How do I repair a wall with mortar turned to sand

[tiswas]

Our house is a Victorian terraced farmer's cottage,which, over the years, someone has seen fit to render with an acrylic render coat

The coating has been cracking and delaminating, as well as pulling off the flashing on the flat-roofed rear extension, both leading to damp inside

To gauge the extent of the problem, and to allow the wall to dry out, I've stripped some of the render

What had been uncovered is not pretty - The brickwork doesn't appear too bad, much of the mortar has turned to sand, and there are some significant voids in the joins (through to the internal brick in some places)

What are my options here? Dig out the sandy bits & repoint / Re-render with a lime mortar?

Cheers!

 

[MatthewC]

Hi tiswas, welcome to the forum.

There's a lot of expertise here and I'm sure someone more knowledgeable than me will be along soon. However, in the meantime, here's my tuppence worth. I've not done this sort of repair on a brick wall, but I have tried it twice on random stone walls in my garden. The obvious danger is that it could all fall down, so I tended to make a small-ish mix and do a bit at a time, possibly in several different places; then when that had set I did a few more places, and so on - it was a sort of therapy I suppose which lasted most of that summer. Obviously you should start at the bottom!

You might find the odd brick is loose and so it has to come out and then be re-inserted with new mortar all around it. As I worked up on one wall, as I neared the top it became more necessary to actually take out a large area and completely re-do that bit. However, I could get away with that on a random wall, but on a nicely coursed brick wall you could easily end up with a lot of wavy lines and varying thicknesses of pointing.

HTH. Best of luck
Matthew
(NB check my blog for how I did my mid Victorian house in 2010/11 - http://houseintheenchantedforest.blogspot.com/)

 

[88v8]

Not a pleasant discovery.

Sounds as if it needs completely repointing in lime. Easy to say, tedious to do.

Our cottage was built with clay/straw between the stones. When I removed the cement pointing internally, I could have carried on through the whole 18" of the wall and not found any 'sound' mortar. There were places where the wind was whistling though, Indeed, I could see right through here and there. One just has to rake out enough depth, then stop.
So don't worry if you're leaving some powdery mortar towards the back of the joint. The front inch or two will be plenty of depth.

Unless the brickwork is very fine, the best tool for raking out is a mortar rake. Don't be tempted by the various power options for raking, too easy to damage the bricks.
Here's a full set of tools, be quick
https://www.ebay.co.uk/itm/Marshalltown-motor-rake-pointing-trowel-bricklayer-ground-worker-builder-tools/273973194979?hash=item3fca1330e3:g:EwkAAOSwAMJdXAVr

And even if you render in lime, the pointing needs to be made good first.

Perhaps a bit late in the year to do the whole house; if you just do one wall, say, be very careful with the gauging of the mortar and buy enough sand to do the whole house, so you can match the colour when you continue.
Reason for buying the sand now, is that suppliers change, and next year's sand may not be the same.

Ivor

 

[paulc]

Perhaps a bit late in the year to do the whole house; if you just do one wall, say, be very careful with the gauging of the mortar and buy enough sand to do the whole house, so you can match the colour when you continue.
Reason for buying the sand now, is that suppliers change, and next year's sand may not be the same.

Buying sand in bulk one tonne bags is certainly a lot cheaper than buying it in 25Kg sacks. The lime used can also affect the colour of the mortar, so it pays to get it from one manufacturer.

I really love the colour of Singleton Birch lime putty. A very nice creamy colour. My local supplier of lime products used carry a sizeable stock of S.B. lime, then they switched to Ty Mawr. The new stock of putty has a very distinct grey tinge to it. Probably not an issue for a mortar, but when mixed with marble powder for plaster, the colour difference really stands out.

 

[Feltwell]

Mortar can be sandy, but still provide perfectly adequate structural compressive strength between bricks in a wall - the grains of sand are locked together effectively within a trapped volume - the problem comes when that trap is released and it's disturbed.

If the wall is showing no sign of structural failure then I would simply rake out to a depth of at least 1" and repoint in a lime based mortar. Don't dig too deep, you'll do more harm than good. Make sure the new mortar is firmly pressed into all voids and that the void is well wetted first.

You say you've removed some of the render - just to be safe, I'd repoint that area before you strip more off, then work in stages.

I've been using coloured lime mortar from Lime Green, dead easy to use, all premixed in a 25kg bag - just put it in a plasterer's bucket, add some water and mix up with a paddle mixer (£50-£100), just like a plasterer would mix modern gypsum plaster. It's an expensive way of doing it but a very convenient one, especially if doing the job in stages. One £20 25kg bag will repoint about 4m2 of brickwork.