Either there was moisture present at the time of sealing or there is excessive build up of previous coats of sealer.

Ensure that the concrete is totally dry before sealing and/or strip off the previous coats of sealers and then reseal.

For foot traffic, 1 -3 hours (depending on weather conditions) and for vehicle traffic, 3 -5 days (depending on weather conditions).

A periodic washing with a gentle detergent (dish-washing liquid) and a soft nylon broom and then hose off will keep your sealed/coloured concrete surfaces in good condition for 3 -5 years.