Need input from epoxy experts

[Chotu]

So, I’m having a little bit of a dilemma here. And I know my helper on the boat can read this so, it’s going to be a little awkward.

I need to settle a bit of a disagreement I am having with him. We have different opinions on how to work with epoxy.

First, the way I do it. If there are multiple layers of glass to put down, I do everything wet on wet. I start it, I keep going until the lamination is complete, and then I stop. My entire boat was built this way. My theory is that it creates complete cross-linking and makes for a stronger part. My other theory is that if you leave it overnight in hot humid weather, amine blush can take place, so wet on wet avoids this.

After talking to the epoxy manufacturer, my helper is of the mindset that you can put a couple layers down, then leave it overnight, and then come back in the morning and put a couple more layers down. I don’t like this at all. I am a perfectionist, we all know that, but am I being too much of a perfectionist?

Am I worrying more than I should about this?

I wasn’t as worried before when he was doing this with the forward bulkheads that hold the cross beam in place. There’s enough of them that go in a complete circle bonded to the hull that even if there was a little portion that wasn’t perfect, it would not cause any problem.

Currently the project is the composite chain plates that hold the rig up so my tension is ratcheted up quite a bit higher now.

Can I trust components that are made by laying down some of it one day, then waiting until the next day to lay down the rest? With no sanding? From what he says, he’s still able to press it with his fingernail. Which does mean a good bond, but it’s not a complete cross-link like liquid epoxy would be. Right? Or am I over thinking all of this?

Because it’s the chain plates, stress is at an all time high. These components are as important as when I made the cross beams that hold the hulls together.

[Rumrace]

If you were vacuum bagging a hull the best guys to ask is X Yachts in Poland.
As far as a glass cloth on a patch you have to let each layer set up somewhat. It’s not a wet laminate like which is interconnecting glass strands. Some folks accelerate the cure which Systems West will say absolutely no to.
If the layer is solid but tacky and very hot it’s ready. The next layer of epoxy even with dissimilar filler will stick and chemically bond. I layer on a canoe can sit over night for the next coat on .30 glass A wet surface makes the finer weaving like .30 & .40 impossible to lay properly.

So traditional fibreglass resin wet or it will delaminate. One time deal Fibreglass. Epoxy is the any place any time and will heat up to burn temperatures curing.

[pcmm]

My experience has been that if you can lay down all the layers at once, then its of benefit to do it that way. You are right then it is guaranteed to be a single unit layup (but epoxy is massively strong with secondary bonds so is OK too) but doing it all in a single layup is neater , less work and simpler. I've patched old through hulls with as many as 15 layers of biaxial and never had an issue with heating.

for chainplates I would prefer to build it in one session.

Amine's aren't an issue if you use peel-ply in your process.

[Chotu]

OK, I should emphasize that this is open mold work. This part is not vacuum bagging.

Just standard every day open mold.

The rest of the boat was built with resin infusion. But these are the last little parts being done by hand in open mold situations.

Note on peel ply: We had not looked at putting peel ply on the part between lamination layers. It never occurred to me because I had never stopped any lamination in the middle before. Also, this part is actually being made in a female mold that we are working with right now. So there is PVA mold release. Peel ply would not be applicable in this case. On the final product

[goboatingnow]

Polyester moulders will say as long as the glass remains “ green “ you can delay lamination and still get chemical bonding

[Chotu]

Originally Posted by goboatingnow

Polyester moulders will say as long as the glass remains “ green “ you can delay lamination and still get chemical bonding

This isn’t polyester. You can bond polyester forever if it stays exposed to air with no wax.

The question is about epoxy.

[Cheechako]

Last I heard ....to put epoxy over epoxy, you must sand it well if it hardens up, otherwise you need to laminate again while it's still tacky. ....?

Are there modern epoxies that dont need that?

[Chotu]

Originally Posted by Cheechako

Last I heard ....to put epoxy over epoxy, you must sand it well if it hardens up, otherwise you need to laminate again while it's still tacky. ....?

Are there modern epoxies that dont need that?

This is absolutely correct. But if you can dig a fingernail in, it has not hardened up and can still be bonded to. That’s the test.

