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I just moved into an old house. The previous homeowner had concrete slabs as the sidewalks that are in touch with the house wall. From what I know, the concrete slabs not only provide a flat solid place to walk on, a nice look but also prevent water coming towards the house foundation.

But now two or three of the slabs have sunk for about half inch at some corners of the slab. I was suggested to cover the old concrete slabs with brick pavement, for a better rainwater protection and a nicer look.

I don't really know much about renovation in general, so before the project starts I would like to have a better understanding. My questions are,

  1. If I leave the old concrete slabs as it is (no bricks overlay), what kind of damage can it cause overtime? I think the slabs are pretty heavy, if they are left to continue sinking, then I imagine it might be bad for the house walls since as it sinks under, it may put a horizontal force onto the wall.
  2. If I decide to put bricks, should I completely remove the concrete slabs first for example by a jackhammer? i) If so, would the jackhammer action cause any damage to the house structure as the slabs are right at the edge of the house walls? ii) If breaking down the slabs are not needed, and I can just overlay the bricks. Is there any special method preferred, e.g. do I just slab on mortar between the concrete and the bricks, or still first put down gravel, then concrete sand and bricks?

Sorry if some of the questions sound silly, as mentioned I'm pretty new. Thanks.

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If the old slab is still “sinking”, then it will continue sinking after the new bricks are installed on top of it. In fact, the additional weight from the bricks may accelerate the movement.

I think you have 4 options: 1) keep the slabs and do not add brick pavers, 2) remove existing concrete slab and install new slab or brick pavers, 3) mortar new bricks to existing slab, or 4) dry-set bricks over existing slab.

1) If you keep the slabs, you’ll need to find the cause of the settlement...sooner or later. It doesn’t sound like it’s a big deal now, but could become unsightly soon. Finding the cause could be difficult, unless it’s obvious, like drainage swale eroding, etc.

2) Wow, removing all that concrete is a lot of work and it sounds like most of it is just fine. (One plus for this option is that you’ll look like Charles Atlas when you’re done.) This is the most expensive option too, because you’ll need to replace it with something.

3) Mortaring bricks to the existing slab is least desirable, because you’ll need to fix the low spots, adjust the layout and install all the joints in the bricks so they align with the joints and cracks in the slab. Otherwise, the new bricks will crack randomly.

4) This seems the most reasonable. Installing dry-set brick pavers on the existing slab, you’ll first install a layer of sand for the base. This base can be adjusted for low spots. Also, in the future, if the slab settles more, the pavers can be removed and additional sand can be installed and then the pavers reinstalled. HOWEVER, the sand base must be contained. That is to say, the sand under the pavers and between the pavers will wash away if it’s not contained.

  • If the sinking is caused by rainwater, then by adding dry-set pavers should help as it raises the height, right? 2) If I remove the existing slabs with the jackhammer, would it cause any damage to the house structure since the slab is so close to the bottom of the side wall? 4) What do you mean by 'the sand base must be contained'? Is it same as edging that holds the pavers in place? – Sam May 25 '18 at 2:48
  • and a follow-up question, if I lay dry-set pavers on top but somehow the slabs keep sinking, as you mentioned I could fill in additional sand, but would the sinking slab put any force onto the wall (when the sinking corner is at the wall bottom) and damage it? Thanks! – Sam May 25 '18 at 2:58
  • @Sam If the sinking is caused by rainwater, the dance (settling of the slab) could be caused from surface water (rain) or from sun-surface (water table). If it’s from surface water, it needs to be diverted. If it’s sub-surface, it needs to be drained. 2) Yes, if you’re not careful the downward jarring could transfer to the wall, depending how close the wall is located. Generally, the load will transfer at a 45 degree angle to the force. 4) The sand base will tend to be washed away by rainwater. Paver manufacturers make a plastic barrier that can be installed around the bricks so the – Lee Sam May 25 '18 at 3:28
  • @Sam so the sand stays contained. Follow up question: Yes, additional weight will transfer as additional load on the wall. However, it will transfer at about 45 degrees angle. So, if the walkway is 2’ from the house and 2’ above the basement floor, it will not transfer any load to the wall. – Lee Sam May 25 '18 at 3:38

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