Concrete base problem in garage shop. Any construction folks?

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my5thmopar

my5thmopar

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I removed a poorly done concrete floor in my shop. It was severely cracked and not level. I found 3/8 clean crushed limestone as a base. I'm sure this was done to make it easy and supposably self-compacting, on the solo pour 25 years ago. I have to add 7-8 inches of fill to get to the new floor level before the pour. I'm raising the floor to fix the driveway approach. It has to be done, so no deviation from the plan. The ceiling is going to be at 8'6'. Here's the issue...The base is already 18-20 inches deep and doesn't seem solid. If you ever walked in pea gravel, you know what I mean. Again 3/8 "clean" crushed limestone. I haven't tried to compact it and I don't think you can. I want to add #57 and compact it but, not sure how that works on top of the 3/8. Any ideas? Craig
 
I have used what's called "bank run" which is various sized gravel/sand specifically meant to pack. We have also used a morter mixed limestone, which is mainly used for filling pot holes in gravel driveways, and turns to a hard base with moisture. If you still need 7 or 8 inches of fill, I would look at topping off what you have with one of these.

Assuming your not pouring your own slab, consult your concrete guy. Some care more than others. I poured in high school and college, and usually uneven or non compacted gravel didn't hurt a pour. Would just take more concrete to fill the voids in say 57 limestone, vs bank run.

If your base under that has been there for 25 years, it's pretty solid.
 
When I had my garage built, The floor was poured by my friend's brother who owns a Cement plant. He suggested 1/2 inch rebar formed into a grid that encapsulated the whole floor to strenghten the floor and remove flex. That was 1994 and I have had zero issues and I'm constantly working on all kinds of vehicles in it. Not a crack or issue anywhere.
 
You have to have some kind of binder if you want to get compaction. In ND a common fill material is what is called Class Five.

www.magnusonsod.com

Class 5 Base | Path and Road Material, MN | Magnuson Sod

Consisting of rock, sand and clay, class 5 base is perfect for parking lots, driveways, and trails. Same day delivery in Minnesota! Schedule your delivery today.
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You note that this has both fines and clay in it. The suggestion of mixing in some sand is a good one but if you could find some clay, the resulting subbase will compact to something resembling concrete using a plate compactor in no more than 6" lifts.
 
If your using clean limestone rock you will not be able to get it to pack, all you can do is run a roller or vibrating tamp over it to tamp it down best you can before pouring your new floor over top of it. Since your base is so deep probably be best to stay off it with any equipment like skid loaders / ready mix tricks after you get it leveled out where you wan it to prevent any
rutting prior or during r-mix placement.
 
So the crushed gravel is used for water drain under the concrete and help with leveling out of the concrete to maintain thickness. In New England we use crushed granite -3/4” washed and compact evenly every 2-3” thick until desired height is obtained. Typically a 4” pour (I prefer 6”) of 3500psi concrete (minimum 30day cure with cuts for stress cracks)with reinforcement like fiber mesh or #4/5 rebar is used per engineered plans. I’ve not worked with lime stone before but from what I was told it does not like more than a few inches and Does not pack well.
 
If the original floor failed, there's a reason for it. Clean rock can be used for significant lifts, but it needs to be contained because it won't pack. When properly contained, it can lock together and be quite stable. But if it's just loose fill over grade, then it can spread and shift and changing the last couple inches of fill may not have much impact if the base continues to shift.
The root cause of failure of the original slab could be many things. If you can figure out the cause, then it will help point you toward a solution.
 
You need to to find some "red dog dirt" part sand, part clay, and very little dirt in it. I am sure you can find some around where you live, it is often used on secondary roads. I am showing you a link what I used on top of 6C road pack. Rent a compactor and spend all day, this will work for what you need.

Red Dog dirt, sandy gravel pit run material and ponds - $10 (pawnee)
 
Thanks for all the suggestions. The new floor will have #4 rebar in a 2ft grid pattern. I said unstable because my Kubota wants to spin in the crushed base. Like suggested, when I compact it, put the vapor barrier on top with the rebar, it will be fine. I usually overthink this stuff since I’ve been a technician my entire life. The floor failed due to a broken and settling footing on one side. It caused upheaval and cracked. That’s been fixed with post and beam installation. The building is stable now and I installed an under footer drain on the low side. I noticed the water draining during the heavy rain today. We have all clay and it tends to hold water if it doesn’t have anywhere to runoff. The floor will actually be floating slab and not anchored to the footer. It was originally a monolithic slab deep pour. I've always used 3/4 or #57 when I poured sidewalks and pads. That's kind of why I was leaning that way. I'm thinking I should just put more 3/8 on it and be done with it. I don't know any concrete folks. Keep suggestions coming. Craig
 
