Carbon & Resin Q&A

I recently bought some carbon fiber cloth, the seller said it was:
3k 70 plain weave, 6 oz. .020 thickness

Is this the preferred thickness, weight, weave (figured twill is not best in thinking of boats I’ve seen) for hulls, fins, rudders, or what is the best? Does uni and bi directional carbon play into chosing cloth?

And epoxy, I use Fiberglast two part. Heard West Systems is best. Is it all similiar (ie: use hardener from FG for WS resin)? Even saw some two part in hardware store for floors. Any preferences?

Guessing there is already a thread on this… (where, pls)
thanks, yar

YAR - do not mix epoxy products !!!

there can be a different ratio of mixing that will with most certainty mess up the batch. Stay with what you are used to using - a lot fewer surprises.

Uni carbon gives strength in line with the direction itis laid. As for weights - I don’t use the stuff finding little in cost effectiveness at the size/weight of our boats. Now on bigger sized stuff it starts to be inmportant. Then again, I am not the “Guru of Lightweight” as some want to be. Sorry - at $32.00 a yard here in US versus $5.00 a yard for glass … the results better be worth a lot more than a few ounces in weight. That said, I do use directional cloth for stiffness in hulls around the keel trunk. But to keep water out and air inside a hull, epoxy and S-Glass works just fine for me. If I need a bit more strength, I do keep some S Glass handy, but that also doesn’t become my hull.

Partly agree with Dick. The difficulty is getting carbon cloth that is light enough - otherwise you are just paying inflated prices to be vastly over-engineered. Carbon tissue at 16 g/m2 can be quite useful if you can get hold of it. IF you use very light cloths (assuming you can find them) you can end up with a structure that has a huge tensile strength but wobbles like jelly on springs because it is so thin that it has no panel stifness. Think sandwich.

When I used to build/repair big boats, I tended to use a family is epoxides made by Ciba-Geigy for making heavy use foundry patterns. They had the virtues of being sensinly priced (albeit in rather large packs for model use) and three, not two component - base. hadener and accelerator separately. This give you very good control of the pot life of quite large volumes of resin. Downsides were a colour like kippers (smoked fish, don’t know whether you have them) and highish viscosity.

Hope this helps

Would 6 ounce cloth be considered “light”?
How do you know you are buying uni or bi? Does it look different?

Dick, I understand your sentiment about mixing brands, but if they are both 3:1, are the actual materials different? Or is that a myth companies want you to believe?

I always run out of hardener first, would like to experiment with such available at hardware store.

appreciate da info.

Hardware store stuff doesn’t do a good job unless itis used only as a glue - and then is questionable. Had a guy make a hull (PeaPod - stitch and glue - and it ‘popped’ apart when sitting in his workshop about two weeks after build. The epoxy just didn’t get a good grip into the wood fibers.

Have not tried using 3:1 between suppliers, and might fool with some test samples first. Have a feeling it may be a “checmical makeup” kind of issue where resin and hardener aren’t compatible.

If you do try it - do it on samples and see what happens to heat, water, torsion, shear, peeling etc. forces.

It is not often that seriously disagree with Dick Lemke but …

I do agree that ‘tube’ epoxides of the 5 min type are useless. One of the useful characteristics of epoxide resin in a comporite matrix is its rigidity. Just think of the epoxide glue joints you,ve made hat were plastic to the touch long after they should have gone off. Enough said. (Yes, I know there may be environmental reasons but we’re not working in a climate controlled laminating shop).

You must not mix and match: epoxide rsin is a generic term for quite a wide variety of substances. Accordingly the make up of the base and hardner may differ - and in a two component system , God only knows where the accelerator is.

If you regularly run out of hardener, you are producing weak structures. Epoxides are precision systems. Unlike polyesters where you can add polyester ad lib, the ratio between the base and hardner components in a given sytem is very precise. You must use measiring syringes/pumps. If for any reason you cannolt do this, you are probably better off using polyester resins, which are infinitely more forgiving.

The carbon cloth: I don’t know the unit area you are comparing the weight with - but I guess it’s about 150 g/m2. Fine for building the Tirpitz!

