What's the best back fill for a new slab?

[ptt49er]

Hey yall!

I am building a 30x40 shop... Got the stem wall up and need to backfill for the slab.

It drops about 24-30 inches across the 50' diagonal.

Getting conflicting advice on fill dirt or 57 stone.

I've got a contact that can get 57 stone for me cheaper than fill dirt.

I plan on a vapor barrier.

What say ye?

Sent from my SM-G930V using Tapatalk

 

[My Old Tools]

I used select fill as recommended by my foundation guy. Seems to be working fine. I would listen to the local pros.

 

[rustyjames]

I've always had great success with my slabs when I used a crushed stone base under the slabs.

 

[Itsjustdirt]

I think a lot depends on your location but after doing a bit of research myself, I went with Class 1 or Class 2 road base, dont remember which. At least, that's what they call it out here.

It's basically gravel and sand together. Per local concrete guys, its what Caltrans uses under all of their freeways. The sand/gravel combo gives a complete fill (you dont have voids to worry about), yet still drains well and can be compacted to some extent.

 

[brownbagg]

depends on where you live, around here, its clean white sand. but then the nearest rock quarry is 200 miles awway

 

[1jjpop]

I don't care what you use . Roll or tamp real good. Wet it down if it real dry.Pays off in the end...

 

[Slednut]

I used recycled concrete, every 6 inches wet and wacked it good with the wacker on the end of the backhoe. When done it was 24 inches deep. It's been 4 years, no cracks.

 

[Marctrees]

Absolutely vapor barrier...

Does two big things...

Facilitates concrete hydration..

And prevents future water migration through slab.

Should be always used even in high dry desert for the first reason.


As far as the fill goes..

It will vary WIDELY on geo local availability.

Learn your local options, and study from there.

Marc

 

[3rdgendslmech]

I'd fill it in with fill dirt and compact it, then put your 57 stone down. unless you're getting that good of a deal on stone that it'd be cheaper to do the whole thing in stone then go ahead

 

[Marctrees]

Whatever you use, compaction is key.

Usually not done fully correctly on by far most residential jobs.

Marc

 

[Marctrees]

Even if the center field is compacted well. the perimeter will in most jobs not be as good.

Marc

 

[RVDan]

Recycled crushed concrete.

 

[dneiding]

I used 30 ton of asphalt road grindings. Compact it, let it rain on it a few times, it was hard as concrete. I had to use a pick ax to put in my floor drains.

 

[bad_idea]

We have no rock quarries around me. We have plenty of sand though. Concrete guy used sand. After he compacted it, it was hard as rock. I would recommend you find a good concrete contractor in your area and do as he says. It is a regional thing, depends on local soil conditions and available fill.

 

[6768rogues]

I have used #1 crusher run, compacted in 6" lifts. You could see if any local concrete suppliers have crumbs of concrete cleaned from their transit mix trucks. I have purchased that for the cost of trucking it, and it compacts great.

 

[77Birdman]

Only problem with 57's is they wont compact. That's ok for the top layer which will allow drainage. I would def. use something that will compact better for that amount of fill you need.

 

[Firebrick43]

57's will absolutely compact????

Don't confuse adhesion with compaction.

 

[rustyjames]

From what I've understood is that clean crushed stone doesn't need to be compacted when placed, just tamped with a plate compactor.

 

[kbs2244]

bad idea has the right idea.
Have the concrete guy do it or have him get it done.
That makes him responsible for it being done right
And he knows the local conditions.

 

[ptt49er]

Thanks for the reponses!
I talked it over with our concrete guy and a couple of other local contractors and concrete guys.

We went with the 57 stone, cost was a bit more than sand (although one guy did quote me more for the fill than I paid for the stone). I think it's the right choice and my concrete guy does too, so we'll hope we're both right!

-PT

 

[Firebrick43]

From what I've understood is that clean crushed stone doesn't need to be compacted when placed, just tamped with a plate compactor.

Tamping with a plate compactor is compacting. You could also call it consolidating aggregate. many names, still needs to be done, and done properly. IE most small plate compactors can only do about 4" so it needs to be done in lifts and should be wetted and done multiple passes per lift.

 

[TommyK]

From what I've understood is that clean crushed stone doesn't need to be compacted when placed, just tamped with a plate compactor.

This is correct. You aren't compacting clean crushed stone you are just consolidating it. Compaction is a term that is applied to soils. Crushed stone is not a soil.

