Tanking/Water Proofing Exterior of Retaining Wall

markavfc2

I live down hill from my neighbour and the there is a retaining wall between our two properties that is about 6 foot high. It is brick built and 9" wide. It is about 25 foot long. There are four drainage/weep holes positioned along the wall approx. 2 foot from the bottom. 

When it rains heavy some water comes out from the weep holes but also bleeds out though the bricks and pointing in between the bricks.

I had a builder round today to see about re-pointing the bricks but he advised tanking the wall and rendering it. He actually mentioned using bitumen for the waterproofing and then rendering. I can't dig out behind this wall to do anything as my neighbour has recently had a new patio laid.

My question is does waterproofing the external side of the wall sound like a good idea. I would obviously not block up the weep holes so water/moisture that builds up behind the wall could still escape here.

FreeBear

Waterproofing the wall sounds like a bad idea to me. Come the winter when the bricks are nice & wet, the water will freeze, causing the bricks to spall. The render will hide the damage quite nicely, and the first you will notice is bulges & cracks appearing in the render.

markavfc2

FreeBear said:

Waterproofing the wall sounds like a bad idea to me. Come the winter when the bricks are nice & wet, the water will freeze, causing the bricks to spall. The render will hide the damage quite nicely, and the first you will notice is bulges & cracks appearing in the render.

Thanks for the reply. Wouldn't the water coming from behind the wall just find its way to the existing weep holes rather than as some of it does at present and weeps through the bricks/mortar?

stuart45

A retaining wall needs a drainage system on the other side of the wall, to direct the water down to the weep holes. Any waterproofing needs to go on the positive side of the wall. Putting it on the negative side will only hold the moisture in the wall, causing spalling as FreeBear said.
Also not allowing the moisture to escape will build up hydrostatic pressure on the wall as well.

ThisIsWeird

I'm with FB and Stu above, tho' I'm not in any way an expert on this.

But, any waterproofing/tanking on such a wall should really be done on the other side, but that's clearly too late.

Some repointing has seemingly been done on that wall at some point? I think what I'd personally be inclined to have done is (a) bore through these weep holes to check they are unblocked, and perhaps even insert perforated tubes a good foot or more into the ground beyond - if such a tube exists - and (b) keep on repointing the wall as and when required.

I certainly wouldn't simply bitumen the existing outer face, as that will just be a thin covering over a multitude of tiny leaks. Rendering the face might possibly be ok, but I'd suggest it would only be so alongside deeply-pointing the weeping gaps. Ie, all remotely loose existing pointing to be removed to a good depth (perhaps done in dry weather!), and then the whole thing rendered, including deeply-setting the mortar into the pointing lines.

My inclination, tho', would be to just keep these weep holes as free-draining as possible, repoint as and when needed, and budget for a rebuild at some point. The latter would include a full DPM on the rear, and a vertical layer of gravel leading to (more) drain holes...

markavfc2

@FreeBear @stuart45 and @ThisIsWeird thank you all for taking the time to reply and for the advice.

I think I will do as advised and re-point it and make sure the existing weep holes are kept clear.

It is actually my neighbours wall and there wasn't so much of an issue as there is now until they had a new porcelain patio installed but the company who installed it failed to put in any drainage and the water just ran towards this wall. Initially the water was coming out of the weep holes like a tap when it rained heavy. I had a lot of hassle convincing the neighbour/company who installed the patio that they had failed to put in adequate drainage and they eventually did install some which has improved the situation although more water still comes through the drain holes/weeps through the bricks when it rains than did prior to the new patio installation. 

Even though the wall is not mine I just want to try to help maintain it and ensure it doesn't collapse. 

ThisIsWeird

markavfc2 said:

@FreeBear @stuart45 and @ThisIsWeird thank you all for taking the time to reply and for the advice.

I think I will do as advised and re-point it and make sure the existing weep holes are kept clear.

It is actually my neighbours wall and there wasn't so much of an issue as there is now until they had a new porcelain patio installed but the company who installed it failed to put in any drainage and the water just ran towards this wall. Initially the water was coming out of the weep holes like a tap when it rained heavy. I had a lot of hassle convincing the neighbour/company who installed the patio that they had failed to put in adequate drainage and they eventually did install some which has improved the situation although more water still comes through the drain holes/weeps through the bricks when it rains than did prior to the new patio installation. 

Even though the wall is not mine I just want to try to help maintain it and ensure it doesn't collapse. 

Of course! D'uh! Yes, that is usually the case - the person whose land is being retained is usually responsible for retaining it.

I would suggest that's another reason for not rendering - if that causes more issues, then you will be responsible!

I suggest you make it clear to the neighb that you are having issues, and suspect you know the cause, but are happy to have some repointing done at your own expense - if that is ok with them? (Ie, have it on record you have pointed out the issue, and have it ditto that they have given permission for the pointing work).

If/when the wall collapses in the hopefully distant future, that's for your neighbour to sort :-)

markavfc2

For the re pointing should I use a lime mix mortar?

stuart45

A general rule of thumb for pointing is to use a similar mix to the original, only slightly weaker. This wall was probably built with cement mortar.