Repairing single skin blockwork wall

[Andyc84]

A little bit of advice please.
I am repairing my boundary wall, as the previous property owner had built a fence on top of the wall, single skin block work 100mm width. The fence was bolted to the top (badly) and in the wind it has caused the top two runs of blocks to become loose. Separating them from the lower courses.
Can I remove the loose blocks, clean the surface of any mortar and build up new? Or should I do something else to fix the new blocks to old?
Secondly I want to add another run to an undamaged part of the wall but the top surface has been painted. Assumed masonry. Do I need to remove the paint before adding a new layer of blocks to help the mortar bond?

The new fence will be posted in my side of the wall so the wall will be free of the loading.

Many thanks ![/list][/wiki]

 

[tony1851]

No special measures needed to re-build with the old blocks, except clean off old mortar.
If it's 100mm block, you shouldn't build too high - wind loading!

 

[Andyc84]

It will end up being 4 blocks high on my neighbours side, but only 2 on mine due to my garden being higher... I was thinking that a single skin was bad as a retaining wall, but it is old and it is still there so can't be too bad.
Anyway it'll be a maximum of 4 blocks high.

Any thoughts on the paint section, I assume I'll have to clear it off. Heat gun and wire brush be sufficient?

Thanks for the input so far.

 

[tony1851]

That might be time-consuming. If you have (or can borrow) a 4" disc-cutter, why not just score the top surface of the blocks with a criss-cross pattern - that should give a good key for the mortar.

 

[Andyc84]

That sounds much easier! I'll give that a go when we get a spell of warmer weather. I'll also do the same Ina spot of concrete that I want to render so even if I have to hire it, at least I'll get my monies worth.
Thanks for the help.

 

[noseall]

External.

Single skin.

Retaining.

Fence fixed on top.

Rendered.

As far as unsuitable walls go, yours ticks just about every box.

 

[Andyc84]

I agree, but it's all historical, I am removing the fence and putting it in ground on my side of the wall. Also the render isn't on that section, as all of the wall is below ground on my side. Short of removing the whole wall and replacing it with a better one, I don't see what else I can do?

 

[noseall]

The minerals in the soil will kill the render.

 

[Andyc84]

Sorry, when I said the render isn't on that section, I meant it is in an area where the wall is not retaining, it is just a wall, I assume this is fine to get rendered?

 

[noseall]

Rendering garden walls can be a bit hit and miss. Some end up looking like a dogs dinner after the inevitable weathering problems.

All depends upon exposure.

I personally would advise against it.

 

[Andyc84]

Sadly half the wall is already rendered, so I've either got to remove the lot and hope the wall is still ok under it, or try and render the rest to match so that it still looks good when I've finished. I do intend on getting someone in to render as I know it is above my skill set.
I'll certainly get advice on it before going ahead as I know it's not the easiest of jobs. Thanks for all the help.

 

[tony1851]

@Andy -re. rendering the wall. Nose is right in that free-standing walls should not really be painted or rendered.
The paint/render traps in moisture which rises up from the ground and prevents it evaporating. That moisture contains salts which can attack the mortar or blocks. Also in winter, the water freezes and the expanding ice can damage the block or render.
If it's already part-rendered, not much you can do, but there will be a risk.

 

[Andyc84]

@tony, I've assumed if I get it rendered, the risk is that the render will fail and that the underneath blockwork could be damaged by freezing and thawing. What sort of timescale could that happen over, in a year or more like 5? Just curious as to what the risk is.

 

[tony1851]

Many variables - will depend on the render mix (a stronger mix will tend to suffer shrinkage cracks - but too weak a mix will not be durable); workmanship (obviously); degree of exposure (north-facing side will have less chance to dry out, etc etc.

It won't fail overnight, but how long.........?

 

[Andyc84]

Fair enough! Thanks for all the advice anyway! At least I can crack on with the brick work, when weather permits!
I'll leave the render until later, when we've had a chance to work out what we want to do!