water seeping through from under slab into post hole

Basher · Mar 10, 2024 11:24 pm

Hi all,

I dug up post holes in my backyard for a pergola. 1 post hole close to the wall keeps filling with water.

I dug up 600mm and since i was close to the wall i exposed the edge of the black plastic under the slab. Water seemed to be seeping from under that plastic. So i put my finger in the area and i was able to remove the mud and make the whole bigger. It fills up in couple of hours.

I dug very slowly because i didn't wanna hit any underground pipes since i was digging next to a gutter pipe and only used a round post digger and small crow bar. I can't see how if i damaged any pipes because there are none there.

Now i am worried if there is a potential problem under the slab.

House is in Mickleham and it is only 3 years old and we are the 3rd owners. Since we are the 3rd owners, will there be any warranty if it is a leak coming from under the slab?
House was built around 2021 and section 23 has building permit for "Australian Building Company" but contact details are of an individual from Metricon.
We really hope it isn't something big which is not covered under warranty.
Any guidance will be much appreciated.

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Ashington Homes · Mar 11, 2024 4:59 am

Hi Basher,

You can't imagine how normal this is, especially in the areas that we build in.

I would only start to worry if water comes through your slab into your home, which can happen if there is an air pocket ( tiny hole) in the concrete. You will know it when it happens and it should be easy to waterproof the affected area provided you dont have to open walls up to find the leak.

For this reason we always waterproof any step downs in slabs.

We have so much ground water here on the North Shore in Sydney. My own home is particularly bad. I have a video of a torrent of water coming out from under my slab in front of my garage when I had to excavate, but in 4 1/2 years I have never had an internal problem.

In conclusion I think you will be fine

Cheers

Simeon

Basher · Mar 11, 2024 8:36 am

Ashington Homes

Hi Basher,

You can't imagine how normal this is, especially in the areas that we build in.

I would only start to worry if water comes through your slab into your home, which can happen if there is an air pocket ( tiny hole) in the concrete. You will know it when it happens and it should be easy to waterproof the affected area provided you dont have to open walls up to find the leak.

For this reason we always waterproof any step downs in slabs.

We have so much ground water here on the North Shore in Sydney. My own home is particularly bad. I have a video of a torrent of water coming out from under my slab in front of my garage when I had to excavate, but in 4 1/2 years I have never had an internal problem.

In conclusion I think you will be fine

Cheers

Simeon

Thanks Simeon. That is a relief. I dug 5 post holes and only the one close to slab was filling up. This is why we were worried.

redfox · Mar 11, 2024 5:38 pm

We literally have water evaporating through 30cm warehouse slab up in campbellfield. Cannot see the water, but where it draws out the salt through the slab that's where you can see it. Comes a few months after a really wet season. There was black plastic membrane put in during the pour, but I don't think you can do much in regards to the water table.

groundzero · Mar 18, 2024 7:23 pm

The soil profile looks like fill which is common in Mickelham. What happens is water permeates through fill and then ponds on the natural soil layer so when you dig it up it looks like a water table but is not. We call this temporary perched water table or seepage. We have had a very wet 3 years so this may not be an ongoing issue. Check your drainage in this area. Is there water being dump into this area eg end of a pavement sloping to this area.Is there a pergola without gutters connection to the stormwater system etc. Shouldn't be a major problem anyway.
Keep an eye out for water salts forming on your brickwork which is called efflorescence then maybe it is an ongoing issue.

Basher · Mar 18, 2024 7:28 pm

groundzero

The soil profile looks like fill which is common in Mickelham. What happens is water permeates through fill and then ponds on the natural soil layer so when you dig it up it looks like a water table but is not. We call this temporary perched water table or seepage. We have had a very wet 3 years so this may not be an ongoing issue. Check your drainage in this area. Is there water being dump into this area eg end of a pavement sloping to this area.Is there a pergola without gutters connection to the stormwater system etc. Shouldn't be a major problem anyway.
Keep an eye out for water salts forming on your brickwork which is called efflorescence then maybe it is an ongoing issue.

