Gaps in mortar in garden wall (staircase pattern)

nowImonboards · 15-07-2024 04:14PM #1

Hello all,

I have removed a flag stone patio with the intention of replacing it with a sun-room. Under the old patio was about 40mm of grit sand on top of a deep bed of (mostly) loose chippings (possibly T2?).
I say mostly because there were areas with a lot of soil mixed into the chippings. One area with considerable amount of soil in the mix was at the garden wall between my neighbour's property and my own. I noticed this mix of soil and stone was particularly wet with a putty type texture, constantly sticking to the shovel in clumps.
Since I'm putting a foundation there I though it best to remove it as it didn't seem solid enough to pour a foundation onto. I ended up taking out about a tonne. When I removed the material I noticed that the joints between the blocks in the wall in a particular area didn't have any mortar in them (see attached pic).
At first I was wondering whether this was intentionally there as a kind of drainage pathway to prevent water pooling within a single property. However looking closer it seems that it follows a pattern and is all located at a boundary point where the (presumably cavity) blocks sit on standard 100mm blocks laid on their sides. This part of the wall is right against the back wall of the house. This gap continues in a staircase pattern down as far as I have dug. I'm wondering now whether it continues upwards behind the pebble dash and worried whether it affects the structural integrity of the wall.

Before I go knocking pebble-dash off the wall to check, I was wondering if anyone could tell me any potential reason that this could be intentional. The house is only 3 years old and, although I have been shocked at some of the shoddy work I have seen on the inside, I just have a hard time believing that someone would knowingly pebble-dash over an unfinished/unbonded wall. Surely there has to be a reason.
Has anyone seen anything like this before?

On the off-chance that there is no reasonable explanation for this and it is localised to the lower area, is this something I need to be worried about addressing when pouring my new foundation. The foundation and floor will be laid on a blanket of DPM in one monolithic pour and the DPM will come back up the side against the wall where these gaps are. Any water that would be seeping through from the next door property will have to seep down behind the DPM and under the new foundation. Should I just try to squeeze a tube of Tech 7 or similar in there?
Remember I mentioned that the soil/stone mix I took out was an extremely soft and sticky putty texture so I'm assuming there is water seeping in. None of the soil I removed from anywhere else in the garden had this texture and seemed like generally good topsoil. There were of course all sorts of pallet wrap straps and random bits and pieces that I dug up so best case scenario I have just removed some random mix of material that they used as a dumping area when building the place. Could there be a bigger problem I need to think about?

standardg60 · 15-07-2024 05:09PM

For me it looks like they weren't too bothered about joining to the blocks on the flat because it wouldn't be seen and it doesn't really amount to a hill of beans there as it wouldn't affect the integrity of the wall too much.

What would though is your plan to pour a foundation and floor against it. What you need to do here is keep excavating down to the wall foundation and extend that out, then blocks on the flat to bring you back up to floor level, then pour inside of that.

nowImonboards · 15-07-2024 06:24PM

Hi standardg60,

Thanks very much for your comment. It leaves me wondering though, if it's just a matter of laziness, why those exact blocks that are laid on the flats? Is it not the same amount of effort as jointing the other side of each block?

Thanks also for your advice on the foundations. I should clarify that when I say it is going to be a sun-room, I mean the veranda, which is a metal structure to hold a glass roof and sliding doors. There won't be any concrete walls as such. See pic for an example.

These can installed on a patio with simple post foundations. We just want to tile it similar to our internal kitchen floor for a seamless indoor/outdoor feel so pouring a concrete slab as the base for the tiles. Although not fully exposed to the elements, this is I wanted to install a proper DPM to cater for the Irish weather so I though I could do a single monolithic pour and do the floor and foundations in one go. With this in mind would you still think I'm going about it wrong?

Even if I did go and put in an encasing wall for the floor, would water seepage from the holes in the wall above eventually cause problems?

I appreciate the input as I don't have much experience here. Most people think I'm overdoing it as-is with the foundations I have (300mmx300mm each side).

nowImonboards · 16-07-2024 10:36PM

Anyone have any more thoughts/comments/advice as to why lack of mortar in wall joints may be an issue/non-issue or why my foundation plans may be a bad idea?

nowImonboards · 17-07-2024 10:27PM

https://www.boards.ie/discussion/comment/122384684#Comment_122384684

I still don't understand why they would leave those particular blocks without jointing them. If it was as simple as them thinking they wouldn't be seen then why would they joint the other blocks beside them?

cuculainn · 18-07-2024 05:52AM

So it looks like they jointed on the flat but not the vertical.... perhaps they didn't have the closed ends on the cavity blocks which would make it impossible to joint the vertical as mortar would fall into cavity block?

