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Patio still too high after extensive works

Postby Mutzgoatz » Sun Jul 05, 2020 6:22 pm

We moved into our mid Victorian terrace in Dec 2018. Soon noticed rising / penetrating damp in the dining room and adjacent sliding doors. At this time, the external ground was 10cm higher than pictured, in line with internal floor level, covering the airbricks under the sliding doors, and made up of fake grass laid over sandy compact soil! Shocking arrangement that surveyor didn't comment on!

I'm December 2019, we got the ground dug out, a patio laid and a French drain gravel over hardcore border around the perimeter and airbricks reinstated. There's also and eco drain that water can drain into in the middle.

Patio is only about 5-10cm below interval floor level, probably less in places.

Unfortunately, this is the lowest it could go, as the soil pipe return running underneath, leading to the sewer was quite high.

We found a modern DPC on the latter end of kitchen extension end (about 5cm above gravel border). Not ideal (less than 15cm), but at least it's above. No evidence of damp ingress that end anyway.

But underneath sliding doors and running along the original kitchen side wall, we couldn't see any DPC. The contractors assured us that despite not being the recommended 15cm below internal floor level, the gravel and hard-core border and fall away from house would make it ok.

The bricks in line with patio height (below where the old black bitumen paint is) have remained pretty damp since. Internally the damp still slowly progresses.

Recently I dug up some of the gravel border, as pictured, and discovered an old slate DPC. But it's so low, like 20cm below internal wooden floor level. And still probably 10cm below current patio level (I.e. The gravel border abuts it and goes well over it by 10cm. Can't believe how much lower it is than the newer DPC at the end of the kitchen.

Does anyone gave any advice in the circumstances? What I fear is that we've been screwed over by patio contractors and it all needs redoing, otherwise it'll be an issue when we sell. But on the other hand it seems they worked within the limits present - the high soil pipe return and old, low slate Dpc etc.

While not ideal, is the gravel border and maybe a DPC injection in line with internal floor level say (plus replastering) a reasonable solution in the circumstances?

Thanks a lot.
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Mutzgoatz
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Postby stoneyboy » Mon Jul 06, 2020 9:25 pm

Hi mutzgoatz
Building up the path/patio so high is a real issue and the presence of a bitumen coating indicates that previous owners have been aware of the damp issues.
Suggest that you dig a channel all round down to the old slate level and then get a DPC injected just above it. This should reduce the amount of rising damp. Leave the channel down to slate DPC level. I may take many months before you see a reduction in rising damp.
Regards S
stoneyboy
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Postby stoneyboy » Mon Jul 06, 2020 9:25 pm

Hi mutzgoatz
Building up the path/patio so high is a real issue and the presence of a bitumen coating indicates that previous owners have been aware of the damp issues.
Suggest that you dig a channel all round down to the old slate level and then get a DPC injected just above it. This should reduce the amount of rising damp. Leave the channel down to slate DPC level. It may take many months before you see a reduction in rising damp.
Regards S
stoneyboy
Rank: Project Manager
Posts: 4819
Joined: Wed Dec 10, 2008 6:44 pm


Postby Mutzgoatz » Tue Jul 07, 2020 8:33 am

Thanks a lot. I pushed the patio contractors many times and they assured me it would be fine given the gravel border. Should have trusted my instincts I guess. At the time I just hadn't noticed the old slate DPC, covered in mud.

When you say dig a trench, do you mean literally leave it exposed like that permanently, or once it's a bit more dried out, can it be refilled with rocks and hardcore?
Mutzgoatz
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Postby stoneyboy » Tue Jul 07, 2020 5:36 pm

Hi mutzgoatz
The channel needs to be about 75-100mm wide and if you are on a non-permeable soil, eg clay, the channel needs to be lower than the slate DPC.
Slate DPCs are never perfect and they rely on the bricks directly above to be able to breath so moisture can evaporate, so the bitumen coating may be making the damp issue worse.
Given the age of your property it is likely that the floor joist have been partly built into the wall so it is important to get thing dried out.
Suggest you leave the channel open until it is established that this and the injected DPC has solved the issue. If ok you could then use large pebbles to fill the channel but you will have to occasionally remove them and clear accumulated debris.
Regards S
stoneyboy
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Posts: 4819
Joined: Wed Dec 10, 2008 6:44 pm


Postby Mutzgoatz » Tue Jul 07, 2020 7:38 pm

That's great, really appreciate your advice, thanks.
Mutzgoatz
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