Hope this is helpful

Angus -

It is not often that seriously disagree with Dick Lemke but …

where do we disagree?

I “opined” that mixing different supplier’s products was not a good idea and that while I had not tried it - doing some test samples might prove my opinion being wrong.

As for hardware brand epoxy packets/kits, we also seem to agree and I hate equating “good” epoxy products with cheap (not inexpensive) ones. I strictly use WEST Systems for a variety of reasons - professional trust in the product as well as personal friendships, and when one pays close to $50.00 (US) for a quaart of resin and a pint of hardener, it can’t equate to a $3.00 syringe from the hardware with epoxy resin on one side and hardener on the other - all controlled with a single push syringe handle.

Also I agree (though not specifically posted) that using a pump - or by weight/volume if that is preferred, it is hard to miss and wind up with a lot more of one than the other. I also admit it has happened to me, but having both slow and fast hardeners, it is difficult to determine if I was off on measurements when only one quart of resin was shared.

Sorry - but I can’t find where we disagree. Enlighten me please? :cool:

(all posted in a light-hearted manner, of course) Also, I concede there are other epoxy products out there - System 3, Maas, Raka, etc. all of which are excellent for marine building applications. In fact, I have used Raka’s brand for a single, strip-build canoe project, but I always seem to have a supply of WEST close at hand, and just continue to use it out of habit and convenience. I certainly didn’t mean to infer that it is the “only” worthwhile product out there. If it was taken that way, I humbly apologize.

Sorry Dick. Fell asleep in the middle of writing thatand reviewed thoughts (but not necessarily text) when I woke up. No conflicy. This is now The Party Line!:zbeer:

… and when one pays close to $50.00 (US) for a quaart of resin and a pint of hardener, it can’t equate to a $3.00 syringe from the hardware with epoxy resin on one side and hardener on the other - all controlled with a single push syringe handle.

Resin comes 32oz, hardener 8oz. At 3:1, I shoulda said I have extra resin, not run out of hardener. I need to buy the bigger size hardener but thi$ $tuff i$ killing me, with $hipping too.

Dick, I’m not talking about the syringes, though I use that epoxy for gluing parts, etc. They sell quart sized containers for construction applications. Would take a lot of syringes, and a lot of dinero, to cast a hull, as you indicate.

Thanks for the loads of good information here; various brands, text on precision helpful, and confirming that its best not to mix brands.


An older (2001) technical article I did for AMYA Model Yachting magazine about WEST System Products.

Sorry, but this Board wouldn’t let me post as .doc or .pdf file, so I had to zip it (4 pages) in order to reduce in size. You will need to unzip to read.

If you are using subsantial volumes, yo can measure into graduated ploythene measuring jugs - available from resin suppliers or your local kitchen store. As said before, decant into a flat tray. You should also mix mechanically - a bent coat hanger i an electric drill - to ensure thorough mixing and a consistent pot life. One hot spot can cut pot life by an amazing amount.

I don’t mean to alarm anyone…I used a particular brand of epoxy resin for the best part of 20 years. It works great…BUT I cannot use it anymore due to serious after effects health wise.I have done some research on this matter and have found my complaint is common amongst boatbuilders who have also used this resin for a period of time.
I am involved with a group of people who are trying to see what we can do about this.
I am not naming this resin for obvious reasons,but it should be obvious in the context of this thread.
Be carefull with this stuff guys…I really do mean that sincerly.

I now use other brands with no problems. My experience with this is not by accident or bad luck,there are many affected by this particular resin.

Dick,I know you will disagree with me and thats fine,just having my say and posting my warning.I will not discuss it further.

I agree with Brett.

Treat epoxidss with great respect. As you get older alergenic reactions get commoner. I have read somewhere and have some practcal confirmation from my own body that the lower the viscosity of the epoxide, the more likely yoiu are to have a reaction.

Note that sensitisation is for life: be carseful

Well, I’m not so sure it’s bad luck, Bret, unfortunatelly your is a normal reaction to a prolonged exposure.
Epoxies are toxic, the fumes are toxic when inhaled, but they (epoxies) also can be absorbed trough the skin, like many other compounds too (organic and inorganic), once they get in you, your system reacts against it like any other foreign substance (of comparable size), you build antibody against it, and once you reach a certain amount your basically immunized against it, and any other skin exposure could generate an immune/allergic reactions to it, reaction that could be mild as a skin rush or as bad as live threatening. Changing brands may help, but on the long run you may build immunity against the new brand too.

