Concrete Floor Dropped?

[carlyai]

Another one of those jobs I'm getting Rountuit. This one is a bit more of a headache.

 

There used to be a huge clump of bamboo on the back right side of the block that we dug out, then filled and let settle for a couple of years. Then put down the slab and built the house.

Seems to have stopped now, but for the last few years that side of the house, just back right hand side has dropped. 

I suspect it's hollow under that part of the slab as when you walk on the tiles that cover the slab there's a drumming sound.

I don't think the pier has dropped just the cement around it.

Need some suggestions to go with my thought on how to tackle the problem. Thanks.

 

My thoughts are to force concrete under the house on the RHS into the gap, then wait to see what happens before I fix the walls. Just mix up strong batches in one of those black plastic tubs. Works well with the correct mix and not too much water.

Difficult to get a cement truck near that area.

The building mob said to use sand.

 

1. Inside the house back RHS pier and plaster crack.

 

 

2. Inside the house back RHS.

I don't think the building guys used any steel to anchor the airated blocks to the pier as well.

 

 

 

 

3. Outside the house on RHS corner.

 

 

4. Eves cracked, I think because wall has dropped, don't think the pier has dropped.

 

 

 

 

 

 

 

 

[Rampant Rabbit]

In Merica they do something called "concrete jacking"

[carlyai]

7 minutes ago, Rampant Rabbit said:

In Merica they do something called "concrete jacking"

Big messy job, but could come to something like that. Thanks

[GreasyFingers]

That is a big problem so the question is why it happened. Soil can subside but it is usually because of water. Is that corner well drained or do you have roof water dropping on it.

[carlyai]

5 hours ago, GreasyFingers said:

That is a big problem so the question is why it happened. Soil can subside but it is usually because of water. Is that corner well drained or do you have roof water dropping on it.

We have guttering. I'll check on the drainage.

[Free the 115]

On 7/31/2025 at 11:45 PM, carlyai said:

We have guttering. I'll check on the drainage.

I doubt if that’s a rain water issue. I would suggest you check for water leaks. 
sliw process but isolate ( individually ) all water in the property, and make note of the water meter reading 

Also, if you can hear hollow sounds, then it definitely needs underpinning, because with the look of it, a partial demolition is going to be required soon. 
are you certain the slab is ok?

[Free the 115]

Sliw is “slow”

[carlyai]

3 hours ago, Free the 115 said:

I doubt if that’s a rain water issue. I would suggest you check for water leaks. 
sliw process but isolate ( individually ) all water in the property, and make note of the water meter reading 

Also, if you can hear hollow sounds, then it definitely needs underpinning, because with the look of it, a partial demolition is going to be required soon. 
are you certain the slab is ok?

Thanks. No water leaking from the water line as we have a bore and pump and the pump is not switching on and off.

House is about 8 years old and the back side slowly moved over years.

No problems until SWMBO decided to enclose the verandah.

Just thinking...we have guttering all round and I'll have to check where the 8" pipe goes that takes water from the down pipe to the street. Maybe the extension builders put a hole in the 8" pipe that goes very close to the house. Can't remember exactly where it goes but I'll investigate.

[NanLaew]

1 hour ago, carlyai said:

Thanks. No water leaking from the water line as we have a bore and pump and the pump is not switching on and off.

 

What does that mean? A pump cycling means there's demand somewhere in the system. A pump not cycling means the system is 'closed'. A pump running continuously means something is leaking. Do you mean the pump is cycling normally, on demand?

 

For the best part of three years, we had an issue with the cement bottom of the sluice-style drains that run on almost 3 sides of the house wash out, so the grey water drained into the ground at one location at the rear corner of the house, about 2 meters away from the building. I advised my wife that this would lead to an unstable back end of the house due to the saturated ground. The back-end was added as an extension without the same deep footings as the main building. Some cracks and settling occurred in the cement in the vicinity of the busted sluice, and the back door started sticking, but it didn't grab anyone's attention. Then the pocket door on the ensuite bathrooom in the main house started sticking and again a few months later after I had rehung it. This time I told the wife that the back end of the house will disappear into a sinkhole unless the grey water drainage wasn't sorted. Took about 10 days to replace the entire sluice with a system consisting of about 10 lengths of 8" pvc pipe, each on a slight reverse incline between a series of small well pipe tanks, finally connecting to the main grey water drain on the soi. With the soil drying out and stabilising, no further subsidence or cracks have been observed around the house.

