Uneven strip footing for small retaining wall. Advice on levelling first course?

[Reedy123]

Hi Everyone,

I'd really appreciate any advice you can offer on the best way to level up the first course of a small retaining wall I'm building to the front and side of my house? I dug the footings myself and had the concrete poured last week. The level is a bit out over one of the lengths (approx 30mm) over 9m. I was doing the tamping and levelling myself, so it's my own fault. The low spots are in a corner where the footing turns down the side of the house and at the opposite end of the same run, so the highest point in the middle of the run (the high point is actually slightly over the right height). I'm going to have to build up the low spots, and I could lay a thin bed at the high spot. How would you do this? Is 30mm too much to even up with mortar (3:1) in one course of block?

Also, if anybody has some general tips that would help with the project then I'm all ears! I'm not experienced so this is a fairly big project for me and I want this to be done right and done once - I don't intend to move from this house so happy to invest my time. I worked on a few sites when I was younger (just labouring) and built a couple of garden walls and generally fairly handy as a DIYer, but otherwise totally unqualified. I figured that if I take my time I could pull it off and learn some new skills along the way.

Bit of background:

Wall is retaining approx 600mm of ground which slopes towards house, and the same to side which slopes away from my house towards my neighbour. Wall will be an L shape. The slope to the front used to continue more or less down to a block path directly in front of the house wall. I want to drop the level in this area (path is only just under DPC) and profile the ground with a fall away from the house and towards the wall I'm building (3m away). The wall will allow for this drop and re-profile (hope that makes sense - hard to explain).

Length is approx 10m down the side and 9m across the front of house - there are two 150mm steps down in the length running down the side.

Footings are are 225 deep x 450 wide C35 concrete, with proper overlaps at steps. Top of footings all 150mm or more below finished ground on low side of wall. Ground is till - silt/gravel/boulders/slate etc.

I'm intending to use one course of block on flat (140mm), then engineering to DPC level on house, then F2 facing above that.

I've though about drainage and will have perforated pipe/shingle/geotextile behind and will drain to a linear soak away in the back garden.

I'd be really grateful for any thoughts or advice. Cheers!

 

[oldbutnotdead]

30mm is doable in 1 course but much nicer across 2.
So your first course (the flat blocks) go heavy on that corner (25mm) & reduce to 10 as you get to level. Repeat with the next course of blocks & you're there, the wonky courses should still be below ground
Staying out of the rest of the engineering stuff

 

[Reedy123]

Thanks oldbutnotdead, much appreciated! I was only going to do one course of block (changing to brick just below ground level on the low side of the wall), but it sounds like I might be best switching to engineering bricks instead of blocks to give me two courses to work with? I could then do what you suggest before it's 'on show'. Do you think it would be easier to make up in two courses of brick?

 

[oldbutnotdead]

Easier to do it in one but i always worry (engineering wise) about compressive strength in massive mortar beds & if you do have to do it visible it looks a bit less obtrusive.
Really up to you, long as your deep bed is good & full you'll be fine doing it in one.

I find bricks easier than blocks but obvs brick is more expensive & time consuming.

Whichever you do, set your line out of level for the wonky course(s) (rather than having the line level & trying to measure an offset)

 

[cdbe]

Use a dryish sharp sand mortar.

 

[Reedy123]

Thanks oldbutnotdead - grateful for all the advice. That makes sense re the line - I'd probably have set the line level and tried to lay up to it to get up to height. If I understand, the way you are suggesting I would have the line at the right height at the high point (I'd use a dead man/profile there) and above gauge at the low end by whatever amount I want to build up in that course. So, line would still be sloping towards the low point but by a smaller amount than the footing is out of level. Then move line to level at the next course if I can.

Thanks cdbe - I take it that should hold up a bit better with a thick bed. I'll do that for the first course(s) until I'm level. Cheers.

I ordered a laser level today because I'm second guessing myself a lot on my measurements. I'm going to set it up at dpc level on the house and measure down to footing at various points so I can get a full picture of just how bad a job I've done with the concrete before I start! I really hope the wall goes better than the footings!

 

[^woody^]

It may be better to double the first bed at the low end, and then lift the gauge a few mm per course rather than try and do it all in one course. You wont notice over 9m

Set some profiles up at each end with the top of the wall level marked, and then gauge down and mark each course level on the profile, and then use these for your line to run the wall in.