what filler should I use to fill the gap between a masonry wall and an aluminium window?
Hi @ennoh,
Thank you for your question.
It depends on where the window is. If it is indoors, I would suggest using Selleys No More Gaps Interior Multipurpose Gap Filler, if it is outdoors, I would suggest using Selleys White No More Gaps Exterior Gap Filler.
Both of these options are flexible, paintable and perfect for this application.
Just make sure you remove any loose material from the gap before application as it won't glue it back together.
Let me know if you have any further questions.
Jacob