Fiberglass and epoxy are great materials for use on boat building projects.  They can be used to make a waterproof seal.

The wooden boat builders have found good use for these materials, and there has been a lot of development especially for that application.

From Youtube A Guy Doing Stuff

In this video I explain how I apply a fiberglass epoxy seal to the outside of my cedar strip canoe.

This is one of the most exciting parts of the building process but it’s also the most stressful and scary. There are so many variables that can affect how the epoxy cures (mixing ratios, temperature, timing, application technique, dust, unknown factors, etc.) – you should make sure you are very comfortable with the process before you start. Do a lot of research and it’s a really good idea to practice on some scrap beforehand – especially to get a feel for applying coats on top of previous coats.

Materials & Supplies:
6 oz, 60” wide fiberglass cloth
Ark Composites Resin and Slow Hardener – This is a 2:1 ratio. I ended up using almost a full gallon of the resin and a half gallon of the hardener. I probably won’t use as much for the inside of the hull because I don’t need that to be perfect.
Premarked cups with the ratios for mixing the epoxy. They also sell pumps that pump the exact amount so you don’t have to measure but I didn’t order those in time as I had to do this on a specific day to get people to help me. The pumps make it easier but the cups worked fine for me.
Stir sticks – just make sure they’re dust and splinter free
4” foam rollers
Friends – If you don’t have any friends this is a great opportunity to make some. It’s nice to have one person mixing epoxy and two people applying it. If you want to make this way harder on yourself you can film it too. It’s a real pain having to film everything you do!

We started at 5am. We applied 4 coats every 3ish hours – I finished applying the last coat around 6pm.
Roll the fiberglass out on the canoe and push the wrinkles out with a paint brush.
You have to continually mix small batches of epoxy as you work. Mix the correct ratio then stir for 2-3 minutes. The pot life is only about 15 minutes and the faster you get it on the easier it is to work with. After about ten minutes in a cup the epoxy will get thick and begin to get hot. It gets extremely hot if you let it cure completely in a cup. There is a lot of videos on youtube about two part epoxy – you should watch as many as possible.
Pour the epoxy on the fiberglass and spread it around.
I start near one end, work towards that end, then return to the starting spot and work towards the other end.
The end of the canoe is the most difficult part. For my first canoe I tried to fold the cloth over the end but it didn’t work very well. For this one I just work close to the end, then cut the fiberglass at the stem. There is no fiberglass on the ends of the stems but I did epoxy the bare wood.
It’s easiest to pour the epoxy on the middle of the boat then work it down. It takes some practice but it’s really not hard.
I pass over areas I did 20 minutes before to take off the excess epoxy to ensure an even coat.

The 1st coat is by far the most difficult and stressful. All subsequent coats are easier because the cloth is already in place. I apply them with a foam roller. I pass over spots after 20 minutes as I did with the 1st coat to ensure an even coat. I could have gotten away with 3 coats but I wanted to make sure all the fiberglass was completely buried in epoxy.

In this video I explain how I sand the fiberglass/epoxy seal on the outside of my canoe and how I apply a seal to the inside hull.