Straighten a foundation wall that is not level

[MrSpudnut]

Hello!

I have a masonry foundation (Leca blocks) for a greenhouse that needs to be completed with one more layer of blocks (190mm + mortar). My problem is that the wall from opening to opening has a level difference of 3-4 cm. No edge has more than about 1 cm difference, but the total becomes troublesome. The wall is otherwise plumb and level in other directions. So, now that it's time to pay for past mistakes, what to do?

It feels significant to have a 3 cm difference in the mortar joint from end to end. Can I "pre-mortar" and lay a layer of mortar on parts of the wall to dry before building on top? "Plane" Leca blocks so I can build with thinner blocks in parts of the wall? Combine leveling with increasing joint thickness with applying thicker plaster where needed? Pray to higher powers for an earthquake so the wall levels itself?

Since there will be a wooden sill on top (it will be a self-constructed wooden greenhouse), there is some opportunity to correct it there, but naturally, the more level the foundation is, the better. The foundation will be plastered, so any aesthetic issues will be resolved there.

Thanks in advance!

 

[MrSpudnut]

I'm replying to myself: After browsing Google, YouTube, etc. a bit more, I've noted

a) quite a few really thick joints are visible in places that, in such cases, should know better (i.e., it doesn't have to be a complete disaster if they exist)
b) plastering can be done as thick as you want

The solution I'm currently considering the most is to build up the last layer as level as I can within reasonable limits (say a maximum of 2 cm of mortar or so) and then fix the rest with plaster/mortar on top (another 1-2 cm on some meters of the wall). Does anyone object to this?

 

[Jan_G]

Place a board on each side of the wall and clamp them together. Set them so they are level at the top.
Fill with mortar.
Alternatively, set up mason's line level around and apply mortar at the correct height. Wait until the next day and lay the last course (with the mason's line set at the correct height ;-) )

 

[MrSpudnut]

Thanks for your response! Am I misunderstanding you correctly: make a separate round with mortar, which is level, either as a finish on top (like plastering) or as a leveling round under the last course? Or are both options as a base for a final course? I promise to use a masonry line this time

great tip with the board to be able to make a nice fill.

Place a board on each side of the wall and clamp them together. Set them so that they are level at the top.
Fill with mortar.
Alternatively, set up a masonry line level around and apply mortar at the correct height. Wait until the next day and lay the last course (with the masonry line set at the correct height ;-) )

 

[mexitegel]

There are no problems with high joints between the courses, just mix the mortar a bit drier, and pre-wet the lecablocks so the mortar adheres properly. Stretch a mason's line level a few millimeters outside the bricks, for example by fastening a nail between the corner post and the line.

You will probably need to press some mortar into the joint and smooth it out with the trowel where you have the highest joint, but that's not a problem - it just takes a bit longer .

It might not hurt to reinforce with bistål so it's guaranteed to be good.

If an adjustment is needed, you can do it when you plaster the wall cap, as you have already figured out.

Good luck!

 

[useless]

I would do as @Jan_G suggests and make a simple mold at the top that you fill with mortar and level off. Preferably with a slightly harder mortar than regular masonry mortar (and a couple of reinforcement bars). Besides getting it level, it's easier to achieve a smooth top on the wall.

Take the opportunity to mount and cast in any fastening details while you're at it.

It's possible to combine this with disguising some of the error by varying the thickness of the joint under the stones a bit.

 

[MrSpudnut]

Thank you all for the great responses! I am happy to receive more advice here (it's probably obvious that it's needed?), but I feel very satisfied with the help.

 

[jonaserik]

Mason's line OK, a bit hard to keep the line but manageable. Clamp two boards so the top edge is about 1 - 2 cm above the wave for the next row's lower edge. Put in mortar and place a stone, measure from the board where the wave is and tap it down so it's in place, same with the next stone. This creates a wedge of mortar towards the end. You can also lay bricks at an angle and then place two boards level and fill with mortar, forming a cap at the top.

 

[MrSpudnut]

In case anyone is interested in my fumblings with masonry: took all this advice to heart yesterday and built up the last course to within half a centimeter of being perfectly level across the entire wall. It went excellently, reinforced with rebar, and used drier mortar on the highest parts. The next step is "casting" the crown using boards. Thanks, everyone!

thought/question: I will be screwing the greenhouse sill onto the wall, is it problematic to do this through the crown/plaster, i.e., is there a risk of cracking?

 

[useless]

Cast in screws or threaded rod to avoid drilling afterwards.

 

[mexitegel]

It might chip a little from the plaster, but cracks are a minor risk. We drilled, filled with chemical anchors and then plug and stainless steel screw. It has withstood the autumn and winter storms at over 20 m/s, so it seems to stay put .