After you’ve sprayed your GFRC mist coat, the general guideline, under typical shop conditions, is to wait about 10-15 minutes before applying your first coat of backer mix. This allows the mist coat to set up a bit and get firm enough that the fibers won’t push through but still wet enough that the mist coat will bond to the backer coat.
The following video shows you exactly what you’re looking for:
- The mist coat should be soft, moist and pliable, but not sticky. Touch the mist coat gently with gloved fingers to test it.
- Mist coat that has been left too long may look the same but be stiff, dry and crumbly. It risks crazing, cracking and delamination.
Note that shop conditions have a huge effect on timing of when the mist coat is ready. Very dry or hot shop conditions will cause the mist coat to dry out or cure very quickly. You must be ready with your backer mix, monitor the mist coat closely, and not leave it unattended.