Filling a Grease Pit

[MattRMagnum]

Hey Folks,

Long time, no talk. After a wonderful run around with the county, I wound up giving up on building a garage on my previous property*, and moved to a house that came with a 30x36 garage. I've run into a problem, though: it has a grease pit. When I first bought it, I thought I'd love having one. Thanks to the water table, it's basically a nasty swimming pool that eats sump pumps.

I've decided, in light of that, to have it filled in. Has anyone done this before? I'm worried simply filling it with cement might cause the building to sink or tilt a little (where as, at present, it's fairly level). The only other idea I could come up with would be having it packed with dirt (and I mean packed, not just filled), and then lay a cement lid across it.


* There's a creek (1' wide by 3-4" deep for most of the year) that runs beside ~85% of the property. The county told me that it's considered protected, and there's a 150' set back for new construction on either side... which is wider than the property is. Only way I could've built would be by proving that the remaining 15% was completely unbuildable. Rather than building there (it would've required tearing out a lot of beautiful old growth trees), I moved.

 

[LXCam]

Fill it with sand or 3/4" gravel and cap it with concrete. I'd highly suggest you dowel into the perimeter slab and tie a simple rebar cage just in case it tries to hydraulic on you and lift.

 

[redmondjp]

Probably the easiest thing would be to use a flowable fill that doesn't require compacting, like pea gravel. Dirt will require compacting every few inches or "lifts" if you don't want it to settle. Then pour concrete over the top - drill into the existing slab on the sides and epoxy rebar into it, to tie the patch to the existing slab.

 

[MatBirch]

I had to do this once. I threw pieces of old anything that would not break down or further crush in there, then a load of riprap, followed by pea gravel. I floated a couple pieces of plywood over that for about a year to see how it would settle. It did... a little touch up then poured my slab.
Only thing I’d do different in your case is dealing with the water. Make sure if it can get in, it can also get out. Then maybe add a vapor barrier layer somewhere in your lifts.

 

[lostmind]

A place I worked at had the pit filled with gravel , 3/4" , and a 4" concrete slab over the top. Was still good when I left 4 years later. Took less than 4 hours total.

 

[66Caprice]

The cement companies have a slurry mix they do that is just like concrete when its hard. Suppose to be cheap fill for jobs like this. Fill to bottom of your slab then our new slab patch over top and done!

 

[EatonEggbeater]

You might be able to get pavement tailings for free from places that grind streets. Evidently, they can only recycle a certain percentage into new pavement, the rest needs to be disposed of somehow. My brother got a couple of trucks worth and had it spread on his gravel driveway. Over the months, it's solidified, not actually pavement, but a lot more solid than gravel. Your cost would be shipping.

 

[ssdave]

You might be able to get pavement tailings for free from places that grind streets. Evidently, they can only recycle a certain percentage into new pavement, the rest needs to be disposed of somehow. My brother got a couple of trucks worth and had it spread on his gravel driveway. Over the months, it's solidified, not actually pavement, but a lot more solid than gravel. Your cost would be shipping.

Do not use millings for this application. It doesn't compact well with most methods homeowners have available to them, and will settle continuously over time. Good for driveways, terrible for fill. I was an expert witness in one case where a guy used recycled millings as fill under his garage, and then had a concrete contractor come in and do a slab. Over the next two years, the floor differentially settled, at one area that was filled 6 feet, it settled 14 inches.

As mentioned before, use gravel compacted in 6 inch lifts, or buy flowable fill from the concrete company, and then do a slab at the top, doweled into the surrounding concrete. Flowable fill is essentially 1 sack mix concrete, and the intent is to have a non-settling, self-compacting fill for trenches. It's perfect for an application like this.

 

[NUTTSGT]

Fill it with sand or 3/4" gravel and cap it with concrete. I'd highly suggest you dowel into the perimeter slab and tie a simple rebar cage just in case it tries to hydraulic on you and lift.

I'd do the same as Cam mentions.

However, I'll add this. Unless it's a small pit and you mix your own, you'll bring in a pre-mix truck. Generally concrete suppliers have a minimum yard charge. You might to figure out your best bang for the buck, depending on the size of the pit or forming up a pad outside your walk in door.





You can use this link to figure your concrete.


https://www.concretenetwork.com/concrete/howmuch/calculator.htm#calculatorPage

 

[Old Man Roger]

Is there no way to keep the water out? Or some type of drain?
I would love a grease pit, but the water table in south Florida is about 6 inches down..lol

 

[K'ledgeBldr]

If water can get in it will certainly still require a way to exit-

So, as previously mentioned I'd fill the bottom 1/3 with rip-rap. Finish with 57 stone and cap it with a 4-6" slab. Rebar dowelled-in and a tied-in grid of rebar.

 

[slow]

Can somebody explain what a grease pit is? I've never heard the term and am interested why you would want to have one. Is it similar to a grease trap? Thank!

 

[NUTTSGT]

Can somebody explain what a grease pit is? I've never heard the term and am interested why you would want to have one. Is it similar to a grease trap? Thank!

Called by other names in different parts of the country.

Basically a trench in the garage floor you park over to "grease" the under side of a vehicle or do other work.

 

[slow]

Thanks! Makes sense why we don't or can't have one easily in FL with a shallow water table.

 

[JimNC]

Is there no way to keep the water out? Or some type of drain?
I would love a grease pit, but the water table in south Florida is about 6 inches down..lol

That’s what I’m thinking. Connect to sewer and put in some steel grate to keep above the damp. Obviously be environmentally conscious, no dumping.

 

[MattRMagnum]

Thank you everyone for the advice. I'll look into the cement slurry option, and see what they say. I want to get my carport paved at some point (I also have a 900sq ft carport right next to the garage), so if I come in under the minimum, maybe I'll bundle with having that paved.

Is there no way to keep the water out? Or some type of drain?
I would love a grease pit, but the water table in south Florida is about 6 inches down..lol

Oh, that's the same here. In the summer the water table is 7' down (the grease pit is ~8ft deep, counting a 'lip' that's about 4-6" tall), but in the winter it's about 2-4" below the edge. The big issue is that the drain placed for the sump pump to sit in is tiny, and is smaller than most of the 1/4th horse pumps I've found. To expand it I would to remove about 2-4" per side, and dig down. into the dirt more, then build a proper 'box' of the top that you could walk into... all to maintain, a permanently cold, damp place where I can work on cars. No thanks. I'd much rather seal it up, and install a lift in the next bay over.

 

[Old Man Roger]

Yes a lift is better..lol

 

[JimNC]

Thank you everyone for the advice. I'll look into the cement slurry option, and see what they say. I want to get my carport paved at some point (I also have a 900sq ft carport right next to the garage), so if I come in under the minimum, maybe I'll bundle with having that paved.


Oh, that's the same here. In the summer the water table is 7' down (the grease pit is ~8ft deep, counting a 'lip' that's about 4-6" tall), but in the winter it's about 2-4" below the edge. The big issue is that the drain placed for the sump pump to sit in is tiny, and is smaller than most of the 1/4th horse pumps I've found. To expand it I would to remove about 2-4" per side, and dig down. into the dirt more, then build a proper 'box' of the top that you could walk into... all to maintain, a permanently cold, damp place where I can work on cars. No thanks. I'd much rather seal it up, and install a lift in the next bay over.

Can’t argue with that, good luck!

 

[redmondjp]

Wow! If the water table is that high during the winter, I can see why you would want to fill it in. In a dry climate, I'd say to leave it, and make a lip on the opening so you can cover it with flush 2-by-_ boards for safety.