leveling shop floor requires thin concrete, bad idea?

benkokes · Feb 18, 2019

I am preparing my shop floor to receive a Kiwa mill ( ~7000lbs). Where it will need to be placed will straddle 2 concrete slabs with an expansion joint in the middle. One of the slabs is true and level, while the other has a 2 deg downslope -- about 1.5 inch of drop over 36 inches.

Should I pour some self leveling concrete into that space (about 36" x 60"), or should I just shim the machine and call it good? The spindle and electronics box will be over the spot where I would have to pour/shim.

Advice?

Thanks!
-Ben

DMF_TomB · Feb 18, 2019

benkokes said:
I am preparing my shop floor to receive a Kiwa mill ( ~7000lbs). Where it will need to be placed will straddle 2 concrete slabs with an expansion joint in the middle. One of the slabs is true and level, while the other has a 2 deg downslope -- about 1.5 inch of drop over 36 inches.

Should I pour some self leveling concrete into that space (about 36" x 60"), or should I just shim the machine and call it good? The spindle and electronics box will be over the spot where I would have to pour/shim.

Advice?

Thanks!
-Ben

expansion joints are famous for one side to go up and down or gap to increase or decrease often every day. i have seen expansion joints easily move over a 0.25" over the years

jrmach · Feb 18, 2019

shim,shimminy
I have the same deal with my 8000 lb. + machine,,except not as much
Above post is pretty much what could happen
That means your new self leveling will crack,IMO

TDegenhart · Feb 18, 2019

You would be better off to have the area for the machine dug out and repoured. As others have said, that area is going to move and depending on the movement, you could put the machine in torsion.

Tom

D.D.Machine · Feb 18, 2019

I would cut out a 6'x8' area with a skilsaw and diamond blade and pore a new 6" slab ... poring new cement over old does not seem to work ..

kustomizingkid · Feb 18, 2019

Be sad once and pour a proper slab for the machine.

Miguels244 · Feb 18, 2019

The expansion joint is there for a reason.
The two slabs will move relative...unless you get really lucky you’ll be adjusting the machine weekly if not daily.

As mentioned, pour a new sub slab.

gustafson · Feb 18, 2019

While things can move, there pretty much has to be a reason, like if they were poured at different times with different substrates

Many expansion joints are simply grooves in the surface of a monolithic slab to give it a place to crack when it changes temperature. In that case there would be no reason to think it was going to move.

Is this a separate slab? Is it sloped because it moved or because it was poured that way?

A 7k pound machine I would think a new foundation is serious overkill

Murf · Feb 18, 2019

Google slabJacking, may be an option for your situation.

Murf

rons · Feb 18, 2019

I have some of these Sunnex adjustable machine mounts. Model like M102. The highest rated one is for 2200 lb each.
In case you don't redo the concrete, these mounts let you adjust the machine if anything moves in the future.
The machine will be elevated by several inches (downside).

If you use shims then the slabs may move and then you are back to re-shimming.

M-Series – Sunnex Mounts

M-Series – Sunnex Mounts

Milland · Feb 18, 2019

Yes, it's a light machine, but in some ways that calls out even more for a proper foundation to support it. If you do cut and pour, do it right and go at least 12" with two layers of rebar or heavy grid mat. A good foundation always gives the best chance of machine accuracy and stability.

Miguels244 · Feb 18, 2019

gustafson said:
While things can move, there pretty much has to be a reason, like if they were poured at different times with different substrates

Many expansion joints are simply grooves in the surface of a monolithic slab to give it a place to crack when it changes temperature. In that case there would be no reason to think it was going to move.

Is this a separate slab? Is it sloped because it moved or because it was poured that way?

A 7k pound machine I would think a new foundation is serious overkill

The cuts are called “control joints” to guide the cracking all concrete has.

Another option might be piers.
Core the existing pad, auger down 6’ or as needed to get below the expansive soils and pour a pier in where the machine pads are.

Worth noting...some parts of the world don’t have a stable layer.
The south metro Denver area is notorious.

Miguels244 · Feb 18, 2019

Milland said:
Yes, it's a light machine, but in some ways that calls out even more for a proper foundation to support it. If you do cut and pour, do it right and go at least 12" with two layers of rebar or heavy grid mat. A good foundation always gives the best chance of machine accuracy and stability.

A thinner slab with thickened edges as grade beams is a money saver.

JST · Feb 18, 2019

Two different issues here.

1) thin leveling cement. Yes, that can work without cracking off the existing slab. There is material made just for that purpose. Which one may depend on how much adjustment, your leveling stuff would be thick, I have done it with thin areas of a half inch tapering to nothing. But don't pour over a joint.

2) Going over a joint with machine mounts on both sides. Not a good plan. It already move, why would it not move again? Never depend on a joint to stay steady.

Milland · Feb 18, 2019

Miguels244 said:
A thinner slab with thickened edges as grade beams is a money saver.

Sure, but this is a small pad, why bother? The cost is in the time and labor, the materials will be trivial.

TDegenhart · Feb 18, 2019

I would think the biggest consideration would be how do you know if the slab has shifted or not? Parts are not coming out true, is it the slab, wear in the machine, tooling or what? Putting in a good foundation eliminates one variable.

Tom

Froneck · Feb 18, 2019

There are some concrete patches that work. I worked in a place that had quite few pot holes in the concrete. Really not deep but not good for fork lifts and steel wheeled tables that sheet metal was transported on. I found a patching material that was allowed to be used on airport runways. A list of those using the patch included most of the biggest airports in the USA. Using concrete and other patching didn't work at all, didn't last long soon crumbled and pot hole returned. We tried this patch I mentioned above and repair was permanent! Before long all the pot holes were repaired with the stuff! Not cheap, if I recall it was $100 for a 5 gallon bucket. I'm sure it will be great for leveling a floor! I don't remember the name but some googling will locate it.

Miguels244 · Feb 18, 2019

Milland said:
Sure, but this is a small pad, why bother? The cost is in the time and labor, the materials will be trivial.

True.
Setting aside the cost the grade beam construction is a known way to stabilize flat work.
Common in expansive soils situations...it floats the pad so expansive soils under the slab don’t distort and break it.

m-lud · Feb 18, 2019

If your correcting a uneven pour a thin layer will work. If your slab moved because of the base moved it may continue to move with wet and dry seasons. It depends on your location as soil conditions.
I have seen slabs in sheds here that move with wet and dry soil conditions. They poured right on the plastic clay. These floors move inches.

Good drainage away from a building can stop slab movement.

Here in Missouri we have a clay that's known as plastic soil. Expansion and contraction is a huge problem. I had 15 tandem loads of wash out hauled in from the concrete plant for my 60x56 building pad making about 24" of rock fill. I topped the wash out with clean limestone screenings. So far its good. Only hairline cracks.

Wash out is what the trucks wash out of the concrete trucks when they return to the concrete plant. Sand,gravel and lime. Watered down cement. They give it away here. You pay the hauler. They load for free

M.B. Naegle · Feb 18, 2019

Is this the last mill you will ever own? It's hard to predict the future, but if it was me I'd be thinking if a bigger mill is on the distant horizon, pouring a slightly larger, slightly thicker slab than is necessary for this mill could save you some trouble later.

leveling shop floor requires thin concrete, bad idea?

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