Confusion about glassing

I am a newbie, building a Skerry, about to start glassing.

- The manual says (p. 65): Start with about 24 oz. of thoroughly mixed epoxy. Pour a puddle of epoxy on the center of the bottom panel.

- I know, from a memorable experience, that mixing a smaller amount in a cup (I think it was 8 oz) resulted in a very hot hockey puck. It got thick and hot, and it was useless.

- I called CLC support to ask about this discrepancy, and they said to mix smaller batches. Can that possibly be right?

So I'm looking for advice on the process of mixing and applying epoxy, and glassing in general.

14 replies:

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RE: Confusion about glassing

You're both right.

If you mix 8 oz and leave it in the cup while you work, you'll get the famous smoking hockey puck.

If you mix 24 oz exactly right and as soon as it's mixed pour it onto the glass and quickly spread it out, it'll work.

To do that with 24 oz, you need to have enough experience with mixing epoxy so that you'll know exactly when to stop and pour. Stop too soon and it won't set right. You'll have sticky patches that will never set. Go on too long and you'll have the smoking hockey puck.

Just to make things more fun, when to stop is also affected by the ambient temperature, the epoxy temperature, the stirring inplement, the shape of the container, your mixing style (whip vs fold vs stir vs ...), etc.

Once you've mixed enough epoxy under enough different conditions, you'll know how it all works and you can actually do 24 oz batches. I personally prefer 6 oz when I work (FWIW I've been using epoxy for 20 years).

Also, if you dump a 6 oz batch onto the boat, and spread it out a bit so that it has a large surface area to radiate heat with, you can mix another batch and pour that out, too, before the first batch becomes unworkable. That way you can work with a a larger combined batch and no hockey pucks.

That said, I find it easier to work with lots of small batches instead of a few big ones. Fewer drips and less chance of mixing up too much.

Have fun,


RE: Confusion about glassing

Hi geophile, 

 i am sure other's will chime in but yes, it's true.   the standard response to prevent things from heating up too quick is to work in smaller batches.  that said, i can appreciate the how odd that can sound especially when you have a lot of glassing to do. it's also particurly challenging to do this as we move into the summer months and if you are in warmer cliamtes.  so let me offer some additional ideas. 

first, you will learn and practice during boat building what you can do.  the factors in addition to how much epoxy you work with in one session that you can typically control that allow you to use larger quantities:

control the temperature.   work when it is cooler - early mornings are best for the lowest temperature of the day.  60 degrees is a great temperature to work at when you have a lot of epoxy work to get done.  you can also check the forecast and see if there are some cool 70 degree days coming and move your work to a cool day vs working during a heatwave.   fwiw, i always have a thermometer in my work area to have awareness of temperature.  over time, it has helped me learn what is possible.

control the chemistry.  if you are not working with slow hardener, seriously consider getting epoxy slow hardener to buy yourself time.

avoid keeping the mixed epoxy in small containers.  as soon as you mix epoxy, try to get it out of any container like a cup as soon as possible.  its a large mass of epoxy that can kick very quickly and dangerously (e.g., the smoking hockey puck).   getting it out and on the boat prevents this phenomenon.

learn to work quick.    learn to mix your epoxy quick and effectively....and learn to get it on the boat quick and work you can get your work done in whatever time you end up having.   having another pair of hands can help you work quickly.  but as important, just get used to timing yourself and be prepared.  by be prepared, i mean do everything in advance you possibly can to set things up so you are litterally going from mixing, to pouring it on the boat, to using your squeegee or whatever you are using to move the epoxy around without delay and in as short a time as possible.

consider a skim coat to break the work up into more manageable chunks.  a skim coat is a quick coat of epoxy on the wood with no glass.  oftern done a day in advance.   the skim coat fills the pores in the wood so that when you do apply glass, it wets out faster becuase the wood is already sealed.  it allows you basically to work faster once you do work with glass.  a skim coat has he added advantage of sealing the wood from outgassing.  in general (not withstanding my recommendation to work in the morning) to have high quality glass work, you don't want your first coat of epoxy on bare wood under glass to happen during rising temperature as the wood will blow bubbles into your epoxy.  so the skim coat allows you to work in the morning when the temperature is going to rise, becuase you have now sealed the wood.

