John in NM
I would only recommend that for West System, although I'm sure there are other similar epoxies. With one to one mixes its not a good idea.

The only reason it works (or appears to work, in deference to Cameron's comments) is that the product develops significant heat while curing. Heat accelerates the cure of epoxies in general, so reducing the catalyst is intended to slow down a reaction that you think will be problematic, preventing cracking and boiling. Without a doubt the West System product we were using was not designed for such massive applications

In general I agree with Cameron that messing with the mix of two part systems is not going to give you better results - it always slows the cure and often makes a weaker solid. In the case I mention, it was done to prevent worse problems.

In retrospect, these days I would probably be looking for a better filling agent than what we were using for massive voids (this was 25 years ago). It was harder to find good solutions then, even though the internet was a thing, it was not yet in widespread use. I bet even then all the boss had to do was call up Gougeon and ask what to do about it. It seems like the better solution would have been a slower cure hardener or a retarding additive.