Nov 192020

Our perimeter wall has a step crack in that needs dealing with before it falls over and gets expensive. I was reading up on repointing walls and stumbled across a technique called ‘stitching’. They use it on buildings where a wall has cracked, so I figured it would be more than good enough for a perimeter garden wall.

Our fig tree has caused this step crack in our wall
If you can see all the way through, it’s not good

So wall stitching involves removing the old horizontal mortar spanning 50cm either side of the vertical crack to a depth of 30mm. Then you inject about 10mm of special anchoring grout and press a helical stainless steel reinforcing bar into the grout. Then you add another 10mm of grout, ultimately covering that with another 10mm of mortar to match the wall. you do this every 4-6 vertical courses of bricks sufficient to cover and reinforce the cracked area. Once reinforced you can then repoint any other bits that need doing.

Obviously tools are required. Diamond mortar raking disc.
And a 35x6mm diamond mortar rake for the verticals and depth

Some investment in diamond equipped toolage is required. The Diamond disc is incredibly fast and filthy dirty, but only hogs out 20mm. I needed 30mm so got hold of a rod shaped diamond bit for routing out the verticals and a bit deeper on the horizontals. Both of these go on the angle grinder.

Three slots overlapping nicely to span the step crack
Helical rod that will go in the slots to reinforce the wall

Once the slots have been dug out a quick hose-down to clean out loose bits and thoroughly wet the area. Then using a gun that’s similar to a large mastic gun, but better, squirt some grout into the slot, push it in firmly with a tuck pointing trowel, and press a helical rod into it…

Mortar/grout pistol. Very good if you get the mixture right.
Helical rod pressed into anchoring grout but not yet covered
Various tuck pointing trowels and a scraper

Then add more anchoring grout over the rod and smooth that in so the rod is properly embedded, creating a really strong composite structure. The anchoring grout goes off quite quickly, certainly a lot faster than regular mortar. I probably wouldn’t mix more than required for two bars in one session.

More grout on top and press it all in firmly with a tuck pointer to make sure the helical rod is embedded
Repeat until you’ve spanned the crack

Then allow to cure overnight (>=5°C) and cover with mortar that either matches the rest of the wall or, if you prefer, you could use some with some cement in that will last a bit longer. If it was the house I would be more bothered about colour matching. But it’s a perimeter wall, so I don’t give a toss if it doesn’t really match. What’s important is that the wall remains in place, opaque and functional.

Three slots made good with mortar (after 24 hours, still not fully dry)

After that it was time to make good the remaining cracks, so first up I had a good look at the mortar and marked the bits I needed to do dentistry on with the diamond disc and mortar rake. I used white paint to make it clear, so I could do all the messy work in one go and be unlikely to miss bits.

Marked up the areas to ‘hog out’ using white paint

This is the messiest job. Filthy dirty work. The disc is worse, but it’s so quick on the horizontals.

Cleaned the visor twice during the job
The whole lot after the carnage
Closer view after washing down the wall and letting it dry
19/11/2020 Next day after repointing the top few rows
20/11/2020 One gun’s worth of mortar into the bottom few rows. Middle bit still left to do
22/11/2020 Finished the middle bit on our side
26/11/2020 Neighbour’s side marked up for angle grinder work
26/11/2020 Neighbour’s side after hogging out dodgy mortar marked above

Pointed the neighbour’s side. Going to have a break now. Next thing will be the curved crack stitching, but might need to wait for a sustained period of weather above 5°C to start that.

28/11/2020 Morning’s work pointed neighbour’s side.
29/11/2020 The curved section from external side, marked up to show cracks (red) and where the stitching will go (teal). Stitching will go on the inner side.

Still to do (as of 19/Nov/2020)…

  • Finish the remaining rows on our side (DONE 22/11/2020)
  • Do the equivalent on neighbour’s side (DONE 28/11/2020)
  • Stitch the curved step crack on the other side of the fig tree
  • Repoint remaining cracks on curved section our side
  • Curved section neighbour’s side
  • Stitch a bit on our straight section that is leaning
  • Do some general pointing in places where it’s deteriorated