How to fix pavers that have lifted?

[VulcanJohn]

Hi everyone, our house is built on a concrete slab which in turn sits on, what I have been told, is called Biscay clay.

We all know how dry this last summer has been but its effect on the pavers at the front of my house is the worst I have seen in my 20 years here. I'm guessing the slab has tipped a bit towards the back of the house as the clay has dried out, and the pavers at the front have also moved as the clay shrunk. The result is an obstacle course of tripping hazards for anyone approaching the front door. I have tried lifting a few pavers and filling the voids below but, to be honest, I wasted my time as I never managed to fill the holes, they must be HUGE!

So, what to do? Should I wait until the Winter rains come along and hope the site settles back how it should be or should I get the pavers lifted and re-laid? If the slab is tilting, what then? I have never come across this situation before and would welcome some guidance from anyone who has overcome a similar situation.

Thanks in advance.

[JacobZ]

Hi @VulcanJohn,

Thank you for your question about your pavers.

I would be surprised if the whole concrete slab has tipped. I'd say it's more likely that clay underneath the pavers at the front of the property has shrunk, causing them to subside in relation to the slab. 

Are there other things happening at your property that make you suspect this is the problem? If so, what were they?

If there was further evidence that the concrete slab has tipped, then I would suggest having a structural engineer come to assess the property to ensure it is safe and offer their recommendations.

As I said, it is more likely that the clay at the front of the property has shrunk with the dry weather, causing the pavers to subside in relation to the slab.

Having only read up on Biscay Clay for the first time, I feel your experience of the area would be invaluable in determining what to do. 

Is the subsiding and subsequent realignment normal during dry spells at your home? 

Clay will certainly swell when it is hydrated, but if it is more than normal, then the pavers may not realign once rehydrated.

Maybe it is best to wait for the rains to come and then reassess. If the pavers are still misaligned once the rain has come, then it would certainly be worthwhile lifting them, adding compactable material such as road base, compacting it with a plate compactor and then relaying the pavers.

Allow me to tag @Dave-1, @Nailbag and @Noyade for their thoughts.

Let me know if you have further questions or details you can add.

Jacob

[VulcanJohn]

Hi Jacob, thanks for your thoughts which tend to align with my plan of waiting to see if winter rains alter the situation, either for better or worse. That option is free and requires no effort on my part! You asked about other signs and all I can add is that we do regularly have doors and windows that bind on the frames, or won’t shut easily, and this happens as the seasons and moisture change, so I know the house is affected. On the upside, there are no cracks in the outside walls nor in the walls or ceilings inside, which is why I was thinking the slab might be tilting and shifting the house in its entirety.

I am interested to see what your colleagues’ thoughts are, so I can get some kind of consensus on the best way forward.

Thanks again.

[JacobZ]

Hi @VulcanJohn,

Doors often swell with moisture, so it is not necessarily a sign of significant movement, but definitely worth keeping an eye on.

It's good to hear that there is no other significant cracking. Hopefully, this means the doors are just swelling and there is nothing more nefarious afoot.

I'm sure the others will respond shortly with their thoughts.

Jacob

[Nailbag]

Hi @VulcanJohn 

I'm no expert here on this topic. But I do have a few mates around the Penrith area of NSW all with homes on clay based ground. They have terrible issues with constant moving of the ground affecting operation of doors and windows. Making physical repairs always results in issues in change of seasons.

Unless the external and internal walls are showing signs of cracking as well as tiled floors, then I think it would be reasonable to say your issues are external. This is a good thing. But for confirmation, you can have the floors within the home x-ray'ed. Its not cheap but might be worth considering for total peace of mind.

as an interim fix, you could remove the row of pavers next to the home. and relay them after sorting the groundwork. There will still be a small lip where the meet the concrete garage floor, but that could be rectified down track if the ground is proven to be settled.

Nailbag

[Dave-1]

Good Evening @VulcanJohn 

Ive lived in two house now were the soil underneath is predominantly clay First house, well the piers looked drunk that were that far out of true, no cracks, no issues as the house was on a hardwood frame. The house was on a hill and over the years things slowly were moving down the hill. Solid as a brick is the way I described it.

Second house (the one were I am now)

Clay and shale but mostly clay Piers are straight and solid as a rock. I have used clay as a base for my paths I have put in, it really works well and yes it does expand and contract with the weather. I am about to lift up the section next to the steps to my patio near the gabion cage. The pavers have dropped a little as that corner I removed the post and never really put anything there to stop the soil moving 😕 silly. However lifting pavers, filling with 8mm gravel (thats what I have under my pavers) and replacing them should be fairly easy. 

If you have no cracks in your slab I would suspect its the outside clay under the pavers more then anything else. Driveways dont always get treated with the care for having a few ton come and go on them and when its wet, the tyre points will be high pressure zones and will gradually "dip" the ground. Id get yourself a long level and check out your floors if you are concerned about your slab, but only if you are concerned

If you look at the pavers next to your garage, that first row is sitting high. Under that you will find the concrete edge of the foundation of the wall of your house. It hasnt shifted, the soil next to it has Does that corner get wet a lot or is there a stormwater pipe nearby?

Dave

[VulcanJohn]

Hi Dave, thanks for your thoughts. I like the idea of using the 8mm gravel to backfill any voids under the pavers, something I can have a go at myself.

As far as the pavers by the garage are concerned, they only get normal rainfall on them plus any rain that hits the garage doors and then runs off, there are no other pipes or outfalls near there.

On balance, and because I haven't found any cracks in the house walls or ceilings, it just looks like the clay soil across the front of the house has severely dried out and shrunk this summer, and has taken the pavers down with it. It looks a real mess and is definitely a trip hazard but I am going to leave it a little longer to see if nature and winter restores what summer has taken away. I am trying to avoid the cost of getting the whole driveway repaired or having the pavers replaced with concrete!

Thanks to everyone for your thoughts and ideas.

[JacobZ]

Keep us in the loop @VulcanJohn.

We're always happy to help if you decide to give some repairs a crack in the future.

Jacob

[Dave-1]

Afternoon @VulcanJohn 

I may end up fixing my pavers before you (I always find other things to do is myt problem) I will try and post what I do as I think its an interesting guide.

Dave