Epoxy resin newbie query

[Captain Sillyboxes]

Hi all.

I've never used epoxy resin before but needed to make a minor repair to the plywood rudder on my wayfarer - I'd removed a section where the water had got in and prepared a replacement piece of marine ply which fitted the gap. I'd also sanded down a few damaged areas and intended to paint a layer of epoxy onto these before revarnishing.

My local chandler gave me a small amount of epoxy and hardener in 2 Styrofoam cups with instructions to mix 2 to 1, I don't know what brand it was.

For the replacement patch I mixed a few ml, estimating the quantities by eye. Three days later in a warm room and the excess from that batch was still tacky so I assumed that its never going to cure, maybe judging ratio by eye was not good enough. So I removed my clamps to try again only to find that the patch has set rock solid. So in this case, the small amount clamped between two parallel wooden surfaces cured while the excess didn't.

Second attempt, this time to paint a layer of it onto the damaged regions. I took no chances and measured the quantities with a syringe to get exactly 18ml mixture, which came to just under 1cm deep in a plastic yoghurt pot. It was ~25° where I was working. 5 mins in and the resin in the pot started bubbling in an exothermic chain reaction, giving off so much heat that I couldn't hold the yogurt pot. A couple of minutes later and all the glue in the pot was rock solid, frozen into strange bubble shapes like an oversized version of the inside of a crunchy bar but not edible. The resin that I'd painted on before this happened seems to have cured rapidly but not so fast that it bubbles.

Seems a bit of a learning curve, does anyone have any insights as to what I did wrong or is it just a case of needing lots of experience to do it right?

 

[Motor_Sailor]

You've probably met two distinct issues with epoxy.

The first, is that the two components are reactants that need not only to combine in a fixed ratio, but also that every part of them must be mixed. With polyester fibreglass resin, all the reactants are already mixed and you are simply adding a catalyst to start the reaction. Once it is pretty well mixed, then the chain reaction will set it all off. With your sort of epoxy, every two molecules of the resin have to physically connect with one molecule of hardener.

So good practice for epoxy mixing uses flat bottomed and smooth sided containers with a (square ended) stick that can reach every corner. The stick also needs to be quite wide so it mixes without entraining too much air. You also need to scrape the bottom, sides and each side of the stick, or there will be a viscous layer that never 'joins in' the mix and when you run short at the end you will be scraping un-curable resin out of the pot.

The second issue is it being an exothermic reaction. In warm weather, as you've found, this can run away with you. The best thing is to pour your mixed epoxy out onto a flatter tray like container where the heat can escape without heating up the epoxy around it. Something like a yoghurt pot keeps in in an almost ball like mass with the greatest mass and the smallest surface area. Pouring it into aluminium take away trays can double your working pot time. If you think these tropical conditions are here to stay, then there are 'slower' tropical hardeners available. But never reduce the amount of hardener - you still need 2 molecules of resin and 1 of hardener to 'get it on'.

 

[macd]

That's a bit weird. The failure of the uncovered stuff to cure, whilst covered stuff did, suggests it was polyester resin, not epoxy. On the other hand polyester resin would dissolve styrofoam in seconds. What was the nature of the "hardener"...as runny as water or rather more viscous?

Whatever it was, it brings to mind an expression including pigs and pokes.

Mixing ratios, incidentally, are critical with epoxy: every molecule in component "A" has to find a mate in "B" and vice versa. Much less important with polyester where the second part is simply a catalyst. You're right, though, to prefer epoxy for the job you have.

Lots of good info on using epoxy on the West website.

P.S. Good info in Motor Sailor's post. I'd only add that with tiny mixes such as yours, the surface area to volume ratio is high anyway: it would have needed to be pretty damned warm for the reaction to run away if the mix was correct.

