Epoxy troubles

[hereselmo1]

Ok so I glued and screwed the keelson and the first chine yesterday. They were done a little bit apart so two seperate pots of glue had to be mixed. We are using boat cote with the glue/fill additive.

The keelson is glued on tight and the glue where it has squeezed out is rock hard today. The chine glue on the other hand is still very soft (and doesnt look like it will harden fully at all) and I am pretty sure it is going to spring apart when I remove the clamp (man there is some tension on that chine!).

So i figure either I just got the proportions of glue and hardener wrong or I added to much glue/fill additive.

So is it possible to add too much glue/fill additive and is it possible for that to stop the glue hardening? or is it more likely i didnt add enough hardener.

I mixed the glue hardener by eye in a platic cup but i cant see how it can have been that far off.

[Daddles]

Don't mix by eye in a plastic cup, you will get it wrong ... eventually.

I use electronic scales and do it by weight (I also use West but it's the same principle) but there are all sorts of methods by volume - quite a few were discussed in the last couple on months on this forum in some thread that I can't remember the name of but it's worth tracking down if you can because there were some creative and good ideas in it.

As for your current mix. Leave it for another day or two to give it a chance.

The standard line is that if you get the mixes a little wrong, they won't work and if you did two next to each other, they should both cure at the same time.

Experience with dodgy pumps tells me that you can get away with bodgy mixes but that you shouldn't rely on it.

Experience also tells me that sometimes the transition from feeling soft to feeling hard is very quick so it might be that your 'soft' mix is still en route for a successful set.

Cynicism suggests that epoxy can be like computers and deliberately stuff you around just to mess with your head :C

I've had mixes inexplicably take longer to set than I anticipated but have gone on to be successful - temperature and humdity both play a part. If you're moderately careful, it's unusual to have a mix not work however, pulling the clamps too early is unfortunately common so ... just wait until tomorrow before worrying about a 'soft mix'. :wink:

Richard

[hereselmo1]

Yeah I had been using the cup in cup method for larger quantities but it seemed a bit OT for the small quantity I was mixing. I will definitely do it next time.

On the plus sid eI just rechecked the pox and it may be hardening up as you said. It is hard to tell at this stage (it is still way to soft) but it does seem a little better than earlier in the day.

[Daddles]

On the plus sid eI just rechecked the pox and it may be hardening up as you said. It is hard to tell at this stage (it is still way to soft) but it does seem a little better than earlier in the day.

You get caught from time to time - the gunwales that are currently on the boat needed an extra day to set whereas they're normally ready the next day. That was in humid weather too.

Richard

[Boatmik]

It is rare that epoxy doesn't go off. The two main reasons when it doesn't are that it either has not been measured properly or it has not been mixed thoroughly in the containers.

The most convenient method for measuring (apart from pumps) is to use a parallel sided tin can - petfood/baked bean and use a stirring stick marked with different distances.

The epoxy I commonly use is a 2:1 ratio so I would mark 20mm from the end of the stick and then another mark 10mm further up. Or any such measure.

Best wishes
Michael

[labr@]

Yeah I had been using the cup in cup method for larger quantities but it seemed a bit OT for the small quantity I was mixing. I will definitely do it next time.

Small quantity could be a large part of the problem - my view is that the smaller the mix the more accuracy is required because an error of say 1g in 5 is 5 times greater than 1g in 25. There is also more effect from material on the surface of the mixing container that is not mixed as well.

I use a 1:5 epoxy so that exaggerates small measuring variations even more but by using an electronic scale I've never had the wrong ratio. The only bad batch I ever had was from being distracted and forgetting to mix it :doh:.

[Boatmik]

Good point Bob, I was going to write that but kinda got a bit slack! The glue stick marking method works particularly well with 2:1 ratio epoxy or other ratios with bigger volume.

[hereselmo1]

The quantities I am mixing up to glue one chine, a tim can would be way too big.

[Daddles]

The quantities I am mixing up to glue one chine, a tim can would be way too big.

Mate, get some electronic scales, you can do very small quantities quite safely and easily. One advantage of the scales over the other methods is that if you squirt in too much, it's not hard to work out how much and compensate ... though we're getting into really pedantic boat building here :rolleyes:

I've got lazy in my old age and just use the pumps and ignore the waste ... mind you, I use West so a 'basic' mix is roughly 1/3 of a 'basic' Bote Cote mix.

