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!

 

[svenz]

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.

I bought the NHL and sand, and am planning to attempt this weekend . As the hole goes through to the cavity, do I need to back it with anything so I can properly pack the mortar? I know some people would just use expanding foam but not sure that is the best way.

 

[aockenden]

I bought the NHL and sand, and am planning to attempt this weekend . As the hole goes through to the cavity, do I need to back it with anything so I can properly pack the mortar? I know some people would just use expanding foam but not sure that is the best way.

Nice, just wedge a couple stones in there tightly (less than flush with the surrounding plinth surface) and then press your lime mortar in around and over top of them

 

[svenz]

Nice, just wedge a couple stones in there tightly (less than flush with the surrounding plinth surface) and then press your lime mortar in around and over top of them

I’ve done that now! The bag says to use 1:1 sand ratio for mortar below DPC. But I usually see 3:1 everywhere. Wdyt?

 

[aockenden]

I’ve done that now! The bag says to use 1:1 sand ratio for mortar below DPC. But I usually see 3:1 everywhere. Wdyt?

1 lime to 1 sand sounds exceptionally lime-rich. I’d do 2 sand : 1 lime powder by volume. 3 :1 is too sandy for me. Add water slowly until the consistency is sticky enough that a big glob will stick to your trowel held upside down.

 

[svenz]

Here is the result. Already started to harden after an hour or so, and I've covered it with a damp hessian cloth. Let's see how it goes. I will brush it down tomorrow. Once fully cured, sand + paint.

 

[aockenden]

Here is the result. Already started to harden after an hour or so, and I've covered it with a damp hessian cloth. Let's see how it goes. I will brush it down tomorrow. Once fully cured, sand + paint.

View attachment 16448

Not bad for a first go, tomorrow should clean it up a bit more.