Stupid, stupid stupid...

NUTMEG

NUTMEG

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www.theblindsailor.co.uk
... Right, got that off my chest and finished kicking myself. Middle son spent last Thursday scarfing a 1 meter piece into the base of my mast to replace a rotten section. He is a violin maker so carpentry top notch. However I am a muppet and suspect I mixed the epoxy (wests) at a ratio of 10:1 rather then 5:1. Visited the boat today to check on the mast and do some other jobs and found that the epoxy is sort of hard but rubbery. Not hard and brittle as I expected. After reflecting and swearing for a bit I suspect that I miss mixed. Any ideas chaps, would it set at all if I mixed at 10:1? Could the slow cure be low ambient temp, in an unheated shed south east UK?
 
Sophie19 said:
... Right, got that off my chest and finished kicking myself. Middle son spent last Thursday scarfing a 1 meter piece into the base of my mast to replace a rotten section. He is a violin maker so carpentry top notch. However I am a muppet and suspect I mixed the epoxy (wests) at a ratio of 10:1 rather then 5:1. Visited the boat today to check on the mast and do some other jobs and found that the epoxy is sort of hard but rubbery. Not hard and brittle as I expected. After reflecting and swearing for a bit I suspect that I miss mixed. Any ideas chaps, would it set at all if I mixed at 10:1? Could the slow cure be low ambient temp, in an unheated shed south east UK?
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Too cold, you need some constant heat applied the the joint. make a tent locally around the joint from polythene
 
Talulah said:
Accurate mixing is required to maintain strength though.
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Sounds a horrible pickle to be in, but Talulah is right: if the mix is 50% out it will not achieve full strength, which is not something you want in a mast. Unlike polyester resin and its catalyst, there is very little leeway with epoxy hardeners: too much or too little and you have a heap of unwedded molecules which which can only weaken the final cure.
 
try warming it in a tent as suggested before you take it to pieces. It may go off with a bit of thermal encouragement.
 
Pull it apart and clean it up. Do it again so that you are sure you've got the mix right. I always tried to keep the temp above 15°C when using epoxy.


Monitoring the temperature.

04floorepoxy01.jpg
 
Lakesailor said:
Pull it apart and clean it up. Do it again so that you are sure you've got the mix right. I always tried to keep the temp above 15°C when using epoxy.


Absolutely.
Epoxy must be mixed in the correct proportions. It cures by a chemical reaction between the two. Polyester OTOH is only a catalysed reaction so the two components need not be accurately mixed. In fact by varying the proportions it is possible to control the cure time.

There are fast and slow hardeners available for epoxy. IIRC the fast hardener allows working down to 5°C whereas the slow hardener requires a minimum of 15° .
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macd said:
Sounds a horrible pickle to be in, but Talulah is right: if the mix is 50% out it will not achieve full strength, which is not something you want in a mast. Unlike polyester resin and its catalyst, there is very little leeway with epoxy hardeners: too much or too little and you have a heap of unwedded molecules which which can only weaken the final cure.
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correct in every respect.
 
You poor sod. Bad luck.

Never mind - take it apart and do it again. You'll laugh about it in the pub in a week or two...
 
Sophie19 said:
Rats. That's what I suspected, just hoping someone would say something different!
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Well there is always a first time! Alright then, just for you - just leave it, it will be OK. Masts don't have a great deal of strain on them, nothing could possibly go wrong! Be reassured that I am a non-expert with many years of not working with epoxy behind me so I know what I am talking about!

(Sorry but I just couldn't resist it, especially picking up on another thread today! I hope you get it sorted out. If you need any help I'll bring my fan heater over as I'm doing nothing except waiting for it to get warm enough to paint outside)
 
Pull it apart clean it all off with acetone and redo it.

Ihave always understood that getting the mix right is critical if a full cure is to be achieved.

Remember the mix is different for different hardners and the ratio depends on if you mix by WEIGHT or by VOLUME.
 
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Well worth buying dedicated epoxy manufacturers pumps for measuring and dispensing accurately. Even these need occasional cleaning through with hot soapy water..
I have standard and mini pumps on board for ' pump n go' on large and small pots of epoxy. Cleaner, quicker, simple, accurate! ( but you have to buy the pumps)

Redo the mast scarf, you know you want to and it will always niggle you if not!
Hot air gun, chisel as a scraper, acetone... Thermometer and wrap the joint and apply nice dry air eg blow heater inside the wrap or heated shed.
 
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I'm really sorry for the OP, but I'm afraid I have to agree. As others have said, the hardener isn't a "catalyst" like with polyester, it's "the other bit" of the finished epoxy - so while it might stop being tacky, it will never be as strong as the fully-cured article.
 
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