So, when handling epoxies, of any brand, always use gloves and protective clothing, the amounts we use in models are not large enough to require specialized respirators (but I’m using it anyway – one should be use – a dust respirator – absolutely when you sand dry epoxy no matter how much you sand – even more when you sand carbon fiber and epoxy), but the area should always bee well ventilated and never breath to close to the wet epoxy, in the pot or on the boat.


Oh, btw, I forgot to mention that exposure is cumulative, meaning it does not go away with time but the effects of exposure sum up, the more exposure, not just epoxy amounts but repeated exposures over time, the faster (and sometime stronger) the reaction.


I don’t think we answered your question re weight. It depends what you want to use it for. I agree with Dick’s comments re weight savings (or lack thereof) v cost of a carbon fiber hull. Having said that - I sail three classes - and carbon is not allowed in the hull of any of them - so what would I know?

I have used 6.2oz twill as the final laminate in keel fins. I believe that the weight standard for carbon cloth is a little different from other fiberglass cloths (i.e. based on a different area?) as the 6.2oz carbon seems light cf 6oz glass. Maybe someone can clarify.

I recently molded a new IOM fin over a light core using a laminate of two layers of unidirectional carbon laid at a slight and opposing angle off straight - about 10-15 degrees each way (the idea was to resist twist) and a layer of the 6.2oz twill, laid at about 45 degrees. Twill was unnecessary - it just looks good compared to regular carbon weave.

I’m yet to mount the keel bulb to the fin and measure deflection - but it seems to be “as stiff as”. The layup was probably overkill and is a little heavy. I did not vacuum bag the fin, but extracted as much resin as possible via sponging and then pressed the layup during cure.

I could not agree more with the comments re care in use of epoxy. I’ve been working with it since I was a kid (my family has always had boats) and these days my father has a reaction to it. I don’t - yet - but fully expect to develop a problem. I’m about the same age as Brett - and used a well known New Zealand brand for years, switching to a well know US brand later on. These days I go to considerable lengths to avoid skin contact with the stuff.

The other thing to watch is the dust created by sanding fiberglass or carbon fiber. In years gone by we were reckless about inhaling dust. These days I wear a dust mask - and sand out of doors it at all possible.

Thanks all, Muzza for confirming 6 oz is appropriate carbon cloth for rc yachts. And I was “avoiding” twill. Still unclear as to how I determine I’m getting uni and bi though.

You know, you (& D.L.) are right about the cost vs need for carbon vs glas. I admit to it being a bit of an indulgence I allow myself to be playing with the material that the best-of-the-best, full sized, performance toys (planes, boats, cars) are made of.

Went to my hardware store, the epoxy they have is System Three. In 3 types; General, T-88, Quickcure 5. In quarts, pints. Their web site includes marine and hobby as “markets”. I suppose General Resin is usuable yet I wrote them to see how they compare themselves with the other manufacturers listed in this thread.


Unidirectional looks and feels quite different from the woven carbon cloth (which is what I am assuming you mean by “bi” - i.e. with a weft and a warp). As all the threads run in one direction only, it is quite easy to tell apart. It has a different look and feel.

I agree that all epoxys are toxic and due care should be taken.
My point is that this particular brand is known to be worse in this regard than other brands.

Yes people please be careful, you really only need to do a few simple things to stay safe in my opinion.

[li]Go down to your local super box store and pick up a charcoal respirator for $30.[/li][li]Work in jeans and long sleeves that will be cleaned as soon as you are done.[/li][*]Shower as soon as you are done.[/ul]

T-88 is an adhesive. You should use the General Purpose resin for
laminating fiberglass cloth. West System 105/205 is comparable to our GP
resin with Hardener #1. Also download a copy of The Epoxy Book from our

System Three Resins, Inc.
Technical Support

I wrote System Three and they replied. Suppose everyone has their favorite brand, I might use what’s available in this very small town… yet West Systems seems to have a following.