How to repair mortar under windowsill?

[PansyPotter]

Victorian terrace, 2up 2 down.

Had issues with penetrating damp in kitchen wall but all sorted now and has been drying for months.
When I took the plaster off I found water had eaten away the mortar under the wooden windowsill and there is a big gap though now dry. I hoped to be able to lift it and redo but it is butted into the walls and under the double glazing so not so easy. What's the best way to repair it? Is there such a thing as injectable mortar?

BTW is this cent render on the brickwork?

 

[Woody3]

Just use a small pointing trowel to push the mortar into the gap. There is a mortar gun you can buy, which is ideal for pointing, but would be overkill for this.

With regards to the 'render', going by the orange/brown colour it looks like the scratch/backing coat of gypsum plaster (for future reference render is external).

I'm afraid I can't advise on what type of mortar or plaster to use, because the construction of your wall is unclear.

ETA: just seen that it's a Victorian terrace, so for the mortar use 1 part NHL3.5 lime to 3 parts sharp/grit sand. For the plaster use a lime based plaster once the gypsum has been removed.

Hope this helps!

 

[MatthewC]

If you use lime mortar/NHL you will find that you can push it in as suggested; you just carry on pushing with a spatula or small trowel - it's amazing how much you can use doing this! If the gaps are really large you can push small pieces of limestone into the holes as well. Lime flows really well, whereas cement mortar hardly flows at all and isn't what you want to use on your old house anyway.

Edit - the mix you want is 3 sand to one lime, not the other way round!

 

[Woody3]

Edit - the mix you want is 3 sand to one lime, not the other way round!

Good spot! I wondered how long it would take before someone spotted that!

 

[PansyPotter]

Thanks for comments. Wall is old (crumbly) brick with a half inch layer of something grey that look like concrete, patched with something very soft clayish grey. On top of that it has had a thick textured vinyl paint with gypsum over that. I've taken the gypsum off and anything else that was crumbling or loose but think house would fall down if I took it back to brick. :? Will be a patch up job I think.