CPES Before Gluing ?

[JohnPlatou]

Should I use cpes before gluing new mahogany to new mahogany. If so how many coats? Glue to use expoxy, resoncinal, or 5200? Seems like expoxy would benefit most from cpes? Could hurt bond of 5200 and resoncinal?

[paul oman]

just an opinion here, but priming with a solvent thinned epoxy could either be a good thing or not so goo thing.

It would depend upon the kind of glue you're using. If something like epoxy which doesn't really 'soak in' by itself the solvent thinned pre-treatment would provide a stronger bonding surface.

If using a more traditional glue that does sort of soak into the wood then the solvent thinned epoxy primer would prevent that.

paul oman
progressive epoxy polymers

[Ian McColgin]

I hope for a sourse more scientific than anecdotal, but I've not seen an actual need for or improved benefit from pretreating with really thin stuff like CPES.

Not all epoxies are happy curing together and if you put down the CPES first to cure, you'll need to reprep the surface to get rid of the blush and make ready for the expoxy glue. Remember that CPES is a sealer, not a glue.

In areas where the presence of end grain can cause the epoxy to wick up into the wood such as a normal scarf joint, everyone starts with some unthickened epoxy on both surfaces. Some let it cure and sand, others just paint it one till it doesn't soak in any more, then add a bit of thickening to the batch, paint that on, and button it up. In my experience, the former does not produce joints superior to the latter.

End grain is the most radical place where a sealer coat, in that case more a soaker coat, might help. In normal along the grain laminations it will not increase adheasion between layers - done wrongly it can decrease adheasion. The CPES might stiffen the boundry layers of wood a little but it seems to me that it might also make them more brittle and prone to eventual failure. Just epoxy laminations ala the GoogeBros flexible amas have an apparently endless cycle, which pretty much establishes that such regular epoxy lams are about as strong as the material possibilities.

There is likely room for some very interesting application of CPES and such in highly exotic applications - that's from whence Smith came after all. I just don't see it in normal building.

I remain inordinatly fond of CPES as the perfect sealer on everything before painting or varnishing. Given its penetration, it makes bothering with various anti-fungals and such pointless as well. Marvelously toxic stuff.

[JeffH]

Ian and I seem to have posted at the same time and with the same ideas, but as his was a much more erudite post than mine, I'll let his stand ;) I'll just add that I spent the past week gluing mahogany with a bungh of other people who have spent a lot of time gluing mahogany, and so can say that Ian's conclusions are held to be pretty much true. I would steer clear of using CPES for anything other than for what it was intended...

Jeff

[Wild Wassa]

Originally posted by Ian McColgin:
"I hope for a sourse more scientific than anecdotal ..."

You have just given other people's anecdotals and you own. Just because you don't want to read other people's anecdotals doesn't mean that they are not more valuable than generic theory ... it wouldn't hurt to post a few photos of what you have actually done.

Well there is no point in me contributing ... I only use the stuff and only tell you what I actually find.

Warren.

[ 04-17-2005, 01:30 PM: Message edited by: Wild Wassa ]

[Bill Perkins]

Warren I think you've misread what I took to be Ian's self depreciating opening line . It's sleep time on your side ; check it in the morning and see if you agree .

[Wild Wassa]

Think what you like ... I'm really sorry that my life doesn't fit into your formula ... :D .

Warren.

[ 04-17-2005, 01:33 PM: Message edited by: Wild Wassa ]

[JimD]

I've never used cpes. Doubt if I ever will. My boats still float.

[Bob Cleek]

Yea, boats float without CPES... but for how long? LOL

For what it's worth, Smith's product literature recommends using CPES as a primer before application of epoxy adhesives. Theory is that it will soak into the wood deeper than the googe alone. The googe bonds to the CPES. Smith has, or had, a great little booklet on wooden boat repair using Smith's products. If it is still available, I'd strongly recommend grabbing a copy from Steve Smith.

I would NOT ever use CPES on surfaces that will be glued with anything other than epoxy. The CPES will prevent adhesives like resorcinol and the rest which rely on mechanical bonding from sticking to the wood itself. You'd only get as much "stick" as would come from the surface of the CPES itself, which wouldn't give you much.

[Ian McColgin]

Thank you Bob. It's been a while since I read Smith's material and I was not at all sure about his recommendation for other propriatary epoxies.

I really did mean my wish for science rather than, let us elevate from anecdotal to, non-systematic empiracle information.

Some sort of soaking is clearly critical with end grain or the joint will be epoxy starved. Other than that, how much does penetration or saturation matter?

I've no doubt that CPES gets in between the wood cells in a way that other epoxies do not. My fun with epoxy goes back to when the GoogeBros changed the meaning of the "S" from "saturation" so I've learned to notice when something is binding surfaces versus reaching below the surface. Like sex and love, the epoxy experience has quite a range.

