Water Resistant Finish

[Burkhardt]

I am building a poor man's sail boat from an inflatable catamaran/raft. For the rudder blades and daggerboards I am using 3/4" "Appleply" , i.e. high quality voidless Baltic Birch with maple veneer skin. It is not a real marine grade plywood, though. These parts will be immersed in water for a few hours at a time or maybe a day and then dry again for a week or two. Not much sun exposure other than the hours used on the water.

I am looking for a reasonable water resistant finish. What do the boat builders and outdoor sign makers here think?

I was wondering about Epifanes varnish but the multiple coats and long dry times suck. Could I just use a 2-part epoxy coat?

Thanks for any advice!

Example of the rudder blade:
IMG_2063.jpg

[coryatjohn]

System Three epoxy. The best epoxy for such a task. Their products are a bit more expensive but they have such a higher quality compared to others that it's worth the extra. To do a really good job, get some lightweight cloth and put a couple of layers over the wood. That will protect it from cracks and delamination. The cloth will be practically invisible if you do it carefully.

The problem with pretty much any other coating is that it's going to crack. Once it does, water will get in and start swelling the wood. Before you know it, you'll be making new parts and epoxying them this time. That's why boats are made of the stuff.

https://www.systemthree.com/

[Burkhardt]

System Three epoxy. ....

Thanks for the tip! I have never used their products. Indeed a bit more expensive but I don't need that much, anyway.
I ordered some of their low viscosity resin through Amazon.

Good idea to laminate glass fiber cloth at least to the submerged portion. Let's see what I got. I know I have some rolls of carbon fiber and carbon/kevlar fabric (probably for 20 years or so...). But I guess that would be kind of overkill and anyway cover up the pretty ply pattern.

[scottp55]

G. ,
Always like your Projects, but this one reminded me of my old boss Earl Baldwin.
Earl built kayaks and canoes...and even once tried hydrofoils on his 2 person open cockpit kayak(and finally got it to work..ONCE)
Always in competition with Old Town's designer Bart Hathaway "Black Bart" They were still designing custom boats to beat each other when in 70's in the Master Class
Earl was always playing with different things!

Benson Gray (great-grandson of Old Towns founder) was usually the prototype tester and was my age(so we raced against each other a few times).
I'll always remember him taking the culvert under Rt 95 on Pushaw Stream....and splitting a prototype early days kevlar boat into 3 pieces on the 6' drop out the culvert!
He's now into restoring old sailing canoes;
https://maineboats.com/print/issue-146/heirloom-canoe
I wonder what he uses?

Also canoe paddles have similar requirements, and best wood kayak paddle I've ever owned was a "Bending Branch" "Impression"....and have a few weeks on their canoe paddles Dad owned.
Their finish is in pic and link;
https://bendingbranches.com/faqs

I too was thinking of something like the Kevlar "skid plates" almost every Maine Guide's canoe has on the bow, on the leading edge of yours?

Make sure and post pics when done Gert!
scott

[coryatjohn]

I have absolutely loved working with the System Three products. Their epoxy sets slowly and once it's hard to the touch, can be sanded. Waiting more than 36 hours to sand will make the job a lot more difficult as the stuff gets as hard as Formica after fully setting. Before it's fully set, it can be sanded with a lot less effort. After it sets to the touch, you can hit it with 80 grit to remove high points. Wait another couple hours and hit it with 120. Then, when you have the right shape and all the crud knocked down, finish sanding with 400 and 600 wet. The result will be a satin finish that feels really nice to the touch and is both hard, waterproof and impact resistant. If you want a glossy shine, wait until it fully sets (about 36 hours) and use any waterproof high quality finish. It will stick nicely to the 600 sanded epoxy surface.

I've gone through many gallons of the stuff and have never been surprised or disappointed by the material characteristics.

[Burkhardt]

I have absolutely loved working with the System Three products. Their epoxy sets slowly and once it's hard to the touch, can be sanded. Waiting more than 36 hours to sand will make the job a lot more difficult as the stuff gets as hard as Formica after fully setting. Before it's fully set, it can be sanded with a lot less effort. After it sets to the touch, you can hit it with 80 grit to remove high points. Wait another couple hours and hit it with 120. Then, when you have the right shape and all the crud knocked down, finish sanding with 400 and 600 wet. The result will be a satin finish that feels really nice to the touch and is both hard, waterproof and impact resistant. If you want a glossy shine, wait until it fully sets (about 36 hours) and use any waterproof high quality finish. It will stick nicely to the 600 sanded epoxy surface.

I've gone through many gallons of the stuff and have never been surprised or disappointed by the material characteristics.

Great, that sounds workable. I am a little concerned fitting the glass cloth to the tightly curved 3-dimensional surface of the rudders and daggerboards but if it fails I can still peel it off before it hardens. I mean, the surfboard makers can do it so it is definitely possible.

