At Home In The Woods

[Obed]

What are you doing to compact the rock under the slabs?

Nothing. The gravel is sitting on undisturbed red clay.

 

[dcyrilc]

Nothing. The gravel is sitting on undisturbed red clay.

Uncompacted gravel will settle over time. Six inches of gravel can settle between 1-2 inches. You're best bet would be to rent a walk behind plate compactor from home depot and use it to compact the gravel before poaring the slab. It will help to prevent settling and cracking over time.

 

[Obed]

Uncompacted gravel will settle over time. Six inches of gravel can settle between 1-2 inches. You're best bet would be to rent a walk behind plate compactor from home depot and use it to compact the gravel before poaring the slab. It will help to prevent settling and cracking over time.

My wife talked to the inspector today. Our slabs will have approx 12 inches of gravel under them. Due to the depth of the gravel, the inspector highly recommended that we compact the gravel or she thought we would have cracking issues. However, according to the inspector, compacting the gravel is not a code or inspection point so the non-compacted gravel would pass inspection. Unfortunately, rebar in the main floor garage was already 75% complete. The basement had wire and plastic on it. I asked the sub to remove the rebar in the main floor garage, remove the plastic and wire from the basement garage, rent a compactor and compact all the gravel under the garage slabs. We aren't compacting the rest of the basement; if it cracks, it cracks. Cost - an additional $600 in labor plus compactor rental fee.

 

[Mark in WV]

Great reading, it is very considerate of you & your wife to talk the time to post the pictures and day to day activities on this very complex project.

Best of luck.

Mark

 

[jayste]

The pregnant wife built an insulated house for the well. This house is temporary until we can put a pressure tank in the basement. My wife is very capable. In addition, she is also a great cook. How'd I ever get so fortunate? Her only drawback is sometimes she wants to drive my tractor.

PIONEER WOMAN! She's got pioneer blood in her, man! Pregnant, builds well house, drives tractor AND COOKS! I bet she knows how to do laundry by beating them on a rock at the river! Not to mention go out and hunt some grub with a shootin' iron! She got any sisters? Just kidding! I've got me a good one already. Obed, we need to talk. You're suppose to get across to her that there's more honor in being the "swamper" for the tractor driver. This means that you get the tractor and she hooks up everything and directs you and moves things out of the way. Tell her that any old monkey can drive but it really takes a "special" person to "swamp"! I'm seeing a pattern here. Before long you'll be (while wearing an apron) calling her in off that old tractor for dinner!.......

Oh! By the way. Nice progress on the house. Finally, take nothing I say seriously!

Jay

 

[dcyrilc]

My wife talked to the inspector today. Our slabs will have approx 12 inches of gravel under them. Due to the depth of the gravel, the inspector highly recommended that we compact the gravel or she thought we would have cracking issues. However, according to the inspector, compacting the gravel is not a code or inspection point so the non-compacted gravel would pass inspection. Unfortunately, rebar in the main floor garage was already 75% complete. The basement had wire and plastic on it. I asked the sub to remove the rebar in the main floor garage, remove the plastic and wire from the basement garage, rent a compactor and compact all the gravel under the garage slabs. We aren't compacting the rest of the basement; if it cracks, it cracks. Cost - an additional $600 in labor plus compactor rental fee.

Glad I got the information to you before it was too late. I didn't realize that you were going 12" thick with the gravel. Plate compactors only effectively compact 3-4", maybe 6" at the most. Normally, that thickness would be done in 4" lifts. Your best bet at this point in time, if possible, would be to use a pedestal compactor (known in the industry as a jumping jack) followed by the plate compactor. Jumping jacks are normally used to compact ditch lines but can be used, kind of awkwardky, to compact flat ground and will compact 12-16" of material. Another thing which can help, if the gravel has enough fines in it, is to saturate the gravel with water while using the plate compactor. Doing this ,however, requires allowing the gravel to dry afterwards before proceeding. This late in the year, depending on your weather and time available, that may not be an option as you need to use enough water to make the gravel pump water while vibrating. It takes alot of water!

