Soft Mortar Joints In Places

[PSE]

Hi

We've noticed in our new build property that there are areas where the mortar joints seem soft and crumbly.  We've reported this to the builder who has said it is surface frost damage.  They've had a company that specialises in brick and mortar repairs visit the site and have proposed that when the weather is a bit warmer they attend and rake out the damaged mortar and re-point.  I've asked the builder that I would like the mortar lab tested to try to find out what was the cause of it being soft and crumbly in places.  I've recently noticed though in a couple more areas where under the surface of the mortar there are areas of black in the mortar joints that is more like charcoal??  I'm obviously now extremely concerned with regards to what this is and what has caused this.  Before I go back to the builder with this I wondered if anyone has or had anything like this problem or what the cause maybe??  I've searched the internet but not really found any answers.

Thank you in advance.

[New Home Expert]

First of all, I have no idea what the black in the mortar could be.
At a guess I would say it could be an iron compound but that would rust, or black powder used to colour the mortar, or indeed black, rotting pieces of wood/charcoal.  It will need to be analysed.

You have a Bellway house and Bellway have some history in building homes with weak mortar, this instance had disastrous consequences for the home owner.  In this instance the roof repair was "botched" and the mortar was found to be weak and the wrong specification of bricks were used. I believe the NHBC bought the house and it was demolished although "Col" probably signed a Confidentiality Agreement aka "gagging order".

It is possible that frost is the cause, with the action of  freeze-thawing. 
It could also be that the mortar had not sufficiently cured (and/or was not protected) and was subject to freezing temperatures.
The mortar [it looks like] may not have sufficient cement in the mix but this would need to be tested in a laboratory to confirm.

Is this in just one section or band (known as a lift in the industry) of about 1200 to 1500mm in height or is it on a whole elevation?
If it was a band it could be just frost damage. 

You could use a car key and twist in into a joint and see how far the mortar crumbles and it goes in.
If it stops or is harder after 12mm or so then re-pointing may be a sufficient remedy.

What you really must do is WRITE to the NHBC now, notifying them of this. It is structural and they may have to sort this out in the years to come!

 

[PSE]

Thank you for your reply and advice again.

It's certainly on two elevations like this but on the other two elevations it's partly rendered so partly hidden.  On one elevation it's at about 1.25m from the ground and also at about 4m.

Thanks again.

[New Home Expert]

As it is not everywhere, it is probably frost damage. It appears to be at the top of the day's lift, the last brickwork laid so that would be the wettest and more likely to freeze and be damaged.

I am also assuming Bellway used ready mix 'Silo' mortar and did not batch it on site from a pile of sand and bags of cement.

[PSE]

The mortar seems soft in a few places and if you rub your finger along the bed you can get sand to fall but if you rub your finger along the mortar say on the detached garage it's very hard and get no/very little sand to fall. 

As for the black in the mortar that's certainly on at least two elevations, and looks like if I were to scrape the light covering away it would be visible in quite a few places. It also looks like the builder has covered this over prior to completion hide it. 

The areas like in the photo where the vertical joint has washed away is only visible though on a few joints.  The house is also 1/4 rendered  (two elevations all brick and two elevations 1/2 render) so obviously well hidden there.

Thank you again for your reply.

[New Home Expert]

Sounds like frost damage to me caused before the mortar had set/cured.

[PSE]

We eventually had a NHBC Resolution Meeting regarding the soft mortar in some places.
The NHBC requested Bellway Homes get the mortar tested on all four elevations with one sample from areas where it showed signs of erosion and one area where it looked ok on each elevation.  The samples would then be split into two, with one sent to the lab for testing whilst the other was left with me so if I required my own testing done. 

