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kfz View Drop Down
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Posts: 96 		Post Options Post Options   Quote kfz Quote  Post ReplyReply Direct Link To This Post Topic: My winter Project
    Posted: 08 Mar 11 at 12:12pm
Centreboard case is on the home straight now.  real labour of love to save this old wood,  would have been much much easier to knock a new one up on the table saw.



and the boom is now plugged and corners remade.



Kev
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Posts: 96 		Post Options Post Options   Quote kfz Quote  Post ReplyReply Direct Link To This Post Posted: 28 Nov 10 at 7:26pm





Not much to say there really.  Its really slow going. But after weeks its starting to look a little better.  Going to be a slog but Im keen to preserve as much original boat as possible.

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Posts: 6661 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 10 at 11:34am
Originally posted by alstorer

We've got a product designed for 2:1 by volume cartridges that is 100:45 by weight. (though formulated with a much smaller tolerance than your marine stuff)


Always worth remembering that: the "retail" resins like SP106 aren't as good as the commercial ones like say Ampreg in many ways, but they are more tolerant of the hamfisted (like me!). And as alstorer says the density of resin and hardener varies so weight!= volume and you need to do the mixes correctly. In my messy cramped and untidy workshop I'm not sure scales would survice so I use SP106 rather than something theoretically superior because it won't be superior with me using it and I don't think scales would survive!
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 10 at 10:14am
Jim's point rather stands though- not great practice to add more "to make it go quicker outside" as you'll make the final resin worse.
 
As for voume verus weight? Remember the proportions are different. They'll hopefully be close, but will vary due to density differences. We've got a product designed for 2:1 by volume cartridges that is 100:45 by weight. (though formulated with a much smaller tollerance than your marine stuff)
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Posts: 96 		Post Options Post Options   Quote kfz Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 10 at 9:10am
Jim,
No you are, its mixed in the correct proportion. I will change the blog, its not clear.

I will leave the post above otherwise the thread doesnt make sense if I amend it.

sorry, I understand not to change the proportions.


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Posts: 628 		Post Options Post Options   Quote I luv Wight Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 10 at 8:55am
It will change the cure speed if you don't get close to the required ratio... to very very very long = never !
I always use digital kitchen scales and never* get it rubbery, - doing it by volume results in duff mixes Cry

* well almost never, it does happen very occasionally, but maybe one mix in a thousand when I get my numbers wrong   Wink

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Posts: 6661 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 10 at 8:45am
I think you're still partially missing the point. Because its a reaction of two components, not a catalysed reaction of the monomer, changing the proportions will not usefully change the cure speed, only waste material, reduce strength and risk it not curing properly at all.

The little plastic measuring cups that come with some cough medicines and the like are handy for measuring epoxy. For even smaller quantities try measuring spoons!

Edited by JimC - 23 Nov 10 at 8:52am
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Posts: 96 		Post Options Post Options   Quote kfz Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 10 at 7:57am
Originally posted by JimC

Originally posted by kfz

epoxy ... easy on the hardener to give a long cure time 

Ah. Not a good idea. Epoxy works quite differently to things like Aerolite or Polyester.

With polyester or aerolite glues the hardener is a catalyst that takes no part in the chemical reaction, it just kicks it off. So less or more hardener, which is in small quanties, just affects cure time.

With epoxy resin the two components combine, so if you mess with the proportions then you end up with unreacted resin (or hardener) so you are compromising the strength and wasting money. That's why you get different speed hardeners with epoxy so that you can control the reaction speed without changing the mix ratio.


Woa Jim calm down.   Its was roughly 5 to 1 (as per the blurb), didnt measure it his time as my measuing cylinder has expired.  I normally mix it a bit more hardener as Im working outside but didnt this time I was inside and the mix was warm to start with.

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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 10 at 6:58am
True- though if well formulated they'll go about 10% of the hardener either way without huge issues- more than that and you'll risk (especially with too little hardener) a sticky mess
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Posts: 6661 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 22 Nov 10 at 11:21pm
Originally posted by kfz

epoxy ... easy on the hardener to give a long cure time 

Ah. Not a good idea. Epoxy works quite differently to things like Aerolite or Polyester.

With polyester or aerolite glues the hardener is a catalyst that takes no part in the chemical reaction, it just kicks it off. So less or more hardener, which is in small quanties, just affects cure time.

With epoxy resin the two components combine, so if you mess with the proportions then you end up with unreacted resin (or hardener) so you are compromising the strength and wasting money. That's why you get different speed hardeners with epoxy so that you can control the reaction speed without changing the mix ratio.
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