Hi there,
I’ve been literally digging myself into a hole, or trench to be more precise, the past while. What I thought would be a small DIY project and what my wife thought would be done in a weekend has turned into a bit of a monster.
I want to build a small container wall in my garden that is to be about 2.5 feet tall by 15 feet in length, holding back earth (a pre-existing raised border) same height and length and 3 feet from wall to back fence. I’ll attach a basic diagram for clarity when I figure out how to do it. There’ll be a smaller adjoining wall but much lower (about 1.5 feet) so I don’t consider it to be a problem. I want to use sandstone uneven (“semi dressed�?) blocks for the wall. I have the trench dug and have begun to spread some hardcore. My intention is to lay a couple of lengths of rebar prior to pouring the concrete footing. I would be grateful for some advice on the following.
- After some googling last night I noticed that hardcore seems to be a no-no for a wall footing. I’ve spread just 3 bags, not yet tamped down, should I rake it back out again and pour the concrete directly onto the ground (it’s quite firm)?
- I was planning on building the wall as just a single-skinned one as I assumed that this would suffice for a small wall. Would this be ok or does the wall’s height necessitate a double skin? If so, should I do a second skin with the same sandstone blocks or would concrete blocks behind the outer skin be a good idea? I really was hoping for just a single skin due to lack of funds and lack of spare time!
- As I had planned to do just a single skin wall, I made my trench width accordingly (around 12 inches). If I must build it double-skin would this trench width still suffice? Because of a problem I had with a large amount of builder’s crap buried there I’d be reluctant to make the trench any bigger.
- For the concrete I’m planning to use gravel and cement ratio 4:1. Good or bad? 3:1 better?
Here's the diagram, thanks in advance.
1, No need for the hardcore in the footing, just concrete at the right depth will be fine.
2, Single skin is a no-no as far as im concerned im not too clued up on calculations but i would reckon a 300mm wall minimum, say 150mm block then 150mm/200mm stone would be great, someone else will clarify.
3, Trench too narrow im afraid for the thickness of wall you need, you need a "spread" so to speak of the footing.
4, need some concrete sand in that mix, if i was you id buy an all in one ballast, and mix as you have said a 4-1 strength, better yet get some volumetric concrete lads in and get them to do it.
Im not a wall building expert, there are better suited people on this site that can help, ive just replied because noone else has yet!
the bit that retains should be at least 215 brick or blockwork
ensure there are weepholes in this
the bit at the front that you intend planting into is a minefield
I have done lots of herb gardens like this but you need to ensure that water can get away
also dont plant anything that will grow to big and put pressure on the wall (seen this happen)
the concrete bases normally should extend 100mm past the brickwork both ways and be at least 300mm thick for a wall of this type
hardcore is a nono
LLL
Thanks a lot for your kind and informative replies. I'll be getting someone in to pour the footing for me (less the hardcore) as I just can't seem to get the time together to do it.
Yeah 40 year time surveyed structural and civil engineer with about 35 letters after his name and some serious projects under his belt.
Building extension at the moment young engineer on that has specified 250x100x10mm plates bolted to all pad stones then welded to the universal beams. That's a new one on me!
Giles
Groundworks and Equestrian specialists, prestige new builds and sports pitches. High Peak, Cheshire, South Yorkshire area.
A couple of other questions, if I may (there's always more!). On the subject of weep holes; should I go about this by leaving gaps between blocks every few feet on the bottom course above grade, or place narrow piping at a slant through the mortar every few feet, or maybe even both? Also, I was given a length of 4" diameter perforated pipe which I may use for behind the wall as advised on this site - however it's corrugated which to me suggests it could collect water. Would it still do the required job (since I was given it for free & doesn't look too good stuffed in beside my shed I'd be eager to use it)? If the pipe needs to go to daylight, any tips on preventing it becoming a rodent hotel?!
lay the pipe through the wall normally 20-40mm ish at an angle then fill with free draining material and if youve got the pipe lay it abutting the weep hole pipes to act as a accumulator for the water to feed into the weep hole pipes then fill with more free draining gravel
Giles
Groundworks and Equestrian specialists, prestige new builds and sports pitches. High Peak, Cheshire, South Yorkshire area.
Thanks again for the comments lads and,er, if I can annoy you with just one more advice request (i'll shut up after this). With the torrential rain we've had here yesterday & today, my trench has begun to fill with water! Should I panic or just remove the water manually prior to the concrete going in? Or is there some kind of pump I could use? Is a little bit of water a problem? Thanks.
If it's not much water you can remove it with Paddy's pump ( a bucket ) then when you have hardly any water left you can pour the concrete from one end, that will push the water along and you can bail as you go. If there is to much water then an actual pump will have to be used.