Thanks Mate. I have contacted the builder and they are sending the drainers to check.

building-expert · Mar 19, 2024 8:26 am

Water this close to the slab edge or under the slab can cause slab heave or subsidence and is potentially a serious problem especially on highly reactive clay soils.
Over the years I have seen many slabs damaged.
One two storey house I saw in Avondale Heights did not have any cracking or visible distress but was 100mm out of level and acquired self opening and self closing doors. The whole house tilted without cracking.
Roll some marbles on the floor.
So do not dismiss what you see or it may come back to bite you. You should have your own independent assessment.
Regardless of the fact that you are the third owner you are covered by builders warranty for 10 years

Basher · Apr 05, 2024 9:51 pm

building-expert

Water this close to the slab edge or under the slab can cause slab heave or subsidence and is potentially a serious problem especially on highly reactive clay soils.
Over the years I have seen many slabs damaged.
One two storey house I saw in Avondale Heights did not have any cracking or visible distress but was 100mm out of level and acquired self opening and self closing doors. The whole house tilted without cracking.
Roll some marbles on the floor.
So do not dismiss what you see or it may come back to bite you. You should have your own independent assessment.
Regardless of the fact that you are the third owner you are covered by builders warranty for 10 years

Thanks for your advice. So far i have not noticed any issues with doors and windows. Builder advised they will organise drainers to inspect 2 weeks ago but no further update since.
What type of professional will be able to investigate this issue? I can't afford to pay someone now but will definitely have it assessed independently as well.

Dtv · Aug 19, 2024 11:04 am

Basher

groundzero

The soil profile looks like fill which is common in Mickelham. What happens is water permeates through fill and then ponds on the natural soil layer so when you dig it up it looks like a water table but is not. We call this temporary perched water table or seepage. We have had a very wet 3 years so this may not be an ongoing issue. Check your drainage in this area. Is there water being dump into this area eg end of a pavement sloping to this area.Is there a pergola without gutters connection to the stormwater system etc. Shouldn't be a major problem anyway.
Keep an eye out for water salts forming on your brickwork which is called efflorescence then maybe it is an ongoing issue.

Thanks Mate. I have contacted the builder and they are sending the drainers to check.

Did you end up finding the problem causing this... I think i have same issue in my home in Keilor East

Basher · Aug 19, 2024 12:23 pm

Dtv

Basher

groundzero

The soil profile looks like fill which is common in Mickelham. What happens is water permeates through fill and then ponds on the natural soil layer so when you dig it up it looks like a water table but is not. We call this temporary perched water table or seepage. We have had a very wet 3 years so this may not be an ongoing issue. Check your drainage in this area. Is there water being dump into this area eg end of a pavement sloping to this area.Is there a pergola without gutters connection to the stormwater system etc. Shouldn't be a major problem anyway.
Keep an eye out for water salts forming on your brickwork which is called efflorescence then maybe it is an ongoing issue.

Thanks Mate. I have contacted the builder and they are sending the drainers to check.

Did you end up finding the problem causing this... I think i have same issue in my home in Keilor East

We pressure tested the storm water and found multiple leaks. It is getting fixed soon. Will see how it goes after this.

Dtv · Aug 19, 2024 12:39 pm

Is there a way i can contact call u?

homeone · Aug 19, 2024 12:43 pm

Dtv

Is there a way i can contact call u?

Please share any personal info via a private message.

Dtv · Aug 19, 2024 3:05 pm

Basher

Hi all,

I dug up post holes in my backyard for a pergola. 1 post hole close to the wall keeps filling with water.

I dug up 600mm and since i was close to the wall i exposed the edge of the black plastic under the slab. Water seemed to be seeping from under that plastic. So i put my finger in the area and i was able to remove the mud and make the whole bigger. It fills up in couple of hours.

I dug very slowly because i didn't wanna hit any underground pipes since i was digging next to a gutter pipe and only used a round post digger and small crow bar. I can't see how if i damaged any pipes because there are none there.

Now i am worried if there is a potential problem under the slab.

House is in Mickleham and it is only 3 years old and we are the 3rd owners. Since we are the 3rd owners, will there be any warranty if it is a leak coming from under the slab?
House was built around 2021 and section 23 has building permit for "Australian Building Company" but contact details are of an individual from Metricon.
We really hope it isn't something big which is not covered under warranty.
Any guidance will be much appreciated.

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pram1403 · Aug 27, 2024 12:29 am

I had a similar issue with my backyard a while back. The water ended up being from a small leak under the slab. I’d suggest contacting the builder or warranty provider ASAP since your house is still pretty new—there might be some coverage for this.

In the meantime, make sure the drainage around your post hole is good and keep an eye out for any more signs of trouble. Better to get it checked out now before it becomes a bigger problem!

Dtv · Aug 27, 2024 12:05 pm

pram1403

I had a similar issue with my backyard a while back. The water ended up being from a small leak under the slab. I’d suggest contacting the builder or warranty provider ASAP since your house is still pretty new—there might be some coverage for this.

In the meantime, make sure the drainage around your post hole is good and keep an eye out for any more signs of trouble. Better to get it checked out now before it becomes a bigger problem!

May i ask what was the leak under the slab?... Sewer, mains stormwater? I have a similar probem...

SaveH2O · Aug 27, 2024 1:22 pm

New home owners are strongly advised to have a forensic examination of all drain, storm water and sewer pipes prior to handover.