alternatives to epoxy

PL with screws = very good build. Worked on my hull. I would not do a large heavy boat PL build without the mechanical fasteners. Although I might use FG drywall tape and do some small row boat with thin plywood and PL.

The Black PL is so resilient and tough, it will yield, not tear free and will return to shape. I dont know if that would make a hull more like a rubber boat, say if you glued plank edges together with a small gap. Some people have complained that hull seams sealed with 5200, the 5200 pops out of the seams, but that could be dirty old plank seams, or just a wedge seam so naturally will want to fall out. We have some planked deadrises here where people have used 5200, but the 5200 runs across a fully flat seam the entire edge span like a cushion so is on both inside and outside filling the entire seam and that has never fallen out of their boats. Also 5200 is a very hard durometer rubber, the black PL is softer so it yields, so less likely to tear itself free from wood when it moves.

Anyway, I have had success with my technique of PL premium in the seams and sealed on the outside with Sanitred Permaflex and also Black PL.
Some doubted it would stay on the wood, but it did and it still does.

 

PAR- glad you chimed in.

" Construction grade adhesives are designed to work with static loads, so they don't need a very good elongation modulus and creep can be controlled with metal fasteners. So, if it's used as intended, to hold plywood to a floor joist for example, it's great stuff.

Now, if you take the same floor joist and plywood combination and start twisting and flexing the assembly (like a boat underway will), this is where the downfalls of this combination start to show up. "

I live in LA. We think about earthquakes. Doesn't PL have to have some sort of flexibility to be rated for construction?

Mt experience is that epoxy is hard and brittle. Are there 'softer', more flexible formulations that accommodate flexy ply structures?

BTW, can someone define 'creep' for me?

 

sdowney
"PL with screws = very good build."

I see that for your comparatively heavy plank boat.
But the stitch-and-glue crowd argue that fasteners actually reduce the strength of a filleted stitch and glue build. Why do they say this?

As far as hull building is concerned, I'm a belt and suspenders kind of guy.

 

https://en.wikipedia.org/?title=Creep_(deformation)

In materials science, creep (sometimes called cold flow) is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods, and generally increases as they near their melting point.

 

Heat can make creep more quickly noticeable, but does occur at room temperatures too (under load of course), which is the problem with many adhesives (and glues). Near here is a fellow that made a popular little sailboat, about 11' and did a birdsmouth stick. It's not a long thing, but he used PL on the staves and it turned out looking pretty good and worked fine, until he was caught by a thunderstorm. It wasn't a severe event, but winds went from 10 MPH to 20 MPH gusts and all the PL seams on his mast opened up. Upon examination, lots of wood transfer in the tears, but also clean shears too, suggesting the PL was pushed past elongation limits and it just let go. This is typical of these types of adhesives.

As far as Californian building codes, the floor joist, sheathing assembly is considered a homogenous unit once the glue cures. The structure it's treated as a slab, so they focus on the attachment of the edges, where stress concentrations will be highest. Their code will require bigger brackets to the rim joists and collars, any perpendicular abutments, cantilevers, etc. The same is true of "engineered" beams, joists, etc. - they're considered a single unit, rather than an assembly of pieces. Interestingly enough, their code doesn't permit screws only nails, even though all tests show screws being much more secure. The reason is only nails have been tested for their code and without verification of pull out figures on the various screws available, they can't certify them for residential construction!

I have no issue with PL for small, relatively low speed, low load craft. Once speeds get over say about 25 MPH or a highly stressed rig is employed, you need to consider what's the better option, in regard to adhesive performance. PL ounce per ounce is more costly than epoxy and as a coating, has very limited usefulness. Some have tried drywall tape, which just isn't very strong for seams. Just not enough fiber in these tapes and not very good ones at that. Also the dramidic modulus difference between the 'glass and the adhesive, means neither is well matched under load. This is the whole point to 'glass (or other fabrics) and resins and why epoxy works so much better than polyester. Simply put, when the 'glass reaches it's elongation limits, the resin is also nearing it's modulus limit, so you get the most from the combination.

 

PAR (and also JK) - thanks!

"Interestingly enough, their code doesn't permit screws only nails, even though all tests show screws being much more secure. The reason is only nails have been tested for their code and without verification of pull out figures on the various screws available, they can't certify them for residential construction!"

yet another case of the law being an ***.