Judging by how wet you described that area would you consider running some sort of french drain or the likes along the wall

nowImonboards · 18-07-2024 07:58AM

Hi cuculainn,

Thanks. It does look like you are right about the flats having being jointed. It just seems to be the right side of the first section of cavity blocks that seems to be missing the jointing. I'll see if there is anything I can do to check your theory and see if I can feel the ends with a length of wire or something.

I'm not sure if I was clear in my original description but this section of the wall is just where the garden wall joins the house. It looks like there is a staircase pattern of flat 100mm blocks doubled up to form the staircase section that joins onto the house. I'm guessing that is normal and just because the house was build with a cavity wall and so they used the 100mm to start the end of the wall that was later completed with cavity blocks. I was kind of hoping leaving out the vertical jointing here was a kind of stress relief / crack prevention measure. Wishful thinking I guess.

Any reason I shouldn't try to seal them with e.g. Tec7 to try to stop the potential for water to seep through. Or is it better to try to mix up some mortar and try to get as much as I can in there?

The french drain is a great idea but unfortunately the depth of the foundations is lower than any of the AJs on the property. These vertical gaps go down more than a meter where I stopped digging. I'd have nowhere for the water to go from the drain.

I'm just thinking, over the long term, would water seeping in under my new patio (veranda floor) foundation end up causing me issues that could be addressed at this stage.

I'm really confused about the consistency of that soil I described. Even now that I have dug it out into tonne bags it looks piles of horse poop due to the way it has clumped together. I'm not sure whether this is just because it has mixed with other material or whether it is due to long-term exposure to water. I'm a total amateur. The fact that it mixed so much with the sub-base (loose stone with little fines) makes me think that 3 years of water seepage has caused the topsoil to settle into the sub-base. Maybe it just wasn't compacted since it is close to the wall. One thing I do know is that before I moved in the builders had to top up the area by the wall with more topsoil due to some sinking that happened. I could see a big patch of fresh topsoil on the grass by the wall when we moved in and the neighbour said it was the same for him. The particular patch that I dug out was under the existing flagstone patio but right beside the patch of new topsoil so it is possible they had to pull up part of the patio, top it up and then put the flags back down. I don't mean to be going off on a tangent here, I'm just hoping this additional info will make someone say something along the lines of "ah yes, that always happens, don't worry about it".

Any and all further input welcome. Thanks to everyone so far!

nowImonboards · 18-07-2024 02:16PM

In case it helps, attaching pictures of the sticky putty textured material I removed form the area in question:

cuculainn · 18-07-2024 04:16PM

Is there there a drain pipe or anything coming down the wall of the house that could be directing water into the area that was wet?

The soil looks like fairly typical fill that would be pulled back to level off after finishing a site....Top soil would usually go on top of that.

It looks like very heavy clay so will hold a lot of water and not drain well

If you put some steel mesh in the foundation you are doing it would strengthen and help prevent any cracking that might occur due to the wet area.

I will say at this point you would be as well to get someone with more building knowledge than me to advise!

nowImonboards · 18-07-2024 10:58PM

Hi cuculainn,

Thanks very much for the input again. There isn't a drainpipe on my side of the wall but there is one on the other side that feeds into a gully. We did test it though and can see water coming through the AJ when we pour it in from the neighbour's side so I don't think it is broken.

It's good at least that you say the material seems typical. Not sure exactly what you mean by "pulled back to level off" but I think I get the gist in general. The main thing is that you think it doesn't look out of the ordinary.

I did manage to dig it all out of the area marked for the foundation though. I plan to fill the area back in with some of the loose stone (T2?) that was under the original patio, give it a whack with the compactor before pouring the floor and foundation (will have 150mm of SR21 inside the main area to support the floor). I'll have some A142 mesh in the floor itself. Do you think I still need some mesh in the foundation now that the clay is gone?

Thanks again!

Gaps in mortar in garden wall (staircase pattern)

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