Richard

for those that don't understand the differences between the Bote Cote pumps and the West pumps:

West (5:1) uses one pump of resin and one pump of hardener, the hardener pump giving 1/5th the amount of goop from the resin pump.

Bote Cote (2:1) uses two pumps that deliver the same amount (roughly the same as the West Resin pump) so you have to pump out two lots of resin and one lot of hardener, a system that can lead to a bit of waste in small jobs.

[Master Splinter]

DIGITAL GEM 0.1 X 1000 GRAM DIAMOND POCKET lab SCALE - eBay, Scales, Medicine, Science, Business, Industrial. (end time 14-Feb-10 23:19:44 AEDST) (http://cgi.ebay.com.au/DIGITAL-GEM-0-1-X-1000-GRAM-DIAMOND-POCKET-lab-SCALE_W0QQitemZ250531665792QQcmdZViewItemQQptZAU_Business_Industrial_Medical_Scientific_Equipment2?hash=item3a54d9d780)

Under $10 including postage. Accurate to 0.1 gram. I have the identical one and they are great for small batches of glue.

[hereselmo1]

Ok Ok i get it i bought them! lol.

I am noe the proud owner of new digital scales that are currently somewhere in china.

[Master Splinter]

ooooh, geee, I wonder if I can get a percentage of that sale... (actually, looking at the listings there just cost me some $11 for three power supplies)

[hereselmo1]

By the way do I need to allow for the density difference between the epoxy and the hardner or do I just mix it 2:1 by weight?

p.s. the Pox is much harder but I can still dent it with my finger nail. looks like I might have to pull it apart again. I will take some pics when I do.

[MiLKey]

I got out my epoxy stuff this afternoon ready to do some gluing, i got the bote coat stuff, with the pumps, but the pumps dont screw onto the bottle of resin or hardener...
I used them anyway hahaha
Mike

[Daddles]

By the way do I need to allow for the density difference between the epoxy and the hardner or do I just mix it 2:1 by weight?

Nah, just mix it 2:1.
Similarly with West (though you use 5:1 there :doh:)

Wrap some Glad Wrap around the scales too, or stick them in a bag or something, they WILL get poxy all over them.


p.s. the Pox is much harder but I can still dent it with my finger nail. looks like I might have to pull it apart again. I will take some pics when I do.Just leave it mate. Give it a few more days ... unless you want to clean it up and do it again.

Richard

[hereselmo1]

I wont be working on it again til Sunday week so I will just leave it till then and see what happens.

[labr@]

By the way do I need to allow for the density difference between the epoxy and the hardner or do I just mix it 2:1 by weight?


Well we're getting past mere "pedantic" and into the realm of "geeky" here now:D.
There are various data sheets available for these resin systems. The safety data also gives density and indications of the chemical composition (which can be handy if you want to assess whether a relatively unknown brand is using similar technology to the big names).

FGI (the brand I use) gives SG figures of 1.1 for the resin and .97 - 1.0 for standard hardener, 0.95 for slow hardener. This means there is a bit over 10% difference and it would be worth using that bit less of hardener when measuring by weight.

West quote the resin SG at 1.15 with different ranges for their hardeners: 205 = 1.04 SG, 206 and 207 = 1.0 SG, 209 = 0.98 SG. They recommend a mix ratio for 205 and 206 of 1:5 for both volume and weight methods. However for the 207 and 209 they recommend 1:3 by volume and 1:3.5 by weight.

I doubt this would affect performance significantly but someone using the volume ratios when measuring by weight could well find they always have resin left over in the bottle when they need to buy more hardener. It's a minor economic penalty.

The MSDS for Bote Cote only quotes one SG figure for the system: 1.12. If there is a need for different ratios between vol/weight then it should be mentioned in documentation provided when you bought the stuff. (...and if you're like me all you have to do now is dig the instructions out of the bin:rolleyes:).

One final thing about mixing small batches: I put the hardener in first. Why? Because it is easy to put in too much when pouring from the bottle ('cos I'm too much of a cheapskate to buy pumps). By taking note of the exact amount I can then put in an appropriate amount of resin. If I go over by a gram on the resin it doesn't matter as much as going over by that much with the hardener (remember the 1:5 ratio!). It always seems to mix OK as long as I remember to mix it at all.