anywa, i realize this is a long message.  but through mastering all these factors, you will sort out how many ounces or pumps of epoxy you can reasonably do at a time without something bad happening.   

during summer, last year, i applied all of these including drafting my nephew to focus on mixing while i just focused on applying epoxy and wetting out cloth.  so he dispense epoxy quickly and would mix (100 seconds) of 20 oz at a time and pour all the mixture on the hull, where i then moved it around and got the glass wet out.   we then reduced the size down to as little as 6 oz as we got towards the end of the work where i simply could not take as much epoxy at a time.

i hope this helps


RE: Confusion about glassing

Thank you for the detailed advice so far. This is FAR more complex and subtle than the manual describes. I'm going to have to figure out my strategy before starting, and then watch the weather. Fortunately, I have two uninterrupted weeks coming up, at my work area, (which is a couple of hours from where I live).

The skim coat sounds like a great idea. One more advantage of this approach is that it will give me experience in mixing and spreading a large volume of epoxy without the added complication of the fiberglass being present.

RE: Confusion about glassing

Almost forgot -- one more questions, regarding ventilation.

Based on the advice so far, it sounds like I'll be working with small batches. I'm thinking that I'll start with 3-4 oz. So mix, apply, mix some more, apply, .... That's a lot of epoxy. Is this safe to do indoors? My good weather work area has a large door to the outside, and I have a fairly large fan. Is that good enough? Or is glassing best done outdoors?

RE: Confusion about glassing

I've worked with MAS, WEST, and System 3 epoxies indoors. They give off no significant vapors so ventilation isn't needed. Can't speak for other brands.

However, keep in mind the hardener can give you allergies. Wear gloves, long sleeve shirts, etc. to keep from touching that stuff when it's either raw or mixed with your resin as you prep it and spread it on your boat.

RE: Confusion about glassing

Sensitivity is an individual thing. If I use epoxy, including the brands that Chenier mentions, in an unventilated space without a VOC respirator I get a nasty headache. They definitely give off fumes, though many less sensitive people can't smell them. So you might want to be on the lookout for strange smells and sensations the first time that you use significant quantities in an unventilated space.

If you're one of the epoxy sensitive folks, keep in mind that the allergy can also be triggered by inhaling the fumes as well as the fumes being absorbed by your eyes. Again, it depends on individual sensitivities. For the vast majority of people the fumes from modern premium epoxies like WEST, MAS and System Three do not cause problems, but until you know how sensitive you are, be on the lookout for trouble.


RE: Confusion about glassing

well ventilated indoors is ok.  but fwiw, i always wear a respirator with the carbon/vapor filter.   

to laszlo's point on sensitivity.....the following is on the MAS site FAQS:

Unfortunately, it’s possible to develop an allergic sensitization to any epoxy resin system. It is quite like the allergic reaction to poison ivy. The severity of the reaction varies depending on the individual and the amount of exposure. Some people become sensitized to the epoxy resin and others to the hardener. Take measures such as wearing nitrile gloves, Tyvek arm guards and an apron to prevent skin contact with the epoxy. If you do get some on your skin wash it off immediately with soap and water. It’s less common, but in addition to developing a rash from skin contact, severely sensitized individuals can also have an allergic reaction to vapors from the epoxy resin and hardener. Symptoms may include tightening of the throat and difficulty breathing. We recommend working in well ventilated areas for precisely that reason. If you must work with the epoxy resin in a confined space, wear a NIOSH approved respirator with an organic vapor cartridge.

RE: Confusion about glassing


Everything posted above is good advice for working with epoxy. Keeping your components at a temperature that leaves them thin enough to mix both thoroughly and quickly but not so warm that it reduces your working time is helpful. Having a thermometer in your workspace should be mandatory! You need to be aware of how your space responds during your working sessions, the better to plan your pace for using the stuff once mixed.

I'm an advocate for pre-coating raw wood & polywood also. Virtually eliminates the outgassing from porous wood when temps climb after coating. Once cured and sanded makes laying out fiberglass cloth much easier as there's no wood texture to grab the fibers.

