# Forum Home Renovation Sub Flooring  Erosion around/under edge of slab-how worried should i be

## PaulKaren

Hi all, 
We have purchased a 2 story brick veneer steel framed  13 year old 2 story house on sloping block on the Gold Coast. The bottom level is on a slab with the top level supported by steel posts (block slopes front to rear.) With a bit of heavy rain lately the side of the house that gets a lot of foot/dog traffic has eroded a fair bit of soil away exposing the foundation edge. I dug a bit around the base of the foundation to fix a downpipe issue which exposed a gaping hole heading down under the slab. It is probably about 3 to 4 inches high and although i havent dug it any further yet im guessing it goes for a metre or so along side of the house. There is a bit around the corner that does the same thing. I can stick my arm right in to the hole/s and it wouldnt surprise me if a snake or two resides there. House appears solid from the inside with no signs of plaster cracking although house was painted before we moved in. Been digging around other side of house to do some drainage and i hit sandstone about 400mm from the top of the foundation. Parts of said sandstone turn black and extremely hard to dig so i assume (and hope) the base under house is solid sandstone. I will post some pics soon but anyone got any thoughts on this? If i wanted to get someone out to check it who would i call? A re-stumper i suppose? Cheers in advance  for any advice 
Paul

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## intertd6

> Hi all, 
> We have purchased a 2 story brick veneer steel framed  13 year old 2 story house on sloping block on the Gold Coast. The bottom level is on a slab with the top level supported by steel posts (block slopes front to rear.) With a bit of heavy rain lately the side of the house that gets a lot of foot/dog traffic has eroded a fair bit of soil away exposing the foundation edge. I dug a bit around the base of the foundation to fix a downpipe issue which exposed a gaping hole heading down under the slab. It is probably about 3 to 4 inches high and although i havent dug it any further yet im guessing it goes for a metre or so along side of the house. There is a bit around the corner that does the same thing. I can stick my arm right in to the hole/s and it wouldnt surprise me if a snake or two resides there. House appears solid from the inside with no signs of plaster cracking although house was painted before we moved in. Been digging around other side of house to do some drainage and i hit sandstone about 400mm from the top of the foundation. Parts of said sandstone turn black and extremely hard to dig so i assume (and hope) the base under house is solid sandstone. I will post some pics soon but anyone got any thoughts on this? If i wanted to get someone out to check it who would i call? A re-stumper i suppose? Cheers in advance  for any advice 
> Paul

   Post some pics
 regards inter

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## DuckCommander

Hi Paul,
Looks like your down-pipe issue has caused soil to erode out adjacent to your footing. As far as I see it you've got a couple of options:
- If you dig along the outside of the house and establish there is no undermining of the edge strip footing, and your down-pipe issue is resolved, you could get away with back-filling with compacted stabilised soil.
- If the edge footing is undermined it's probably best you get someone in to check it out. I'd say you'd need a geotech engineer, a mob on the Gold Coast I'd recommend is Border-Tek.
Cheers

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## PaulKaren

> Hi Paul,
> Looks like your down-pipe issue has caused soil to erode out adjacent to your footing. As far as I see it you've got a couple of options:
> - If you dig along the outside of the house and establish there is no undermining of the edge strip footing, and your down-pipe issue is resolved, you could get away with back-filling with compacted stabilised soil.
> - If the edge footing is undermined it's probably best you get someone in to check it out. I'd say you'd need a geotech engineer, a mob on the Gold Coast I'd recommend is Border-Tek.
> Cheers

  Thanks for that...i just googled the above company and they seem like a huge mob...not sure if they would be interested in a few holes on one side of my house...Will try them anyway....Was thinking of mixing up some cement/concrete and forcing as much as i can down there? Would think this would be better than soil but maybe i wouldnt get it in deep enough? There are no signs of anything in the house moving yet so hopefully i have caught it in time....Thanks again for your reply.... 
Paul

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## intertd6

Are you insured? Best tell your insurance company, could be expensive or nothing much at all, they will send someone to assess the damage.
regards inter

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## PaulKaren

Hi All, 
Thought i would post to let anyone who might have a similar problem the advice i just received. Had an honest bloke out from a long established  underpinning/ structural building mob here on the coast to check my erosion issues. Due to no visible movement in any of my expansion joints/window and door frames etc he said the slab must have been built with piers otherwise the damage we have would have caused cracks by now. He had a good look at the way the house was built and said it had been built well and even asked if i knew who the builder was  :Redface: )... so that was all good news...he recommended just mixing up a grout mix and pouring it in the holes to fill the void. Exactly what i wanted to hear! So he said a coarse river sand mix with not too much cement and some detergent...guess ill just make up a mix and see how it goes?

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