Repair small retaining wall

ed110220

With the recent frosty weather part of the small stone retaining wall next to my front door has collapsed. It is about 25cm high by 50cm wide and made of irregularly shaped stones mortared together.

More worryingly, it supports a concrete slab into which an unglazed steel porch is founded and this looks as though it has subsided slightly.

As I don't want it to get any worse and buckle the porch, I'd like to repair it. Would it be a good idea to wedge some bricks or a concrete block in behind the stonework before I repoint it for some extra support? The stonework is pretty thin and doesn't look as though it had much strength to begin with - more decorative than structural.

bobthedambuilder

I would take down sufficient of the wall to give you access to the subsided area under the concrete slab, clean out the loose material then mix up a very dry concrete mix, and ram it into the void under the slab. Use whatever is suitable to push and compact the concrete in to all the spaces (4" x 2" timber, steel rod, lump hammer etc.). If you use sufficient force, you may just be able to lift the slab slightly back to level. The moisture in the soil will cause the concrete to set in due course. Rebuild the stone wall, packing behind with rubble and mortar as you go so there are no voids left there. Ideally the facing stone plus mortared rubble should be 250 to 300mm thick.

27col

Re-pointing it is not going to do much good. You need to do a proper repair along the lines suggested by bob.

ed110220

Thanks very much for your advice, it sounds like something I can do without too much trouble. As you say, the stonework itself and its pointing does not look as though it ever provided adequate support, though it has lasted 62 years.

Here are some photos just to show what I'm dealing with - as you can see it is only a very small wall. However, looking more closely I can see that the roof of the porch has subsided too slightly on the side where the wall has collapsed so I'm eager to prevent any more damage.

bobthedambuilder

I would certainly do what I said in my earlier post. I would try to jack up / support the RH ironwork which is holding up the porch while you work under it. There's lots of ways of doing that - one would be to put a beam under that fence thing, between the step and the lower level path (on an angle), and ease it up from the path end. It seems to only need to go up a few millimetres.

ed110220

Thanks again. It really is only a few millimetres it seems and to be honest I'd be happy to stabilise it without trying to jack it up, but I hadn't thought of doing that, which would make it look better... though I'd be a little worried of breaking it.

As you can see the retaining wall beyond there is falling forward too, but as that isn't structural it's less urgent.

ormus

if you wish to keep it,
then as above. i would jack it up and pack concrete underneath it.
then repair the small wall.

ps.
to be honest i think its ugly and would simply demolish it.

ed110220

I'd rather keep it as the style goes with the house and I like it, it'll look fine once repainted. The housing association have replaced theirs with little wooden pitched roofed things which I think look tacky and out of place, a bit like fake leaded light windows in a modern house.

Few things look worse in my opinion than a road of similar houses where everyone has done something different - a porch hacked off here, another glazed in, another replaced with something complete different - it makes a mismatched mess.

bobthedambuilder

Just thought I'd post a little image of a wall I did in the garden a couple of years ago, using the method I described above. I didn't carry the rubble / mortar backing up to the top - just left the last course of stone natural for looks' sake.

BTW, the division of responsibilities in my household is I do the hard landscaping, OH the planting.:D

ed110220

bobthedambuilder wrote: »

Just thought I'd post a little image of a wall I did in the garden a couple of years ago, using the method I described above. I didn't carry the rubble / mortar backing up to the top - just left the last course of stone natural for looks' sake.

BTW, the division of responsibilities in my household is I do the hard landscaping, OH the planting.:D

Very nice! The whole house and garden is on a sloping site so I will need to build some more retaining walls like that at some point, especially as I want to put in a koi carp pond.

At the back at the moment it's half sloping, half terraced ie a shallow slope then a bank etc and I'd rather have small walls like that rather than banks.

bobthedambuilder

Another option for small retaining walls (less than about 500mm high) is sleepers on the flat. You can see them on the sides of the steps in my photo. I drilled a vertical hole through each sleeper into the underlying one at several points, then dropped in a short length of steel bar, just to tie them all together.