 

[Cockaigne]

Good advice from Motor Sailor and more information available here if you need it: https://www.westsystem.com/wp-content/uploads/User-Manual-2015.pdf

WEST is not the only epoxy available, and it's certainly not the cheapest, but it is readily available and the instruction manuals and videos are excellent

 

[Motor_Sailor]

Good sources of info:

West epoxy in the UK: https://www.epoxycraft.com

Main West Epoxy site including FAQs: https://www.westsystem.com/instruction-2/epoxy-basics/problem-solver-faq/

 

[Captain Sillyboxes]

> What was the nature of the "hardener"

It was somewhat viscous, like water that had a lot of sugar dissolved in it. Noted re importance of accurate mixing ratios, I am used to araldite which seems to work fine when mixed by eye. And placing it in a shallow tray makes sense too

 

[knuterikt]

Mixing ratio is important.
There are different types of hardener fast/normal/slow.
using a wide container will reduce heat buildup

 

[gjgm]

Some years ago did a day course on West systems epoxy, and in fact I was recalling as I used some today...
So, the ratio is 5 to 1
Question,.so what other ratios can I use..
Err... none its 5 to 1..and we don't mean 4.5 to 1, or 5.5 to 1.. or any other ratio...we mean 5 to 1...exactly. That is why we produce dispenser pumps to be dead accurate....
In small quantities this gets harder to get right...of course your epoxy might well be another ratio, as they do differ, but the message I got was be very accurate in the ratios or you will have a problem. You can get syringes or small scaled plastic cups (like 50 ml in size) to get that ratio right. These are pretty cheap to buy.
I have used a number of epoxies, and I don't think there is a major difference,personally, but I do tend to keep reverting to West systems even if it is a bit more expensive. They do various small packs for 20 to 30 quid...depending if you want fillers or fibreglass etc, and they do have plenty of info on their web pages. Their 20 page guide is excellent.

 

[William_H]

I find the description of exothermic reaction causing the pot to get too hot rather strange. That sounds more to me like polyester resin with far too much hardener. The hardener looks like/runs water for polyester. I know you are getting some nice summer weather a the moment in UK (we get that for 4 months every year) I have never known an exothermic reaction in epoxy no matter how hot the weather. Nor in polyester in small quantities. As suggested perhaps buy a new container(s) of branded epoxy and try again. Whilst yes it is important to get ratios correct I have always used just eye to judge 2 to 1 no problems. ol'will

 

[Motor_Sailor]

. . . I have never known an exothermic reaction in epoxy no matter how hot the weather. . .

It's extremely common in warm/hot weather as typical hardeners used in the northern Europe are optimised for 16 degree workshop temperatures.

From the West System website;

Epoxy Problem Solver – Overheating- Epoxy became very hot and cured too quickly

POSSIBLE CAUSES & SOLUTIONS

1) Batch too large:
Mix smaller batches of epoxy.
Transfer the epoxy mixture to a container with more surface area immediately after mixing.

2) Temperature too warm for the hardener.
Use 206 Slow Hardener or 209 Extra Slow Hardener with 1o5 Epoxy Resin in very warm weather.

3) Epoxy application too thick.
Appy thick areas of fill in several thin layers of epoxy.

 

[Budgiecat]

It's extremely common in warm/hot weather as typical hardeners used in the northern Europe are optimised for 16 degree workshop temperatures.

From the West System website;

Epoxy Problem Solver – Overheating- Epoxy became very hot and cured too quickly

POSSIBLE CAUSES & SOLUTIONS

1) Batch too large:
Mix smaller batches of epoxy.
Transfer the epoxy mixture to a container with more surface area immediately after mixing.

2) Temperature too warm for the hardener.
Use 206 Slow Hardener or 209 Extra Slow Hardener with 1o5 Epoxy Resin in very warm weather.

3) Epoxy application too thick.
Appy thick areas of fill in several thin layers of epoxy.

 

[Budgiecat]

Just browsing through this thread and thought it would be a good place to start. I’m making a couple of marine ply sand rudders for a Windrush Surfcat 14. I’ve cut them to a template and shaped them to the right size and profile. Now I need to decide how to treat them.
I’m thinking of applying some coats of epoxy resin to the wood (how many? Not sure!) followed by a coat or two of epoxy paint. The question is should I coat the rudders in glass cloth first or apply the resin straight to the wood?
Any advice here would be well received. One point to note is that the rudders are not likely to be submerged for any great length of time as the boat is stored in a garage. Will only be in water for an hour or two at a time.

