Building a new shop, any tips? (lighting, slab, HVAC, etc.)

[swatkins]

For the walls between suits. Frame in doorways. Run the electrical up and over that doorway. Drywall over the doorway, will have to add a stud or two.

I'm currently adding on to my shop with a 20 x 40 area. The 40' length is the current wall of the shop and I have been struggling with what to do with that existing wall.. Removing it is an option but that wall is useful for hanging things , like racks and cabinets, and serves as a sound break. I have decide to just leave the wall and punch out two 6 foot wide x 9 foot tall door openings. That way I get all the benefits of the wall and can still move easily between the two spaces...

 

[baran3]

I didn't read all the comments so I don't know if someone has already suggested it, but I would consider getting LED lights. Would cost more up front, but you wouldn't have to worry about changing light bulbs as much among other benefits. If you have high ceilings then you start putting machines in your shop accessing lighting fixtures can become difficult. It's not really something you think about until you need to change a light bulb and realize how difficult it has become to get to.

 

[Matt@RFR]

A year and a half later, and we finally have concrete down. It's been a fight the entire way with CalTrans, PG&E, the dumb asses at our town hall, etc.... but we're finally rolling. Or so I thought, anyway. What do you guys think of the cracks in this concrete? It's not even 2 weeks old. Concrete - Google Photos

This is a map of where all the cracks are. Black lines are expansion joints, highlighted lines are cracks. These are cracks that my wife could see stood upright, we weren't on our hands and knees looking or anything stupid like that. But you can see that if you stick to the rule of not spanning a crack with a machine, I'm about 75% fucked.



As far as I know, all the prep was done right, with compaction tests being done on the bare dirt (which is red clay... tractors literally leave rubber on the dirt when doing tight turns), and compaction tests done on the fill rock, 1/2" rebar on 12" centers both directions, 4300psi concrete mix (they called it "six sack"), and expansion joints every 12'. It's a 6" x 50' x 96' slab, all poured in one shot.

You can see that the cracks go all the way through the slab, based on all the cracks that run to the edge of the slab where you can see how deep they are. I don't know if that indicates all of them are that deep, or if they just go that deep at the edges.

The pictures of the one expansion joint with the crack propagating from it is the only expansion joint that has a crack that I could see.

Thoughts? Am I being one of "those" owners who is up in everybody's shit because things aren't exactly 100% perfect according to their own skewed view of the world?

 

[Modelman]

My best guess, without seeing it poured, is too much water in the mix, which causes shrinkage. Concrete jockeys like to "piss it up" because it flows with less work. The universal protection from this is the slump test, preformed by your architectural or engineering firms inspector on the job to each and every truck, who then watches that they don't add water after the test is preformed.

Unfortunately, I'd say if there was no language requiring slump tests and specifying maximum allowable in the contract, you're pretty much fucked.

Dennis

 

[true temper]

One thing is a giving, concrete is gonna crack. Sounds like you did every thing right. I would be very unhappy with cracks that big.
My two shops I had expansion joints sawed in after the pour. I am not sure I would have that done if I was to do over. Still some very small cracks and the saw cuts edger fracture very easily, and soon you have a big groove to deal with.

 

[TimD]

Sounds like it was a good plan. I'm currently doing a largeish addition on my house that required far more than normal concrete work (ICF). I had a structural engineer do all the bar layout and calcs. I've learned a lot along the way.

That said. My first two concerns are was the rebar in they slab during the pour or did they drive on it and push it into the stone? What was the slump? How hot was it on the day of the pour?

The ready mix supplier should have a job sheet that indicates what they left the plant with and how much if any water they added on site. My engineer says that for structural purposes concrete should never go over a 6" slump. Calcs start going out the window when you do. As a rough indicator adding one gallon or water to one yard of concrete will increase the slump by one inch. So a if you add 10 gallons to a 10 yard load you'll increase the slump by 1". Now if the concrete has already started setting adding water will increase the theoretical slump but it won't show on a slump test. You'll see the reduced strength of a higher slump but won't gain the workability.

