Making Small Fiberglass Parts...




There has been a small but obnoxious rain leak in the aft cabin of my small sailboat.
It looks like the source is where the outboard motor control cables pass through
in the cockpit foot well wall.  There was just an open hole there and the rain was getting in.

That ought to be easy to fix. It just needs a cover that will keep the rain out instead of funneling it into the locker.
But where would that come from?
Who has the right size and shape in stock?

I couldn't find exactly what I thought I needed, so I decided to bite the bullet and make it instead.

This picture is the end result.  Just a small cover to divert the rain water away from the hole in the wall.

This was made in one afternoon and evening - hand laid fiberglass...

Step 1:

First thing you need is a mold!
Use your imagination!
This one is a soda bottle (filled with water to hold shape)

Three layers of glass cloth were laid on and wet out with West epoxy.

West System has a lot of information on how to mix and use their resins
as well as safety precautions.  
Read the books and follow the directions. 
It's not complicated, but mix ratios are important - so get it right!

Step 2:

After cure, the molding is rough trimmed with shears.

Step 3:

Here the flange is being laid up.
Several short pieces of glass cloth (small scraps) were used to form the flange.
Then a couple more layers of cloth were added over the whole thing to cover all the edges

Step 4:

Wet out the covering layers and cover the layup with plastic wrap (epoxy won't stick to it).
The wood pieces press the flanges to make it nice and flat.

If I were going to make several parts like this, I'd probably cut a piece of plywood
into a "U" shape for this step, but for a one-off, just a couple of pieces of wood worked fine.

Then put some weight on the wood parts to compress the flange a bit while it cures.

Step 5:

When cured the plastic can be peeled off very easily - but the resin wicked up under it leaving a
pretty ugly surface. 

Don't Panic!

We are not done yet.

Step 6:

Rough trim to get rid most of of the excess flange...

Step 7:

Grind off  the excess resin that was clumped up by the plastic wrap...

Dremel tool with a 1/2" sanding drum.
Or just a stick with 60 grit sandpaper glued on one side?

Health warning - breathing fiberglass dust is not a good idea.
Wear a mask - and keep others away while grinding.
Also - vacuum up either while grinding (!) or immediately after.

Step 8:

Now we can trim the flange to final size and shape...

Looks a little better now, doesn't it?

Step 9:

Traditionally, fiberglass parts are coated with "gel coat", a wax rich polyester resin.
Gel coat is thick, heavy and brittle, so it doesn't take a lot of it.
But it provides excellent protection against UV damage from the sun.

It goes on like thick paint, and cures in a few minutes.

Once WELL cured, it can be sanded smooth (start about 220 grit for shaping
and 400 for smoothing. 

Lastly a touch of polishing compound on the buffer and - it's ready to go to work.

Step 10:

In this Instructible I made a part for a boat.

But the basic ideas and techniques can be used to make ANYTHING
from a blue water yacht - to space craft parts - to Princess Lea's slave bra.
Or?  A cover for a robot? 

Literally - just about anything.

What do YOU want to make today?



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    24 Discussions


    2 years ago

    Nice instructable, I have a boot too and will use your instructions to do new instrument covers as the old ones are almost falling apart and I don't think 3d printed ones would stand the mediterranian sun.


    2 years ago

    Outstanding! I do a lot of small boat repair and you have opened a lot more ideas for special molds... Thanks.


    4 years ago on Introduction

    nice work , next time use gloves , cause the fiberglass will leave red stains on your skin and maybe small burns .


    5 years ago on Step 10

    I am in the middle of a 1963 Sailboat Restoration, well versed at Expoxy, but this Post gave me some great ideas. I especially liked your side by side 'before and after' picture. As you know this is 99% ugly and that last 1% makes it beautiful.

    Thanks for Sharing, this was a great post.


    7 years ago on Step 10

    This is great. I have soo much west system just lying around and this gave me some inspiration to develop a fiberglassing tallent. I'm gonna go play around right now and see what i can make

    2 replies

    7 years ago on Introduction

    How about "getting fiberglass splinters out of your skin" for a future instructable :). This is really going to help. This will work great to protect the back side of speakers so shoving life vests into storage compartments doesn't damage them. Thank you!!!

    3 replies

    I use either duct tape or packing tape. The sticky side grabs up those glass hairs quite well, and cactus hairs as well. Very good job, Cavelamb.

    Using a really sticky tape has helped me romoved a few splinters in the past. Not getting them in the first place is best obviously.


    Reply 6 years ago on Introduction

    COLD shower! :)

    But the best advice is to avoid getting fiberglass splinters/dust/shavings on your skin.


    6 years ago on Introduction

    That is a beautiful piece of work, cavelamb! If we add your custom fibreglassing to the PVC inspiration we get from Thinkenstein, there're really no limits are there?

    1 reply

    7 years ago on Introduction

    I want to make a fingerboard for a ukulele. But i'll use paper instead of the glass cloth. That's another instructable, though.

    That's a beautiful piece of work. Did you use caulk to seal it to the bulkhead, or some kind of gasket material?

    4 replies

    Thanks for the paper idea-- I can think of all sorts of textured/fibers/printed papers that would create beautiful fingerboards!

    Take a look at these two 'ibles. I got the idea from them.