Are these slab specs acceptable?

[astrohip]

Getting ready to have my barn built. Contractor has built several barns for people I know, and all are very happy. So I have no reason to question his specs.

Having said that... I know nothing about concrete specs. Nothing. Can I get some general feedback as to whether this is sufficient for my needs?

50x70 slab, 50x50x13 steel barn, with 10x50 lean-to (covered, walls open, AKA porch) on each side. Typical ranch barn use, will store tractors & equipment, and will build a workshop inside (later). No lifts, no unusual heavy items. Will be driving a truck (F-150 type) thru the barn, pulling a trailer (in one door, out an opposing door).

~~~~~~

* 3000 psi 4'' concrete slab in building and both lean to
* 12''x24'' perimeter slab with 6#5 rebar on enclosed building
* 12''x18'' perimeter porch beams and all interior beams with 4#5 rebar
* #3 rebar 16'' on center both ways in slab
* Anchor bolts included
* Slab elevation to be 6'' above customers existing compacted dirt pad

 

[BillK]

If you ever plan on getting a lift, you will probably want the floor to be thicker. Probably would not add much cost at all to make it 5" instead of 4" When I built my detached garage I made it 5" and it added very little to the cost.

 

[larry_g]

IF YOU NEED SOME KIND OF FLAT OR LEVEL SPEC THEN put it in there. You see a lot of members whining because they have dips or slope that they did not want, yet had nothing in the spec to specify what they wanted. What you have looks ok to me.

lg
no neat sig line

 

[Thumper68]

I would go 5 or 6 inches since you plan on storing equipment and tractors in there. Tractors can be heavy with a fairly small foot print.

 

[In2toys]

I would think 4000 psi would be the norm. maybe the rebar offsets that???

 

[72Anthony]

Did you have any soil borings done for the barn or your house?

Not sure if Brenham is further enough away from Houston, in terms of soil composition, but Houston has clay soil that is expansive and usually requires perimeter beams and beams within the slab. Sort of like a waffle pattern.

The expansive soil shrinks and expands with changes in moisture level and can create huge stresses on the foundation. When the soil expands it is pushing up from below while the load of the structure is pushing down. When the soil contracts, there can be voids and the slab has to carry.

These conditions are very different than many other parts of the country.

 

[JimbosGarage]

Those specs sounds pretty much the norm to me, A lot of rebar in the footings and slab. maybe 4'' of sand or base under the slab.

 

[CNGsaves]

+1 to plan a location and put in 2 post LIFT. Those locations could have much thicker concrete, depending on what lift you get. Every big shop like yours really NEEDS a lift !!

Also, recommend the 5" for some safety factor and put in WRITING your expectations for finish (ie smooth, rough, etc) and any slope you want for draining or just flat. Good luck and start a new GJ Build Thread for the shop . . . everyone on GJ loves new gallery threads for new shops !!

P.S. You might also consider putting some pull cans into the concrete so you'll have anchor point for pulling vehicles into the garage, or other attachment purposes (ie body/frame straightening, etc).

 

[boobag]

in my experience, you're better off skipping the rebar and use that money elsewhere. like maybe a bit thicker slab or higher strength mix. the main thing i would do saw cut the slab as soon as its set, with the cuts being 12 feet apart max. the cuts are for the slab to hopefuly crack in the cuts and not be noticeable.

 

[astrohip]

Great responses, again. Thanks!

* I'm very reluctant to say never to anything. Heck, my barn was gonna be 30x40 until I kept reading here how you can never have too big a barn. But I'm going to do it anyway... I'll never use a lift. Just ain't gonna happen. I wouldn't even know what to do if a car was on a lift.

* Talked to the builder this morning (the guy is responsive as heck). He said (1) 3,000 psi is more than enough for what I'm doing. I could drive a fully loaded dumptruck thru the barn and not come close to straining the slab. He said unless I am using some sort of heavy equipment bolted to the slab (eg, machine shop, which he also builds), I am more than ok. But he did say for less than $500 I could jump to 4,000, if I really wanted. But he said that's overkill, and he wouldn't waste the money. He also mentioned his concrete guys always have a psi cushion, and it usually is closer to 3,500-4,000 anyway.