[carlyai]

52 minutes ago, NanLaew said:

 

What does that mean? A pump cycling means there's demand somewhere in the system. A pump not cycling means the system is 'closed'. A pump running continuously means something is leaking. Do you mean the pump is cycling normally, on demand?

 

For the best part of three years, we had an issue with the cement bottom of the sluice-style drains that run on almost 3 sides of the house wash out, so the grey water drained into the ground at one location at the rear corner of the house, about 2 meters away from the building. I advised my wife that this would lead to an unstable back end of the house due to the saturated ground. The back-end was added as an extension without the same deep footings as the main building. Some cracks and settling occurred in the cement in the vicinity of the busted sluice, and the back door started sticking, but it didn't grab anyone's attention. Then the pocket door on the ensuite bathrooom in the main house started sticking and again a few months later after I had rehung it. This time I told the wife that the back end of the house will disappear into a sinkhole unless the grey water drainage wasn't sorted. Took about 10 days to replace the entire sluice with a system consisting of about 10 lengths of 8" pvc pipe, each on a slight reverse incline between a series of small well pipe tanks, finally connecting to the main grey water drain on the soi. With the soil drying out and stabilising, no further subsidence or cracks have been observed around the house.

Pump is working normally, not cycling but working on-demand.

 

Briefly talked to wifey about the drain from the guttering and she is not sure where it goes, but think down the side of the house not the back. Have a look tomorrow

[carlyai]

I'm only working on this problem part-time as completing other half finished jobs as well.

 

I'm starting to think that the major problem is that as it was initially an outside open verandah, (it stepped down from the main house) there are no foundations to support the enclosing wall, which is too heavy for the concrete verandah floor.

So it probably means taking the outside walls down, putting in small piers and putting up the walls again.

Maybe I'll just do with what they did in Pattaya with Theppasit road; everytime it caved in with a big depression, they filled with more concrete and resurfaced.

Will have to ponder the problem more.

I think first (of many firsts) is to see the back structual beams that support the roof are not moving or sinking.

[Free the 115]

On 8/3/2025 at 6:01 PM, carlyai said:

Thanks. No water leaking from the water line as we have a bore and pump and the pump is not switching on and off.

House is about 8 years old and the back side slowly moved over years.

No problems until SWMBO decided to enclose the verandah.

Just thinking...we have guttering all round and I'll have to check where the 8" pipe goes that takes water from the down pipe to the street. Maybe the extension builders put a hole in the 8" pipe that goes very close to the house. Can't remember exactly where it goes but I'll investigate.

Sounds like a good shout. 

Lot of water in an 8” pipe. 
 

[giddyup]

On 7/31/2025 at 6:42 PM, GreasyFingers said:

That is a big problem so the question is why it happened. Soil can subside but it is usually because of water. Is that corner well drained or do you have roof water dropping on it.

If bamboo or even trees were removed without getting rid of the roots the soil will drop to fill the hole after the roots rot.

[OneManShow]

On 8/4/2025 at 8:37 AM, carlyai said:

So it probably means taking the outside walls down, putting in small piers and putting up the walls again.

Are those walls siting on any "footing" over deep piles ? Or just on a concrete slab ? 
If there is no footing this is what happens soon or later with or without bamboo story. 
 

[AgMech Cowboy]

On 7/31/2025 at 9:33 AM, carlyai said:

Big messy job, but could come to something like that. Thanks

If you find a contractor here in Thailand who does this type remediation, I'd like to know who they are and where they're located.  I tried to find one 4 years ago without any success.

[carlyai]

17 hours ago, OneManShow said:

Are those walls siting on any "footing" over deep piles ? Or just on a concrete slab ? 
If there is no footing this is what happens soon or later with or without bamboo story. 
 

No piles, just concrete slab.