DIY base prep?

[VietGnome]

Hey all,

In the process of committing to a 30x40 stick build in Atlantic Canada. Gonna need to hire out the pad, and a little electrical, but looking to do the rest myself/with help to save a hell of a lot of money.

Has anyone tackled the pad prep themselves? Going to reach out for some quotes. One company tried me at $15k ballpark for prep for a mono pad. Few other red flags for them.

Few other places on FB seem to be advertising in the 150-200/hr range. Meanwhile I can rent a mini excavator or skid steer for around $200/day, and go to town myself.

No need to haul dirt away as I got enough land to spread it.

Zero experience with anything this large, but I built, compacted, and graded a gravel base for a patio a few years ago so I understand the concept.

Seems totally feasible to me, just dont want to find myself in over my head.

And preference on machine? I feel like a skid steer would be easier to skim the top and move dirt to dump.

Guessing I'll have to go down around 12" in the center, and upwards of 24" on the edges.

 

[signcrafter]

What size are your footings on the edge? Do you have a laser and grade stick? A skid would be best for clearing the top layer and then for grading the fill. A mini would be best for the footings.

 

[mm08822]

Get your design done first. Know what the footings will require - piers or alaskan slab? Piers could be done with an auger on the skid steer. Alaskan slab would be better with a backhoe or excavator.

A roller attachment or at least a compactor plate for sub-base compaction, gravel compaction, backfill/grading.

Rent out the skid steer at a monthly rate to eliminate the daily timeline stress.

You may want to get a few site prep estimates and compare against your rental & purchase costs.

Formwork materials will run a few $. any thought to CMUs on a footing? The CMUs could act as the formwork for the slab. It's also easy to insulate the inside surface of CMUs. The footing, CMUs, and slab become 3 distinct work processes that enable more control vs. one giant pour. A lot depends on your skill, available labor and their skill.

 

[VietGnome]

What size are your footings on the edge? Do you have a laser and grade stick? A skid would be best for clearing the top layer and then for grading the fill. A mini would be best for the footings.

Likely in the 16" range. I have a standard laser level.

Get your design done first. Know what the footings will require - piers or alaskan slab? Piers could be done with an auger on the skid steer. Alaskan slab would be better with a backhoe or excavator.

A roller attachment or at least a compactor plate for sub-base compaction, gravel compaction, backfill/grading.

Rent out the skid steer at a monthly rate to eliminate the daily timeline stress.

You may want to get a few site prep estimates and compare against your rental & purchase costs.

Formwork materials will run a few $. any thought to CMUs on a footing? The CMUs could act as the formwork for the slab. It's also easy to insulate the inside surface of CMUs. The footing, CMUs, and slab become 3 distinct work processes that enable more control vs. one giant pour. A lot depends on your skill, available labor and their skill.

Its a floating (alaskan) slab.
Thanks. I haven't thought about CMUs. To be honest I was planning on letting someone else do the form work, and I just clear the land, haul in and compact the base.

I guess I'll et my plans, see exactly what I need, and start comparing options from there.

 

[ConCretin]

The nature of your native soils will determine how much of them you need to remove and replace. You mention needing to excavate 12 and 24 inches, which presumably is for the interior slab and perimeter haunch respectively. Let's say your native soils are decent and your new slab will be 3" above the existing grade, I'd excavate the entire pad down 9" and then build the middle up 8" with well compacted granular material. This would give you an 4" slab with a 12" haunch, which is probably over-kill.

Again, depending on the nature of your soils a mini-ex might be easier for the excavation but you could probably make do with a skid steer. For moving material in and rough grading, a skid steer is the answer. Don't forget to factor in the cost for the compacter. They are surprisingly pricey.

Figure the rental time you think you'll need for each piece of equipment and then double it. Figure the cost of the materials you'll need to import and compare it to your quotes to determine if doing it yourself is worth it. If you're not proficient with operating equipment, be prepared for a LOT of handwork to get the grades right.

 

[floatinghat]

Having a place onsite to spread the excess soil would have been huge in my site work. I "needed" approx 200yds removed and dumped and another 200yrd of gravel/rock. I $32K over on my site work and have another $10k to complete (with a different contractor.

 

[VietGnome]

The nature of your native soils will determine how much of them you need to remove and replace. You mention needing to excavate 12 and 24 inches, which presumably is for the interior slab and perimeter haunch respectively. Let's say your native soils are decent and your new slab will be 3" above the existing grade, I'd excavate the entire pad down 9" and then build the middle up 8" with well compacted granular material. This would give you an 4" slab with a 12" haunch, which is probably over-kill.

Again, depending on the nature of your soils a mini-ex might be easier for the excavation but you could probably make do with a skid steer. For moving material in and rough grading, a skid steer is the answer. Don't forget to factor in the cost for the compacter. They are surprisingly pricey.

