Crumbling cement in New Extension

MKJRH · 24 Jul 2014

Hello,

I'm hoping someone can advise me...

I am having a small extension built and I am in a bit of a battle with the builders as the cement between the bricks on the outside of the extension can be scraped away with gentle pressure - in places just with a rub with a finger... In less than a minute I scraped out 50 - 60mm with a blunt screw I picked off the floor that the roofers had dropped! Give me 5 minutes and I could start taking bricks out!

The builders have promised to repoint it all, but have so far just done a "patch" job and there are still lots of weak areas.

I am going to push them to repoint it all, but my concern is that even if they take out just 20mm or so, and fill it with decent cement the stuff behind will still be very weak and barely bonded to the bricks.

I strongly suspect that the cement in the blockwork is the same - crumbly, weak and barely bonded to the blocks - but that has already been covered with plasterboard so I can't be 100% sure.

I'm not an expert so can someone tell me if a simple repoint be enough to solve the problem and what are the long term implications of crumbly cement in these walls? Will the structural strength be reduced? Should building control sign it off?

Any help / advice gratefully received.

Thanks.

freddiemercurystwin · 24 Jul 2014

After a couple of years your extension will be approximately 300mm lower!

/sorry couldn't resist, someone more sensible will be along soon!

Coaster · 24 Jul 2014

that sounds worrying! did you get the builders
on recommendation?

If the cement mortar was like that the day after then I'd stop the work and get a second opinion from another reputable builder or get advice from the CAB ASAP.

If they've messed up the mortar I don't think they'll have done a proper job elsewhere either.. e.g wall ties/damp proofing foundations etc.!

if they wanted paying up front.. could start work immediately or in just a few days (good builders are usually booked months in advance) they could be poor quality builders.

Actually! call trading standards too.. ASAP

tony1851 · 24 Jul 2014

freddymercurystwin said:
After a couple of years your extension will be approximately 300mm lower!

/sorry couldn't resist, someone more sensible will be along soon!

You are horrible!

Joe Malone · 26 Jul 2014

It seems fairly obvious that the builders have used an overly weak mortar mix but you have to prove it and the only way is by petrographic analysis. Try to get on record what mortar mix the builder claims to have used then have a sample of the mortar sent off to a lab that does petrographic analysis. If it's as weak as I suspect then I would have it taken down and rebuilt, repointing won't be good enough if you want a building that stands the test of time. With the test results in hand you have evidence with which to take more formal action.

jeds · 28 Jul 2014

Joe Malone said:
It seems fairly obvious that the builders have used an overly weak mortar mix but you have to prove it and the only way is by petrographic analysis. Try to get on record what mortar mix the builder claims to have used then have a sample of the mortar sent off to a lab that does petrographic analysis. If it's as weak as I suspect then I would have it taken down and rebuilt, repointing won't be good enough if you want a building that stands the test of time. With the test results in hand you have evidence with which to take more formal action.

Second that. Have it tested. Know exactly what you are dealing with. then take advice from a professional. I would advise a chartered structural engineer or building surveyor.

fmck · 28 Jul 2014

What did your local authority building control say? If they say no then the builder has no option but to redo.

JohnD · 28 Jul 2014

have you paid them?

simonjay · 29 Jul 2014

MKJRH said:
Hello,

I'm hoping someone can advise me...

I am having a small extension built and I am in a bit of a battle with the builders as the cement between the bricks on the outside of the extension can be scraped away with gentle pressure - in places just with a rub with a finger... In less than a minute I scraped out 50 - 60mm with a blunt screw I picked off the floor that the roofers had dropped! Give me 5 minutes and I could start taking bricks out!

The builders have promised to repoint it all, but have so far just done a "patch" job and there are still lots of weak areas.

I am going to push them to repoint it all, but my concern is that even if they take out just 20mm or so, and fill it with decent cement the stuff behind will still be very weak and barely bonded to the bricks.

I strongly suspect that the cement in the blockwork is the same - crumbly, weak and barely bonded to the blocks - but that has already been covered with plasterboard so I can't be 100% sure.

I'm not an expert so can someone tell me if a simple repoint be enough to solve the problem and what are the long term implications of crumbly cement in these walls? Will the structural strength be reduced? Should building control sign it off?

Any help / advice gratefully received.

Thanks.

What does the building inspector say ?

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Crumbling cement in New Extension

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