Again according to my engineer. Bar can be used for two different applications in concrete strength or crack control (all concrete cracks). When used for strength the bar needs to be in the tension zone. In the case of the floor that would be in the bottom third. For crack control you want it closer to the exposed surface. Wire can work for crack control but needs to be done right, my particular engineer won't spec it as it's rarely done properly. He goes straight to bar.

Not that it helps you at this point but if I'm ever able to build my own shop part of the concrete work will require test cylinders. That goes a long ways to keeping very one on their toes. http://www.nrmca.org/aboutconcrete/cips/34pr.pdf

Again concrete will always crack, steel of some sort is used to try and control the cracks and prevent them from spreading.

 

[Modelman]

My apologies fro my rather curt reply above... but it is the truth of the situation.

A couple further comments... Test cylinders are nice, but yeild results long after the fact (21 days at least). Slump tests are predictive of test cylinder results, and are useful for heading off a problem batch before it is poured. I'm not an engineer, just a ground pounder when I was in the construction trades, but more than once I've seen a truck load fail the slump test and be sent back to the yard still full. Of course, the truck most likely didn't actually go back to the yard; it would be diverted to pour some poor sucker's garage or basement floor. No tests there, and the concrete guys love the easy-to-push mix.

The big problem with test cylinders (for compression tests) is that they are worthless unless there is language in the contract that specifies what the remedy is for failure. Ideally, it is to break the questionable concrete out and do it over. In reality, most small contractors will declare bankruptcy before they pay for a tear-out, still leaving the customer holding the bag, so to speak.

I just walked the 3000 sq. ft. floor I had put in back in '95. The three cold joints between the separately poured strips are still in line, and there is one crack that has developed right at the overhead door, where the rigger likely overloaded the floor carrying molding presses in. No slump tests or test cylinders, but I was on-site when it was poured, crabbing about water in the mix. Guess it did some good.

Dennis

 

[Garwood]

That's a lot of cracks. I had a 4K sq ft 6" slab poured last spring. I did all the prep and I cut the control joints myself. I didn't put any metal in the slab (just didn't have time). All the control joints have fractured and I have a few stray cracks through an office area that only got a 4" slab and we didn't focus on compacting that as much.

I'm prepping to do another 3K sq ft this fall. I'm hoping for no cracks at all since the two feet of compacted rock has been settling and getting further packed in for the past 6 months. I'm also going to put metal in this slab.

 

[Modelman]

Cracks over time (years) are from poor sub-grade prep. Cracks that appear in the first four weeks are from shrinkage... have nothing to do with the sub-grade. I base this on my work years ago on reinforced concrete buildings. Second (and third, and fourth, etc.) decks have nothing to do with sub-grade prep... and they don't crack. Most people don't get to see this, as the decks are all carpeted, but think about parking decks... how many times have you seen major cracks in the pavement of parking decks? Same thing... proper control of water in the mix = no cracks.

Look at new highway construction... no cracks. Admittedly, the concrete is poured so stiff that it cannot be worked by hand, requires the paving machine to strike and level the surface before it can be finished, but no cracks.

Properly hydrated concrete (just the amount of water needed for the chemical reaction) is so stiff it sits where it drops. When it starts to come down the chute, it won't come down the chute without help... it just sits there, and starts to overflow the chute where it comes out of the drum. Of course the concrete guys are not happy, they just want to drop the chute in the corner of the slab and have it fill and self level... it's a constant fight. Unless there is no one protecting the customer's interests to fight with. Any water beyond what is needed for hydration has to go somewhere... away... leaving a void that results in cracks.

The problem is, no small building job can afford to have an inspector on site at each pour, it just doesn't happen, and the concrete contractors take advantage of this.

Dennis

 

[Matt@RFR]

After speaking with a metric shit ton of people about this, the conclusion is that I, once again, over-reacted.

