How to fill large void under concrete slab?

Reply

  #1  
Old 04-11-19, 02:16 PM
A
Member
Thread Starter
Join Date: Jun 2005
Location: Suburban Washington DC
Posts: 202
Received 0 Votes on 0 Posts
How to fill large void under concrete slab?

There is a large void under the slab of the garage where it meets the asphalt parking lot. Not really sure how the void developed but the opening to it is as big as your foot, and it's size I would guess in the one cubic yard range. I guess I could fill it in with sand or gravel but that wouldn't get it all the way to the top. What about expanding foam like: https://www.youtube.com/watch?v=gWJvrhZlzaM Is this a DIY fix? If not, what companies do this service?
 
Sponsored Links
  #2  
Old 04-11-19, 04:57 PM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 23,734
Received 627 Votes on 579 Posts
Expanding foam would be my choice. You'll have to search for companies that perform the service. I did it as a DIY and was pretty easy.
 
  #3  
Old 04-12-19, 04:16 AM
pugsl's Avatar
Forum Topic Moderator
Join Date: Mar 2008
Location: United States
Posts: 9,029
Received 74 Votes on 67 Posts
If you go with a co. that does this get several estimates. I had some work done and got estimates ferom 500 to 4000.Works great.
 
  #4  
Old 04-12-19, 05:19 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,514
Received 37 Votes on 34 Posts
Not sure how the expanding foam will will perform out in the sun and weather. If you fill it with gravel and tamp it through the opening you mentioned it will move towards the far end of the hole. Even if it doesn't fill it completely it will fill in front and provide support.

Once you use an expanding foam it could become very difficult to do more filling should erosion continue.

Bud
 
  #5  
Old 04-12-19, 05:49 AM
A
Member
Join Date: Jan 2013
Location: U.S.A.
Posts: 2,079
Received 67 Votes on 61 Posts
I agree with Bud in regard to being able to tamp fill through the hole, but my choice would be pea stone over sand or gravel as it will flow easier and provide better compaction. I think you would find that would provide pretty substantial support by itself, but could always cap it with a lesser amount of foam if you wanted to.
 
  #6  
Old 04-12-19, 07:12 AM
H
Member
Join Date: Nov 2012
Location: USA
Posts: 1,752
Received 95 Votes on 84 Posts
I'd start by figuring out where the material went to create the void...

Limestone in the area? Could be a tree stump that rotted out, or a contractor using frozen dirt for fill.

I'd start by dumping a bag of dry concrete mix down the hole, yes dry mix, no water.

Get around 3 feet of tubing, either old car brake line or perhaps plastic compression tubing. Place that in the center of the hole.

Get a cubic yard of 2A (clean 2" stone). Backfill the hole with stone, around the tubing.

Get a big can of expandable spray foam, securely connect the foam nozzle to the 3 foot tube, and trigger the foam.

The expandable foam will slowly spread out THROUGH the gaps in the 2" stone, both lifting the stone up from the bottom, and creating a "foam-crete" of stone aggregate held together by the foam.

Pull the tube out, or cut off at the surface.
 
  #7  
Old 04-12-19, 08:36 AM
Marq1's Avatar
Member
Join Date: Sep 2016
Location: USA MI
Posts: 6,546
Received 370 Votes on 345 Posts
First step definitely need to figure out where the material went.

It didn't just disappear it some how was washed away.

Once that is resolved and if you have a 1' dia opening, start shoveling in sand and small gravel, fill about 4" then hose it down to compact.

Repeat as many times as needed to fill the cavity!

By watering it down it will remove air, compact the material and you should be able to fill completely.

Since you have a hole you may have to open up some but it's going to need repair anyway!
 
  #8  
Old 05-08-19, 05:28 PM
A
Member
Thread Starter
Join Date: Jun 2005
Location: Suburban Washington DC
Posts: 202
Received 0 Votes on 0 Posts
Just getting back to this and stuck a camera into the hole.



 
  #9  
Old 05-09-19, 05:13 AM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 23,734
Received 627 Votes on 579 Posts
Holly cow! That's quite a hole. To save on foam cost I would fill in the hole with clean crushed stone like #57. Stone like that naturally assumes a relatively high compaction. Then use expanding structural foam for the last 4-6" at the top.
 
  #10  
Old 05-09-19, 05:29 AM
A
Member
Thread Starter
Join Date: Jun 2005
Location: Suburban Washington DC
Posts: 202
Received 0 Votes on 0 Posts
That's about what I was thinking too. I see Lowes has 0.5 cu ft bags of gravel. https://www.lowes.com/pd/Sakrete-0-5...vel/1000489233 Probably need about 10 bags.
 
  #11  
Old 05-09-19, 10:06 AM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 23,734
Received 627 Votes on 579 Posts
What you linked appears to be pea gravel. You do NOT want that. It does not compact or "firm up" unless completely contained. It tends to just roll around like a bag of marbles. You want a crushed stone that has jagged edges.
 
  #12  
Old 05-09-19, 10:26 AM
A
Member
Thread Starter
Join Date: Jun 2005
Location: Suburban Washington DC
Posts: 202
Received 0 Votes on 0 Posts
OK I'll make sure of that.
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: