What causes epoxy to do this?

Mike at fiberglassite actually suggested a UV lamp, or, better yet, direct sunlight, to help accelerate the cure, so I've located a couple 24" UV lamps on Craigslist for cheap.

It's been sunny the last several days in Washington, so I have rolled it out of the garage to do the scrubbing and drying for several hours. Interestingly, the side that is still sticky is also the side that is facing north and in shadow and the sunny side is more fully cured.

At any rate I am feeling better about things; problem solving is the fun part...right?

 

Just FYI - a Craigslist UV blacklight definitely accelerates the cure of stubborn sticky areas! even in a cold environment.

 

Glad to hear you got something to help.

But if all is done right there should be no need to photocatalyze the reaction - it is normally a chemical polymerisation process?

A common mistake is to warm the resin - much better to warm only the substrate (Wood, Foam, deck, etc.)

When you warm the resin it will 'go-off' much faster, so people add less catalyst to extend the 'pot life' then the mix can be much less 'balanced' (this sounds like what you did and then compensated with the UV).

A better way is to use room temperature / cool mixing with more hardener, mix it thoroughly and use a flatter container to apply it from - the foil turkey tins are good as it doesn't build up its own heat and then go off half way through.
If you put it in a jug or pot there is much less surface area and the reaction can't dump its waste heat causing a rise in temp, leading to ever faster reaction, leading to heat and so it sets in the pot.
Though that works FOR you when the cooler resin mix is painted onto warmer surface as it does the same spiral and set much quicker.

 

Hey Andy, thanks for the reply.

I think the issue came about from a couple things:

The structure felt warm, but it was most likely cooler than the air temp. I should have made more of an effort to ensure that it was, in fact, quite warm. Next time I will put the electric heater in the boat and heat the fore & aft compartments and structure, plus use a heat gun before I apply the epoxy.

I actually over-catalyzed it by about 10%, but this particular brand of epoxy says it needs 10-hours of 77-degrees to tack-free. I'm not sure how this compares to other brands, but when I used it last summer in repairs it was slow-setting even then, so even though a 'medium cure' epoxy I suspect it leans towards a slower formulation.

While I had at least 77-degrees at application and maintained it for several hours, I didn't have the electric heater then to maintain temps (or at least slow the temp decay) and not wanting to leave a kero heater running unattended, I allowed the air & structure to cool to 50-degrees or less, overnight. I suspect that this might have stopped the cure process.

I warmed the resin (it had been in a cool garage) in a warm water bath to room/slightly over room-temp just to get the viscosity up to mix, and then spread it in a disposable paint tray before rolling it on, but honestly, I wouldn't be above accelerating things a small amount given the relatively small area I am working with in this particular application providing it doesn't significantly degrade the epoxies performance.

So, clearly, I need to get up early next time, start the heaters and get the air temps as high as I can, pre-heat the structure and try and maintain the temps as long as possible next time and run the electric heater all night.

Thanks, everyone, for your support & advice!

Curtis

 

That won't help. With epoxy part A and part B link. When the ratio is too far off you get the unmatched part a or b staying as goo. Hope not your problem. I got cocky and mixed a little bit of a and a little bit of b without measuring. Thought it was cured fine. When I sanded it turned to sticky gum and pealed off and ruined my sand paper. It was a pain.

 

That's most definetly the problem.. Epoxies must be measured following the instructions becouse the hardener must have something to react With. It's not a catalyst! Only way to do is to scrape everything away..
Sorry but that's about it, BR Teddy

 

Hi,

Can you clarify

Are you using a polyester resin - which is catalysed with a few ml/cc of clear, almost watery, MEKP per gallon, i..e less than 0.5 %

or is it an A + B combined in a 2:1 ratio vol:vol or weight:weight product.


Many places do indeed refer to the first one as 'epoxy resin' even though not strictly correct
It's like in England all vacuum cleaners are called hoovers, be they made by hoover, electrolux, dyson etc.

Cheers


Andy

 

He used a 5:1 epoxy, which if is 10% hot on the hardener side, he's way off the ratio and the batch isn't going to cure. It may harden to some degree but being off this much on a sensitive formulation means it's lost a huge amount bit it's physical characteristics.