The concrete contractor, the developer, the developers engineer, various experts and even the batch plant all agreed that this slab is as good as it gets, and that it's the luck of the draw that I got cracking like I did. (I think this is complete bullshit, but I had enough people say the same thing that didn't have skin in the game that I have to go with it. Seems to me that a $34,000 hunk of concrete should be free from all defects, but what do I know...)

I'm told that the fact that it tests at 4200psi after only 2 weeks is proof that the correct amout of water was added, and no more. I'm also told that these cracks do NOT go all the way through the slab (not from testing, but from experience of several people) and that I shouldn't be too concerned with straddling one of these cracks with a machine.

Also, everyone I contacted about the issue, reacted the same way when told who the concrete contractor was... "Oh, well that's not your problem then". Absolute Concrete has one hell of a reputation in northern California.

The QC guy from the batch plant told me to just watch the cracks as the erection crew start to drive heavy shit on the slab, and that if any of the cracks open up to 3/16" wide or wider, to give them a call immediately.

 

[WILLEO6709]

At this point you may well be screwed into living with it but I'd be using a different contractor next time. one question - how much bar, spacing, and placement?

none of my floors have cracks like that ( unless we rolled a 40k forktruck with a 40k machine on fork) over an unreinforced 6 inch floating outdoor pad.... that was a bad day.....slab popped like microwave popcorn as it drove over it. but its days were numbered anyway and it came out real easy after that.

 

[Matt@RFR]

one question - how much bar, spacing, and placement?

1/2" rebar on 12" centers both ways, 3" off the ground.

 

[WILLEO6709]

Unless more serious issues arise when you move in ( no idea how heavy of stuff you have ) I'd make some money on it before. One thing- if your rigger is in the area with the big forklift invite them to do a drive around.....before the equipment is on the forks. That way if anything pops up ( no pun intended ) at least you are not committed yet with something priceless with nowhere to go.

 

[Heavey Metal]

No mention of cushion sand or flexbase.

 

[Matt@RFR]

No mention of cushion sand or flexbase.

Like I said in the original post about the concrete, the dirt here is red clay that tractors leave rubber on it's so hard, then they put 4" of some light grey rock down and compacted it. That's all I know.

 

[rbdjr59]

Don't worry about what you can't change now. It sounds like what you are calling expansion joints are actually sawed control joints, which should have been cut in just as soon as the slab would support the weight of the saw. Next day cuts will sometimes be ok, if it's not too hot. How hot was it the day of the poor? The concrete dries from the top down, and it shrinks as it dries. This sometimes causes cracks to form as the top shrinks and the bottom doesn't. It's is almost like the surface has tears in it. If they are wide enough to cause concern, say 1/32" or bigger, you can pour some epoxy in them to seal them up and keep them from spalling further. It is also advisable to fill the sawn control joints with a semi-rigid joint filler to help protect those edges from breaking under the load of a forklift or even a hand dolly. Those edges are a weak spot. In my experience you will have a hard time proving negligence on the part of your contractor or the supplier without having an engineer on site to observe the pour and to have lab test done on the concrete. Those guys do this everyday and have probably seen it all, as far as complaints from customers. From what you say I'm guessing it was hot and dry which also accelerates shrinking. Fill your cracks and never look back.

 

[Matt@RFR]

Don't worry about what you can't change now. It sounds like what you are calling expansion joints are actually sawed control joints, which should have been cut in just as soon as the slab would support the weight of the saw. Next day cuts will sometimes be ok, if it's not too hot. How hot was it the day of the poor? The concrete dries from the top down, and it shrinks as it dries. This sometimes causes cracks to form as the top shrinks and the bottom doesn't. It's is almost like the surface has tears in it. If they are wide enough to cause concern, say 1/32" or bigger, you can pour some epoxy in them to seal them up and keep them from spalling further. It is also advisable to fill the sawn control joints with a semi-rigid joint filler to help protect those edges from breaking under the load of a forklift or even a hand dolly. Those edges are a weak spot. In my experience you will have a hard time proving negligence on the part of your contractor or the supplier without having an engineer on site to observe the pour and to have lab test done on the concrete. Those guys do this everyday and have probably seen it all, as far as complaints from customers. From what you say I'm guessing it was hot and dry which also accelerates shrinking. Fill your cracks and never look back.