But in good gluing, the glue itself does not fail. It's the nearby wood that fails. To the extent that it's the very nearby wood that fails, I accept that CPES could perhaps help. I've seen failures - really extreme stresses - that were down the middle of a lam, depths to which I've observed the solvents of CPES penetrating but not observed the epoxy structure itself. In cases like that, CPES would not have helped.

I've also seen times when a surface material like fiberglass stripped because the soaking of the wood under made tearing off the glued wood boundry easy. Again, perhaps CPES could help there.

I also think some forms of wood are well to be CPES'd inside and out and everywhere anyway - especially plywood but perhaps some other woods prone to easy water penetration and damage.

This is why I wish I had objective scientific information. My experience leads me to believe that done rightly, CPES is a very good thing but that there are many glue-up applications where the actual increased strength, longevity or whatever appears to be small, at best, compared to the cost in material and labor.

In the absence of such scientific information (which I imagine many epoxy engineers have under their own propriatary trade practices, especially in the aerospace industries) we amateurs need to share the anecdotes, what we've done and how well it appeared to work. Hopefully that sharing provides enough information that we correctly connect successful outcomes with actual methods, and don't have unexamined variables causing successes or failures.

[Seth Wood]

When Custom Pack adhesives was still supplying resorcinol I asked them about CPES. Their clear and quick answer: No. Wood to be glued with resorcinol should be clean and NOT primed with CPES or anything else; in fact, it should be roughed up with some 80-grit paper.

CPES as a "primer" for epoxy is a very different story because epoxy is a very different glue than resorcinol. I've epoxy glued with and without CPES with success either way ... though ask me again in 20 years which is longer lasting.

[Venchka]

Perhaps the best information would come from the Horse's mouth? I have spoken to the folks at Smith and they were always helpful. One thing for sure, you will have to coat again with C.P.E.S. just prior to applying the final finish.

Smith & Co.
5100 Channel Ave.
Richmond, CA 94804

Mon - Fri
8:30 - 4:00 pm P.S.T.
Sat
10:00 - 3:00pm

1-510-237-6842
1-800-234-0330

Good luck!

Wayne
In the Swamp. :D

[Stan C]

I tried asking the guy with the CPES display at his booth at the WB Show in Rockland a couple of years ago about CPES blush and he insisted it was never a problem cause the stuff was so thin that it all would just soak into the wood and leave the grain exposed. He didn't seem to see my point that no matter how thin the stuff is- if you completely saturate the wood then there will be a layer of epoxy puddled on top. He implied that I was the one who didn't get it.
So I just gave up without an answer to whether or not it was going to be necessary to clean off the blush and then sand wood that had been sealed.

SC

[ssor]

I posted this link a while back but it is worth a second look.
http://www.fpl.fs.fed.us/documnts/pdf2001/chris01a.pdf
It is concerning the strength of and durability of epoxy bonds in wooden aircraft structures. I know that we deal with boats here but making sure your homemade airplane doesn't come apart seems pretty important. :D

[Bob Cleek]

Stan, you got the right answer from the CPES guy at the show, you just didn't hear it. CPES doesn't "puddle up." It soaks in. There is no recommendation to remove "blush" from CPES in any of Smith's product literature. I've never done it and know of no one else who regularly uses the product who does. Nobody's had any problem. CPES was initially formulated for priming glue lam layups with regular epoxy. The thickened epoxy doesn't soak into the wood like CPES. When regular epoxy adhesive is laid over CPES within a day or two of application, the two epoxies molecularly bond to one another. This creates a two stage adhesion. The lower layer is CPES soaked into the wood and the upperlayer is the thicker adhesive. The company rep gave you the straight scoop.

[ 06-05-2005, 03:22 PM: Message edited by: Bob Cleek ]

[RodB]

I agree with Bob because if CPES does what its supposed to do per the literature and Smith and Co's speal....then it can only provide a better bond...

BUT

I asked Mr Smith this exact question when I first bought my CPES. I told him I was building an 18 foot stitch and glue boat with quality Okoume plywood (along with some other structural pieces of Honduras Mahogany and Douglas Fir) [like my sandwhich const transom...3/8 Okoume on the outside and Doug Fir nominal two by material (planed) as the core], etc.... and wondered if it was worthwhile applying CPES in joints before applying the epoxy...ie., did it buy me anything? At the time I called him I was about to glue in my transom to the side and bottom panels.

If I remember right, he said "he doubted it was worth doing and probably would not buy me a significantly higher quality bond in "new construction"..." which makes sense considering the extra time (one day ) and expense. Besides, if one uses epoxy correctly in bonding, the glue bonds are much stronger than the wood anyway, so this would most likely be overkill and thus a moot point.

It certainly makes sense that the deeper penetration of the CPES results in a stronger bond, but Mr Smith admitted it would be hard to justify its use under the parameters I had set forth.