 

[Hacker]

I find the description of exothermic reaction causing the pot to get too hot rather strange. That sounds more to me like polyester resin with far too much hardener. The hardener looks like/runs water for polyester. I know you are getting some nice summer weather a the moment in UK (we get that for 4 months every year) I have never known an exothermic reaction in epoxy no matter how hot the weather. Nor in polyester in small quantities. As suggested perhaps buy a new container(s) of branded epoxy and try again. Whilst yes it is important to get ratios correct I have always used just eye to judge 2 to 1 no problems. ol'will

We were restoring a Flash boat which needed 100ml of epoxy resin plus hardener for each panel. Mix was done on a scale so accurate. Weather wasn’t quite as warm as present. Every pot exothermed towards the end.

 

[howardclark]

Ok - done a fair bit of epoxy work on dinghys and my wooden boat and built a strip dinghy from cedar/ epoxy coated so I am a total expert on what did not work but still a beginner on how to get it right first time! I did go on a West Systems course which was very informative.

on the first point I suspect the epoxy under the repair was not fully cured but still set well enough for the repair to take. As long as any uncured resin is stripped off the top I would leave it and just apply a further coat of properly mixed resin as has been described and add varnish to protect the epoxy. If the varnish sees any uncured resin it will bubble/flake after a time.

for the surfcat rudders as long as they are made from marine ply and not left in water for extended periods I would not epoxy them. It’s really quite a job to get epoxy coats really flat & beautiful- just apply a good marine varnish. Personally I’m a fan of 2 pot varnish because it doesn’t flake and gives good protection though many find it fussy & expensivè. I believe it is a resin so accurate mixing is required. I certainly would not encapsulatè the rudders in glass - again not easy to do beautifully and unnecessary unless you plan running onto rocks!

hope that helps
Why does my iPad keep adding grave accents?

 

[Budgiecat]

Ok - done a fair bit of epoxy work on dinghys and my wooden boat and built a strip dinghy from cedar/ epoxy coated so I am a total expert on what did not work but still a beginner on how to get it right first time! I did go on a West Systems course which was very informative.

on the first point I suspect the epoxy under the repair was not fully cured but still set well enough for the repair to take. As long as any uncured resin is stripped off the top I would leave it and just apply a further coat of properly mixed resin as has been described and add varnish to protect the epoxy. If the varnish sees any uncured resin it will bubble/flake after a time.

for the surfcat rudders as long as they are made from marine ply and not left in water for extended periods I would not epoxy them. It’s really quite a job to get epoxy coats really flat & beautiful- just apply a good marine varnish. Personally I’m a fan of 2 pot varnish because it doesn’t flake and gives good protection though many find it fussy & expensivè. I believe it is a resin so accurate mixing is required. I certainly would not encapsulatè the rudders in glass - again not easy to do beautifully and unnecessary unless you plan running onto rocks!

hope that helps
Why does my iPad keep adding grave accents?

Thanks for the advice. I’m thinking of a painted finish. Can you varnish over paint? And if so what paint would you recommend?

 

[howardclark]

Technically I’m sure you can varnish over paint- probably an oil based varnish would sit on an oil based paint- but again I’m not sure why you would do it. The paint or the varnish is designed to protect the substrate so only one should be needed. Is the ply end grain exposed or is it capped somehow? When I’ve dealt with dinghy rudders they have always been solid wood -( those I’ve come across have usually been mahogany).
if the end grain is exposed I would be using several coats of varnish to completely seal it off and would probably sand and ‘top up’ each season.
if you use 1 pot varnish and there is any sign of flaking take it back to the wood and redo.

 

[Captain Sillyboxes]

I just noticed this thread was still active so I thought I'd give an update re the O.P. After just under 3 years the repair to my dinghy rudder failed and I've had to redo it. In the time since I started this thread I have used epoxy for many things and am now a bit more au fait with it. My mistake in the original rudder repair was to judge the ratio by eye instead of measuring it properly. Suspect I had too much hardener and this in conjunction with the warm temperature caused a runaway reaction. Now I use pumps to mix large (for me) quantities or medical syringes for small quantities.

 

[Ceirwan]

I have never known an exothermic reaction in epoxy no matter how hot the weather. Nor in polyester in small quantities. As suggested perhaps buy a new container(s) of branded epoxy and try again. Whilst yes it is important to get ratios correct I have always used just eye to judge 2 to 1 no problems. ol'will

Epoxy gets warm all the time, if you've used it semi-regularly I'm surprised you haven't noticed. Normally the small amount left in the cup gets warm, but in summer I once got distracted after mixing a full batch for a repair, when I came back the cup was literally smoking and too hot to touch.