I have a wall that is cracking in a couple of places. Two important points:

  • This wall is not part of a building, it's like a fence or property boundary wall, but it's made of blocks of some sort, covered up so they look like one continuous surface
  • It's not really so much cracking as it appears to be separation along the joint lines of the blocks. It goes all the way from the front to the back of the block.

There are two places in the wall which are cracking and both are near trees, so I'm wondering if the roots could be pushing up the ground under the wall and causing the cracking. None of these trees are on our property, so we can't remove them.

One of the set of cracks is occurring near a corner in the wall, and the cracking has formed a stair-step pattern starting about 15 feet from the corner and moving up towards the corner to within about 3 feet. When we purchased the property 3 years ago the previous owners had put expansion foam in the cracks to seal it (the cracking was around 3/4" or less, but within the last few months there was movement and now the cracks are at least double that.

My initial thought was to perhaps seal up the sides and pour mortar mix or concrete mix in the opening from the top. However there are a number of problems with this: due to the stair-step nature of the cracking, the mix wouldn't go all the way to the bottom; (but conversely, I don't know how I would force the mix into cracks to make it go all the way through); if the problem is caused by the ground moving it might just crack more as the ground continues to move, possibly in a different location on the fence, and I'm not sure concrete or mortar mix would hold the fence together against such forces anyway.

I'm trying to find a solution that will fit in the budget, i.e. I can't afford to have the fence removed to fix the ground and the replaced or something like that. I can afford some raw materials, but all the labor is going to have to be myself. Are there any solutions that will allow me to effectively deal with the problem?

  • If, in fact the trees (seems likely) are destroying the wall, you may have recourse to the owners of those trees (or their insurance company) to effect repairs. This may, however, cause "neighbor friction" - on the other hand, they are currently causing the same in the other direction, it would seem. Think about it and consider starting with non-confrontational conversation, if that's possible.
    – Ecnerwal
    Dec 21, 2014 at 19:12
  • @Ecnerwal - I wouldn't bother with that conversation. As a home owner in almost any state I am not liable for my trees unless you can prove that I did something purposely negligent with them (I cut it down and it falls on your house). This is the law in every state I believe - maybe there are 1 or 2 not like this but doubt it. It is considered an act of god in most clauses. But if it were tree roots it may be covered by his own insurance however this wouldn't probably justify a claim. I would laugh (on the inside) at a neighbor complaining of tree roots.
    – DMoore
    Jan 25, 2015 at 7:04
  • @DMoore Some quick research suggests you can go after the neighbor for trespass and general nuisance for root damage, but falling limbs require negligence. My homeowner's policy doesn't cover "movement of earth", and from talking to my agent that is common in my area, so it seems unlikely anybody's insurance will cover anything.
    – Michael
    Jan 25, 2015 at 15:50
  • I would definately need some pictures. I'd like to see these cracks, their lenght, direction and so on. Jul 24, 2015 at 13:39
  • @MarekOleszczuk Ok, I'll try to take some this weekend and upload.
    – Michael
    Jul 24, 2015 at 18:34

4 Answers 4


Short answer is: there is no quick fix with any kind of patching material. The trees will eventually destroy the wall.

You said the trees are not on your property so you can't remove them. You can however remove any part of them that does come over onto your property including the roots.

The only way you can affect a long term fix is to excavate behind the wall removing the offending roots and heavy soil. Replace it with sand or light gravel to increase the drainage and reduce the attraction of organic growth. You can rent a mini-excavator for a few hundred dollars and have the sand delivered for around $100 a dump truck full. Depending on the size of the wall you could get out of it for less than $1000.

After excavating, and before backfilling you need to straighten the wall and insert 1/2" re-rod into a core every couple feet and fill it with light concrete mix. This will help to stop the cracking from happening again in the near future and support the wall for backfilling. Let it cure for a week before backfilling. People falsely believe that the mortar between concrete blocks gives them strength, the truth is the mortar is only there to seal the joints. A poorly reinforced block wall is easily pushed in. Sounds like whoever built the wall didn't understand this.

Good luck!


Try masonary adhesive (the kind they use to bond retaining wall blocks with). Press it into the cracks with a putty knife as far as possible. When dry, that stuff is very tough.

  • 1
    If the damage is caused by roots of a tree, then Your solution seems to be rather temporary. Jul 24, 2015 at 11:49
  • @MarekOleszczuk any solution that involves tree roots as the problem will be temporary, short of tearing it down and putting in a different fence anyway.
    – James
    Jul 24, 2015 at 19:27

Not really fixable. The way masonry works is that it goes up from a foundation. If the foundation is unsound the masonry will crack. Doesn't matter how big the rocks are. The Great Pyramid will crack if something happens to its basement.

You cannot repair a crack in masonry by putting gunk into it, you can only hide a crack. Naturally, there are many vendors who sell crack-hiding gunk of various kinds. Crack hiding only works on complete idiots. Anyone with any knowledge will be able to tell there is a crack there.

Basically you have a crack and there is nothing you can do except curse the moron who built the wall in the first place.


If there's water or a wet spot at the bottom or surrounding the entire crack area it may be due to improper or no drainage. Water will weaken everything & will settle at the grout's indent line as the furthest point & then also walk its way down to the bottom in those channels. If so, then you can dig out the back side (if allowed), install gravel & a drain outlet for a lasting re-pointing.

But, if it's tree roots spreading & pushing you can only just keep up with patching the crack until you move out. Hydraulic cement would be your best bet in filling the bulk & then caulk over that to hide everything with paint. Caulk will stretch quite a while longer until the crack widens too much & needs another re-fill, re-caulk & re-paint.

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