I am doing some garden remodeling, which includes making sunken beds for veggies. To separate the beds, I am stacking cinder blocks. The problem is that the base is not level, and there are some places where existing work means that the blocks can be offset vertically by as much as an inch.

So what I need to do is to get the second level of blocks level, and get the gaps/vertical differences filled. How do I do this? Mortar? Concrete?


I need to be a little more explicit. I have the base line of blocks as level as I could get it, which is fairly close (I can usually get to about 3-5 mm). The bigger problem is where there is existing stuff that causes the office. These include fence bases, old walls, and old, buried railroad ties. I try and line up the blocks so the tops are at the same level as the obstruction, but I can't get it perfect.

The top of the cinder portion of the wall has concrete tops (landscape blocks), and even a little bit of a gap causes the blocks on top to be unsteady. I was thinking that mortar or whatever I should use might make everything more stable.

I will be walking on these (to weed, etc), and I noticed that some I built earlier are not stable. I think that the gravel might have settled, or something else. I'm not a pro, so I have done the first level incorrectly.

Thanks for any help/suggestions!


  • Why can't you level the base? Mortar will bond your blocks, but will be awkward for adding an inch of height. Also, if your base is uneven or unsteady, your mortar will crack. Have you considered instead using lumber instead? Jul 2 '12 at 20:45
  • 1
    it sounds like your wall foundation is extremely varied and uneven. I'd suggest tearing it out and starting with a solid base of compacted crushed rock.
    – DA.
    Jul 3 '12 at 4:07
  • Possibly should be migrated to landscaping.SE? Jul 3 '12 at 11:06
  • I thought this was gardening AND landscaping site, right?
    – nettle
    Jul 3 '12 at 13:37
  • There's a separate landscaping SE site?
    – DA.
    Jul 3 '12 at 18:19

Mortar or cement will not help you in the long run if you have an uneven base. Ground moves, particularly in the presence of water and will overcome the bonding strength of cement.

One crude but effective method is to buy metal T-bars which are available in six foot lengths. Use a sledge hammer to put the T-bar into the ground through the holes in the cinder blocks. It can be tricky to line up the holes but if you start with that goal in mind then it is possible. Use an angle grinder to cut them off flush with the top.

If possible put landscape fabric (geotextile) on the outside of the block wall and back fill. This will prevent earth from moving in through any irregularities in the walls.

The best solution is to make a good base. It takes much more time but provides a longer lasting solution. A trench filled with six to eight inches of crushed gravel without fines (stone dust) and mechanically compacted is considered a norm. If you suspect the presence of ground water or soggy conditions then my good friend, four inch drain pipe with sleeve at the outside base of the wall, will help.

Edit: I agree with @Grady Player a sand base might work. Are you building to last five years or twenty five years? Heavy clay soil will "push" any wall in the spring where a sandy soil will drain nicely. There's a lot of local soil information only you can "base" your judgment on. :)

  • You love that 4" drain pipe:) I agree with this post, but it may be easier to underlay one layer of solid block on some quartz sand... Jul 3 '12 at 14:18
  • +1 for making a good base. I'm not even sure it ends up taking that much more time: you invest in making a good base, and laying blocks becomes easier and faster.
    – bstpierre
    Jul 3 '12 at 16:02
  • Thanks for the information. I think it is time to plan a rebuild. I was a penny wise, pound foolish.
    – Erick T
    Jul 3 '12 at 21:50

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