Today I’m going to start filling the big holes and gaps in the hull. I will fill them with an epoxy mixture. There is a little resin and hardener left over from the last canoe. This stuff doesn’t go bad, but the hardener does darken considerably over time. Even though it has darkened, it will still dry clear. Here is the old and new hardener for a comparison.
Any holes or low spots will haunt you later. When you fiberglass the hull any holes will trap air and cause bubbles to be trapped under the cloth. If there is too much air the cloth will lift away from the wood in that area. The good news is this mixture will take care of the problem, and not be very noticeable. The bad news is these hole patches will give you reason to sand again. Here is an example of spots to fill.
I also have a bunch of bad joints where the strips come together. This is due to not getting the bead and coves right. I find it really difficult to get these to meet perfectly. In a perfect world I would have two router table setups so I could try the fit before doing all the strips. But, this isn’t the case so it’s trial and error. I thought it was better than this but I guess not, so the only option now is to fill. Fortunately, as I said before, the fills don’t really show that much. So here are the long joints I am talking about.
Here’s the stuff needed to do the fills.
Here’s a quick rundown of the mixing. This epoxy system requires a two to one ratio. One part resin to two parts hardener. The pumps are a big help. Just pump the resin twice, then hardener once, a perfect batch every time. It takes time to fill gaps so I mix a small batch. One pump resin, half a pump hardener. You don’t want to just slide the putty knife over the hole, depositing the mix in the hole, you want to force it into the hole to be sure the hole is filled to the bottom. The last thing you want is to have air trapped in the bottom of the hole under the epoxy, it will rise up through it later and make a bubble. Also, you want to clean up all the extra material before you move on, this stuff sets up to be unbelievably hard. It takes a lot of sanding to get rid of the extra, and clean up around the fill. So, I did a bigger batch the first time so you could see it better. Two resin, one hardener.
Now to thicken it. All the fiberglassing materials, liquids, cloth, silica, and cotton, were purchased from Raka. This is the thickener, it’s called Fumed Silica. This stuff is really fine, ( thus the name silica, I guess) it really floats in the air if you thrash it around too much. You don’t want this stuff in your lungs.
Here is the first time you will need the cedar sanding dust I told you to save earlier. This helps thicken the mix, although you don’t need it for that, the silica will thicken it enough by itself. You want the cedar dust to give the mix some color. If you don’t add the cedar it will dry clear even with the white silica. First you stir the epoxy for about a minute. I have some small scoops I use. After stirring, add about half a scoop of silica, and half a scoop of cedar.
As you stir this up the silica will clump up. These clumps don’t get hard, and will break up as you stir.
If this is what it looks like after, you need to add more. you don’t want it runny.
This is what you’re looking for.
I would say the mix should be the consistency of peanut butter.
The book suggests a degree or two either side of 75, this seems to work well for me. I don’t like it that hot in the shop but what are you going to do. At that temp you can usually get about a half hour of working time out of the mix. I just spread the mix around in the pot and that disperses the heat and gives you more time. This is the first pot done. It will set up over night and I can peel it off of the pot and use the same pot over and over.
Before we continue I must tell you this. When I fill holes I tend to get out of control. There is really no need to use as much mix as I use. I just can’t help myself. I guess I figure if a little is good a lot must be better. The main thing is to clean up the extra before it sets up. You have to sand these spots when it’s set up (usually overnight), so I just sand the whole thing and you would never know I used that much mix. I guess what I’m trying to say is use your own judgement when filling. Maybe you will understand why I cover so much area. I think it’s quicker than trying to get just a small spot. Here’s some of it all done.
I’ve got one side done, and almost half the other side.
Tomorrow I’ll try to finish all the filling and maybe start sanding it. I won’t take anymore pictures until I’m done, All the filling looks the same. If I get it done I’ll post it but I don’t expect to. I won’t be in the shop on Wednesday, so it may be Thursday or Friday before the next update. See you then.
-- Jeff in central Me.