The two most common causes of problems are inaccurate measuring and incomplete mixing of the components.

Stir the resin and hardener together, before stirring in any fillers that may have settled out during storage.

When fully mixed, continue stirring and scraping both the bottom and sides of the container frequently.

If you are not certain it is fully mixed — keep stirring! A couple of minutes longer here can make the difference between a good and a scrapped part.