Garage Dilemma

Hi,

Not a true gardening problem, but it is in the garden ..

We have a concrete block built garage with full foundations that all ok, but many years ago a small extension was built on to it in the same blocks, but it was just put onto a 100+mm concrete raft that was the excess concrete from the original base pour.

It has suddenly developed some 1mm cracks all down one side of the wall, plus a shift of 6mm can be seen on the rear walls dpc where the top part has 'slipped'

While the solution/s may be clear it a case of whats the best way to remedy it in a practical sense, as we are not as fit and young as we used to be, though we have the time to do it steadily.

A friend who has done a lot of diy building work suggests just leaving it and pointing up the cracks as he reckons it only slight compared to some of the movement he has seen, though not so sure I share his confidence ..?

We could remove the whole lot and rebuild with proper footings etc, but for that extra 4ft is probably not worth all the effort and time.

Underpinning seems like an option, though we can get to all sides it is a bit limited, but being right at the back of the garden its a lot of digging and mixing of concrete and moving it all about etc.
Don't know if anyone has done such similar work and can say how difficult such hand excavation is ?

The last way would be to just knock down the block extension , leaving the raft base there and put up a 8x4 lean to shed instead, at least half of its weight would be taken by the wall of the garage.
There would little stress on the raft, compared to the weight of those dense concrete blocks, plus if it did move any more it would be easy enough to compensate for by putting the shed on adjustable feet / blocks.


Any thoughts please....

 

Hi i have a brick shed and extention oppersite but I have a wide gab between the two unlike yours but if I HAD that problem I would get an expert in to it check what could be done you could find several in checkatrade orTrustATrader and ask several dont go for first opinion

 

Its on the rear wall of the extension, seems the raft has dropped slightly at the back and rather than create a gap , the blocks have slipped on the damp proof course by about 6mm.
Also where the raft meets the main base there is a similar gap, if you can see what I mean from the exaggerated pic below, though the cracks all up the wall above the dpc are just 1mm.

Have filled in those 1mm cracks with a hard filler so if there is any more movement it should show up easily ,done similar things to see if those raft movements increase.

Perhaps being too finicky ..? its not as if its a danger to life or limb or housing the crown jewels, just a workshop space etc.

 

Actually the inside of the extension walls already have 2x2" wooden battens and insulation running up them so think even if the raft slipped a lot, its not just going to crash down without a fair bit of notice, but equally did not want to have lots of metal straps showing as it would not look good to any buyer if we do move. ( unless someone changes her mind again , shhh)

Thought about underpinning but with the concrete raft being thin, though not yet cracked, if we were to dig out a section at a time, the raft then might be too weak to support the wall and cause a major break before we could get the concrete in and set.

 

It actually has 2x2" timbers running up the extension walls with insulation etc so doubt it would crash down without plenty of notice.
Don't really want to have loads of metal straps showing as it might not look good to a buyer ( unless she changes her mind again , says he quietly ! )

Never done underpinning but our concern was with the raft being so thin, if we dug out a small section, would the raft and wall crack badly before we got the concrete in and set ?

Better go, some little beasties are banging on the tank wall for food, hope they do not need underpinning

 

I think as we get older we worry far more than we would if we were younger.
It may not apply, but these days, if I ever have a problem that doesn't require immediate H & S attention, I make a decision based on, "Will it see me out?" If I think it will, I'll leave it.

 

I wouldnt worry about it . Have you checked the guttering and drains to see if theres water leaks undermining the foundation.
Is there any vegetation nearby with roots damaging the foundation or using the water causing shrinkage?

 

Underpinning wont cure lateral movement.

Have you put a spirit level on the 'extension' floor?

 

Hi,

Thanks for the comments, no drains to worry about and some run off from the neighbours garage roof now redirected well away, no small trees/large shrubs etc closer than 10 mtr.

Have not been able to spirit level the floor as its covered with a floating insulated chipboard floor , though the concrete was never perfectly leveled in the first place, but have checked the walls above the dpc and they all seem quiet true, give or take the odd mm with my 900mm level.

The cracks have gone up the wall in a diagonal fashion which suggest (?) its more the rear of the extension thats sinking a little, rather than the raft pulling away as cannot see any gap at the bottom of it.

 

If it really bothers you it would be worth taking up the chipboard floor and seeing if the pad has cracked. We had a similar issue in an outbuilding where the pad had cracked around one of the supporting pillars and the rear wall had moved. We ended up removing the wall and rebuilding on fresh foundations.

Looking back, I don't think the wall would have moved further and would be still standing now.

I'd leave it and monitor further movement.

 

I can't envisage exactly what the cracks are like, but when I was involved with susidence (and heave) remedial works, the structural engineers would fit 'tell tales' like these Linestorm Standard Tell Tale Crack Monitor | eBay

An old tip to save a few quid was to make some out of strips of wall tile with score marks for initial alignment.