Figure the rental time you think you'll need for each piece of equipment and then double it. Figure the cost of the materials you'll need to import and compare it to your quotes to determine if doing it yourself is worth it. If you're not proficient with operating equipment, be prepared for a LOT of handwork to get the grades right.

Thanks! It depends on what the engineer says, but id like a 6" slab. Soil my way is mostly clay. If I were to do let's say 10" gravel base, I would do 10" under the haunches too correct?

Think a mini excavator would be better all around for clearing? I assumed it would for the haunches, and a skid steer would be better for the middle pad area?

Thanks for the rental time tips. Hard time im having is assessing how much time I think ill need.

Front half of the garage will be built ontop of a gravel driveway, but the back half drops off into some woods
/brush I need to clear. For that back half, I assume ill just clear the brush/stumps, dig up the top soil, then just build it up with compacted gravel? Will i need to backfill behind it after its poured? I've attached a photo with rough placement for clarity.

I also assume once I clear stumps, etc ill need to dig the top soil? Don't just build up ontop of of the existing soil?

 

[ConCretin]

If I were to do let's say 10" gravel base, I would do 10" under the haunches too correct?

Think a mini excavator would be better all around for clearing? I assumed it would for the haunches, and a skid steer would be better for the middle pad area?

Front half of the garage will be built ontop of a gravel driveway, but the back half drops off into some woods
/brush I need to clear. For that back half, I assume ill just clear the brush/stumps, dig up the top soil, then just build it up with compacted gravel? Will i need to backfill behind it after its poured? I've attached a photo with rough placement for clarity.

I also assume once I clear stumps, etc ill need to dig the top soil? Don't just build up ontop of of the existing soil?

If you have clearing and grubbing to do, a mini-ex will be your best bet. You can dig out some pretty good sized stumps if you are patient and work at it.

The first step is always to remove all organic material completely, which includes stumps, vegetation and topsoil. It's a good idea to 'proof roll' the sub base after grubbing by running a compactor over it to re-compact any disturbed soils. You'll also want to fill and compact your stump holes with your base material.

If the grade is low at that point, bring it up to grade in well compacted lifts. The depth of each lift depends on the material used and the size of the compactor.

I wouldn't generally over-excavate under the perimeter footing unless the soils are questionable. Think of it this way; footings are placed on un-disturbed native soils all the time - your perimeter haunch is basically just a footing. With that said, since you are excavating and filling anyway, you could put 6" of new material under your footings to make it easier to fine grade and provide a stable work surface that won't get as mucked up if you get rain like clay will.

It sounds like your slab will sit partially on native soils at the driveway end and structural fill on the other? This isn't an issue but it will require some care when placing and compacting the fill. A slab first and foremost requires uniform support. Your biggest risk is settlement.

For reference, I have a 28x32 structure on a mono-slab on native soils and a later 14x32 addition that has 6'+ of structural fill. To this day, you can't see a crack at the joint between the two or anywhere else for that matter. It's doable but you need to be very diligent when constructing the structural fill.

Take a look at my Guide to Floor Slabs in the link below for some additional thoughts.

 

[VietGnome]

If you have clearing and grubbing to do, a mini-ex will be your best bet. You can dig out some pretty good sized stumps if you are patient and work at it.

The first step is always to remove all organic material completely, which includes stumps, vegetation and topsoil. If the grade is low at that point, bring it up to grade in well compacted lifts. The depth of each lift depends on the material used and the size of the compactor.

I wouldn't generally over-excavate under the perimeter footing unless the soils are questionable. Think of it this way; footings are placed on un-disturbed native soils all the time - your perimeter haunch is basically just a footing. In reality, you can even place a slab on native soils if the grade happens to be right and the soils are stable but generally some fill is required.

It sounds like your slab will sit partially on native soils at the driveway end and structural fill on the other? This isn't an issue but it will require some care when placing and compacting the fill. A slab first and foremost requires uniform support. Your biggest risk is settlement.

For reference, I have a 28x32 structure on a mono-slab on native soils and a later 14x32 addition that has 6'+ of structural fill. To this day, you can't see a crack at the joint between the two or anywhere else for that matter. It's doable but you need to be very diligent when constructing the structural fill.

Take a look at my Guide to Floor Slabs in the link below for some additional thoughts.

Thanks! I've definitely read it through, I hope i didn't miss the answers to these questions.

I was planning on digging the droveway down and adding in new base. Mostly because the driveway was there before me, and I'm not sure what's under it. If im spending this kinda money on a pad id rather make sure the base is suitable.

If anything ill clear out the back, dig up the droveway, and use that as fill to compact in layers to bring up the back, then bring in more gravel for the rest. Then I can also rest assured that its all compacted evenly.