 

[firemanchad]

i built a 30x40 had 20ton of 3" rock brought in, spread it, a month later I had 20ton of 1" rock, spread it, then a moth later I had 20ton of crush and run. spread that and about 2 -3 months got ready for concrete, packed it and vapor barrier.
concrete was poured 5" with fiber mesh and wire. 8" thick where the lift was laid out.
Time spacing was to use cash
Middle TN

did awesome for two years, cancer hit family and we had to down size home and moved closer to family.

 

[joes169]

From what I've understood is that clean crushed stone doesn't need to be compacted when placed, just tamped with a plate compactor.

You are correct, it's classified as "95 Proctor"" from every structural or geo engineer I've worked with. You can run over clean stone with a compactor all day and see little to no difference, which is why it is generally the fill of choice for situations like this anywhere but a third world country....

 

[ptt49er]

i built a 30x40 had 20ton of 3" rock brought in, spread it, a month later I had 20ton of 1" rock, spread it, then a moth later I had 20ton of crush and run. spread that and about 2 -3 months got ready for concrete, packed it and vapor barrier.
concrete was poured 5" with fiber mesh and wire. 8" thick where the lift was laid out.
Time spacing was to use cash
Middle TN

did awesome for two years, cancer hit family and we had to down size home and moved closer to family.

FMC - I'm glad you were able to get closer to family during a time of need! Things can be replaced - those relationships are priceless!

Your process sounds involved and solid!

You are correct, it's classified as "95 Proctor"" from every structural or geo engineer I've worked with. You can run over clean stone with a compactor all day and see little to no difference, which is why it is generally the fill of choice for situations like this anywhere but a third world country....

J169 - Thanks for chiming in! We're pushing forward with the stone and should have back fill completed today.

 

[maxpat82]

in my garage build: compaction sand...compacted every 6-12" with the big diesel compaction plate.

 

[gmtech]

I just finished mine very similar. After many sleepless nights I ended up with about 90 tons of #57 slate. I paid a little more but I didn't have to worry with renting compacting equipment etc. My biggest corner was 5 blocks which was about 40" luckily I installed a French drain inside the back wall and while it sat with just the #57 we got over 20'' of rain so I feel like that helped things. .

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[ptt49er]

That's a nice looking slab! I'm ready to get mine poured!

 

[gmtech]

That's a nice looking slab! I'm ready to get mine poured!

I bet so. My concrete was poured 4 weeks ago tomorrow. Ive taken time to get the landscaping around the foundation done and the driveway made. Im taking a break now letting my funds build back up.

Are you doing a stick built garage or a metal carport style or? Wish I had went 30x40 instead of my 30x30.

 

[ptt49er]

Going stick built - hoping to place my material order this week!

 

[velocipede]

gmtech..
First time I've seen a slab poured like that and it looks like a great idea. Am I correct in thinking the half blocks on the top row serve as the form for the pour, and the whole slab rests on the second layer of block? What's the size of the base block? Do you think the expansion/contraction of the slab affect the joint below it? Very interesting.

 

[gmtech]

It's called a "header block" it serves as your concrete form and your top row of block. As for the expansion/contraction of the slab, I'm confident it will be fine. It's pretty common practice to use header blocks for houses built on a slab. Although in a house you wouldn't ever know of it cracked LOL it's an 7" slab with #4 rebar on 18" centers with plenty of saw cuts. I'm hoping for the best. Time will tell. I've built this all myself and have no experience in the field lol

gmtech..
First time I've seen a slab poured like that and it looks like a great idea. Am I correct in thinking the half blocks on the top row serve as the form for the pour, and the whole slab rests on the second layer of block? What's the size of the base block? Do you think the expansion/contraction of the slab affect the joint below it? Very interesting.

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[gmtech]

Header block

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[garagelogician]

Only problem with 57's is they wont compact. That's ok for the top layer which will allow drainage. I would def. use something that will compact better for that amount of fill you need.

57 stone is considered "self-compacting." The fractured faces of the stone do need to be oriented to each other though, so vibratory compaction is used. On a typical lift thickness, it will typically compact about 1" in height when properly compacted.

57's will absolutely compact????

Don't confuse adhesion with compaction.

The correct term in this case would be cohesion (like materials). Adhesion is two different materials.

 

[velocipede]

It's called a "header block" it serves as your concrete form and your top row of block..... I've built this all myself and have no experience in the field lol....

gmtech, Thank you for the header block information. My hat's off to you. That is a professional looking job and that foundation is solid as a rock. It looks like you are doing things right!