Hello all,
My son and I are in the process of building a small dinghy. Our goal here is...well, just for the fun of it - and perhaps as a tender for our Weekender. We have the hull completed but have a few small "imperfections" that are going to need to be filled before finishing. Some of these repairs may be below the water line but won't be subjected to constant in-water pressures. This boat will not be glassed or have any epoxy. We will simply finish the boat with latex enamel exterior paint, since it is a quick build that will spend most of its time in the dry. The entire build has used about $8.00 worth of PL Premium for the glue. My question is this; do any of you have experience mixing fine saw dust with PL Premium for filling holes? I know there are air bubble issues but I have heard that these can be minimized when mixing in filler and working the air out of the product as it cures. Also, can you sand this stuff or will it just gum up the sand paper? Any other non-epoxy filler ideas would also be welcomed.
Thanks,
David
PL Premium doesn't sand worth a damn and definately will gum up sand paper. My usual practice is to scrape off any squeeze-out when it's mostly cured with a putty knife. Past that I use a surform shaper (or an auto-body rasp) or wood rasp to grind it off.
For a cheap build I would suggest you spend another couple of bucks and pick up a small can of auto body filler. "Yes" it's not very adhesive and "yes" it can absorb moisture, but you don't see it falling off of old cars very often after a hard rainÂ
 Mix it up in small batches and slather it on using a plastic putty knife. Again, a surform shaper or rasp will get rid of your worst mistakes quickly and without much sanding dust. A skim coat of filler after that will take care of any gouges you happened to make.
On the subject of paint - I've come to like the "rust" type paints. They generally have an opaque pigment, dry hard fairly quickly and last well in the sunshine. I don't bother trying to clean my brushes - I wrap them in plastic between coats and then throw the brush out after letting it dry - I feel that dry paint in the landfill is better than washed down paint in the water table.
Andrew,
I bought a can of Bondo the other day but was afraid to use it after reading all sorts of horror stories about boats with Bondo rotting, Bondo falling out in the water, etc. etc. Is it safe to say that most of the warnings against Bondo apply mostly to boats that spend their entire lives in the water? Or is it possible that the "don't use Bondo ever!" crowd are simply purists? I'm not trying to be a wise guy, just trying to figure this stuff out because I'm very ignorant on this whole boat building thing.
David
The reason Bondo or other polyester fillers, designed for automotive body work don't do well is because these products are intended for non-porous, stable surfaces. The metal of a car body is very stable and not porous, so it's fine there. On a piece of wood, particularly one that isn't encapsulated, the wood will change physical dimensions with moisture content. The filler can't expand and contact at the same rate so it shears at the contact point. This coupled with the fact it will absorb moisture from the wood, further decreasing it's ability to stick, plus several other reasons, are why it's not recommend, by experienced builders. It's not a matter of if it will fail, just when it will.
If you mix any filler material (except possibly a small amount of silica, which it already has in it) PL Premium will not stick.
Thanks for the input, Paul. It's great to have the experience of people in this forum to draw from.
So it sounds like I am probably going to need to go with epoxy. I am going to have to cross this bridge eventually anyway. I guess I'm just intimidated by the idea. Mixing seems to be somewhat of a science, from what I have read on the subject. I have nightmares of a smoking gloppy mess in my shop.
Thanks again.
Epoxy is easy. If you live in a hot area buy a kind that cures slowly. After you mix it pour it into a shallow container and only mix as much as you think you need at one time.
I'll second the epoxy is easy stuff. You can make it complicated, but basic epoxy skills are easy. Use a brand that has pumps, which makes dispensing accurate and easy. All the major formulators have DIY user's guides that you can download, so it's not very difficult to learn.
For the contrary view - I've got my little sailing canoe which I built over 6 years ago. It's luan bathroom underlay glued with PL Premium and faired with body filler. I have a couple of minor cracks along a seam in the aft deck otherwise it's holding together just fine. My mouse boat is 7 years old, built in a similar fashion and is also just fine.
Since I can't go out every weekend they sit outside under a sheet of plastic the bulk of the time so they are "protected".
I think you'll agree Paul that you are one of the "purists" and that I'm definately on the other side of the mountain from you ;D I will agree with your comments - I just don't think that they're anything to worry about for a cheap and cheerful build.
Thanks for all of the input guys. In the end I decided to go ahead and order the epoxy and some wood flour. Part of the reason for building this dinghy was to learn the basic skills that I would need for my Weekender, and epoxy is surely a skill I will need. I ordered West System epoxy and hardener from Jamestown Distributors - and I bought the pumps. I actually called and talked to them, describing exactly what I wanted to do and they were very helpful - even going so far as to talk me out of spending too much on stuff I really didn't need. I got the wood flour from Duckworks because they were cheaper (hey, I have to hold on to some of my cheap skate ways).
I am curious about something that Andrew said though; Andrew, you said that you used "auto body filler" on your canoe and it is holding up well. If this stuff doesn't stick to wood, as others here have said, how did you get it to stick?
Not to put words in other's mouths - the "doesn't stick" comments are more a "doesn't stick as well as other products".
The basis of an autobody filler is generally polyester resin mixed with filler (talc I think usually for autobody work). Polyster resin is not nearly so adhesive as an epoxy. Additionally, the comments that Paul made about the expansion and contraction of the wood affecting the bond are right on the money - I have a small section on the bow of my sailing canoe that I have to re-do the putty on every few years because the filler pops off. This is a section though where I have 3 pieces of plywood (sides and deck) meeting up with 3 pieces of lumber (stem and chine logs) and have a handle screwed on. Lots of pieces that could expand/contract at different rates.
I used this as filler for screw holes and for fairing on my Weekender which has been outside for a few years so far and have had no delamination issues to this date - considering that temperatures have varied from -35C to +35C multiple times I'm not too worried. Additionally, the boat sits on a trailer 99.99% of the time, usually covered up and there's a couple of coats of paint over the filler.
With that all said - home-made fillers based on epoxy will undoubtedly work better than this, just like stainless steel screws, marine plywood, and Harken blocks would work better than the other things that I've used too. But - I've got a nice little boat that I can play with and on that didn't cost me a lot of money so I'm happy - even if it won't last long enough to give to my grandkids that I keep telling my son that I need.