Renewing mortar in a garden wall

[mrsbruce]

I have a quick question about repairing a low garden wall, where the mortar has given up the ghost. Now I know that I should use a mortar mix, but is there any reason that I can’t use a ready mix bag of concrete I have lying about.

I’ve googled, and they all say you can’t but most explanations stop at “concrete is stronger than mortar.

Just curious.

 

[123hotchef]

It's very stoney and will be hard to point with. If it is poste crete it goes off very quickly also.

 

[gaz1]

it sets too fast and is loaded with lumps best not to use the stuff than its desired purpose

its easy enough to get a small bag of cement and some sand for small repairs but for bigger repairs best to buy bags of the stuff as it always comes in handy somewhere else

the other thing its a whiter mix and really shows other pointing up badly

 

[mrsbruce]

It's very stoney and will be hard to point with. If it is poste crete it goes off very quickly also.

It’s a surprisingly smooth mixture, not obviously as smooth as mortal, I assume, though. I shall get a bag of the proper stuff anyway.

 

[gaz1]

sharp sand has a bit more body to it than river sand when your laying bricks or concrete blocks

you maybe surprised on how much it can be pushed out with a wet mix between the differences of sand

the smoother mix is like water and will just ouze out of the joints just by the weight alone as you rebuild back up

 

[SierraV6]

I have a quick question about repairing a low garden wall, where the mortar has given up the ghost. Now I know that I should use a mortar mix, but is there any reason that I can’t use a ready mix bag of concrete I have lying about.

I’ve googled, and they all say you can’t but most explanations stop at “concrete is stronger than mortar.

Just curious.

I would have thought that the concrete would contain relatively large aggregate which would prevent you from using it for pointing. Even if you could get it into the raked out joints you'd not get a smooth finish.

It's also as you say far too strong. Mortar is actually slightly "flexible" and is effectively sacrificial; it's softer than the masonry itself. If you use too strong a mix (or indeed concrete!) you'll find that the bricks spall, similar to a stone wall that's been pointed with cement mortar as opposed to lime based.

 

[brightspark]

just buy a bag of builders yellow sand and some cement rake it out and point it in with a builders bucket pointing trowel job done , dont make it sloppy point it in and rub it up with trowel when nearly dry and it wont get slurry over the brick face then a gentle rub with a soft brush to get the snots off

 

[Blue Chips]

Mortar is actually slightly "flexible" and is effectively sacrificial; it's softer than the masonry itself. If you use too strong a mix (or indeed concrete!) you'll find that the bricks spall, similar to a stone wall that's been pointed with cement mortar as opposed to lime based.

Yes, mortar should be softer than the stones/blocks/bricks in your wall. I don't know what grades of mortar mix you have available in the UK, but there are several different grades that we use here, depending on several factors, including hardness. In the old house that we're restoring, I've been using a traditional lime-putty-based mortar to repair some of the relatively soft, low-fire clay bricks in the chimney flues.

 

[brightspark]

if the mix is two strong and the bricks are porous in winter when its freezing and bricks are wet they blow the face off because the water cant escape ok if you treat the whole wall with thompsons waterseal though when there all dry did the whole of my house with it after pointing and sandblasting it

 

[mrsbruce]

Thanks everyone for the proper explanations, I didn’t realise it was the strength of the concrete that was the problem, and what the consequences were of that strength.

One of my neighbours has handed in about 7 litres of brick waterproofing, and I will be giving the wall a good going over once repointed.

 

[Blue Chips]

When in doubt about mortar hardness, it's best to err on the soft side, especially if it's just a low garden wall and not a critical load-bearing structure. And for waterproofing I'd recommend a silane/siloxane solution that is water repellent, but vapor permeable.

 

[Matrixx]

One tip is to dust the mortar with some close by soil to blend it in.

 

[S-Rail]

It’s a surprisingly smooth mixture, not obviously as smooth as mortal, I assume, though. I shall get a bag of the proper stuff anyway.

Are you sure the bag of concrete you have isn’t Post Crete , for fencing ? . As a few of them have no stone , just a gritty texture , as concrete without stone / aggregate isn’t concrete .

 

[mrsbruce]

On investigation, the biggest stone I’ve found in the concrete is smaller than a red kidney bean, I then resorted to sieving it to find the dinky sized gravel mixed in there.

I think I bought it from Wickes, and it is a concrete base premix of limited depth capacity.

 

[arian]

You don't say what your wall is made from.

As a general principle, the mortar needs to be the same strength as the bricks/stones. If it's stronger, the bricks will crack; weaker, the mortar joints. [Edit: I'm late to this party]

Old-fashioned people would think of lime mortar, which will likely be weaker than bricks. 9 soft sand/3 lime/1 cement is one version.

 

[Hitch]

If its been kicking about a while, chances are the cement aspect has gone off.

Not expensive stuff, wickes do a 'mortar mix' bag. Sand along with the right amount of cement in a separate bag.