 

And yet another case - an historical quotation being taken as unacceptable language. oh well...
from http://www.phrases.org.uk/meanings/the-law-is-an-***.html
This proverbial expression is of English origin and the *** being referred to here is the English colloquial name for a donkey, not the American '***', which we will leave behind us at this point. Donkeys have a, somewhat unjustified, reputation for obstinance and stupidity that has given us the adjective 'asinine'. It is the stupidly rigid application of the law that this phrase calls into question.
It is easy to find reference works and websites that attribute the phrase to Charles Dickens, who put it into print in Oliver Twist, 1838. When Mr. Bumble, the unhappy spouse of a domineering wife, is told in court that "...the law supposes that your wife acts under your direction", replies:
"If the law supposes that," said Mr. Bumble, squeezing his hat emphatically in both hands, "the law is a *** - a idiot".
In fact, 'the law is an ***' is from a play published by the English dramatist George Chapman in 1654 - Revenge for Honour:
Ere he shall lose an eye for such a trifle... For doing deeds of nature! I'm ashamed. The law is such an ***.

 

we will now return you to your usual boatdesign.net programming

 

Speaking of elastic limits, I read about this one guy that tied his *** to a tree and walked for miles.

 

heh heh

 

avoiding toxics with ply/glass

Like many of us, I'm getting to that age when I'm more concerned about exposure to toxic things- having been somewhat cavalier about VOCs, heavy metals and other nasties in the past So I'm wondering about avoiding epoxy as much as possible. Clearly for filletting and glassing, there is no substitute. I'm going to experiment with PL premium and weldwood (and resorcinol if I can find it) for scarfs and joints.

I wonder about sealing the ply - epoxy is usually recommended, but why not use polyurethane varnish (thinned?). Will epoxy bond to it well? - I know titebond3 does not leave a good surface for bonding. Any other ideas gladly received!

 

Polyurethane varnish is way down on the list of things that prevent moisture vapor from passing through it. Epoxy will bond to it, but why sacrifice bond strength with a contamination coat of polyurethane first. Anything thinned (varnish, polyurethane, epoxy, etc.) will be less effective at sealing stuff, because you've diluted it. The only reason you thin stuff is to get it through a spray gun without stipple, help flow control and self leveling properties, compensate for environmental issues and to improve substrate penetration.

PL and Weldwood cost more ounce per ounce than epoxy and require much higher clamping pressure and very precise joint faces, to be effective. These are the two major reasons epoxy is so hard to beat. Joint pressures need only to insure good contact, with the goo on the faying surfaces. Secondly, you can cut your joints with a hatchet, butter them up with epoxy, some very light pressure and it'll hold great, simply meaning any wood butcher can do it. Try that with the other adhesive choices.

 

For stitch and glue, I don't think you can beat epoxy. The cohesive strength alone when compared to alternatives will give you a clue why!. For just straight tight wood to wood joints, laminations, including ply panel scarfing I still use Urea Formaldehyde. Easier to clean up, glass clear, and strong enough ie stronger than the wood. Much cheaper too. Just remember to wash the Formic acid from the hardener off your hands...

If you really want to use a cheaper resin than epoxy, then polyester will do (as in stitch and tape) but it is far from ideal. However there are still many thousand Mirrors sailing about and they were built in the 60's and 70's mainly. I tend to use epoxy to repair these, if any joint areas start to let go. As for VOCs', I'd hazard that the styrene out of Polyester resin is not too good for you.......

One adhesive to really avoid is the old formula Cascamite, based on the whey in milk. I've lost count of the number of boats I've seen starting to fall apart due to the builder (pros included) using it.

 

Urea Formaldehyde adhesives can't tolerate immersion, though have some usefulness inside the boat, though I've never been able to trust them. Resorcinol formaldehyde is suitable for immersion, but as previously listed requires a thin glue line, only possible with very well fitted joints. I've seen both of these adhesives turn brittle and pulverize to dust, in highly loaded joint, given enough time. I use to use resorcinol all the time, but now have all but stopped, for the reasons listed.

 

Due to developing a pretty nasty epoxy allergy where I break out in hives when using it and have difficulty breathing, this thread interests me greatly.

I have done my own research on the topic and have found plenty of alternatives to epoxy that are working well. You just have to use the right stuff in the right application.

First, for coating wood, it depends where the wood is and what it's doing.

I use epoxy on all outdoor wood. Most of that outdoor wood is trim stuff like door frames, etc. These are epoxy coated, painted and glued onto my epoxy/corecell boat using hot melt polyurethane adhesive which is 100% waterproof and will tear up the bonding surfaces the same as epoxy does in destructive testing. That exposes my to isocyanates, but I far prefer working with isocyanates over epoxy.

Interior wood is all hot melt PU bonded, epoxied only at the hull joints. Interior wood is sealed with off the shelf "polyurethane" and it's holding up beautifully. Some is painted over the "polyurethane" some isn't. It doesn't get wet so it doesn't matter all that much.

I need to eliminate my exposure to nasty epoxy in every way possible and these techniques have helped a lot.

IDGAF if I have to fix up some little things in 10 years.At least I'll be alive to do it.