New Build - Cracked Render

[dtaylor1984]

Hi,

Last year I bought a new build semi (it was built approximately 18 months ago). It is timber framed with rendered brick exterior. The gable end has now developed a number of cracks in the render -- this is affecting both ends of this house, and the one next door (four properties in all).

The builders are now stripping the affected render off, and their plan appears to be to nail "chickenwire"-style reinforcement to the blocks before rendering again.

I am concerned that the mortar used was either unsuitable or incorrectly applied, as it is loose in places. I'm wondering if the builder is just attempting to cover up the problem with a botch, or if I am worrying unnecessarily?

I have a number of pictures here .

The biggest crack is at the right (rear) of the gable end between the ground/first floors:



After the render was taken off:



Loose mortar:


This appears to be the extent of their planned repairs (picture of next door):



Thanks for any advice,
David

 

[karun]

Chicken wire is normally used on very old brickwork or when you expect a lot of movement in the wall.

The problem is that a sand cement based render is always going to crack. The chicken wire may 'reinforce' and hold the render together but eventually as the building moves, expands and contracts, the sand cement render just does not have enough elasticity to move with the building and will crack.

If you can, I would recommend that you use a modern render which can certainly handle movement. The only disadvantage is that it comes at a price.

If you chose to stick to sand cement. Make sure the mix is 1:1:6. Lime softens the render hence lowering the possibility of cracks

 

[JimLoskot]

personnaly I would be worried that mortar between the blocks is coming out so easily in an 18 month old house.
I'm not a builder so it could just be settlement

 

[karun]

was the house built during the winter?

 

[dtaylor1984]

Yes, whilst the cracked render isn't great, I'm more concerned by the stability of the underlying blocks.

I'm not 100% sure when the house was built, but it was around Autumn 2010 -- I think it was completed before winter, but I'm not certain.

 

[^woody^]

It looks like you have a few things going on there

There are a lot of vertical cracks in the blockwork - which will be due to shrinkage (drying) of the wall and too strong a mortar. The strong mortar was not flexible enough to allow the blocks to contract, and hold them rigid - so they crack.

The loose mortar is normally related to this (ie strength) but could be due to workmanship, or building in very dry/hot weather - it can be dry in winter too. But there are some seemingly large joints there - which is not a good thing

The crack around the lintel is related to shrinkage of the masonry around it

The stepped cracks can be shrinkage or the way the wall was built (workmanship).

The may also be issues with poor design/specification of the frame or external leaf of masonry

From the photos, it does not seem like there is a major structural or foundation issue. Most probable just relating to shrinkage. But around that would be issues of workmanship, quality management and maybe design. So its not normal shrinkage.

The cracks may need reinforcement in the bed joints to hold it together and mesh across them to prevent any more movement cracking the render

Get an independent local report done (structural engineer or experienced surveyor) if you need to make any claims - ie the builder not accepting liability

 

[Nige F]

there are some seemingly large joints there

Christmas Joints - You always have a big joint @ Christmas

 

[karun]

i agree with woody, your best bet is to get a survey done

 

[ConcreteDrBill]

The main thing with rendering is matching the render with the materials used in the wall. Looking at the photos, it appears that even the mortar betwen the blocks has not bonded properly, suggesting that the blocks were too dry and sucked water out of the mortar.

If the blockwork was not dampened down before rendering, the same would happen to the render. If the mortar is too strong, its shrinkage will also help to cause cracking and debonding.

I agree that an independent survey is the best way forward, so that any repairs/rerendering is fit for purpose