I use a heat gun, not a hair dryer, to reheat the first pour in my open pour swimbaits to get a better bond with the second pour. Just be careful not to overheat, or your first pour can scorch and discolor. It take some experimenting to get the timing right, but it has allowed me to be able to pour two layers at different times, even the next day, without losing a good bond. When I put my second pour into the microwave to heat, I begin to reheat my first pour with the heat gun. When the top of the first pour seems to be melting again, I do my second pour. It's not perfect, and not as good as a twin injector laminate, but it works.