Filling gap in wall - cement okay?

[svenz]

Hi all - just moved into a property built circa 1900, to discover a gap that rodents have been getting in.

I'm a DIY noob so - what's the best way to fill it? Should I be using lime mortar on this? Or should a portland cement mortar be okay? Am I massively overthinking it?

I'm questioning using cement because it looks like this may have been where an original air brick was installed... and whatever was used to fill it up has crumbled away now.

 

[aockenden]

That whole black plinth is almost certainly cement anyways so a tiny patch of a couple square inches isn't going to impact the building health if you decide to use cement. If that's the only thing your comfortable with, then go for it.

Otherwise, if you wanted to take this opportunity to start getting more comfortable with appropriate materials, you could pick up a bag of Naturally Hydraulic Lime 3.5 at your local builder's merchant and use that instead.

Either way, I'd blob some mortar into the hole, then wedge a few angular rocks in there to take up some space, then fill the rest in with the mortar and smooth it out into the surrounding plinth.

 

[svenz]

Cheers! I was going to try filling w/ lime mortar as you suggest, watched a few youtube vids. Hole is not that big so I think it will be doable.

Yes it's a cement plinth, unfortunately. May remove it at some point depending if I see internal damp. Thanks for the advice!