Hi @nutt522,
Welcome to the Bunnings Workshop community, it is wonderful to have you with us.
To seal up the gaps around the windows in your brick veneer, you should use a polyurethane sealant such as Sikaflex 11FC Purform.
As some of the gaps look rather wide, first, you should push some gap filler rod into them. The foam will compress into the gap and sit, via friction in the gap. This will then act as a backing to prevent your sealant from falling through.
Once the gap filler rod is in place, you should apply your sealant over the gap, ensuring it bridges fully from one side of the gap to the other in one continuous bead. This can be done by snipping your nozzles so that the hole is wider and a wider bead comes out when applying.
After application, the sealant can be struck off and smoothed using a Silicone Scraper. Use the corner with the widest radius edge as it will give you the best finish on a wider bead like this.
Check out How To Silicone a Gap for some guidance on applying sealants.
Let me know if you have any further questions.
Jacob