Thanks for all of this. Yes, "expansion joints" = "sawed control joints". They were cut, just as you say, as soon as they could get the saws on the concrete. It was probably mid 90's that day.

Can you recommend a semi rigid joint filler for the control joints?

 

[specfab]

Congrats on making progress on your shop. Stuff like that ends up taking a long time, it seems, from concept to actual activity. I would concur with RBDJR59's comments above, as well as the general feeling that it's unlikely that there is a serious fault on the part of the concrete contractor. I had a slab poured about 12-14 yrs ago, and saw hairline cracks within weeks. Not a huge number, but probably similar to yours on a per SF basis.

My slab was much smaller, 20 x 20, 6" thk. 3500 psi, with 10 ft sections separated by control joints. The control joints cracked, as expected, but the hairlines have not grown appreciably over the years. The loads are also (I suspect) much lighter in my shop than they will be in yours, but having 1/2" rebar on a 12" grid should make your slab pretty stout. For my slab, I "designed" it with 3/8" bar on 18" grid, mostly because I knew nothing, but also did consider that the soil was heavily compacted and had been baking in the Az. sun for the previous 15-20 yrs.

 

[I_AM_MACHINE]

Thanks for all of this. Yes, "expansion joints" = "sawed control joints". They were cut, just as you say, as soon as they could get the saws on the concrete. It was probably mid 90's that day.

Can you recommend a semi rigid joint filler for the control joints?

Try the products these guys sell: Concrete Crack & Joint Repair - Watco Industrial Flooring. I've never used this expansion joint filler, but I have used their epoxy concrete deep fill repair on my warehouse floor. I drive a forklift over it many times a day (and have for several years now) and it has held up very well.

Back to the cause of the cracks, this excerpt is from the Portland Cement Association's website:

"In general, if the temperature at the time of concrete placement will exceed 77 degrees Fahrenheit a plan should be developed to negate the effects of high temperatures.

The precautions may include some or all of the following:

Moisten subgrade, steel reinforcement, and form work prior to concrete placement.
Erect temporary wind breaks to limit wind velocities and sunshades to reduce concrete surface temperatures.
Cool aggregates and mixing water added to the concrete mixture to reduce its initial temperature. The effect of hot cement on concrete temperature is only minimal.
Use a concrete consistency that allows rapid placement and consolidation.
Protect the concrete surface during placement with plastic sheeting or evaporation retarders to maintain the initial moisture in the concrete mixture.
Provide sufficient labor to minimize the time required to place and finish the concrete, as hot weather conditions substantially shorted the times to initial and final set.
Consider fogging the area above the concrete placement to raise the relative humidity and satisfy moisture demand of the ambient air.
Provide appropriate curing methods as soon as possible after the concrete finishing processes have been completed.
In extreme conditions consider adjusting the time of concrete placement to take advantage of cooler temperatures, such as early morning or night time placement.
With proper planning and execution concrete can be successfully placed and finished to produce high quality durable concrete at temperatures of 95 degrees Fahrenheit or more."

Link: Hot Weather Concrete Construction.

I know it's too late to help you, but it may help others. Also, I hope this reinforces to you that your slab is fine, these shrinkage cracks are only cosmetic in nature.

Kevin

 

[garyhlucas]

My dad poured his own concrete driveway and everyone convinced him it didn't need an expansion joint up the center of the 20' slab. 50 years later it is nearly perfect, except for the huge crack right up the center of every slab!
We poured our own floors in our electrical shop about 40 years ago. On top of 5 feet of fill dirt I compacted in 8" lifts. My dad insisted no slab bigger than 12' x 20'', with expansion joints between slabs. 5 large trucks get parked inside every night. Some of the big rigs come inside to be worked on too. No cracks anywhere! I wheelbarrowed all that concrete in place, then hand screeded it and hand troweled it. Cracks happen because concrete is simply done wrong today.