MGS hardener cure time

[Dean Head]

Group,

Question on fast/slow hardner combinations. I am currently using 50/50

fast/slow mixture of hardner. I want to slow the cure a bit to allow the more

involved layups of the bulkheads. I thought of trying 25% fast to 75% slow. I'm

in Florida...Any idea on the extension of the cure time as compared to the

50/50 mix? I have read the slow by itself could have extremely long

cures...dont want that. Is there any hope that the mix ratio to cure time

relationship is linear?

Thanks

Dean Head

Cozy #1040

[John Slade]

Dean,

I built my Cozy in Florida using MGS. I experimented with various mixtures and temperatures from 100% fast in 90 degree weather - boy you gotta be QUICK to 100% slow in 60 degree weather - 3 days and still tacky. I don't think the times are linear. Everything depends on the temperature of the parts and the ambiant air.

Mostly I used 50/50, but I learned to dump a little more fast or slow into the pump based on the ambiant temperature and layup size. I used about 90% slow for the wing lay-ups and got a good 5 - 6 hours before it was too tacky to squeege.

Bottom line is that you have to learn what works by experimentation. Err on the slow side until you get the hang of it. Another important variable is the thickness of the layup. If you're doing a 2 BID bulkhead all fast might work fine, but don't try this with a spar cap where the epoxy can exotherm due to self heating.

Regards,

John Slade

[dust]

we use all slow and keep multiple items going so that the cure time doesn't matter.

 

for example last saturday we

laid bottom skin on wing 3

laid up aileron pocket on wing 2

cut off top of nose on fus 2 (this one got behind and we are slowly catching it up.

fabricated parts for hidden belhorn

 

 

this saturday (time permitting) we will

put spar cap on top of wing 3

install antennas and rudder conduit wing 3

sand aileron for attaching counterweignt

sand aileron wing 2 and top/bottom/sides for fit

cut extra for hinges wing 2

glass inside of fus nose top

repair inside nose of fus 1 where we accidentially cut between glass and bulkhead(oops)

sand balast compartment fus 1 and glass

install pitot on fus 1

 

 

see - always plenty to do and we never run out of time for layup or lose any epoxy to exotherm