Also, make sure they don't just make one or two passes on the dry gravel. It takes time and a lot of passes to compact gravel. Especially since you are trying to compact 12" with a machine designed to compact 3-4". To give you an idea, I would spend about an hour on an average garage floor to compact a 3-4" lift. They won't get it done in 20-30 minutes. I would expect about 4 hours per floor with your 12" depth.

If you use a pedestal compactor first and get good compaction, you'll find that the 12" of loose gravel will end up being about 9" of compacted rock. You will need to add more gravel and finish with the plate compactor to bring it back up to grade.

 

[Obed]

So what does everyone think about the gravel compacting issue? Do you agree with dcyrilc? It's supposed to rain tomorrow (Wed) so probably nothing will happen tomorrow. The sub really doesn't want to redo the rebar and wire. Will trying to compact 12 inches of gravel be a waste of time and money? How much do you think 12 inches of #57 gravel on top of undisturbed red clay will settle?

Thanks in advance,
Obed

 

[tommu56]

On your wall back fill you could have done with dirt in 3-4 " lifts compacting between and saved some stone the same go's for the stone compact it in small lifts.

to check it they use a drop test for our machine foundations sub soil

I just goggled it sounds like a proctor soil test

link Proctor Test Soil

Proctor compaction test - Wikipedia, the free encyclopedia


Their tester was a little different at the plant they dropped a known weight and measured the depression of the soil to determine if it need more compaction.
tom

 

[dcyrilc]

So what does everyone think about the gravel compacting issue? Do you agree with dcyrilc? It's supposed to rain tomorrow so probably nothing will happen tomorrow. The sub really doesn't want to redo the rebar and wire. Will trying to compact 12 inches of gravel be a waste of time and money? How much do you think 12 inches of #57 gravel on top of undisturbed red clay will settle? I've got until sometime tomorrow (Wed) to make a final decision.

Thanks in advance,
Obed

I don't think it will be a waste of time or money. I think it's very important if you don't want cracking and settling down the road. The thicker the gravel, the more important the compacting is. With 12" of uncompacted gravel, I would expect cracking within 5-15 years. Maybe sooner. I also, would like to hear feedback from others in the construction industry.

I'm not familiar with the sizing used in your area, so I can't visualize #57 gravel. Out here, gravel is make by crushing rock and then sifting through a screen. It's measured by the size of the squares in the screen. 5/8"-, 1-1/4"-, 2"-, 3"-, 4"-, etc. Anything which fits through the screen in the shaker qualifies for that size. Anything caught by the screen goes back through the crusher. To further comfuse things, rock is also sold as clean. Clean rock, is shacken twice with two sizes of screens. For example, after shaking 5/8"- and removing anything smaller than 5/8", they run the rock remaining on the screen through the 1-1/4" screen to get 1-1/4" clean. Anyway, I'm getting off subject here.

To give you some understanding of my experiance which I am using to state my claims, I spent 26 years as a contractor building traffic signal and street lighting systems. For the last 5 years, I have worked for a local city maintaining these systems. My specialty lies with roadways not residentual construction. As a city, if we are replacing a sidewalk and a contractor (or us, if done in house) lays one inch of gravel, it will be compacted! The city can't afford the liability of settling and having someone trip over uneven sidewalk.

I'm not looking to try to scare you about the compaction, but it sounds to me like you may live in this house for a long time, and I want you to be happy with it for as long as you're there. I don't like wasting money, which is why I suggested using the jumping jack followed by the plate compactor after finding out that you had 12" of gravel. From the pix, I thought it was only about 3-4". To me, trying to dig out gravel and compact in lifts at this point would be wasting time and money. However, using two different types of compactors to get penatration on the compaction would be money well spent.

I'll PM you with my cell #. You're welcome to call me if you would like to ask any questions.

 

[dave1949]

I would take the time to do the compacting. It isn't just cracks in the concrete in your basement floor, think of the stress it will put on your plumbing waste lines too as it settles.

Not an expert, but I think compacting a gravel base below a concrete slab would be considered SOP.
Dave.