Freaking out about cracks while I’m still building!

[Rob broom]

Hi!

I have a few concerns about some cracks on my self build that I am half way through.

This is my first project, I might add!


I have found a few hairline cracks and wonder if I should be freaking out?

Here is the story:

the site is 8m x 7m

I dug the foundations myself! I dug down around 2-4 metres in places into fresh/virgin soil in our uneven garden.

The concrete in the trench is a minimum of 375mm deep by 600 wide. It’s probably a bit deeper and wider in places. I made sure that the digger bucket excavated with the teeth slightly upward, so as never to drag the bottom of the trench. So all soil in the trenches is nice and compact.

Everything has been done to the structural engineers calcs.

the building control officer has inspected the soil and trenches prior pouring the concrete and blocking up the foundations. He then also returned to see DPC.


he was happy through the process.

The concrete was poured in august last year. I then began to lay the courses of blocks in the evenings, at weekends and in some spare days off work.

It’s 100 wide block outer leaf, with 140 block inner, with a concrete filled cavity up to 200 ish below DPC! Above DPC is n7 outer leaf with 3.6 aerated inner leaf.

The build is a 1 & 1/2 story build, with a room in the roof basically. To keep the rooms free of any load bearing support, the engineer specified a RSJ ridge beam and 200x47 rafters at 600 centres. The RSJ sits on a padstone, above a Heavy Duty Lintel in the wall, and upon a 100x100x5 box steel uprights elsewhere.

I was able to progress a lot more due to being at home during the lockdown in January to April.

I eventually lifted the RSJ ridge be into place in February/March. I have since then been adding roof rafters, building dormer windows and rolling out membrane and nailing in battens!

in the last two weeks, I have noticed some cracks they mainly follow the mortar, but has split a n7 dense block in half too! All issues are in the centre of the window reveals on the first floor, about 2 courses above DPC!

There are no issues, as far as I can see, in any other areas of the walls or the directly bearing block work sections. It’s just under the windows. I’m guessing that there is less pressure on these areas?

The cracks do not go down near the DPC (yet) and are not visible in the foundations.

My main question is, would anyone expect me to see some cracking under the windows, due to the fact that these block corses were laid back in September and october last year, and have only just recently started to take to load of the roof above?

Could it be a little bit of uneven settlement, with the load bearing bits settling a deeper and heavier than the unloaded sections? Is so, should this stabilise once the roof is finished and the tiles are all on etc?

Or should I be getting the digger out and get down to the foundations and have a better look at them?

Would bad weather have kept these areas moist, moist enough to make them softer than other areas, due to the fact that the rain can soak down through these exposed window reveals?

The cracks are only hairline, and you really need to look hard to see them! But now I know they are there, I can’t un see them! I have no idea how long they have been there, I only spotted them recently! They could have been there for ages!

i re pointed one crack about two weeks ago and it hasn’t returned. (Touch wood).

the only loading left to go on this wall is the roof tiles! The floors are supported by the returning walls!


Should I just keep calm and carry on?

Im pretty confident that I’ve done a good job, but a little bit of doubt is creeping in!

Any help would would be really appreciated!

i can’t sleep!

I will try to upload some images later!

 

[tony1851]

Normal shrinkage of concrete block!

don't doubt yourself!

nothing to worry about!

sleep soundly!

 

[Rob broom]

Hope so!!!


Thanks!

the more people that say the same as you the better!

To anyone else that is looking at my post, and the sketch that I made, I hope you will concur that it is just a bit of loading settlement and shrinkage as the point loads are absorbed!!?

Thanks!

 

[oldbutnotdead]

4m deep trenches (or even 2.4m) and strip founds? Thats insane.
Summary of your problem- you've got some cracks in the walls below windows. Those sections of wall are lightly loaded so there's a bit of settling going on. Did you use any plasticiser in the mortar? Is your house built on made ground (ie is there an old industrial site or mineworkings or anything similar below). Did you pour the foundations in one 2 hr go or did you do them in stages?

 

[Rob broom]

Hi!

Good relevant questions!

I did everything all by myself and have the following answers...

defo used admix every time.

its a quite a sloped garden, that was untouched, so I had to dig out a lot to get down to a working height, then I dug the foundations. So defo not made up ground.

Foundations, they were stepped, and i did each strip on separate days, in stages, so definatly not done in 2 hrs or even the same day.

I added re- bar to all connections and washed/wetted the aggregate around the joins each time, as per engineers instructions.

cheers

 

[Rob broom]

Also, defiantly no mines, drains, trees or weird things underground!

the ground is very dry and stoney! No clay!

