Damp retaining wall

Hello,

I have a garden retaining wall that seems to never dry out. The wall is constructed from bricks with three stretcher courses and then one header course repeated through its height. The wall is two courses deep with what looks like a thin cavity inbetweeen. Two thirds of the wall is below ground, the other third is above ground. At the bottom of the wall there are some spaces in the mortar, presumably weep holes.

What puzzles me is why is the whole wall damp, even the part that is totally above ground? Any moisture coming from the earth that is retained would I guess fall down the cavity and out the weep holes, so I can't believe it is coming from there.

Next to this garden wall is part of the house wall, this is dry, so not damp from rain penetration. So maybe the whole garden wall has rising damp, but why not the house wall?

And after reading this article I am doubtful that rising damp even exists:

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is really bugging me, I would really like to know the cause of this damp!

Thanks,

Graham

Reply to
Graham Jones
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Part of that statement isn't clear, weep holes are usually just above ground level (but in high walls, there can be more than one course of them) and not two thirds underground, Is all the wall (except footings) exposed on your side, and the ground level behind that rising two thirds up the wall?

From what I read with the header and stretcher course description, you have a solid 9" (one and half brick thick) wall and not a cavity, and as it is a retaining wall, then you are correct, the holes at the bottom are there to stop water pressure building up and pushing the wall over. Believe me, it happens!

As for the damp, you don't say what the water table is, but there may be a high one there, a small underground stream nearby or even a leaking water/sewer pipe causing the wall to be damp.

The damp is probably not 'rising' but explained above. Now lets assume that you are correct, then with the normal garden wall construction, there are

*NO* built in damp courses to prevent rising damp nor damp proof membranes behind the wall to stop penetrating damp due to higer ground levels.

The house will have all sorts of damp proof membranes built it.

In the wall it could well do (contradiction of what I have already said) but if the water table is low down and near the footings, the wall will drag that moisture up naturally - but to no more than around three feet in height from the water table.

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> This is really bugging me, I would really like to know the cause of > this damp!

Now you possibly know - but I'm sure other will have different ideas that would also be possible.

Cash

Reply to
Cash

Hello,

Thanks for your reply,

By two thirds underground I meant that two thirds of the wall retains earth, the upper third retains nothing.

There definitely is a small cavity between the two skins, the bricks are old imperial size, 2 x the width of the brick does not match the length.

Graham

Reply to
Graham Jones

That's what I thought you meant - thanks.

Too small to be called a cavity Graham, the construction would be two 'stretcher courses' side-by-side for about four or five courses or so up, and then a 'header course' at right angles to these as reinforcing method (if the wall is 9" thick, then it will be classed as a 'solid' wall [1]).

The variations in the brick sizes may cause two stretchers side-by-side to be slightly smaller than the length of a standard 9" brick and the old brickie would have made adjustments for this as he was building the wall - hence the "thin gap" between them.

[1] Cavity walls are usually a minimum of 11" thick and all stretcher courses (generally) - I.E. stretcher course, 2" gap, stretcher course.

Cash

Reply to
Cash

I see thanks.

I suppose my next question is, will the damp affect the life of the wall and if so is there anything I can do about it?

Thanks,

Graham

Reply to
Graham Jones

The answer to that could well be yes, more so when the weather is cold and the temperature drops freezing, the water in the bricks then tends to freeze and expand, causing the face of the bricks to 'blow' - especially if they are 'concrete. bricks.

If the bricks are made of clay and 'FL' rated (or engineering bricks such as the Staffordshire reds) then these frost resistant and more durable to the cold.

As for doing anything about it! Generally no, but if you are feeling energetic enough, you could dig the earth away from the back of the wall, brush the wall clean and make good any defects - and then give the back of the wall a few good coats of something like Synthaproof and then backfill.

On the exposed faces of both sides and top the wall, again check for, and rectify any defects, and then give the wall a couple of good, heavy coats of a clear silicone liquid (put the stuff on fairly heavily [using a spray is best] and then let that soak in before giving it another coat.