The results from the tests should be sent to Bellway, the NHBC, and myself.  I opted to have my own testing done on two samples with one being from an elevation that showed signs of erosion and the other from another elevation where it looked ok.  I had my results back today from my tests and it shows the mortar to be a 1 : 8 cement:sand  mix on both tests, I checked with the NHBC Technical Dept. and they informed me it should be 1 : 4.5 for my area.  I'm yet to receive the results back from Bellway for one reason or another.  I also have a meeting tomorrow with their Customer Care Manager.

Obviously as the NHBC are involved so they will probably have the final say but what should really be done regarding this and what should I be asking for (apart from my money back)?

Any help and advice will be gratefully received. 

[New Home Expert]

You might like to look at this.
A Taylor Wimpey buyer with exactly the same problem.
https://www.facebook.com/Taylor-Wimpey-Disintegrating-Mortar-637387146438116/

For a start you should get the test results from Bellway.  Call your NHBC contact and ask if they have had the test results. 

The "solution" is likely to be to rake out 25mm of the joints and re point with stronger mortar.
This might be acceptable for frost damage but not for weak mortar.
However, most wall ties will not extend to within 25mm of the face of the brickwork. Whilst this will weatherproof the brickwork and stop the weak mortar eroding further, it does not mean the wall is secure and fully attached to the inner skin.
This will mean the cavity wall stability is in doubt.
You may have seen on the news what happens when this is the case as in the school in Edinburgh.

As far as I can see, the only solution is to take down the brickwork and re build it with the right mortar.
The trouble is, your home is unlikely to be the only one and this extensive work will mean others will complain too, perhaps the whole development!
Neither Bellway, the NHBC and perhaps you from a hassle point of view will want to do this.

[PSE]

Thank you for your reply and advice.

I did contact the NHBC yesterday and they have not yet received their copy of the testing results. 

The builder is visiting today as we should be moving out next week for them to do the remedial work to the bay windows and the supposed frost damaged mortar joints.  I will now cancel this until we have their testing results and have accepted their and NHBC proposals on this.

Thank you once again.

[PSE]

Just to update you.

The builder verbally gave me the results from their testing today and from the 10 tests that were done the results were virtually the same as mine, ranging from cement:sand 1:7 to 1:9. 
The mortar company that supplied the mortar have said it should have been class M4 but looking on the Cemex site M4 equivalent would be 1:5-6.

[New Home Expert]

From the NHBC Standards, the mix the NHBC quoted -  1 : 4.5 would appear to be for masonry cement, not ordinary Portland Cement (OPC)
The correct mix should be -  1 : 5.5.

Now the big question is, clearly the supplier didn't supply the right mix, which lets Bellway off the hook financially, although they should be putting it right for you.  CEMEX will no doubt try and fight this too.
But the facts are clear, the mix supplied is 1:7 at best.
From CEMEX website mix tables this means the strength of the mortar is around half (2N/mm2) what was specified (> 4N/mm2) and presumably ordered.
Worthy of note,  CEMEX website also states:

Advantages
CEMEX Dry Silo Mortar systems have a number of advantages over traditional site mixed mortar.

• Guaranteed strength
• Guaranteed cement content
• Controlled air content
• Consistent colour
• Increased site productivity

[PSE]

Thank you for your reply.

The actual mortar supplier was Marshalls Premier Mortar.  I used the Cemex site to compare a 4N/mm2 to show what mix ratio it should have been.

Thank you once again for your help and advice.

[PSE]

This is the actual (or should have been) M4 Ready To Use mortar that was used above DPC.

http://www.premiermortars.co.uk/mortars/ready-to-use-mortar

The data they supply does not give you an actual mix ratio and only compressive strength, and shear strength for each Ready To Use Mortar class unlike the Cemex site.  I have emailed them for a equivalent mix ratio but I'm not sure if they would supply me with this information??

[New Home Expert]

I suspect that the mix ratio might be commercially sensitive.
Nevertheless, The mortar they have supplied failed to comply with Bellway and NHBC specifications.

[PSE]

Thank you for your reply.

They did reply and the mix ratio is 1:6