I used the hardener on some of the paint, mainly the Omaha Orange exterior. I managed to find a couple half pint cans of ALK-201 online. Otherwise I’d have had to buy a quart. The 1/2 pint is all you need for a gallon of paint and the instructions say it has to be used within 14 days of opening the can. I wasn’t going to bother with the hardener till I found the smaller containers. I think it would be fine without hardener.