This should stop most (if not all) of the damp and give the wall a longer life - if the damp *is* rising, then for the above methods to be of use, you will then have to consider inserting a chemical DPC to stop the rising damp as well.

Now, down to the nitty-gritties - is it really worth the cost and hard toil to do all that work, when that wall (even as it stands) may well have a life of around 50 to 100 hundred years before it falls down (depending on type of brick)?

In my case, if all looks ok now with its structural integrity - I would personally leave well alone - as by time any real work is needed, I will be long-gone and it will be somebody elses worry. ;-)

All the best.

Cash

Reply to
Cash

Does it have lime mortar or cement?

Reply to
Maria

Cement

Reply to
Graham Jones

If the bricks are perpetually wet, they will probably spall over time (erode away behind the cement mortar) because the cement is stronger than the brick. Is it just pointed with cement mortar over old lime mortar, or is it cement mortar all through?

Reply to
Maria

Maria,

Just out of interest, where does the cement jointing come into the equation with the actual spalling of the brick - which in most bricks (clay or concrete) is caused simply by weather [frost] damage and leaving the joints relatively undamaged?

If the joints are affected to any major degree by a poor mix, incorrect material or weather damage, then that usually results in vertical or horizontal cracking or lifting which, combined with water pressure or ground movement can cause the wall to 'lean' or collapse.

The only time bricks will spall "behind" the morter is if the wall has been rendered.

If you live anywhere near Stoke on Trent, [1] have a look a the canal system that winds its way through parts of the place, the walls of some of the buildings actually form the retaining wall for the canal and have no other form of water proofing than the bricks themselves. The bricks by the way are either Staffordshire Reds or Blues and are engineering quality - and seem to last forever!

[1] I once has a 6 month contract up there at Hanley, working on some properties.

Cash

Reply to
Cash

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>>>>>>>>>>>> This is really bugging me, I would really like to know the

Cement mortar does not allow the passage of water as lime mortars do, trapping water in the brick. The brick then degrades rather than the mortar, the latter which is what is meant to happen.

That too!

Have to disagree on that one. If the building brick/stone is softer than the mortar, then the mortar is not the weakest part. Water is then forced out through the surface of the brick.

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really like this pic (which once had some stone in it!)

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Are they constructed with Ashlar joints? Engineering bricks are amazingly strong, and would take a lot more to destroy them. I am currently repointing with some hydraulic lime mortar, which can be used under water!

I would take a guess and say that Graham's wall is older brick (on which the facings may have been damaged), which has been repointed or rebuilt using cement mortar. Assuming he can find no point of ingress. But I'm better with photos. :)

Reply to
Maria

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>>>>>>>>>>>>>> This is really bugging me, I would really like to know the

But the problem is that the wall consists of probably around 95% of brickwork and only around 5% of cement jointing - you can ignore the cement jointing in any form here, adding more weepholes to the wall at higher levels by drilling with a 3" core drill will have more effect.

Also, I would be very wary of using a weaker lime mortar in a retaining wall for very obvious reasons.

Water is not generally 'forced' through the brick, most bricks are naturally porus and absorb the stuff - and in the low temperatures of winter, the water freezes and expands and simply 'crack' the brick during that process.

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is a very soft brick by the look of it and very susceptible to water absorption and ultimately frost damage - and the laying a point aren't that good.

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> If you live anywhere near Stoke on Trent, [1] have a look a the

Didn't get that close to them, I was simply driving past the buildings.

From the lack of information (and past experience) I would suggest that his wall is a lot more recent and is not suffering from damage as yet, and has neither been repointed or rebuilt - he simply asked what damage would be caused by the water, which is simply being dragged through the wall by the capillary action of a porus common brick [1] (as he hasn't stated if water was coming through the existing weep holes.

As for point of ingress, that's through the ground that rises two thirds of the way up the rear of the wall.

[1] And unlikely to be frost resistant.

Cash

Reply to
Cash

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