And (2), as far as clay, and expansion/contraction, that's why he uses a lot of rebar, and heavy rebar. He builds all over the SE Texas Gulf Coast, and is used to our terrible soil conditions. Lots of heavy rebar is how you counteract the stress a floating slab endures.

And yes, he mentioned how important site prep is. Absolutely must be level and well-compressed. He said he always comes and inspects the site before any slab work, to make sure he's happy with what he sees.

 

[AndyCBR]

If it's only $500 to up the psi I would do it.

If you never plan on a lift the 4" should be OK provided proper compaction of the sub grade/fine grading material is done. People say they do and rarely do it. Fine grading with sand for the last 3-6" and not using a compaction device is quite common in practice but the wrong way to do it. On commercial jobs a vibratory plate packer is used for the fine grading material.

A good subgrade followed by uncompacted fine grading material is not a good foundation.

 

[2Big2Ride]

in my experience, you're better off skipping the rebar and use that money elsewhere. like maybe a bit thicker slab or higher strength mix. the main thing i would do saw cut the slab as soon as its set, with the cuts being 12 feet apart max. the cuts are for the slab to hopefuly crack in the cuts and not be noticeable.

Do not skip the rebar in Texas.

 

[astrohip]

If it's only $500 to up the psi I would do it.

If you never plan on a lift the 4" should be OK provided proper compaction of the sub grade/fine grading material is done. People say they do and rarely do it. Fine grading with sand for the last 3-6" and not using a compaction device is quite common in practice but the wrong way to do it. On commercial jobs a vibratory plate packer is used for the fine grading material.

A good subgrade followed by uncompacted fine grading material is not a good foundation.

Thanks for this info. Knowing nothing about slab prep, I now know a little more. And will make sure I get the subgrade I need.

Do not skip the rebar in Texas.

Absolutely!

 

[wgasa84]

I'm an Project Manager / Estimator for a concrete company in Southern California and see these garage slabs all the time. Your end pricing will vary quite a bit from what is normal in our area due to the ready mix companies, labor rates, base requirements, etc.

I would go 5.5" thick (so they can use a 2x6 to form with) and #4 @ 16" O.C. #5 in the footings. The cost of concrete is low when you are adding 2" of thickness (3.5" to 5.5"). I don't think you need 4,000 psi concrete, but that depends on a lot of factors. The cost to increase the psi is nominal. Call your ready mix suppliers if you think your builders upcharge sounds expensive. Expect ~10-20% margin on top of materials. I have seen a lot of 4" thick driveways damaged (I.E. new cracks) by dumptrucks driving on them, most drivers in our area are very hesitant because of this. You're going from max ~6,000 lbs to ~45,000 lbs


A cushion is true, but not 1000 psi. His comment is ******** - call your ready mix supplier and they can give you the latest batch reports that will tell you what their 3,000 psi concrete has tested at for the last 30 days. Its easier for his finishers to finish the 4,000 psi concrete. The cost of the psi increase really should be low.


ALWAYS USE REBAR! We have replaced more concrete than I can think about because WHEN concrete cracks (not IF) the rebar will keep the small crack from turning into a huge problem. Rebar is cheap compared to replacing the entire slab. ~$0.30/lf for material... ~$1-1.50 sf installed for @ rebar mat laid at #4 @ 18" O.C. Concrete will crack, expansion joints and control joints tell the concrete where to crack so you don't see it in the slab. You can still get visible cracks! Timing, location, spacing, hard corners of walls/structures where the slab is poured around... etc. it all comes into play... Concrete cracks because of the constant expansion & contraction of the material and the surrounding materials (base, structures, etc).

Make sure they slope the concrete to either area drains or wherever you want the water to go. It doesn't take THAT much more work to float the concrete where you do not have low and high spots. It just takes finishers (and a company) that care about their work.

As stated previously in this thread the prep of the base is one of the most important factors. Compact the native soil (we get 90-95% in So Cal, depending on location), add your base (we use Class II Base and sand depending on what/where we are pouring) and compact it. It really depends on the soils on your base. If you have an expansive soil then you'll probably need 2" of Sand / 15mil vapor barrier / 2" sand. That will increase your cost but you will greatly reduce the chance of heaving. The vapor barrier keeps the water from wicking up through the finished concrete, causing efflorescence.