Most epoxies can tolerate some couple of percent, one way or the other. This become problematic with higher ratios, where a little is a lot.

The unfortunate result is, you now have to remove this gooey mess.

 

Actually, this particular epoxy is 3:1, but at any rate, I have been much more precise in the measurement and am having much better results. I have noticed that very thin films are slower setting where the thicker films are setting up faster. Makes sense as a thin, scraped on sealing coat isn't thick enough to retain it's heat as well. One or two places where I noticed an errant drip was rock hard whereas the sealing film around it was still tacky.

 

I have had it happen once or twice to me too, always a mystery. I think the thing to take out of this is to always apply a thin solvent thinned base coat of epoxy on your surfaces if not using glass. This will test and seal the surface. The solvents it help it level out and if craters etc. still form, they are very very thin (maybe 3 -4 mils) and not so bad to sand off.

paul oman
progressive epoxy polymers

 

If the sealing coat is applied without any epoxy pooled on the surface, you don't need to do anything special or dilute the initial coat. The first coat on raw wood should seal the open cells and cut/torn fibers only. If the epoxy pools, you've got way too much in that area and it should be pushed to an area that needs more or is still raw wood. The end result should have a quite modest dull sheen, with some areas looking like they could have used more, but on closer inspection these areas do have goo on them, but it's sucked it.

Once this initial sealing coat cures, you can apply epoxy as you like, though the goal is uniform thickness coats.

 

Fish eye is still a problem...

Air temp: 85F Structure pre-warmed with 1500-w heater to/near air temp. This is after a sealing 'mash & go' coat of epoxy, blush wiped clean with warm water and clean rag, wiped dry and a light sanding with non-stearated sandpaper and no solvent wipe. Epoxy applied with 8" short-nap foam roller from Taps Plastics.

I'm really beside myself over this issue. Luckily, this is pre-glass and not encapsulation over what will be bare wood (I've seen that heartbreak in some videos...), still...

I'd prefer to assume it is something I have done, but I followed all advice & instructions precisely. (I might add that the tiny micro-bubbles have yet to burst after two hours). I'm thinking of selling my unopened gal. kit of fiberglassite.com epoxy...

The only thing I can think of is the age of the wood and the fact that it was previously covered with poly resin and glass. Who knows if the original builder used some preservative...? Though I have never heard of any issue with epoxy over previous covered surfaces other than poly doesn't stick to epoxy but epoxy will stick to poly.

 

How about a quick sanity check (I don't mean you should visit a 'shrink' though you may feel a bit like that's a good idea right about now ).

Can you repeat the process EXACTLY using a new piece of clean ply?

Same Sanding, same cloths, same acetone, same batch of resin, same method yada yada yada.

Now, if you get perfect results on the new wood, it tells you your technique, methods & materials are good.

Conversely if problem repeats on the new wood then there is something you're missing.



One of my pals was rebuilding a car and we had a small piece to prime - wiped the panel with cellulose thinners prior to spraying and cr@p... more fisheyes than the london aquarium.

He'd used the thinners can to support one end of the steering box while cleaning the bearings = nice coat of WD40 (water dispersing silicone oil) on top of the can - transferred to cloth with thinners, and thence to panel...

 

I agree, do a "base line" with a hunk of scrap. A sealing coat, then the same techniques used for the next coat, that you employed on the other piece. If it's the same (craters), it's the epoxy. I don't know a lot about Fiberglassite, though Paul might have an idea if they're just rebadging or actually formulating.

On the other hand, if the base line test comes up clean (lays down neat), you'll instantly know it's a contamination issue on the first piece your tried this goo on.

 

Kinda hard to pick in the pics but looks from over here that the "fish eye" effect is aligned mostly with the summer grain...... maybe imagination` but again hard to pick in that later pic with lighting that the lighter grained areas worse affected.... maybe like more porous areas sucked something up in the past.
Once I was fixing an old hyro.... horrible deadly thing & had to fish scale repairs in- thats unrelated but the boat engine had let go plenty of oil on quite a few occasions & old fastening holes had oil, tried plenty of washing etc. etc. & finally got those capped neatly with a thickened epoxy mix... like a 1mm thick broadknife application over the area & peel plyed it, come back & peeled the peel ply, came up good then.
Jeff.