Can't say enough about protecting youself from the chemistry of epoxy! It's not so much the resin that's the issue, it's the aggressive chemistry of the hardeners that you do NOT want to have impacting your body! Keep in mind that, once you're sensitized, it's entirely likely you'll never lose that sensitivity, which mnay mean even being in the same room with something that's been epoxied will trigger a reaction... long after that epoxy's cured 100%.

All those caveats extend to sanding it as well. Leave it alone before attempting to sand, at least 24 hours, and then wear that respirator and gloves when hand-sanding. The reaction that makes it so useful to us isn't 100% complete for quite some time, depending on the components you use and the temperatures it cures under. Unlinked hardener is present in under-cured epoxy dust that's maybe worsde for you as the stuff before it's mixed because it's so easily inhaled. Vacuum-equipping sanding machines to capture as much of the dust from sanding epoxy is highly recommended to reduce your exposure as much as you can along with that respirator of course!

And once last comment abiout the manuals: if they put everything into them about how to go about building a kit, the manual would weigh more than the boat being built! They're intended to be a guide at best. Filling in the 'holes' is where this and other forums is helpful in this Internet age. You have the collective experiences of hundreds of other builders to help once begin looking for answers to questions you may have.


RE: Confusion about glassing

(And youi can blame 'polywood' on a new Mac laptop's keyboard firstly, then the lack of an <edit> button here or I'd have fixed it by now, along with any other typos you might find. I know how to spell pretty well, find spell-check annoying enough to disable it. Enjoy your days!) 

RE: Confusion about glassing

I am a newbie also and am building a Shearwater 17 hybrid.  I will soon be starting work on the outside of the hull.  I like the idea of a skim coat to eliminate outgassing and making it easier to spread the fiberglass.

What grit sandpaper do you suggest for sanding the skim coat?

It sounds as if 24 hours is a minimum wait time before sanding the epoxy?  I am guessing 48 hours is better and would be sufficient with a 70 degrees build space. Yes?

Thanks in advance for your feedback.   

RE: Confusion about glassing

in general i do not sand the skim coat.

i ensure the hull is fully sanded and ready (as if i was going to go directly to glassing) and then use a yellow foam roller and quickly roll on a very thin coat of epoxy.   the purpose is just to 'wet' the surface......not make it glossy.... and just to plug the pores.  the wood after the skim coat, will just be slightly darker indicating that epoxy got onto it...and will still appear rough/flat.   if you are making it glossy,, you are using too much epoxy.

i then let the epoxy set, typically no more than a day, then move right onto glassing. any signficant sanding would only expose back to bare wood defeating the purpose of the skim coat.   

that said, i will run a gloved hand over the skim-coated hull (after the epoxy has cured) to ensure i don't have any rough spots due to a bug or some other contaminant getting into the epoxy on the surface...which could then hang up the glass.

below is a picture of a hull i am working on after a skim coat.  you can see it looks flat, not glossy.  

skim coats are also important when working with stains to lock the stain in place and prevent it from moving.   but the main advantage is when you do get to glassing, you work faster becuase now you are just wetting out the cloth vs wetting out the cloth and dealing with the wood simultaneuously drinking the epoxy.  so you are using less epoxy during the glassing process and it just goes smoother and more reliably.


RE: Confusion about glassing

   1.  sensitivity of fumes..........true modern epoxies vent less fumes, but they do give off vapors.  Yes you may have handled them for years with no problem, but you also may be alergic to them tomorrow. It is common for technicians to become sensitive after prolonged exposure.  Sensitivity develops suddenly and does not go away.  Wear the mask and the correct filters. 

2. I make epoxy two person task.  The wife with her nurse training mixes an exact mix each time. Each pump exact travel, each mix with the same number of stirs.    We usually work with the pumps and do either a five or ten pump batch. She mixes I spread. The "art" in this is in the spreading. Its easier with a consistant flow of mix. But I'd get tired and slow before a 24oz batch could be used. We can control mix time with small batches and work in a factor for old hands. 

3. hockey puck...........Make sure you have the proper mix ratio and "speed" for your hardner. 



RE: Confusion about glassing

   Thanks for the info, h!

I did just receive some rollers from CLC.  They are blue, not yellow, but I am assuming they are similar.  Didn't see any yellow ones on the website.

RE: Confusion about glassing

   I don't use the rollers much. I prefer a squegee. My last roller was white. They come in many colors. 

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