Laminating Goof

bcooke · Post by **bcooke** » Tue Mar 23, 2004 9:05 pm

Hi all,

I haven't laminated much with epoxy before, so this one caught me for surprise. Maybe someone out there can tell me what I did wrong.

I was laminating strips of fir for a center frame in a Nutshell pram. I coated both sides of the strips with West System epoxy and clamped them around the form. I then left the assembly clamped up for about 36 hours in my basement which may be a little cool but not uncomfortable (60-65 degrees?). I took the lamination out of the mold and roughly dressed it into its final form. So far so good...

Then I left the assembly for about ten days and when I came back it seems the ends shrunk IN towards themselves. I had anticipated some spring back but I was not expecting the laminations to curve into themselves. Needless to say I scrapped the assembly and will start again. Anyone have an idea as to why this happened?

If I don't solve the problem I expect I will leave the assembly clamped up longer and screw a strip across the ends to keep them from creeping until they are installed. I would like to have the lamination stabilized and not worry about them trying to creep away after I start planking the hull. It could be embarassing to be rowing out to my boat with a full load and suddenly have the middle frame spring loose or curl up, separating all the planks at the midpoint.

Thanks,

Britton

Figment · Post by **Figment** » Tue Mar 23, 2004 9:17 pm

1st of all.... building a Nutshell.... very nice!

As for the reverse-springback, all I can speculate is that either the inner or the outer laminations experienced a drastic change in moisture content during the intervening ten days.

Were all the strips of the lamination completely encapsulated, or did something happen where the inner could breathe but not the outer? or vice-versa?

What kind of wood are you using?

I'm just shooting in the dark. I've done dozens of laminations similar to yours, and I've never had that happen. Don't toss it into the fire just yet. Hang onto it for a while and see if it creeps farther or springs back over time, or with changes in humidity.

Post by **dasein668** » Tue Mar 23, 2004 9:54 pm

Along the same lines as Mike's discussion, I would suggest that you would want to use well seasoned wood, too?less chance of weird moisture changes. Still, the whole thing seems pretty wild. I'm surprised that any wood you would get that wasn't green would have that much moisture...

Post by **Tim** » Wed Mar 24, 2004 8:15 am

I concur...it definitely sounds like you had a moisture-related problem with your wood. Make sure you're not using green wood, or wood with an otherwise high moisture content. Most hardwood is air dried to about 7% or lower moisture content, which is relatively stable and avoids this sort of thing. But you never know. I've had wood act strangely during cutting, but wood from a good supplier usually offers more consistent results than what you're describing. Fir is one of those woods that I think might have a better chance of being inconsistently dried, though. And it shrinks a lot, so this only reinforces the belief that it just wasn't dry enough when you used it.

You certainly left that assembly clamped plenty long at the temperatures you quote, so that's most likely not the culprit--and besides, it would want to spring outward, not inward, if there was a problem with that. Longer clamping won't solve the problem...you just need to ensure the moisture content of your wood to avoid this problem again. Basements can be pretty dry in the winter when the furnace is running a lot. Had the wood been down there long before you used it, or did you bring it down shortly before making your assembly? At a minimum, I would suggest allowing any wood you bring down there a good bit of time to acclimize to the conditions before you cut it or otherwise use it. Give the boards a chance to get used to the environment for a couple weeks (assuming it's not green wood), and your results should be more consistent.

bcooke · Post by **bcooke** » Fri Mar 26, 2004 7:28 pm

I thought the Nutshell would be a good, useful, project that could be completed over the winter months before I started on the big boat in the spring...

In searching around on the web I found very few builders of Nutshells that had problems with the frame. I am thinking it is a weird issue with the stock I was using.

The wood I was using was clear, vertical grained, quarter sawn, fir 2x4's. I assumed that most 2x4's were dried pretty severely and was more concerned with them being too dry. After cutting the boards into strips I left them for about two weeks. I had some trouble making the 1/8 inch strips bend around the form but I thought that would indicate being too dry again (a scattering of other builders have had bending problems).

Partly out of curiousity and partly out of frustration I stress tested the lamination to failure. I was concerned that I was using too high a clamping pressure and squeezing out too much epoxy. As it turns out it held it up quite well but it did fail first along a glue line (One end on the ground and me jumping up and down on the other end forcing the two ends towards each other). I am going to try a new source of fir this weekend.

Thanks for your ideas. I will let you know how it goes.

-Britton

Post by **Tim** » Sat Mar 27, 2004 7:50 am

Most dimensional lumber is very wet compared to cabinet-making stock. Given the type of wood used, I am not at all surprised by the result. Not only is it often very wet (though not to the eye), it tends to do weird things at random times down the road. It's just not a very stable material, as the wood tends to be low quality cut from young, quickly-grown trees. Probably not the best choice for a bending, laminating situation. Live and learn!

I'm sure your "stress test" would have been amusing to watch from a fly on the wall perspective! I've never done anything like that...nope, never! ;<)

When laminating, use just enough clamp pressure to ensure squeezeout from all the joints, and also to pull the wood closely into the mold. The beauty of epoxy in this application is its gap-filling capabilities and strength; it only needs to be clamped so the joint comes together. (assuming a thickened adhesive mix)

bcooke · Post by **bcooke** » Sat Mar 27, 2004 11:10 am

Aha,

Well at least I feel better thinking I have learned the problem. I am off for some discriminating lumber shopping this morning.

So, Tim, are you recomending adding a thickener to the epoxy mix when laminating? I was just using straight West System out of the can(s). The strips seemed to pull up quite tight to one another so I didn't think I had any spaces to fill. My problem was getting the strips to pull tightly up to the form.

Thanks,

Britton

P.S. I am leaving the house now WITHOUT a wooly jacket!

Post by **Tim** » Sat Mar 27, 2004 11:22 am

I always thicken the epoxy when using it as an adhesive. If anything, it makes it stronger, but the main reason is for the gap-filling qualities--even though it looks tight outside, there may be smaller voids and inconsistencies inside. Also, using a thickened mixture means the glue stays where you want it. How much you thicken it depends on the application, but usually ketchup-mayonnaise is about right. For gluing, I use cabosil or plastic mini-fibers.

bcooke · Post by **bcooke** » Sun Mar 28, 2004 9:39 am

Thanks Tim, I will try that. So much to learn, so little time...

I spent most of the day chasing leads on the 5/4 fir I need. No one seems to have it anymore. I thought I would substitute but one yard worker seemed to think I would be better off being persistent and sticky with fir. I guess next Saturday I will venture further afield into N.H.

I stopped in at the Lowell's Boat Shop (makers of dories since late 1700's). The advice I got was to enjoy the process of building because it can be a long and frustrating journey to the finished product. So much for slapping a Nutshell together over a couple of weekends!

Now I am off to look at a late model Alberg 30. Not exactly what I was looking for but...

-Britton

Post by **Tim** » Sun Mar 28, 2004 11:00 am

bcooke wrote:The advice I got was to enjoy the process of building because it can be a long and frustrating journey to the finished product.

That's excellent advice. One should definitely not build (or take on a significant repair/restoration project) with only the end result in mind. It's easy to get hung up longing for the completed project, and therefore miss out on the pleasure of the building process. Doing so also tends to be highly frustrating, as all building projects take far longer than anticipated--particularly for us amateurs.

Relax and enjoy the process...otherwise it's not worth doing! I have to often force myself to slow down and enjoy what I'm doing, as I am also results-driven. If it weren't for all that pressure to keep good updates coming for all the websites, I might be able to go even slower! ;<)