Follow the instruction in this link
and you should get a perfect glue without bubbles
I tried to apply glue with edge of a plastic smear knife instead of brush, which results an even and wide spray area. I used it on both ribs and inner layer, put them aside for about 10 minutes, then apply both side contacted, with a dry towel I carefully rub in small circle on inner layer , to check if any bubble exists.
Then I apply all surface with iron in mild temperature, no hard pressure, for about two minutes.
The result is perfect!
and with part of other side revealed. Lower right corner shows the plastic smear knife.