Repairing a section of wall

[charlie12]

I have a section of wall that needs to be repaired. It originally looked like this:


It was a horrible patch job done by the previous houseowners using what appears to be polyfilla. You may not be able to tell from the picture but this section of wall is not level with the rest of the wall - it protrudes out by up to 1cm in the central section. The plaster around the central section was loose so I carefully removed the loose bits and then I could see why this section was protruded. There were two metal brackets embedded in the wall that stuck out so they skimmed over these to hide them. The brackets were not attached to anything and came loose as I removed the loose plaster, I'm guessing they were used for something like a shelf.

After removing the loose plaster, the section is now almost flush with the rest of the wall (1-2mm difference). I think I can chip/sand away the edge to make it completely flush. Currently looks like this:


The darker outer shade of plaster is shiny and sound and the inner lighter shade is more crumbly but sound (if that makes sense!). Underneath this is about 8mm of crumbly black material which is very porous (anyone know what this is?), and then the brick is underneath that.

Closeups of the two main holes:


On the edge there is a "step" that varies between 1-2mm:


My question:
What would be the best way to repair this? I will be double lining all the walls before emulsioning.

I have plastered small areas before with good results.

I have:
Some Thistle bonding and multifinish
Gyproc Easifill
Polyfilla ready mixed regular
PVA

and can obviously buy anything else that's required

Cheers!

 

[roughcaster]

Hi Charlie,
Whoever did that repair wasn't fussy anyway. It looks to me as if they have coated out the wall with some rough kind of cement mix,and finished it off with whatever they had in the shed, but anyway a poor job. This doesn't look a very big area,and you said you have plastered small bits before with good results. Ok. If it was me, instead of chipping and sanding, I would cut with a stanley knife around the edge and take out the whole patch,right back to the brickwork and start again. Give the brickwork a good brush down to remove any loose bits, wet the wall and PVA, especially around the edges and bring it out with Bonding Coat*(maybe). You can use the original plain of the wall to rule it off flush, with a small length of wood. I think you would know how to do this anyway. It could be that the wall was originally coated with a cement based render, so you might think about filling out the patch, or scratch it out half the depth,with waterproof render,and then use bonding coat/multi finish,especially on old red bricks. *Sometimes with gypsum plasters onto old red brick, salts/damp can come through from them,especially on the internal side of an outside wall*
When/if you cut out the patch, you'll soon see what it was plastered with originally. I wouldn't get anywhere near it with Pollyfilla ready mix anyway. Even with double lining paper on,a bad bump would still be very noticeable.

Roughcaster.

 

[charlie12]

Roughcaster, many thanks for your advice.

It is the internal side of an outside wall, and having lived in this house for 15 years we have not had a damp problem on this wall, although there were a couple of very small patches of mildew on the walls after removing the wallpaper (which have now been cleaned off). This indicates to me that whatever's been used to coat the bricks has worked well, so I am somewhat reluctant to remove it. Or perhaps we might have a cavity in the wall that is preventing damp and the stuff they used is not really doing much.

I do like the idea of using waterproof render and then bonding and multifinish on top of this. This would make it a more solid repair, and a smoother surface for the lining paper to sit on.

I would appreciate it if you could advise me on the type of waterproof render to use, as I have never used this before. I'll only need a small amount of it. The patch is about 1m wide. Cheers.

 

[roughcaster]

Thanks for that Charlie,
I don't know if you have any builder friends who could help you out here ,because the amount of render you would need to scratch coat a patch that size is small. Use building/plastering sand,(soft sand) and ordinary portland cement. The mix: 4 or 5 sand to 1 cement. The water to mix it with must contain a waterproofer/plasticiser admix,(it does two jobs in one). The mortar is then mixed to a buttery spreadable consistency, and after wetting and PVA'ing the area, apply it to the wall (half the depth) and scratch it to give it a key. Leave it a day or two and then use your bonding coat/ multi finish. As I said earlier, I hope you can get what you need from a friend, because for all you would need, (a bucketfull if that), otherwise you're looking at around £20 for materials, most of which you wouldn't need. I wish you well.

Roughcaster.

 

[charlie12]

Thank you once again Roughcaster, very well explained

I don't have any builder friends unfortunately, but I've priced up the materials and it's not too bad (unless I've picked the wrong stuff!).

From Wickes:
Liquid waterproofer 5L 3.49
Mastercrete cement bag 3.25
Building sand bag 1.35

total = 8.09

And I'll have plenty spare to practice with in the garage before I do the main job.

Cheers