See those horizontal join lines near the bottom of a few of the planks in the picture above? This particular foam is A550 offcuts from Noah's and it came from the factory with those join lines. While fairing the foam yesterday some of those join lines started to crack, especially where they were under tension from a mold curve. Arggh -- just what I needed. Anyway, something for the rest of you to watch out for. I fixed them by dremeling a small slot over the join, bogging it, then screwing the two halves back together with screws and small pieces of wood.
After dremeling the grooves between the planks yesterday, I went ahead and started bogging them as well. Unfortunately, the dweeb that's in charge of this project (that would be me) managed to run out of epoxy before the job was done, and it was too late to make a run to Seattle to get more. Thankfully my loving and patient wife agreed to be an HOV lane dummy this morning, so we could be at Fiberlay as soon as they opened (8 am) without having to sit forever in traffic.
I've been thinking hard about this practice of using bog between the planks, and I'm wishing I had explored the polyurethane approach more. The groove and bog approach has the following drawbacks:
- It takes a lot of bog, especially if you're using V-grooves like I am, which adds a lot of weight (bog is heavy). Henny grooved his planks in order to guarantee a good vacuum seal, but I'm doing it mainly because it's easy.
- It's difficult to guarantee that you've filled the groove 100%.
- If the groove is open to the back (e.g., if your planks are not perfectly fitted to one another) then you end up with squeeze-out, aka wasted bog.
- If you are filling gaps\grooves which are open in the back, then the bog has a tendency to settle as it cures. (I've learned that thixotropic means "resists gravity", not "immune to gravity".) Which means that after several hours, your carefully screeded bog lines are now bumpy, low valleys between the planks. This happened to me, and I ended up going back a second time to apply a thin skim coat over the bog lines to bring them back up to level with the planks.
- If you over-bog and leave it too high, sanding it back down is difficult (as always) without damaging the foam on either side.
Polyurethane glue would seem to fix several of these issues: it's lighter than bog (I think), its easier to trim off excess squeeze-out, it's cheaper than bog, and its foaming tendency would help to fill gaps. I think I will give it a more serious try, on the starboard hull half. I didn't do it on this one, because I had this image in my mind of dancing around with a plank-in-hand, with wet glue applied, and not being able to get it screwed down next to its mate in time. The groove+bog approach is easier in that respect.
If you are still dedicated to using bog but don't want to apply it as you're planking, I would suggest close-fitting your planks a small distance apart (maybe one or two popsticle-stick thicknesses), and not doing the dremel treatment - that way you only have a tiny area to fill with bog, to minimize the weight. Not that I'm an expert in any of this stuff.
Anyway, last job for tonight was the skim coat on the bog lines. Here's how it looks currently: