Badly made mortar?

[akist]

I had a set of bad/weird builders working on a garage conversion/annexe. They seem to have a strange idea of how to mix mortar, in particular how much cement to use in the mix. I believe they made the mix too lean, not enough cement. About two months on, I can take the mortar out using a wooden pencil, I can certainly dig into it and it crumbles like dust. I have tried the same on other mortar around the house, and if you rub it there is some dust that comes off, but nothing like how they have made it.

What is the best course of action?

 

[ktuludays]

If it's that bad, dig it out and repoint unless they're prepared to come back and remedy for you

 

[akist]

I have heard of repointing but had thought it was a decorative procedure to replace worn out mortar just at the visible front. Can it also be done for structural purposes by replacing most of the old mortar?

 

[Alastairreid]

Rake it out 25mm and repoint as already advised.
You cannot replace the mortar beds and perps without taking it down.
It's not going to fall down, the new pointing will weather it better.

 

[akist]

OK thank you for the advice.

 

[akist]

Just one more thing, I checked "repointing brickwork" on youtube, and the guy used a tool that runs on small wheels and a nail into the joints in between the bricks. As he was using it he explained that if the mortar is easy to remove, old type with lime mortar, or more difficult if it has cement in it. He proceeded to take out chunks of it using this nail. I presume therefore that it is common to make mortar with little cement and very easy to scrape off if needs to. If my assumption is correct, what is the advantage of not using adequate cement in the mortar mix (eg 1:3 - 1:4) and thus make it really strong?

 

[JohnD]

excess cement increases the shrinkage cracking, and costs more money.

Your weak mortar may also have been caused by drying too quickly, e.g. the sun was shining on the wall the day they built it. Cement hardens by chemical reaction with the water. For the very best results, cloudy, mist and drizzle for a week.

Once it has dried out, curing stops and will not restart.

p.s.
this is taken much more seriously with structural, precast and slab where strength and hardness are critical. Often these are covered and sprayed with water for a week or two. In Southern France (and presumably other sunny places) roadmakers do not place concrete until after noon, so that it will not be exposed to strong sun until it is about 24 hours old.

Underground concrete, such as tunnels and drainage chambers, that never dry out, can continue hardening and gaining strength for a hundred years or more, though it gets slower and slower as time goes by. if you ever try to break up old concrete in damp ground under a fencepost, you may notice it is harder than you were expecting.

 

[akist]

I am also aware that in hot countries after pouring concrete, they then visit daily in the evenings and hose everything down.

For our discussion, would a 1:3 or 1:4 cement:sand mortar mix seem excessive? Because I think I overheard the builders say 1:7 for the mortar which does not sound right.

 

[^woody^]

excess cement increases the shrinkage cracking, and costs more money.

Your weak mortar may also have been caused by drying too quickly, e.g. the sun was shining on the wall the day they built it. Cement hardens by chemical reaction with the water. For the very best results, cloudy, mist and drizzle for a week.

Once it has dried out, curing stops and will not restart.

p.s.
this is taken much more seriously with structural, precast and slab where strength and hardness are critical. Often these are covered and sprayed with water for a week or two. In Southern France (and presumably other sunny places) roadmakers do not place concrete until after noon, so that it will not be exposed to strong sun until it is about 24 hours old.

Underground concrete, such as tunnels and drainage chambers, that never dry out, can continue hardening and gaining strength for a hundred years or more, though it gets slower and slower as time goes by. if you ever try to break up old concrete in damp ground under a fencepost, you may notice it is harder than you were expecting.

Cool story. It's got FA to do with the OP though,

As shiite as the builders were, I don't think they have used concrete to lay the bricks.

 

[^woody^]

If my assumption is correct

No it's not.

You're shiitest, shiite, crappy builders just keep on giving don't they.

The only place that it is "common to make mortar with little cement" is at your house.

 

[stuart45]

Just one more thing, I checked "repointing brickwork" on youtube, and the guy used a tool that runs on small wheels and a nail into the joints in between the bricks. As he was using it he explained that if the mortar is easy to remove, old type with lime mortar, or more difficult if it has cement in it. He proceeded to take out chunks of it using this nail. I presume therefore that it is common to make mortar with little cement and very easy to scrape off if needs to. If my assumption is correct, what is the advantage of not using adequate cement in the mortar mix (eg 1:3 - 1:4) and thus make it really strong?

The tool on wheels you are talking about is probably the one used for making recessed joints in new work rather than raking out for a repoint.
Mortar needs to be weaker than the bricks so 3/1 is normally too strong. NHBC guidelines are 1/1/5.5 lime/opc/sand or 1/1/4.5 for more exposed face brickwork.

 

[Charlie George]

stuart45 believe it or not chariots are sold as a tool for raking out prior to pointing, but the only way i ever see them used is the way you said.

 

[^woody^]

stuart45 believe it or not chariots are sold as a tool for raking out prior to pointing, but the only way i ever see them used is the way you said.

They (Marshalltown Scorpion) are for raked out pointing, that's why they have the tail to iron the joint afterwards.

You'll kill your wrist trying to use it on set mortar.

 

[Charlie George]

The MARSHALLTOWN joint raker is a great hand tool to rake out mortar for restoration and repair.
From marshalltowns own website


FFX website

Designed for clearing out mortar from between brickwork prior to pointing.

The strong aluminium handle is contoured to fit the hand and squared off at the end.

With two large hardwearing wheels and replaceable point.

 

[stuart45]

They are only really any use on really soft crumbly mortar such as old lime mortar, apart from new work, but I suppose it's up to them how they advertise the product.