Best exterior silicone sealant for this...

digannio

Thanks... dangerously, you're giving me confidence😃

digannio

FAO Stuart. Could i just use your expertise a little bit more for this job? The glass box does have a mortar surround as you said. The grout between the glass blocks is OK so the job will entail digging out the length of mortar at the top between the brick and glass. Sone questions... will a grout rake do the job on this mortar, the gap between the bricks above and glass is less than 5mil and to what depth should i be looking at to rake out to ensure a watertight seal with the new Carlton mortar I'm filling it with? Do i also spay some water in before putting in the new mortar and is there a good way of forcing the mortar into this gap effectively  to ensure coverage?

One last question that may seem daft. Is it definitely better to fill the raked out gap with mortar rather than Dow weatherproof sealant, given the flexibility of silicone in the event of some movement?

Thanks.

stuart45

If you're using the sealant it's better than the mortar. If you don't want to buy the sealant and use the mortar you need to rake out about15-20mm, wet it down and push in the mortar with a finger trowel. 
Sealant is a better job as it won't shrink.

digannio

Thanks for all your help with this.