Starting to get that deja vu feeling - have I posted this crap before? Anyhow that's enough geek for tonight - now you can forget it all and just get on with boat building :).

[Geary]

Most epoxy spec sheets list the ratio by volume and weight, since the densities of the resin and hardener are different.

My epoxy ratio (System3) is 2:1 by volume and 100:44 (I think) by weight, printed right on the bottle.

[PAR]

Seems at least interesting that System Three elected to use 100:44 when 25:11 would have been a little easier to work with.

[Geary]

I read the System3 bottle again yesterday evening ... it says 2:1 or 100:50 by volume and 100:44 by weight. I suppose people get less confused by parts per 100 compared to parts per 25 when measuring on the scale.

I started daydreaming and thinking about this thread when I was mixing a large cup of epoxy last night! After I finished stirring, I couldn't even remember if I mixed in the hardener! I decided to take a chance and just apply it on the boat. Luckily this morning the epoxy is hardening up. Whew.

[PAR]

This is a common issue with repetitive tasks. You'll find it's very difficult to remember if you use a turn signal, when you pulled into you street. You think you should have, but when pressed to actually remember the task you can't, unless you were spilling coffee in your lap at the time. Most of these things become "muscle memory" and your brain stops participating so much in the process and lets you body "remember" how to do it. This neat little trick of human behavior, permits the brain to focus on more important things and is a primary reason we can multi task.

[indiedog]

This is brilliant. Not only am I picking up lots of info re' epoxy mixes and boat building, but also excuses I can use for my fading short term memory. :)

[Boatmik]

This is a common issue with repetitive tasks. You'll find it's very difficult to remember if you use a turn signal, when you pulled into you street. You think you should have, but when pressed to actually remember the task you can't, unless you were spilling coffee in your lap at the time. Most of these things become "muscle memory" and your brain stops participating so much in the process and lets you body "remember" how to do it. This neat little trick of human behavior, permits the brain to focus on more important things and is a primary reason we can multi task.

Exactly .. and if wanting to accomplish higher level tasks like being a good sailor or piano player this needs to be developed.

I ran into the idea reading "Sail, Race and Win" by Eric Twiname - who writes marvellous books on improving your sailing - or wrote - he died quite young.

It is one of the few books that can improve both your sailing and your piano playing at one reading. Possibly helps with tennis too.

MIK

[PAR]

Sailing blind folded is also a great teacher. I use to do this a lot as well as moonless night sailing. It forces other senses to pick up on the subtle clues of sail trim, boat speed, wind pressure and direction, etc.

[Boatmik]

Twiname mentions this ... also he suggests trying things during races to see the effect and also to build skills. For example sailing the whole race with windward heel.

The point is to learn things that improve your future results rather than help you win the current race.

Also doing practice out of races doing things like slow spinnaker hoisting or tacking to work out where the slow bits are.

His books are a lot of fun too.

MIK

[hereselmo1]

Checked the epoxy this morning, hard as a rock. Might be OK after all

[q9]

As always, I'm a couple of days late...but here goes:


Epoxies are pretty fussy about the mix ratio. If in doubt it is better to err on the side of less hardener in the mix. Apparently the strength of the bonds is affected less having slightly less hardener, than having too much.

If a mix is taking it's time to go off (ie it gels but is soft) - mild heat to get the reaction going can do wonders. Not too hot, but if you can get a surface temp between 60-80 deg C you should be ok.

Patience pays dividends if the mix isn't 100%. It'll go off in most cases, but because of the incorrect mix, it may just take longer.

If it is really bad, and early enough (still jelly) - acetone, and lots of it.


I don't know if it makes me qualified to give the above "advice", but I worked in resins research for a Composite Fibre facility at the University, and talked a lot with the chief chemical engineer (who made some awesome stuff). I also did Lloyds testing of laminate samples...

[Boatmik]

Howdy,

Spot on. Only thing is that I would stress that if the epoxy doesn't go off it is almost always a case of not measuring properly or not mixing properly.

You can't trust the epoxy to compensate for sloppy procedure - though as per the third point - sometimes you get away with it when you shouldn't ... PHEW!

MIK