Yet another epoxy vs vinylester ...

What is the "open window" of your epoxy compatible polyester gelcoat? Is it ISO-NPG?

For the topicstarter:

Another solution to infuse epoxy behind a polyester gelcoat is to apply a skincoat (VE) after the gelcoat (CSM225, for larger projects even use 2 layers if needed). Use a peelply which releases well in this skincoat.

After removing the peelply, build your laminate and infuse with epoxy.

On the epoxy gelcoat (Sicomin or others). These do yellow over time, so are not recommended for products we are dealing with (boats). Modelling guys, tooling guys etc. however love them. We sell quite a lot.

 

Hi Herman,

as far as I know, the build an sale of the Farr 40 became a disaster due to the fact that despite using a VE skin coat between the epoxy laminate and outer gelcoat layers the hulls delaminated at the joint between the materials, so IMHO it is a quite risky and perlious attempt because it can become a disastrous failure.

You surely know better but it is a risk I would not get involved with, It would be like the russian roulet: a game I am not interested in

If anyone does as you have tested to be good which basically consist in using a peel ply layer that you tear off a VE skin coat prior to infusing with epoxy my question would be why bother doing all that ??? for the properties of epoxy ??? in case of the answer being yes then it should not be forgotten that to obtain the true mechanical poperties of epoxy it also has to be postcured, and yes it can be done relatively easy in a low temperature simple oven, but for the sizes of all but the smallest of boats the oven while simple, is a quite large object and even doing the enclosure with flexible isolating materials it becomes a quite large job so the same question arises again: Why bother ?? particularly when considering that the mechanical properties gains when choosing cured epoxy resin infused parts over infused vynilester parts can be so marginal.

This had led us to change our initial idea of using epoxy and now are going to use Vynilester instead ..............

 

We did a lot of testing, using UP gelcoat, VE skincoat, and EP laminate, for a couple of moulds that a client planned to make.

Our conclusion was that only with a peelply there was sufficient bond. Even with sanding, the bond was not perfect between the VE and the EP.

I guess (and it is not more than guesswork) that the Farr40 was VE skincoat, sanded, then epoxy.

As for postcuring: Once you get used to it, it is not that big a deal. A couple of heaters (Andrews Sykes), some tarp, and off you go.

As for using VE instead of epoxy: Sure, why not. A good vinylester should do the job as well. Do some testing to gain control over the cure time. And do not forget, also VE improves when postcuring. In your case, roll it out in the sun for a while...

 

One of my customers that specializes in making epoxy tooling says the cost of correctly post curing the tool can be as much as 30% of the total price.

The epoxy compatible gel coat is used like a normal gel coat, it does have better physical properties and water resistance than normal gel coat though.

 

There is no "normal" gelcoat. Against what gelcoat are you comparing? Ortho? Ortho-NPG? Semi-Iso? Iso? Iso-npg? VE? Epoxy?

And what is the "open" time? Loading a mould can take from a couple of minutes to more than a week.

 

The short answer is…

Recommended open time….60 minutes or so.

“Normal gel coat?” The vast majority of product we supply (and others in North America) is either ISO or ISO NPG.


The long answer…

For all practical purposes there are only two types of gel coat sold in North America, ISO and ISO-NPG. Ortho is history, although there may be some suppliers that still offer it. VE’s are special order only and are made in such low volumes many suppliers stopped making them. There are a few other specialty products, but the volumes are so low they wouldn’t be included in “normal gel coat”.

Recommended open time for this product is the same as other gel coats we offer, and is the same as recommended by most other gel coat suppliers in North America. In the proper environment gel coat is typically ready to laminate on in 45 to 60 minutes and for the best results lamination should start within the next hour or so, and we don’t really change this recommendation for product type. This doesn’t mean you can’t extend this time out, only that the longer you wait the more chance there is of experiencing some type of problem. What problems you may experience can be influenced by the type of gel coat, exact formula for that gel coat, catalyst %, ambient conditions (temperature, humidity and elevation), shop conditions, mold shape, skill of the gel coater, etc. We can’t control many of these variables so we always recommend lamination should start as soon as the gel coat is cured to the proper state.

After saying all that, we have customers that build everything from very small parts to 200’ yachts with our products and it’s not always possible to start the first layup in a few hours. In these extended time periods before lamination we always make sure the customer is aware of what we recommend and let them know they should test production methods in their shop to ensure the final quality of the product meets their needs.

I know you are aware of all this, I just go into detail for people reading the thread that may not have the same knowledge base.

 

Over here it is basicly the same, although a lot of semi-iso gelcoat is used, for various projects. For boats iso-npg is recommended, but many projects do not call for such a gelcoat. (interior work, etc). I presume your story above is targeted at the marine industry. Do you also serve other industries?

The 60 minute window is relatively short, if you are to be infusing a laminate behind it (at least for large projects). That is where skincoats jump in. Basicly to get a controllable bond, and to be able to walk in the mould.

 

Ondarvr can you post a link to the epoxy gelcoat, thanks,

 

I tried, but the data isn't on our website yet, we just did a major over haul and that updated info isn't in place yet.

I'll PM you a data sheet.

 

Can you copy me?

 

You need to PM me with your email address so I can attach it, I can't do it from a PM or email from this site.

 

Seems that I was completely underestimating the manufacturing constraints of composites.

 

Ok factory reps..

How does one find a solution to all these variables?

For infusion, looking for max strength / weight.. Doing glass / vinyl ester now.

#1 Idea, go to carbon as opposed to glass fibers..

But maybe vinyl ester can't hold on to the carbon as well as glass so maybe the strength is lost?

#2 Go to epoxy resin to get the grip back and more favorable mechanical properties.

But infusion epoxy looses much of its mechanical properties. So maybe we're worse off than vinyl easter? Which might be worse off than just going back to vinyl and glass?

Arrgh!!!

Is there a graph of this somewhere that can give us some idea to what the different magnitude of these variables are? I'm finding this impossible to solve in text alone.

-jim lee

 

Are you seriously thinking about carbon construction?

 

Yes I am, I'd always figured I could swap carbon for glass and perhaps epoxy for the vinyl ester. Suddenly everything would be lighter and stronger.

But of course there's that old, "its not as simple as it looks" deal cropping up again.

I have friends that do the carbon/epoxy thing, but they always use prepreg material. I was all "Ha ha! Wait 'till you see my infused carbon parts!" But then I read that vinyl ester doesn't grip so well to carbon. Not good, but no problem, the chemical companies make infusion epoxy I can still laugh and my old carbon friends! Alas no, infusion epoxy seems is not so hot either.

Good lord what am I to do?

In all seriousness one of the parts were looking at is a carbon rudder. The racing folk are yapping that they want one. It was supposed to be a quick formula swap. Ya'd think I'd learn by now huh?

-jim lee