise on the block.

If everything went well you will have a shape that resembles more to the final form but it has sharp edges that have to be rounded of. To make that happen you will need to take some sandpaper and carefully round off the edges of your shape.

There are no methods to measure when you have the correct radius, you will have to do this by eye. The only thing you can do is mark the outlines of your radius with a pen or some tape.

First put some cardboard on your workspace because polyester resin is really sticky and will make everything dirty even when you work really carefully. Also put on some dirty clothes and protect your hands with a pair of plastic gloves.

Take the fiberglass and pull small patches out. Lay these out on your workspace so you can easily access them.

Take a plastic cup and pour a desired amount of polyester resin in the cup. Now pour the MEKP in the cup. The MEKP has to be 3% of the amount of polyester resin you have poured in the cup. The more MEKP you will put in to the cup the faster the resin will harden. That's why it's better to use small amounts of resin. Like this you will never waste to mush of the resin.
Now mix with the wooden stick until the the resin and the MEKP are nicely blend together. You only have 20min until the mixture is fully hardened.

In order to stick the first layer of fiberglass easier on the foam model it is good to put a layer of resin mix on the foam model.

Now the fun can begin. Take a piece of fiberglass an put it on the foam model, then put your brush into the resin and start dabbing on the fiberglass. Do not rub on the fiberglass because you will move the entire patch or you will pull it apart.

Dab on the fiberglass until most of the air bubbles are gone and the entire patch lays completely flat with the model. You will never get all the air bubbles out but these uneven areas will be sanded away after the resin has dried.

When you have put two layers of the thick fiberglass you can finish it of with a final layer of thin fiberglass. The thin fiberglass is applied on the model with the same dabbing technique.
The thin fibre is the last layer to apply and gives your model a nice flat and even finish.

When you are done you can throw away:

- the brush
- paper towel
- cardboard
- plastic cup
- wooden stick

Everything can only be used once because the hardening process will affect all the materials and tools you will use. So only use tools that you can throw away.

WARNING: the plastic cup in which you have mixed has to cool down before you throw it in the bin because the hardening process is a chemical reaction which releases heat. If you throw it to early in the bin it can start a fire.

When the resin and the fibreglass has dried for one night you can sand the fiberglass. Try to sand the fibreglass as flat as possible. For the flat areas I recommend to use a sand block. The best way to see if the surface has no more uneven areas is to put it under a light or just by sliding your hand over the surface. Using gloves is recommended because the dust and the fiberglass will dry your skin really quick.

The remaining uneven areas can be flattened with polyester putty.

When you are done with sanding you can draw the form of the chair and cut it out on a band saw.

After cutting the final shape you can sand the edges.

After all the sanding on the outside of the shape it is time to remove the polyurethane foam to sand the inside nice and flush.

The shell of the chair is finished or any other shape or size you have made. The next step that I will explain very briefly is to fill the little uneven areas with polystyrene putty and paint your model.

If you want to make your model perfect. You can fill the uneven areas with polystyrene putty paste. You mix the polystyrene with the hardener (also 3% hardener of the amount of polystyrene you have used). After mixing you apply the paste on the uneven areas. After the paste has dried you can sand the excess away.
You repeat this process until you are happy with the result.

Then you can use putty spray to fill the small holes and finish your model with a fresh looking colour of paint. Enjoy making some cool projects.