I have used CPES in my "new construction" in places where I knew water would be trying to get in like prior to glassing of the inner surface of the bottom panels of my boat along the keel stringer... where water will drain and sometimes settle during use. I also used CPES in any end grain before coating with epoxy...such as the interior of the holes through my transom for mounting the outboard... or the bilge pump throughhulls, and the top of the transom after radiusing it and then glassing it with two layers of 6 oz cloth...etc.

It would be interesting if quality scientific tests were performed with and without CPES in joints...It could be illuminating .

RB

[ 06-05-2005, 05:38 PM: Message edited by: RodB ]

[Scott Rosen]

Smith says you should NOT use CPES as a "primer" for his tropical wood epoxy.

I've used it to treat old wood prior to gluing with epoxy, and I've had great results. But that was old wood. And there's nothing scientific about my experience.

I probably wouldn't use CPES to prime a glue joint on new construction. I don't see the point if you're using new lumber.

[Dave Lesser]

OK. So I am going to glue up a mahogany stem using 8 laminations, each 3/16" thick. My plan was to brush un-thickened slow WEST epoxy on both sides of each piece, then add some wood flour/silica to another batch before the first one set, spread some thickened epoxy on the surfaces to be joined, and then clamp them. Should I be using CPES instead to un-thickened epoxy to "prime" the surfaces? Or can I just use thickened epoxy without "priming" first?

[RodB]

SOP for gluing is apply unthickened epoxy to both surfaces of bare wood, let sit for 20 minutes or so to soak in, then apply thickened epoxy (thickened only with cabosil, no wood flour) to one or both surfaces and clamp her up.

With both surfaces coated with unthickened epoxy you don't really have to apply thickened epoxy to both surfaces, just apply plenty to one of the pieces and you will get plenty of epoxy spread out in the joint. Watch for epoxy to ooze out when you clamp the laminations, but don't clamp too tight.

By the way, some folks heat up the pieces to be laminated, then apply the unthickened epoxy...assuming they get more penetration.

RB

[Bob Smalser]

Originally posted by Dave Lesser:
Should I be using CPES instead to un-thickened epoxy to "prime" the surfaces? Or can I just use thickened epoxy without "priming" first?I think you'd be both wasting money and maybe even screwing up your work buying into this manufacturer hype.

1) CPES is expensive.

2) CPES has zero adhesive value.

3) H. Mahog is soft and child's play to glue.

4) Letting the unthickened epoxy rest for a while before spreading the thickened will accomplish the same thing as priming with anything. For a specific problem where you need deep penetration, then playing a heat gun over unthickened slow epoxy thins it to the consistency of CPES with the added bennie of being...voila...adhesive.

An exception is end grain, where Ian's double gluing is probably best....but if you are gluing end grain at all, you simply aren't building it right, because end grain ain't either a gluing or a screwing surface.

Whether you need to slop a coat of thickened epoxy in between the unthickened coats depends on whether you expect a gap or two to wind up between your lams after clamping. That depends on your wood grain/defects and your forms. For a first effort, I'd recommend the thickener.

And congrats, BTW...I'm delighted you're not planning to use Titebond. ;) Your work can be repaired when the time comes.

[ 06-05-2005, 11:47 PM: Message edited by: Bob Smalser ]

[Cuyahoga Chuck]

This thread has turned gluing with epoxy into rocket science.
Mix your epoxy. Brush some on straight. Add thickener to the rest. Apply same.
If you are finicky about color match you can use different colors of wood flour as a thickener so your glue lines will be close to or in contrast to the color of the wood being glued.
CPES again! Sheesh!
Charlie

[RodB]

Chuck and Bob are right, you don't need CPES. I would also say for most gluing purposes with epoxy, epoxy thickened only with silica (cabosil) is the preferred method...( I'm talking about pressed together joints, not fillets).
RB

[Lion]

Boy, does this go round in circles!

Is Smiths CPES a solvent? If so, the local very popular epoxy, Bote-Cote, has tested solvents and various epoxy combos on various timbers, including ply and they strongly recommend against its use.

Bote-Cote say best penetration achived when useing TPRDA (Timber Preservative and Reactive Dilution Agent - whatever that is!), 15-20% added to basic mix, which apparently thins it considerably.

Not tried either yet but have CPES on the shelf and am soon to start a ply,strip hybrid kayak.

So, is it a coin toss?; to CPES or not to CPES!!??

Lion

[Wild Wassa]

Key the CPES well, otherwise it sticks like wax to BP's epoxy ... I find.

I use both TPRDA and CPES (not in that order mind you). I use TPRDA because thinned with denatured alcohols (which are not reactive agents with BP's epoxy unfortunately), the structure of BP's epoxy will be weakened, if the thinners are not reactive agents.

Boat-Cote (BP's) epoxy will not adhere to CPES well, without a good scratch pattern ... then chased in by TPRDA (to thin the epoxy), then followed by a normal coat of epoxy, for best results.

Warren.

[ 06-07-2005, 05:22 AM: Message edited by: Wild Wassa ]