Looking for advice on window sill / brickwork finish

[SimonB]

I appreciate that I'm mostly read-only on here, and it's not woodworking but hoped to call upon your collective wisdom.

I'm looking for some advice on weather proofing exposed brickwork under a window sill. The photos hopefully illustrate the construction. It seems it's a custom cill, separate from the main window frame, and was finished pretty shoddily. I had to remove the sill to complete some running repairs to the glass panel seals as well as the gutter underneath. The sill was only loosely held on with some sealant along the back edge and was resting on a whole mix of mortar, foam and sealant.

Whilst it currently rests in place just about, and there is a roof overhang above protecting it from the worst of the rain I am worried about driving rain onto the glass and running between the frame and the sill and into the brickwork below. This is on the first floor so there is finished wall beneath that could potentially be damaged by the water ingress.

My non-expert thought was to remove all the crud under the sill and apply a layer of mortar to a height for the sill to sit at a suitable position, and run a generous bead of sealant (something like Stixall) between the sill and the frame. Does this seem a reasonable DIYable solution?

Should I add a waterproofing agent to the mortar or apply some other some other product to the mortar once set?

I don't want the sill permanently fixed down in case I have to do repairs to the sealent in the future.

Comments and any other suggestions would be gratefully received.

Many thanks
Simon

 

[Jonathan]

The gap underneath the window where the packers are looks like it is missing expanding foam, we foam all around our windows before we think about sealant. We always use a low expansion foam especially formulated for windows and doors.
The sub cill will keep out any moisture if fitted correctly and sealed, we normally use a polymer based sealant, I’m not familiar with stixall so can’t comment on the brand.
You could run a layer of mortar but I think it would only help as a packer and not a waterproofer.

 

[RogerS]

What Jonathan says but if you really want to puts s9me mortar down I’d use lime mortar

 

[SimonB]

Thanks Jonathan, something like this - Soudal Genius Gun Window & Door Foam?

Yes, the mortar would just be a packer to bring the sill up to the right height, with the current assortment of supports it droops, but also to seal the brickwork against wildlife, particularly wasps. However if I was going to the effort to do that I had wondered if it was worth going the extra mile to waterproof it as a secondary barrier, should, for example, the sealant fail.

Stixall is a hybrid polymer sealant and adhesive - does that sound suitable? If not can I ask what you recommend please?

Roger - why lime?

Thanks
Simon

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[Jonathan]

Simón I’m not in the uk so not familiar with the brands you suggest but they sound perfectly good. With the foam I would highly recommend the professional gun dispenser and not the plastic nozzle thing, with the professional gun you have more control.