lamination failure

[Richard Kagen]

I am trying to make some small laminated trays with mixed results. I did end up making an interesting (to me) adjustable jig that I will post pictures and details of later.

The problem is the glue lines are failing. I made my first (12 x 6ish x 3/4) blank out of Stepeli (1 1/2), cherry (3/4), maple (1/2), Black walnut (1/4) repeat maple, cherry, stepeli. First time I used epoxy (2 to 1 very thin) thinkened with cabo sil and several joint failed when I had and incident at the router table. I reglued with 15 min epoxy and still some joints are opening. Thoughts?

[Dave Richards]

Two thoughts come to mind. First, is it possible you are using too much pressure and driving the eopxy from the joint? Epoxy doesn't appreciate high clamping pressure. You shouldn't need to thicken the epoxy for a lamination glue up if the surfaces are smooth.

Some woods don't take epoxy well but that can be improved with a wipe down of acetone shortly before gluing. I would try that. Then coat both faces with epoxy--the thin stuff (Raka, West, etc.) with slow hardener and no thickener. Then clamp up with just enough pressure.

There was a fellow named Robb White who built wooden boats down in Georgia. He would impregnate the wood with epoxy by heating it and his shop to over 100°F, apply the epoxy and then cool the shop. Evidently this would cause the epoxy to soak into the wood.

You might give that sort of idea a go. Warm the wood slightly, spread on the epoxy and let it begin to kick. Apply another coat of epoxy and then clamp up the parts. You will end up with a better mechanical bond between epoxy and wood and a chemical bond between coats of epoxy.

[Richard Kagen]

I have done a lot of fiberglass work, including building a kayak, etc and the objective is always to get each coat as thin as possible. I really cranked the clamps to get the joints very tight as I assumed i would end up with invisable transitions between the shades and color of the woods.

[John Lucas]

[QUOTE=I used epoxy (2 to 1 very thin) thinkened [/QUOTE]

Some epoxies are meant to be mixed at 1:1....is yours?

[David Rose]

John is right. You have to use the mix that is stated by the epoxy manufacturer. Nothing else will work.

What is the purpose of the filler? It can be murder on cutting tools. The "sil" can be silicon (sand, basically).

David

[Richard Kagen]

The thickener was actual ez-thick from http://www.epoxyproducts.com/2_fillers.html the mix was correct and cured perfectly (in fact I made a classic trick, fake spilled cup (pics below). Progressive is a well respected source with great prices btw.

Using thickeners is very standard practice in wooden boat building to keep the epoxy from flowing out of the joints as the epoxies used tend to be very slow setting. Also, heavy clamping is also common.

I will try the wipe down with acetone and see how that goes. The black walnut seemed to be the worst.

[Dave Richards]

Good trick.

When epoxy is used as an adhesive, thickeners are added to make the epoxy gap filling. In the case of your lamination, I'm guessing you don't have any gaps. If you don't want to see the glue lines, you certainly don't want gaps. If you apply enough pressure to close up the space between pieces of wood, you most certainly would eject the thickened epoxy.

Try wiping as I said. Then coat the faying surfaces with straight epoxy. Let them sit for a few minutes so the epoxy can soak in. Apply another thin, even coat and put the parts together.

When I built my sailboat, I made the taffrail using layers of mahogany and maple. I epoxied the 1/4" thick laminations as I outlined in the previous paragraph. The form I clamped over consisted of a piece of 2" copper pipe in the center of a length of 2x6. The only clamps were at the ends. The copper pipe created the desired crown. It's been about 5 years since I made that piece and there's been no problem with delamination.

Good luck. Post some pictures of the laminated project, huh?

[Matt Calder]

Richard,

Two considerations. Did you give it enough time to cure? I used Raka epoxy to build a sailboat and I seem to recall the rule is 24 hours at 60F degrees or more. If it is colder, you wait longer. If it is real cold, it won't cure at all.

Second, did you get wax on the pieces? Perhaps you just waxed your table saw? That one is a stretch but I waxed my planer bed yesterday on some pieces I plan to be finishing today and I keep telling myself, 'clean those boards, clean those boards', so that voice said, 'hey, maybe Richard didn't clean those boards'. Annoying voice.

By the way, when I use epoxy for gluing, I mix it with wood flour. It is cheap, and can convert epoxy to glue, to filler, to putty depending on how much you use. And it is my understanding you -must- mix something in the epoxy to use it as an adhesive (I'm speaking of epoxy not explicitly sold as an adhesive, the big jugs, not the little tubes). There are mixtures designed for this (they contain mostly glass fibers I think), and there is wood flour. The flour is cheaper by far.

Matt

[Cliff Rohrabacher]

Some woods don't take epoxy well but that can be improved with a wipe down of acetone shortly before gluing. I would try that. Then coat both faces with epoxy--the thin stuff (Raka, West, etc.) with slow hardener and no thickener. Then clamp up with just enough pressure.

I'll offer something about that I have learned. Acetone is fine, so too laquer thinner. I prefer laquer thinner as it is more aggreessive lifts oils out from much deeper in the wood, evaporates faster, and more completely.

Acetone is less toxic but who cares, hey you aren't drinking the stuff and if you are planning on using gallons of it then you need commercial equipment to deal with the fuems anyway.

BUT the Cream of the crop when using epoxy is Naptha.
Naptha can actually be used to thin a wide variety of (not all) epoxies.
Another is Xylol.

Alcohol will destroy the catalyzing process and just wreck the epoxy. So to will most solvents so unless the maker tells you what to thin with ya gotta experiment.

But in both cases what I do to test it is simply to make some epoxy in a cup, stir in a little of the thinning agent I am hoping woll work and just let it set up.

If the thinning agent is a bust ( the wrong chemical) then the epoxy won't set up and it will be a gooey mess for days and days until you give up hope and throw it out.

Too much thinning agent is always bad - just like it is in paints but for different reasons.

So I use the same chemical solvent to strip the oils from an oily wood that I'd use if I were thinning the epoxy. Any residual solvent left in the joint ( and there is always some) won't interfere with the proper catalyzing of the molecular structure.

[Dave Richards]

Cliff, FWIW, I wasn't suggesting that he thin his epoxy. I only meant unthickened epoxy.

[Richard Kagen]

Wood flour, ez-thick (cellious?) and micro ballons. Next time I think I will try the wood flour. I have great luck with this epoxy even thinning it with acetone up to 50% to make penatrating epoxy that I use to finish carved cedar traditional greenland kayak paddles.