New build, crack advice

Shinogi · 16 May 2016

I finished my shed build around October last year but I seem to have some cracks in my mortar, in the step formation, on both walls in the center of the building. The cracks are on the interior and exterior but show more on the internal with the gap being wider at the top. Does this sound like it's settling or is it too early to tell? The crack at it's worst is a fingernail width in size.

Worst internal wall

Other side below a window

External under window

The cracks are in the same place on opposite sides, inside and out. The external wall of the first picture has a very faint hairline crack so didn't take a picture. Researching on the net and it seems like a step crack is more than likely settling in a new build but a few say subsidence. What would your thoughts be?

Bit of background, double skin wall with 75mm celotex insulation, flat warm roof and insulated concrete floor. Build has been complete for around 7 months and foundations are in hard clay 750mm deep (clay started at 300mm)

Thank you in advance...

^woody^ · 16 May 2016

Stepped cracks on both sides of a cavity wall are more likely to be foundation movement than anything else.

It might be really settlement, but you won't know unless you monitor it for a year or so.

Shinogi · 16 May 2016

Thank you for your reply. I don't plan on doing anything with the shed till maybe next year now, besides a second/third coat of exterior paint, so the block work will be exposed till then so I'll keep my eye on it. With it being a shed, what size does the crack need to get to before I have to be concerned? If it does get bad in the future, would replacing the mortar with fresh be satisfactory?

stuart45 · 16 May 2016

Any trees close by? All buildings have settlement in clay, but as long as it's the same all round it's not a problem. When there's differential settlement you can get some cracks.

Shinogi · 16 May 2016

The next door neighbour has an apple tree quite close to one side.

KenGMac · 16 May 2016

Shinogi, hi

As woodie has posted, keep an eye on the cracks, but?

Were the blocks dry when laid? or were they damp / wet when laid, given there was a load of rain last year.

Also if the Cement mix was too cemented it could be brittle? and or too strong for the blocks, there is a definite Co-Relation between the strength of the mortar and the stated strength of the blocks, or indeed the brick, where used

As an aside, sorry to mention it but? you really need to insert more fixing screws into the roof hold down strap, as far as I can see on the image you have uploaded there is only one screw holding the roof H/D Strap?

Ken.

Shinogi · 16 May 2016

Hi Ken, there are 9 screws in the strap, I had to zoom in on the picture on my phone to see them too

The blocks were stored outside in the elements but most of them were bone dry when laid, apart from a splashing from a wet rag from me as I believed that is what you had to do, unless I was wrong? The build was completed over the space of about 5 months as I did bits here and there after work so some of the blocks would have been damp, not wet, from the weather.

My cement mix was 1:5 cement and builders sand with plasticiser.

stuart45 · 16 May 2016

KenGMac said:
Shinogi,

As an aside, sorry to mention it but? you really need to insert more fixing screws into the roof hold down strap, as far as I can see on the image you have uploaded there is only one screw holding the roof H/D Strap?

Ken.

Could be my eyesight, but it looks like there's about 6 in the strap, although it is hard to be sure.

Shinogi · 16 May 2016

Defintley 9

From the top holes down, 3,4,5,6,8,13,14,15,16

KenGMac · 16 May 2016

Shinogi, hi

Too many numbers for the Euro-millions?

ken

stuart45 · 16 May 2016

Shinogi said:
The next door neighbour has an apple tree quite close to one side.

Apple trees are moderate water demand, but I would guess that it's not a problem as it's much higher than the footings. Also depends on whether the clay is the shrinkable type as well as being high/medium/low.

KenGMac · 17 May 2016

Shinogi, hi again

OK Plenty of fixings, on to many occasions i have had to pull up a contractor on these?

As for Clay Subsidence??? as previously posted, Apple are considered as moderate, but there is a layer of top soil to consider, also remember last Autumn / Winter? it was far from Dry? again we are not into the Clay shrinkage season yet, not in a drought situation, no huge days / weeks / of schortching sun and high temperatures

As I do i work in the Subsidence Insurance "industry" there has not been a large Clay Subs Event for some time now, even in London, which is notorious for such problems, weather conditions have conspired by raining to prevent such large scale events

As an aside? what is the condition of the garden wall? is it showing indications of Subsidence? it is after all nearer the Apple tree than the Workshop, and the walls foundations are much less robust than your Workshops foundations?

Ken

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New build, crack advice

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