Preventing moisture ingress through retaining wall

I'm extending my garage to give more non-car user space. Because of the land slope the current garage sits on a concrete and brick plinth - to avoid a large infill, the extension is going to have a suspended wooden floor which will supply some storage for pipes and the likes under it.

The question is this - I've cut away part of a 600mm high bank for the extension; I've laid a found and built a 3 dense concrete block high retaining wall with a couple of buttresses. Currently there's about

300mm between the bank and this wall. I would like to prevent moisture getting into this wall - I know it will come up from the bottom but with ventilation that won't be serious. But if I just in fill the soil back against it the moisture penetration will be significant.

What does the collective recommend ?

Thanks

Rob

Reply to
robgraham
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It sounds to me as though you intend the "retaining wall" to be the garage wall as well. Is this so, or is the garage wall to be built inside the retaining wall?

Reply to
Chris Bacon

Sorry if the description isn't clear. The garage is timber so the timber frame extension wall sits on top of the retaining wall. I'll put a dpm under the wood frame which is to be covered with weatherboard.

Hope that makes it clearer !

Rob

Reply to
robgraham

If it's to retain anything you'll have to backfill it, or just let the soil crumble in.. is the soil normally very wet? You could put in a vertical DPM on the outside, or on the inside (using bitumen emulsion and/or mortar with a waterproofing admixture).

Reply to
Chris Bacon

My thinking was to put a vertical DPM on the outside and then back fill. But what sort of DPM - I've got a roll of the polythene stuff, but unless I back fill with sand or something then anything hard is going to go through it - and that includes anything sharp on the blockwork too. Oh... and just to make that awkward the bank is 600mm and one end and zero at the other.

I know that strictly I should backfill with pea gravel and have drainage holes etc - I've done that all before for a garden terracing, but I don't think this applies in this case as the height to be supported is so low and the soil is not damp - in fact it has a beech hedge on it to keep it bound and dry.

Rob

Reply to
robgraham

Render it, then, and put a dollop of waterproofing in the mix. It'll look better than blockwork too, where it's exposed.

Reply to
Chris Bacon

Give the soil side a coat of bitumen. This is tougher and much longer lived than soft polythene. You want the dp layer on the souil side really.

NT

Reply to
meow2222

The message from "robgraham" contains these words:

The soil might not be damp now but cover it up and at certain times of the year at least it will be so to my mind back filling with soil is not an option without a vertical damp proof course. You can get a material that looks very much light ashfelt shed roofing that is bonded to the blockwork by the application of heat (large blowtorch). It was used on a neighbours barn a few years ago but has not been totally successful. However in that case it was 60 feet long and 4 foot deep and the backfill was subsoil (a mixture of clay and stone).

However I would be tempted to back fill with pea gravel (or something similar without any fines) using a permeable membrane between bank and fill to prevent it silting up. If it were a long section of wall I would put in a perforated land drain along the bottom as well.

If I understand you correctly this is on a slope so any ground water can discharge at the end of the wall without problems.

Reply to
Roger

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