Will A

Hi, I'm pretty sure that the blocks are from H+H and are either Aircrete or Celcon, they have a green stripe on their edge which seems to indicates that they are 2.9N/mm. Around a year after we bought the house (new build 2017) we noticed that mortar joints were falling out, just 4 or 5mm deep, this turned out to be where they had repointed, we found that the mortar under this was soft and flaky, the developer engaged the BRE to carry out an inspection, they removed multiple bricks from different locations in the outer leaf and took mortar samples for petrographic testing, they also gave me samples so that I could get my own tests done, when the bricks were removed it was found that they had been laid frog down and that the perps were mostly just tipped, an inspection scope inside ethe cavity found that a lot of the bedding joints were deeply recessed and there were a limited amount of wall ties present in the areas checked, both ours and the BRE petrographic tests found that the mortar contained between 32 and 40% voids, the BRE claimed that the additional air in the mortar mix was due to the use of a dry soli mix, I did a bit of digging on this and it appears to be true, dry silo mixers are unable to control the amount of air added into the mix, although some of the newer silo mixers are now able to control air intake. Obviously the more air in the mix the more voids will be present once it cures, and the more voids the weaker is it, it also appears to have an impact on bond strength due to the lime in the mix being unable to protect the shell of the voids, over time this leads to smaller voids to coalesce, the mortar manufacture doesn't use a silo when batch testing their mortar, so while batch samples might meet the compressive strength testing for M4 the actual mortar is much weaker. As with most new builds the otter leaf of brickwork isn't loadbearing and only needs to carry its self weight and lateral wind force, and most are protected from severe wind when in large developments, the problem that concerns me is the cracking to the blocks which I assume is holding the outer brickwork in place to some degree, the vertical cracks are logically just unbonded joints and given that they are present in the gables there would be limited compressive force holding them, which I assume is why we don't see cracks in the blocks at the peak of the gable.

No I don't believe there is

Thanks Gus, It was the manufacturer who said that the blocks shouldn't shrink 5 years after the drying out process should have completed, that said the blocks appear to have a darker shading around there edges which looks like moisture, the outer leaf is brick which we discovered has been laid frog down and unfilled, plus a large amount of the bedding joints are recessed on the cavity side and the perps are mostly tipped and not fully filled, on the outer joints it looks like some repointing was done and you can see chipping to the edges of bricks where a tool was used to removed the mortar, petrographic tests on mortar samples from the joints appears to show that a second layer of mortar was applied, samples from the edge and the middle show very high air/void content in the mortar (between 32 and 40%). There's not insulation within the gable cavity, which I understand isn't required, so I'm wondering if wind driven rain is penetrating the outer leaf and soaking the inner leak of blocks, although that seems a stretch. Some of the blocks sound hollow if you knock on them so I suspect that those are cracks in their width, assuming that the vertical cracks are caused by shrinkage then it seems probable that the shrinkage would be equal to the blocks width, heigh and length, all 4 roof verges have failed and rain water is leaking in, so maybe the heigh shrinkage has created a small gap to the verges, we've also had around a dozen roof tiles crack along their join channel, which I suspect is being caused by a downwards pressure, the leaking first appeared towards the end of last year and the cracking to the blocks started around Jan this year, the cracking stopped around July but has started again in the last month.

They said that the blocks shouldn't shrink 5 years after the drying out process would have completed and advised that I have a structural inspection performed, my house is under NHBC warranty so they agreed to have one done, not that I hold much hope of that report being unbiased, once I have that I'll have my own performed

These are the gable walls, the black lines are where the crack run

My neighbor has the same blocks and none are cracked, both houses built just a few months apart in 2017, my blocks started to crack this year, probably 80% of the blocks to the gables have cracked. However I suspect that the cause of the cracking is due to water ingestion, I can see a darkening around the edges and moving to the center of the blocks which have cracked, most blocks are jumbo length 162mm and contain between 2 and 4 cracks. So my blocks likely shrunk, what I don't understand is why they cracked if the shear bond strength of the mortar and the blocks are both 0.15N/mm, the compressive strength shouldn't be a factor since its the shear strength which holds the block in place and causes it to crack when it shrinks. Even if these blocks shrink but didn't crack wouldn't this then leave gaps between the block and mortar joints?

Hi, I've read a number of times that vertical cracking in aerated blocks is often caused by the mortar being stronger than the blocks, this causing the blocks to crack if they shrink, however why is the compressive strength of the mortar a factor in this? surely its the shear bond strength which would need to be greater in the mortar to prevent the block from cracking when it shrinks.

From my understanding if its a normal 2 story house with egress windows then you can follow the basic advice given in Approved Document B, this being a smoke alarm in the hallway/landing and in access rooms, if the house has an internal garage then there are additional requirements. If the house doesn't have egress windows but rather an escape strategy of protected stairway/corridor, then you need to follow the advice in the Building regs and have a fire assessment performed.

Hi, Looking for some input regarding the sudden appearance of cracking to the Aircrete blocks to the gables. The house was built in 2016/17, the mortar used to construct the block walls is M4. Cracking to one gable started to appear 5 months ago, and to the second last month. The run of the wall is just over 8.5 meters and no movement joints were installed, the outer leaf is brick. Should I be concerned? Thanks in advance The white X marks where each crack is, the cracks appear to run vertically and the mortar is also cracking.