G. ,
Always like your Projects.........Make sure and post pics when done Gert!
scott

Sure, will do. So far only a CAD rendering... but I hope to be done in a week or two.
This is an attempt to build a functioning sailboat for under $1000. I found an inflatable frameless cataraft intended for whitewater rafting for $499 on the Internet and a sail for a Sunfish dinghy for $175. Now add some spars, hardware and plywood and I guess I have a fighting chance. The rudders, daggerboards, rudder flanges, tiller arms and the transom are all cut on the CNC from Baltic Birch and bamboo plywood. The boat does not have a mast but rigid rigging like the "Flying Lateen" concept.

Cataraft3.jpg

Cataraft4.jpg

[coryatjohn]

The amount of curvature a particular cloth can handle depends on the weave. The typical plain weave, which is like regular cloth, can handle slight curvature and if it's a lightweight cloth, a decent amount. You can also dart the cloth (cut triangles out so that it bends without folding, just like making a shirt), and can get it to pretty much fit anything. A "twill" weave will take a significant amount of curvature before it starts to lift and bunch up. I've seen this grade advertised as "aerospace" grade for some reason. It's a bit more expensive than plain weave but it certainly can get the job done.

I suggest going the easy route and get a lightweight (4oz and under) cloth and darting it. The method I've used to dart is to lay the fabric over the piece, tape one edge with blue masking tape and then lay it flat as I can. Look for the bulges and where the cloth clumps and make a cut from the edge towards the center of the bulge until the fabric lays flat. Tape that edge and move around until you have the cloth laying flat. Then, trim the overlapping edges carefully. If you're going multiple layers, use this cloth as a template. Be sure to rotate the weave a bit so that the layers have different orientation.

If you haven't done a lot of fiberglass before, I recommend doing a single layer at a time. Once the resin is hard to the touch, look for bubbles and where the cloth has pulled up and cut them out with an exacto knife. Then sand with 80 grit and apply a second coat. You'll find it's a lot easier to get a solid coat if you do this. Once you get the hang of it, you can do multiple layers in one shot. I've found it can be easier to wet out the piece with resin before placing the glass. That way, there are no dry spots and bubbles are easier to find and work out.

The only special tool you need for any of this work is a 1-1/2" chip brush. You can buy all sorts of groovy tools for use with glass but the real work is done with a cheap, disposable brush.

Another little tip is if you mix more than 3oz, pour the mixture out onto your work piece rather than leaving it in the mixing cup. When it's in the cup, it generates a lot of heat quickly and that spoils the batch. You can mitigate this somewhat by continuous mixing with the chip brush.

You can pop the bubbles that are left on the surface with a torch by lightly waving the flame over the surface. The bubbles only matter if they're big. They usually self-pop and any marks left by them are easily removed with light sanding.

The best approach that I've found is to do one side at a time. Overlap the cloth to the other side and about 2" or so past the edge. Leave enough cloth so you can tape the edges of the cloth on the back side. Careful taping can really make the job of keeping the cloth from lifting around a sharp bend easy. Epoxy is not a set and forget material. If you see some glass pulling up at a corner, wait until the resin is firm yet still sticky and cover the area with kitchen plastic wrap, stretching it over the area with the problem. The plastic wrap will stick easily to the not cured epoxy and allow you to use your fingers and hands to mold the glass back to where it should be. Once cured, the plastic comes off clean, leaving a shiny surface behind. It's incredibly satisfying to pull what seems to be a failure back to success by saving it with a simple plastic film.

One last fun fact about System Three resins. They have virtually no VOC's. I apply them in my shop without any sort of respirator or special ventilation. The vast majority of VOC's that are emitted by their epoxies is an alcohol and it's something like 2% by weight.

Clean up with alcohol. Many use acetone, which works great, but is way overkill.

I could go on and on about Fiberglass. It's my favorite material to fabricate with.

[Brian Harnett]

I work with carbon fiber on occasion a bit stiffer than fiberglass I would vacuum bag if you have a pump that can pull at least 15 inches of mercury. No fancy bags needed I use clear hardware store bags wrap the item put it in the bag now wrap a piece of fabric like an old towel around the bag and put it in another bag stick the vacuum hose in the bag and it will suck it all down tight.

For applying the epoxy I like to use a bondo spreader. I lay out the fabric on plastic and squeegee it in. My first carbon fiber mountain bike I used this technique, I made two female molds did the main frame in two halves and joined them After that bike I started using bladder molds.I wish I had taken pictures of the process it was 19 years ago so I did not have a digital camera yet. I still ride that bike.

[Brian Harnett]

Another way of wrapping on smaller parts is plastic electrical tape, or shrink wrap.

[coryatjohn]

>> For applying the epoxy I like to use a bondo spreader.

Another useful tool... How would life continue without bondo spreaders? I use them primary for glue ups and thickened epoxy.