Hi,
No problem, let's try to figure this out because there certainly shouldn't be any problem mixing fast and slow hardeners with the EL2 or IN2 epoxy resins.

So, the most important questions (and I'm sorry if these seem like really obvious ones!) but firstly, can you confirm the following:
1. Two hardeners that you're trying to combine state "AT30 FAST" and "AT30 SLOW"?
2. Both hardeners are within shelf-life (they are less than 12 months old)?
3. When you mix FAST and SLOW, the mix ratio you add them at to the EL2 resin is still 100 (parts by weight, resin) : 30 (parts by weight mixed hardener)?

To elaborate on point 3; when you mix FAST and SLOW (at any ratio) the blended hardener should still be added to the resin at a ratio of 100:30. For example, a 50/50 blend of hardener would be 15g of FAST, 15g of SLOW and this would give you 30g of blended hardener that you would then mix with 100g of EL2 resin. We have had customers in the past add 30g of FAST and 30g of SLOW to 100g of EL2 (thereby achieving a resin to hardener ratio of 100:60).

Please confirm the above points and then we can continue with the diagnosis.