Concrete floor revisited

[wbrent]

Planning to put in a concrete pad for my mill this summer. Unless you guys talk me out of it. Mill sits under the lean to off my garage right now. Stable ground with 3/4 minus crushed rock. Lean to is 12x36. undecided on whether i need concrete to fill the whole space or just enough to cover the mill. Leaning towards filling most of the space. I guess cost will dictate that. Im in atlantic Canada. Is there options for concrete these days? HAve i heard of concrete with fiberglass in it or something? Does that negate putting rebar or steel mesh in it?
What thickness do i need? Im a hobby guy so not doing any production milling. But my mill can tske a 29" diameter log up to 16 feet. I still anticipate putting cross sleepers on top of the pad and then tieing them together. Mainly to bring mill to a height im comfortable with and to stabilize the mill from moving. So wondering if its worthwhile embedding some thredded rod in the concrete in the areas where the cross sleepers will go. Or is it just as easy to bolt them down after the fact?
CAn you offer advice on other prep work and tips before i get into this? Thanks in advance

[tule peak timber]

We poured a 6 inch slab with a lot of steel in it and drilled for bolts later. The slab has held an LT 35, an Lt 70 , and now holds an Lt 15. You will find opinions vary as to making the mill hard and fast. WOC

[Sod saw]

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Our saw is siting on  slab that is between 6 and 8 inches thick.  That slab is sitting on 2 inches of foam board and that board is sitting on 6 inches of pea stone (for drainage).

There is 1/2 inch diameter rod in the slab and I requested fibers to also be mixed in the cement when delivered.  The mix is 4000 PSI.

Why so much?  Our saw has a bed extension requiring the slab to be about 40 feet long.   We also have 4 feet of freezing depth in the ground.  I also am cutting oak etc. that is over three feet diameter and over 20 feet long.  sometimes they land hard when they fall on that slab and I prefer not to have to replace it.

The saw is not bolted down to that slab.  When those logs roll on to the mill they bang into the backstops and the mill frame will scoootch over slightly.  To prevent that movement across the slab I drilled oversized holes and epoxied 5/8 inch diameter rod into the slab where the feet are located.  Those solid rods prevent the saw from scoootching across the slab.  Plan on installing more than one rod at every leg (foot).  Not bolting the mill frame down to the slab prevents it from bending out of shape as those larger logs roll.  The mill frame will just settle back down where it was before the log rolled.  A little give and take is not a bad thing.

That's the way we did here.  I suspect that others have found different solutions.

I am delighted with the cement as it is easier to clean up and more comfortable to walk on.


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[doc henderson]

I use steel rebar, when possible, at least along the edges, with heavy matt 8 x 20 feet all across.  I like the fiber reinforced for thin stuff, like the floor over plywood with pex for heat in my shop floor, over I trusses.  Only cracks are where 4 inch would have cracked also, like a narrow dog leg section.  I also added it to the 1.5 inch shallow end floors and slope walls and floor of the deep end of our pool.  no cracks when we change the liner.

[scsmith42]

I think that more of an issue is slab thickness where you are loading logs.  You're dealing with the weight of the loader as well as the log.  

We've had logs weighing up to 4 tons on the Baker, plus the 4.5 ton weight of the baker.  But that pales compared with the 19 ton weight of the articulating loader.

So I'd study if/where your loader will be rolling onto the slab, and make sure your perimeter footers are strong and that there is no organic material in your sub-base (and that it's very well compacted).

[wbrent]

Thanks guys. Glad i asked. HAd no idea people were making these so thick. I was thinking more like 4" thickness. Might have to re think this. The loader will never get its wheels on the pad. So at least dont have to worry about the weight of the tractor. Love to hear others thoughts.

[doc henderson]

I think a steel reinforced 4-inch pad will be fine.  a well compacted base so the settling is minimum.  I like the idea of a wood plank under the jack to absorb some of the forces and spread out the impact over more sq. footage.

[NewYankeeSawmill]

When I worked in the print-biz I watched a press or two get installed. They would form up and pour 2 parallel rectangular supports for the press to set on. Maybe 2' tall x 2' wide x long-as-the-press... This provided clearance underneath the press for various maintenance tasks in addition to a stable base. The form was over 2 feet deep into the ground (e.g. 4+ ft of concrete)... those presses had to be stable to run right. I was looking at doing something similar when considering a stationery mill. I figured it would make handling the sawdust easier and make it a good working height for me (I'm 6'4", nothing is built to my size).
I ended up buying my mill w/ the trailer package in-part b/c a local old-timer recommended it to get the mill at a good working-height; and he was right! Prior to that decision I looked at stationary mills and pouring a pad vs the press-column idea and it was a huge cost savings on the volume of concrete. Almost $10k IIRC... Run some numbers on the back of an envelope or get a local contractor to quote something.

[SawyerTed]

Thickness and rebar are important but compression psi of the concrete is equally so.  

Ask your concrete contractor about higher compression ratings - 6,000 pound or 8,000 pound concrete.  Unless specified most concrete for slabs is 4,000 pound concrete here.  

[barbender]

 Concrete is expensive enough now that it may make sense to engineer your pad with thicker areas for where you know increased loads will be. If you have a definite layout, there's no reason you couldn't increase the thickness to whatever is required just beneath the mill feet, and log deck supports. 