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my5thmopar said:
Thanks for all the suggestions. The new floor will have #4 rebar in a 2ft grid pattern. I said unstable because my Kubota wants to spin in the crushed base. Like suggested, when I compact it, put the vapor barrier on top with the rebar, it will be fine. I usually overthink this stuff since I’ve been a technician my entire life. The floor failed due to a broken and settling footing on one side. It caused upheaval and cracked. That’s been fixed with post and beam installation. The building is stable now and I installed an under footer drain on the low side. I noticed the water draining during the heavy rain today. We have all clay and it tends to hold water if it doesn’t have anywhere to runoff. The floor will actually be floating slab and not anchored to the footer. It was originally a monolithic slab deep pour. I've always used 3/4 or #57 when I poured sidewalks and pads. That's kind of why I was leaning that way. I'm thinking I should just put more 3/8 on it and be done with it. I don't know any concrete folks. Keep suggestions coming. Craig
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It sounds like you already fixed the root cause, so no reason add more work than necessary.
More of almost any clean rock will probably be fine. I think adding mixed bases over the clean without a filter fabric might cause settling at some point, only because you know there's water down there and who knows how high it might get under the slab in any given year? The mixed bases aren't going to do anything that clean rock won't, so personally I'd stick with more clean rock. IMO, availability is likely more important than the actual rock you use.
 
I used 3/4 clean fill. Also, used a 200lb vibrating compactor anyway for $60 bucks rental. It's cheap insurance even though most contractors wouldn't have done it with 3/4. I ran it every 6 inches of fill for 4 hours. I did all the forms, fill and laser level where I wanted floor. Poured it today 6mil plastic, rebar grid, expansion material against block. and 3500 psi with fiber. Thanks for all the advice. I helped pour to be third man to pull up rebar during pour and kept an eagle's eye on the contractor. Got a break on labor from contactor when he realized I knew something about concrete work. Photos to follow if interested. Craig
 
my5thmopar said:
I used 3/4 clean fill. Also, used a 200lb vibrating compactor anyway for $60 bucks rental. It's cheap insurance even though most contractors wouldn't have done it with 3/4. I ran it every 6 inches of fill for 4 hours. I did all the forms, fill and laser level where I wanted floor. Poured it today 6mil plastic, rebar grid, expansion material against block. and 3500 psi with fiber. Thanks for all the advice. I helped pour to be third man to pull up rebar during pour and kept an eagle's eye on the contractor. Got a break on labor from contactor when he realized I knew something about concrete work. Photos to follow if interested. Craig
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Definitely interested. Please do post some photos.
 
Somewhere in the middle after I lifted building. Compacted 3/4 washed stone and floor was rock hard. Lastly, waiting on concrete to firm up. Finished off the floor with power trowel and light broom on ramp. I have the concrete wet and covered for a few days. I have to run the garage ceiling mounted heater again tonight since it’s going to get down to 30 degrees. I’ll post the finished product when the tarps and plastic come off. Craig

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Just a note to the folks thinking about getting concrete or footer work done. Actually, any kind of work. I have the DIY curse in that I do everything and can count on one hand, the times I've had to hire someone. It's very rare to find a tradesman that really has pride in their work. If ya have one, you're lucky. Although I have built and helped build several structures, I never paid attention during the foundation part. My advice, learn everything you can about your project and question anything that doesn't seem correct. I didn't know that 25 years ago when I built the garage. Now you see the mess I'm dealing with. My unsolicited advice. Craig
 
Around here, bank run is what you would use as a base. Its a mixture of gravel, sand and red clay and packs like a mutha. I also use recycled concrete which also makes a great base. You can tamp it down and its hard as concrete.
 
I finished trimming the garage doors today. Now begins purging stuff before it goes back in. I’m going to build in some organization.

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my5thmopar said:
I finished trimming the garage doors today. Now begins purging stuff before it goes back in. I’m going to build in some organization.

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Just some observations.... While the garage is empty.

Put in overhead LED lights.

Run some new electrical outlets for easier access.

Run some piping for compresser air around the garage.

If you are considering sheeting up the inside walls, great time to paint them white. Makes a huge difference in lighting up the interior.

If the garage is for storage only, disregard.
 
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