concrete floor for sawmill

[AvlSteve]

I have built a 20' x 40' open shed barn for a cooks 3238 sawmill (ordered Feb. of this year, hopefully to be delivered in December.  I currently have a 3/4" gravel floor.  I planned to have a large canvas tarp in the sawdust discharge area, to be removed as needed by pulling folded tarp out with a tractor (idea obtained from this forum).

I am interested in opinions on whether or not I should "bite the bullet" and install a concrete floor. If I do, I think that 4" of high strength concrete with fiber added, and with a 4' x4' grid of #3 repar installed would work.....edges thickened to 8". Excavator with thumb used to load large logs would not be on the pad, but an L series Kubota tractor with forks would bu on the pad to move pallets of cut wood.

Thoughts on concrete floor and if so any other concrete design details would be appreciated.

 

[firefighter ontheside]

My mill is under an 18x26 carport.  I poured concrete about 7x18 across one end.  My mill sits sideways in the carport.  The rest of the area is just gravel.  I never drive onto the concrete.  It works well for me.  Someday I expect to build a new home for the mill and use the carport for my kids when they start driving.  I will pour more concrete for the floor at that point.

[doc henderson]

I have used the fiber additive for thin stuff   1.5 inch cap over my trussed floor in my shop and in the shallow end of our pool floor (under the liner).  it has held together well but for a dog leg along a stairwell opening in the shop,  I would use re-mesh panels 8 x 20 feet on a 6 x 6 grid.  the "heavy matts" have close to a 1/4 inch rebar sized wire, and then add the heavy rebar along the "beam"  you describe along the edge.  I have not used the fiber in a traditional slab, but it may work well.  it is plastic fibers so I would hate for it to fail you and or be an added expense that makes no difference in the long term.  others will have opinions as well.  will the slab be 20 x 40?
800 square feet,  266 cubic feet, just under 10 cubic yards of concrete + another half yard for the beam.  so 1,155 bucks for the mud.

[charles mann]

When i poured mud for a living, both commercial and inductrial, we put our rebar on 12” for industrial and some res, and the rest of the res, customer rested 16” centers. 
Only time we used mesh was for sidewalks and drive ways, unless the driveway/entry way was to handle big trucks, then we used rebar. 

If using fibercrete, heavy mesh would probably be fine, but i would think mats on 4’ centers. 

[jrsloan1]

All of those a good suggestions. I would add that the base/sub base under the slab is very important. Without a good compacted base the slab will not be able to carry as much load. It’s a “system” not just the slab. Next, use a good design strength concrete maybe 3500 - 4000 psi mix with about a 3” to 4” slump. DO NOT ADD much water at the pour because that lowers the water cement ratio and therefore strength. Talk to the contractor or batch plant. If it needs to be wetter to make it easier to work, use a plasticer ad mixture. It won’t lower the strength. And finally, cure it properly. Keep it wet for 10 days, use a curing compound, or cover it with wet burlap, or wet it and cover with visqueen, etc. do all that after it has set enough to not damage the surface. This will slow down the moisture loss caused by the chemical reaction (causes heat) and will result in a much stronger slab. The slab should reach minimum 75% of the design strength in 7days. So after about 10 days you are safe to start putting loads on it. Most of the equipment you’ll have around will not have a load anywhere near the design strength of the concrete. Roughly calculating, a 10,000 lb load equally spread over 4 tires that each have 1 square foot bearing on the ground will result in less than 20 psi load. Hope this helps. 

[Southside]

Just remember, walking on concrete all day is miserable, so if you pour a big enough slab for everything then plan on buying rubber matting for all the work / walk areas. 

[doc henderson]

Old conveyor belting like in a quarry makes and ok rubber walkway

[AvlSteve]

Thanks to all for the information.  I saw a post on the forum indicating that adding rock dust on top of the gravel (and then using a plate vibrator to compact) might work.  I would be interested in feedback from anyone that has used or seen this application.

My base, where not original deep soil (very hard and compact), used clay fill placed in 6" lifts and compacted by multiple passes of my 12,000 # excavator.  

[dean herring]

Go for it and pour concrete,you’ll be glad you did 

[Crossroads]

I’m on the fence about pouring a pad when I build a shed. I’m considering building a wood deck, but we’ll see when the time comes. 

[WDH]

Removing the sawdust will be a real pain without that concrete pad if you are on gravel.  The tarp is a temp solution at best.  Sawdust is heavy and you will have the opportunity to deal with many torn tarps  .

[Tom the Sawyer]

I have set my mill up on grass, dirt, gravel, asphalt, and concrete.  Being mobile means you have the opportunity to try many surfaces.  My setup here at home is on concrete - wouldn't have it any other way.  I understand that some have difficulty walking on concrete for extended periods of time, doesn't seem to both me and, after a log or two, I'm walking on sawdust anyway.  I do have a horse stall mat at the control end of my B-20.  Concrete makes clean up so much easier.  I usually clean up when I remove the mill for a mobile job but sweeping under the mill and shoveling up the sawdust isn't that bad either.

[Don P]

I think over that clay I'd use 57's and shape the fill clay to drain readily through the open gravel and out of harms way, at 8" you are well shallower than A-ville's frost depth, make sure the water doesn't hang out under it.

[Warren]

Removing the sawdust will be a real pain without that concrete pad if you are on gravel.  The tarp is a temp solution at best.  Sawdust is heavy and you will have the opportunity to deal with many torn tarps  .

The voice of experience... My saw shed is 30x70 with gravel floor.   IF I had the money when I started, it would be concrete.  Yes, I have walked on concrete all day for a living.  In this situation, concrete would make clean up much simpler.

[jrsloan1]

As far as the rock dust,  I might be inclined to use the #57 stone and plate compact that.  It should make a nice surface for the concrete to sit on.  I'm not sure what benefit the rock dust would provide over 57.  If the base installed is a good clay placed in 6" compacted lifts, then 3/4" stone, the 57 should fill the voids nicely and be a good foundation.  I recommend a vapor barrier be placed over the stone prior to pouring the slab. 

[Larry]

My thoughts on concrete. 

Fiber can be expensive, hard to finish, and slick.  Its main purpose is to prevent shrinkage cracks while it cures.  Does that very good.  My experience is from 15-20 years ago and may not be valid today.  They do make different types of fiber so get advice from a pro.

Rebar doesn't allow the crack to widen or move.  Expensive (I bet really expensive today), labor intensive to install, and hard on my knees installing it.

Mesh is cheap, easy to install, and works fairly well.

My best slabs have been with #4 rebar on 12" centers and mesh.  My worse slabs were when I used #3 rebar on 2' centers and when a pro advised me to use nothing in a basement slab.  I have never tried the heavy duty mesh now being sold but it is tempting.

Concrete always gets hard and cracks!