 For instance, in our basement I poured a 4" floor, but doubled the thickness under a post that is supporting loads all the way down from the ridge beam of the house. 

 The downside to this is that it looks you into one layout if you wanted to change anything down the line.

[doc henderson]

I did the same in the basement of the shop.  ran a 12 inch deep 2-foot wide beam down the center under the floor, for a wall in the basement to support the I truss', that are now supporting tools that are at 2K pounds.

[YellowHammer]

I love my slab, WM recommended 6" thick, rebar on 24" and I thickened it on the edge, basically a footing, when the loader or forklift might get on it.  

[kelLOGg]

I was a hobby sawyer like you. Max log dia was 32" and I rolled them onto the mill via mill-mounted winch so no heavy equipment rolled onto the pad. Turning cants was the most stress the setup experienced. I had a 4" pad poured w/ no rebar. Sounds minimal or worse but I never had a problem/crack with it. I used it for only 4 years until I sold the mill. Do a search for it. Happy pouring.

[longtime lurker]

My existing shed floors were all poured at 6" thick, double reinforced with mesh and re-bar down the sheet joins, plus a rat wall around the perimeter. They've held up well. The " temporary" extension I did last year I went differently: double reinforced 40mpa (6000 psi roughly) footings where required only. 

Concrete has got expensive, and aside from where it needs to carry load all it really does is make sweeping the floor easier. I'd rather see overkill footings than have a larger area at a constant depth that doesn't really do much. Mind I don't know how frost works in that equation.

[Larry]

Is there options for concrete these days? HAve i heard of concrete with fiberglass in it or something? Does that negate putting rebar or steel mesh in it?

Originally fiber was used to reduce or eliminate shrinkage cracks as the crete cured. It worked good for the purpose but sometimes was hard to finish and slick when wet. Now days their are choices dependent on the desired outcome. I would not take the advice of most concrete guys or the plant as the answer is usually financially driven.

I've always stuck to the basics for a strong slab. 6,000 psi mix, well compacted substrate, and #4 rebar on a 12" grid. I've went cheap a few times on non critical slabs with mixed results. Last one was my house. On the house slab I went with rebar on a 2' grid and got a few cracks. On the attached garage slab I went with a 12" grid and zero cracks after 14 years.

[dogbo2013]

ALWAYS put steel in concrete. Just as Larry said, fiber helps reduce fine cracking,but is no substitute for steel. Concrete is very strong in compressive strength but does not have much tensile strength. That is where steel rebar and wire mesh comes in. Spend the little bit of extra time and money now and avoid regrets in the future. 

[kelLOGg]

Correct me if this is not true, but I thought mesh in concrete is to equilibrate temperature. This may be more important in colder climates like Canada as opposed to NC.

[rusticretreater]

When I had my garage/workshop put in I added another inch under the auto lift area.  So maybe you put in three thickness areas, one at each end of the mill and one in the center.  You also need that bed of gravel to allow the slab to settle in.

Rebar is a must or a slab that long will crack in the center eventually.  Anyone think a vapor barrier would be needed?

[barbender]

 I'm of the opinion that a vapor barrier should always be used. Certainly there are areas that it's not needed, but you can't install it after the fact. 

 A local fleet store bought a building that had been a Wal-Mart. They wanted to redo the whole floor in the building with some really fancy decorative epoxy. The general contractor advised them against it because there was no vapor barrier under the slab. The company persisted, and finally got their epoxy. It looked awesome! For about a month...vapor would come through the slab, get trapped under the epoxy, and then when they were running their pallet trucks across the floor the epoxy would basically burst like a blister. It flaked off everywhere and looked awful. They redid areas several times but it never held.

 Even if I was building a cold storage shed, it would have a vapor barrier under it just to keep that moisture from coming through. A lot of moisture comes through the soil.

 Poly sheeting is cheap.

[doc henderson]

concrete is porous.

[Magicman]

There are two completely different kinds of concrete.  Concrete that has a vapor barrier and concrete that wishes it had a vapor barrier. 

[farmfromkansas]

Had to look up vapor barrier for concrete, and most of what I found was 6 mil visqueen.  Read the rest, and they said foam board.  So guess if you want to do it right use some dow board, hold it away from the edge, and thicken the edge and run a row of rebar around the slab, kind of like a reverse curb.

[Magicman]

What is necessary here is the visqueen which is all that I have ever used.  I have seen slabs that were poured without visqueen and it stays wet and constantly "sweats".  I am familiar with an office building that finally was demolished and rebuilt because the floor continually stayed wet.  They tried sealants, etc. that never worked.

[TimW]

1979, I was working at a Piper, Mooney Service Center.  We used electric (with real cords) screw guns on creepers under the planes to install and remove panels.  The hangar floor sweated and sometimes the old cords would get wet and give us a shock.   No plastic under the concrete.

Down here, every slab I have poured gets plastic.  Even my barn has plastic under the concrete, and under the right conditions, still sweats under anything blocking the air flow.

We don't use gravel as a  base, down here, mostly red clay.

[doc henderson]

a vapor/moisture barrier can work both ways.  for an open slab uncovered, you may get a pool on top of the plastic and be saturated.  I would not put plastic under a driveway as an example.  The basement of my shop is as dry as the conditioned upstairs and my house.