 

[^woody^]

I'm freaking out about deja-vu

 

[Rob broom]

Yeah.... the de ja vu was the thermalite and celcon blocks!

I got over that! I realised that everybody had a dim opinion of them!

But the exterior blocks and mortar cracking started to worry me again!

 

[cdbe]

That's an impressive looking DIY job! As someone doing a similar (painfully slow) DIY job I think the advantage is that all the minor settlement/shrinkage etc occurs before you get to the final finish of render and internal plaster which would almost certainly crack all over the place if you'd had a builder throwing the whole lot up in a few weeks.
I'd ask on the plastering forum for advice on mesh or reinforcement over the cracks when you get to that stage.

Here's one of mine, it's mid span on a 4m steel with another floor and roof on top - if you can't see it by zooming in it's just above the bit of wood. Doesn't worry me.

In other areas of the original house I have steels supporting first floor walls which now have cracks in, and while a little disconcerting at the time I'm not worried because I figure this means the walls have now firmly settled onto the steels and are not "floating" as masonry sometimes does and they're not going to "drop" onto the steels in the middle of the night in 6 months time.

 

[Rob broom]

Wow.


Thanks for taking the time to reply!

Yeah, I’m really pleased with my achievement so far, considering this is all new to me, but I’ve got to admit I am feeling concerned about the cracks.

I’m hoping that it is a minor bit of differential settlement between the outside walls and the end wall, as the different parts of the build take to load of the roof?!

With the exterior blocks, Should i just let everything sort itself out and repoint the cracks in a year or so?

Should I chop out the cracked blocks and insert new ones, or should I fill the cracks with some mastic type Filipe prior to external render.

The ground conditions were brilliant when I dug the foundations. Solid and bone dry! Then we had a wet spell over the winter months, followed by glorious sunshine now.

Could the changing conditions have effected the ongoing settlement?


I’m ever so slightly in the verge of staring to have a melt down over this!

Many thanks for anyone that offers advice or suggestions!

 

[^woody^]

I hope you will concur that it is just a bit of loading settlement

Settlement, is anything significant would normally be even and so should not cause any cracking in a new detached building. There should be very little shrinkage in concrete blockwork.

It is certainly unusual for a 7N block to split, and even more so when it is in only two course of blockwork.
Not impossible, but unusual.

Is the mortar super strong?

 

[Rob broom]

Cheers

I didn’t measure the mortar absolutely perfectly, and it’s probably a tad stronger than a ratio of 1 to 5.

I think it’s probably about 1 to 4.5.

basically it was 4 decent scoops of sand to one scoop of cement. With admix added.

The cracked blocks in question are pretty much in the centre under the windows.

it goes down though a mortar joint, then directly through a block.

cheers

 

[^woody^]

Assuming there are no other cracks on other elevations, best guess would be a combination of exposure - the orientation of that elevation, and the rain being allowed to get into the top of the wall via the cill being uncovered, and this leading to rapid changes in moisture content in a relatively small section of blockwork.

It may need repairing before rendering.

All walls/sections should be covered to prevent moisture getting into the top of the wall until the final/permanent topping is formed

 

[Rob broom]

Thanks Woody.

Another rookie mistake then to leave the blocks exposed.

I looked back through my photos and They have been exposed since mid October. So that would be 5 months to date, through rain, frost, and now lush warm sunshine!

Hopefully your right with the moisture getting in there.

When the cavity trays were installed with the lintels above, I noticed that that obviously encouraged more water to drip down into the exposed blockwork in question.

during rainy day periods, there were frequent wet patches all around the area in question.

as I say, there are no cracks in the other areas, so i suppose the vertical load running down through the columns from above is helping to tie them together. This would encourage the shrinkage and movement to be let out in the weaker section of the wall under the window where there is zero loading from above?

If it’s settlement, maybe the settlement is acting down along the bottom of the end wall in a M shape, causing the 3 points under the most load to push down and the areas under the windows to heave upward a fraction?

hopefully this will be a one time issue that will fully settle in a year or so?

mum in no rush to render it yet, so I’ve got at least a year to watch and monitor it.

The cracks are all hairline at the mo, and I’ve seen that you need to wire when it’s a few minutes apart, any you can get a pound Cohn in there!

I’m just hoping that somebody out there can say “I had exactly the same issue, and it either stopped, or further work was required!

many thanks to you all once more.