Full length wall crack Thermalite ? blocks

[VinnieG]

Greetings all

The crack in question is in an integral garage ( right hand side as you look at the picture of the house ), is hairline, runs pretty much vertical, through mortar in places and in other places straight through the blocks (which I think are thermalite but may very well be wrong ) themselves.

There is a beam running across the roof with a concrete block underneath this ( pic 3 ), I assume is supporting the outer upper front wall of the house which is recessed from the garage entrance. The crack starts pretty much underneath this and runs down to the floor.

House is built by Miller, approx 9 years old. Can't say how long this crack has been there, first time I've noticed it. No noticeable cracks anywhere else in the walls and the concrete underneath the supporting beam is intact.

Being completely clueless, should I be worried or is this common? Any thoughts v. much appreciated.

Regards

Vin

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• VinnieG
• 5 Mar 2014
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• VinnieG
• 5 Mar 2014
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• VinnieG
• 5 Mar 2014
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• VinnieG
• 5 Mar 2014
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[conny]

I would suggest you just keep an eye on it for now to see if it opens up any more.

You can glue a few strips of glass across the crack in various places, (they only need to be about 100mm x 25mm x 3mm thin glass), and if there is any movement the glass will either shear or become unattached on one side.

 

[tony1851]

Perfectly normal as long as the crack is roughly the same width all the way down.
Due to shrinkage of the concrete block, and the lightweight ones are notorious for this.

 

[VinnieG]

Thanks very much for taking the time to reply folks.

Tony, the cracks get slightly wider towards the bottom and where they go through the mortar, but even at their widest they are only approx 1.5mm.

Further to my previous post the cracks don't actually go all the way to floor level, they stop approx 6 inches from floor where there is some sort of membrane layed in between the blocks.

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• VinnieG
• 9 Mar 2014
• 1

On closer inspection there are quite a few more cracks about the garage, couple of them full length wall cracks.

Just had a few questions if someone could help?

1. What causes the shrinkage that Tony talks about, why is it so common. Should I expect to see more over the years?

2. Why do the cracks run through the blocks at some points and at others through the mortar?

3. The cracks appear to be at random ( don't seem to be load related ) however the main ones are where I have a treadmill and weights bench. Could hefty weight, vibration be a factor or just coincidence?

4. Are the cracks just cosmetic or could they potentially cause a structural problem. Worth attempting repair/replacing or just stop being neurotic?

Thanks for patience

Vin

 

[tony1851]

Further to my previous post the cracks don't actually go all the way to floor level, they stop approx 6 inches from floor where there is some sort of membrane layed in between the blocks.

That membrane is the flexible damp-proof course. The fact that the cracks don't continue below that is further evidence that the cracking is not serious.

The vertical cracks are due to initial shrinkage of the blocks, which can be pronounced for lightweight blocks, the more so if they were wet when laid, and/or a strong mortar has been used. The damp-proof course provides a slip-plane; the blocks below that are probably permanently slightly damp, so won't shrink quite as much.

It's nothing serious; the time to worry would be if you saw similar corresponding cracks in the external skin.

 

[VinnieG]

The vertical cracks are due to initial shrinkage of the blocks, which can be pronounced for lightweight blocks

Thanks very much for the info Tony. You talk about initial shrinkage, so presumably the cracks have been there for ages and I just haven't noticed. And does that mean that I shouldn't expect to see more develop over time?

Cheers

Vin

 

[tony1851]

The vertical cracks are due to initial shrinkage of the blocks, which can be pronounced for lightweight blocks

Thanks very much for the info Tony. You talk about initial shrinkage, so presumably the cracks have been there for ages and I just haven't noticed. And does that mean that I shouldn't expect to see more develop over time?

Cheers

Vin

They generally form soon after construction, when the place is drying out; won't be an ongoing problem.

 

[VinnieG]

Thank you. Very much appreciated.

 

[Emeraude119]

VinnieG - Tony 1851 is correct regarding the width of a vertical crack. if it is of uniform width top to bottom, it is most likely to be a tension crack, At the foot of a wall movement `may / can' be arrested by the junction of the wall with the ground floor, which is why they sometimes do not go all the way to the bottom.
Cracks which change in width may be more serious, as those which are wider at the top than the bottom can be formed by hogging e.g something which lifts the wall from below, e.g a root from a nearby tree under the foundations, or where the foundations under a return wall have settled slightly.
Where cracks are wider at the bottom than the top, this `may' indicate settlement under the wall in question. but from your description it seems to be a simple drying shrinkage crack. Once the materials in the wall have returned to the normal (equilibrium) moisture content further drying shrinkage is possible but unlikely.
All blocks undergo drying shrinkage, but this varies depending on the type of block, and how well they were protected from bad weather during the site storage / building in phase of a project.
The aggregates in dense blocks tend to be impervious, and do not take on water, so the only way water can get into them, is via the cement / sand matrix between the aggregates. hence shrinkage in this type of block is less than that for lighter types.
Aircrete blocks are water resistant to the extent they float when placed on water, but if kept in wet conditions for long enough, water will travel through the cement, sand matrix which forms the body of these blocks, filling the tiny air bubbles (which are what gives aircrete blocks their lightweight and highly insulating properties) as it goes.
Consequently if allowed to get excessively wet, A. they can hold more water than an aggregate block, B. they can take longer to dry back to their normal moisture content, and C movement joints in aircrete blocks must be at a smaller spacing than can be used with aggregate blocks.
This is why protecting blocks (all types) from wet weather on sites is so important.
Whilst unsightly shrinkage cracks are rarely hazardous. therefore if sufficient time is given for the wall dry completely before the cracks are
repaired, they are unlikely to return.
Bear in mind that a Protimeter type moisture meter cannot be used to determine the moisture content of an aircrete block, because trace aluminium is used in their manufacture. So this will always give a high moisture reading. even if the block is actually bone dry

 

[kam2014]

Hello VinnieG - I am looking into buying a house which has got the similar issue in the garage as you described in your post. how's those Full length wall crack now ? are they any wider ? Did you got them fixed in the end... Thanks

 

[KenGMac]

kam2014, hi

The original post that you have found is over a year old.
Thermalite is notorious for vertical cracking especially is not covered with Plaster.

If the cracks are as described in this old post then there is not a lot to worry about.

 

[Tipper]

I have similar cracks visible in the thermalite type blocks in my garage walls now about 35 years old. Mainly below the flat roof joists where no padstones have been used. I'm not worried about them as I've always assumed they are shrinkage cracks and they are not changing in any way. Although cutting out and bedding in a padstone under each may be worthwhile I suppose.

Can cracks like these be cut out and repaired with mortar successfully?

Any advice on best material/mix to be used?

I'm only wanting them to be less noticeable to be honest, but there is the possibility that the garage could be converted into another bedroom in the future and so will be modified and plastered or dry-lined.

Thanks.