epoxy, hardenr, flour mix

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firestang
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epoxy, hardenr, flour mix

Post by firestang »

Hi all.
Well ive started a build of a canoe :)
I am now up to the point of getting the joints together and my question is this.

What is the ratio of resin to hardener to flour.
This is what ive tried so far.

Ive used a course wood flour from dust extraction from a saw, mixed the resin/hardener as in a normal mix of epoxy to hardener ratio. This has worked really well with the course and the test fillets have set nicely on the test pieces.

When i tried the same resin/ hardener ratio and added wood flour colected from sanders the mixture will not start to cure. Ive tried larger amounts of hardener, smaller amounts of flour etc the change the ratios, but no go.

Is there any allowances that need to be made at all?

Thanks :D
jem
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Re: epoxy, hardenr, flour mix

Post by jem »

What does the label on the epoxy say? The type of woodflour should not impact the cure significantly... if at ll.
-Matt. Designer.
OnkaBob
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Re: epoxy, hardenr, flour mix

Post by OnkaBob »

Fillers should not affect the cure time at all as Matt said.
The only time they might is if there is some contaminant in them but if you have collected you own carefully this should not be an issue.

A word on epoxy ratios - and I know someone will come up with an exception to this but I say it is a hard and fast rule - Always use the ratio given by the supplier for your brand of epoxy. This is not like polyester where cure time is adjusted at will by mix ratios. Most brands of epoxy are fairly tolerant of variation but tolerance is all it is - the best strength will be obtained at the recommended ratio and if the ratio is far enough off it will not cure. (This is how most of us know when we haven't mixed it right :( )

The 2 main things that go wrong in the process are
- not adding the part 2 epoxy
and
- forgetting to mix after adding part 2 (I've done that once - made a hell of a mess :roll: )
These don't happen often and you have had more than 1 crook batch so it's unlikely to be one of them but keep them in mind.

The main thing that I've found affects cure time is temperature and since we are at that time of year when seasons are changing I wonder if this is part of your problem. You don't mention where you are from but if you are in the southern hemisphere then the weather is getting cooler on average - although wherever you are there are day to day variations. Was the first troublesome mix done on a day that was cooler than the previous ones? If so this would have slowed things down and the next attempt could have been affected by varying the mix ratio.

As for filler ratios, I always mix the epoxy first then add sawdust or whatever a bit at a time until I get the right consistency for what I want to do eg filleting, gluing, end pour etc. Compared to the careful way I measure the epoxy this is really sloppy practice - but it always works.

Good luck with the build and I'm sorry if I've just told you a heap of stuff you already know :)
Cheers, Bob

Laker 13 - christened and slimed (just).
Laker accessories underway.
firestang
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Joined: Wed Apr 07, 2010 10:30 pm
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Re: epoxy, hardenr, flour mix

Post by firestang »

Thanks guys.
Its actually polyester resin so the amount of curing time relies on the mix of hardener.
You may be right about contamination as once enough flour was placed in the mix it wouldn't go off and if it did it went rubbery.
Ill keep playing about with it and figure out whats going on. I made a batch and tested some fillets today so ill check them in the morning and see whats happened, it was basically a glue mix.
Ill let you know if its gone off. :D
tx river rat
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Re: epoxy, hardenr, flour mix

Post by tx river rat »

On poly add hardner and mix well before you add the wood flour. The wood flour soaks up the hardner if you try to add it to the mix last and it will do just what you said.
Ron
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Re: epoxy, hardenr, flour mix

Post by Oldsparkey »

Working with the normal epoxy.........not the Poly stuff......Ron's the expert on the poly.

Back to the normal epoxy...........
I ...ALWAYS..... mix the wood flour with the resin and make it a little thicker then it needs to be. Then I add the hardener which thins it out and even ...... sometimes i have to add more wood flour to get it right.

The idea is the hardener sets the whole mess off and the clock is running on it ...... The better you can mix it with the resin then add the hardener the more time you have to work with it.

Chuck..
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Amateurs built the Ark...... Professionals built the Titanic
Visit some fine paddlers at The Southern Paddler
firestang
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Re: epoxy, hardenr, flour mix

Post by firestang »

Thanks guys, ill give that a go right now :D
firestang
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Re: epoxy, hardenr, flour mix

Post by firestang »

Well i gave it a go. Works fairly well however a couple of joins seemed to be a bit brittle. One or two snapped fairly easily when the ply was moved. Any ideas as to why?
jem
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Re: epoxy, hardenr, flour mix

Post by jem »

Someone else will have to comment on poly resin. Never worker with it.
-Matt. Designer.
firestang
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Re: epoxy, hardener, flour mix

Post by firestang »

Ive read out there on the net that its doesnt or isnt really there to be strong just join, its the glass thats the reinforcement, fair enough i say.

Ive played with about 10 different mixtures and some come up very hard , some brittle and ive done samples with more and less hardener of which ill take pictures of on the weekend and post what they look like and how they "feel" for want of a better word.
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