Insufficient curing agent will usually slow the epoxy reaction down and lead to softer cures, which never really harden up. A slight excess of between 5 and 15% may not be obvious as the epoxy may cure hard and firm. Too much hardener however, may lead to softer cures, as the excess hardener becomes in effect a plasticizer for the cured mass. Avoid this by using the correct mix ratios of base to curing agent (4:1 by volume).