Best exterior silicone sealant for this...

digannio

Hi, I've got one of those thick bathroom windows that don't open and in a small area at the top there is some water ingress when it rains. It looks like the top bead of exterior sealant needs to be dug out and replaced.

Can anyone recommend a good quality, long-lasting, clear silicone sealant for this job. It will need to have good adhesion to both the external brickwork and the glass. Thanks.

twopenny

Is that double (glazed) glass, a box of glass or what?

Are you wanting to do the glass only or brick as well with the same sealant?

digannio

It's not double glazing, it's those great big thick units of glass joined together that make up the bathroom  window. I think they're called glass brick or block windows. I need to replace the sealant on the outside that runs between the glass bricks and the brickwork of the house where the old sealant has obviously degraded at the top. Simple as that.

stuart45

Dow 799 is a good one. 

digannio

Thanks for the recommendation.

digannio

It just got more complicated. Closer inspection reveals that the glass blocks are bedded in with mortar (which must have fine cracks letting in rainwater) and silicone sealant has been clagged on top of this mortar as a "fix". Now looks as though there is a hotch-potch of sealant to remove and then the mortar needs renewing/replacing. Might be time to call in a window repairer/specialist as pointing isn't a strong point.

stuart45

Bedding them in mortar used to be the standard method. Nowadays there's special ready made mixes, or plastic strips.
You need a grout removal tool to rake out the joints, then you can regrout as you would for tiles. You can also use a Dremel for raking out.

digannio

Thanks for the help but it's probably outside my comfort zone in terms of the effectiveness of my finished mortaring and how it will look. But I can see the problem already with getting a window firm in... too small a job to bother with and a handyman may leave it looking like I would😄

stuart45

I doubt if a window firm deals with glass blocks. They aren't really that common for windows, and seem more popular for showers. Traditionally it was the bricklayer's job, but nowadays you are more likely to find a tiler, or bathroom fitter doing them.

digannio

If i do attack the surround mortar (and sealant) on the exterior wall with a rake in a sudden fit of confidence, would a standard bag of Carlton general purpose mortar mix  (just add water) do the job? Yes I've got some left over! And if the mortar on the sides and bottom seems intact is it ok to leave that untouched. The leak is only on the top horizontal run of mortar and in a very small area of it.

stuart45

If you're only doing one joint use the mortar. Not worth spending £20 on glass block grout. Once you've raked it out, damp the old mortar joint down a bit. Don't worry if you get some over the blocks, they clean up easily.