My question is: Is it better to go full wet on wet, or if it’s just as good to wait until the thing hardens, but you can still put a dent with your fingernail, to add another layer?

[rslifkin]

Amine blush wouldn't scare me too much as it's easy to scrub off. I'd be mostly concerned about whether the epoxy is still green enough to make a good chemical bond or if it will need sanding for a good mechanical bond (which still won't be as strong).

[HeywoodJ]

Why not go straight to the horse's mouth?

Stage 2: Gel—Initial epoxy cure
The epoxy mixture passes into an initial cure phase (also called “the green stage” in epoxy chemistry) when it begins to gel or “kick-off.” The epoxy is no longer workable and will progress from a tacky, gel consistency to the firmness of hard rubber, which you will be [sic] dent with your thumbnail.

Because the epoxy mixture is only partially cured, a new application of epoxy will still chemically link with it, so the surface may still be bonded to or recoated without special preparation. However, this ability diminishes as the mixture approaches its final cure.

Stage 2: Solid—Epoxy’s final cure
The epoxy’s chemical reaction is complete. The mixture has cured to a solid state and can be dry sanded and shaped. You should not be able to dent it with your thumbnail. At this point in epoxy chemistry, the product has reached about 90% of its ultimate strength, so clamps can be removed. It will continue to cure over the next several days at room temperature.

A new application of epoxy will no longer chemically link to it, so the surface of the epoxy must be properly prepared and sanded before recoating to achieve a good mechanical, secondary bond. See Surface Preparation

That is also my understanding of how it works, so why risk it with a critical component? You know that the chemical bond strength will decrease as the state of cure of the previous application increases. Exactly where you are in that curve is a guessing game, fingernail test or not.

How hard is it to plan and prep your (your helper's) layups for small components so that they can be completed in a single session/day?

[Sand crab]

+1 on wet on wet.

[Sailor Sailor]

You should be guided by the directions for your particular epoxy. The directions for the cycloaliphatic epoxy I use (Aeromarine #300/21) does not require sanding between layers.

Here is the disadvantage to your approach:

Excessive heat from the exothermic reaction can weaken epoxy. Applying more than 3 or 4 layers at a time will cause continuing excessive heat buildup. It will kick and cure faster, but the bonds will be weaker.

Epoxy takes longer to cure with thin layers, so you have longer to apply those additional layers, maybe even a day or more.

Epoxy differs from polyester resin. Cured polyester must be roughed up before applying new layers. Epoxy is an adhesive.

[Chotu]

Originally Posted by HeywoodJ

Why not go straight to the horse's mouth?



That is also my understanding of how it works, so why risk it with a critical component? You know that the chemical bond strength will decrease as the state of cure of the previous application increases. Exactly where you are in that curve is a guessing game, fingernail test or not.

How hard is it to plan and prep your (your helper's) layups for small components so that they can be completed in a single session/day?

Well, seeing as how I learned from reading the giant , blue hardcover book that you are quoting from, that is my approach as well.

And I don’t like playing this guessing game on the chain plates.

He however, does not agree. He thinks it’s fine to leave it overnight and then keep going the next day.

That’s why I made this thread. In order to see if I could get some more input on this. Because the two of us don’t agree.

[rslifkin]

I would expect the concerns of splitting up the lamination could be reduced by using a slower hardener. The longer it takes to cure, the longer it'll be acceptable to walk away and come back later.

[Chotu]

Originally Posted by rslifkin

I would expect the concerns of splitting up the lamination could be reduced by using a slower hardener. The longer it takes to cure, the longer it'll be acceptable to walk away and come back later.

It’s the slowest Hardner in the universe. Raka tropical Hardner. But it’s also 95° there today and probably 75 to 80 at night.

And what we are talking about in our case is leaving it overnight. Quitting work at 5 PM or whatever and starting laminating the next day again at 9 AM.


This is from the manufacturers website @77F temperature:


Raka 260 Tropical hardener

The tropical hardener has an extremely slow pot life of about 45-60 minutes(3oz in cup at 77F). You will have several hours to work with the epoxy once you put it onto your project. At 77F this hardener reaches a hard finish that can be sanded in about 24-30 hours. This hardener does have a tendency to blush after curing and will require being sanded or washed with warm soapy water before apply the next coat.