Probably more information than you care about!

 

[astrohip]

<snip>Probably more information than you care about!

No, it's exactly what I needed, a lesson in concrete. Thanks!! And interesting.

One area I never would have thought about is slab level/draining. Several of you have mentioned this. I'll talk to him about this, and see what his SOP is.

 

[pcmeiners]

What about testing the concrete before it is poured? Go for an extra inch at least and 4000 psi
Get the specs laid out for compaction? What does that mean to the contractor? 10 minutes with a machine or 10 hours? How much gravel does he plan to use? Any area of the footing dug out should be back filled with gravel or sand not dirt and compacted. Best time for concrete work is in spring or fall, no extremes of temperature. Set a definite start date, requiring the contractor to finish work within a specified time.

Personally since you have no knowledge of concrete specs and contract development you should pay an Architect (Engineer) to lay this out with all the specs and testing, they can produce a contract. Leaving it in any part to the contractor is not a good idea; a sleazy contractor can hang you out to dry easily without a good contract. Will guarantee you will not be able to produce a decent contract because your a novice (no offense).

 

[CNGsaves]

Another thing to make sure you have in writing is what the garage door closing surface will be.

a) You want flat and only rely on rubber seal of garage door to keep out dirt ??

. . . or . . .

b) You want notch in concrete so that garage door ledge is about an inch LOWER that makes a better seal to keep out blowing leaves, dirt, etc ??

 

[DIC]

In Texas I would go 4000psi 5" and rebar

 

[wgasa84]

No, it's exactly what I needed, a lesson in concrete. Thanks!! And interesting.

One area I never would have thought about is slab level/draining. Several of you have mentioned this. I'll talk to him about this, and see what his SOP is.

No problem and glad to help. Feel free to ask any questions you have.

You'd be surprised how many people don't think about drainage or slope.

Ask your builder what percent of fall he is going to give you (unless you want a flat level pad). Area drains can create problems with machinery or tables because the slope comes from multiple directions, and sloping a slab toward a strip drain or garage doors can give you a pretty good difference from one end to the other. For example a 30' deep garage with 1% slope from the back wall to the doors will have the stem wall/curb wall at the doors 3.75" taller than at the back wall, it only gets worse with the more slope.

 

[wgasa84]

What about testing the concrete before it is poured? Go for an extra inch at least and 4000 psi
Get the specs laid out for compaction? What does that mean to the contractor? 10 minutes with a machine or 10 hours? How much gravel does he plan to use? Any area of the footing dug out should be back filled with gravel or sand not dirt and compacted. Best time for concrete work is in spring or fall, no extremes of temperature. Set a definite start date, requiring the contractor to finish work within a specified time.

Personally since you have no knowledge of concrete specs and contract development you should pay an Architect (Engineer) to lay this out with all the specs and testing, they can produce a contract. Leaving it in any part to the contractor is not a good idea; a sleazy contractor can hang you out to dry easily without a good contract. Will guarantee you will not be able to produce a decent contract because your a novice (no offense).

What do you mean have it tested before its poured? That's why I suggested to get the batch plant testing results, around here they are required to keep them for all of the city projects and most of the big commercial jobs. If that is what you were talking about

You don't want concrete sitting in a truck for very long, it can cause..... problems.

OP....

While its true you don't want to pour in extreme temperatures, a good concrete company knows what to do to keep the concrete from curing to fast or too slow.

It depends on the native soil on if you can use it for compaction, but most of the time a soils engineer will want a compacted aggregate or sand base.

Getting a soils engineer is a good idea if you can afford it. And yes get a solid contract. Read it multiple times before signing it.

 

[WVBrady]

I would have one section flat and level, so that you can do your own alignments.

 

[astrohip]

My list of To-Do's is getting longer!

Thanks guys...

 

[pcmeiners]

Why a batch result? I used to get the driver to sign as to psi, then we would get slump tests, if it did not pass truck was not unloaded. The driver signed so I did not have to check the amount of water added was correct (not to much) toward the end of the load. On large building we kept cylinders of concrete sent out to labs.
" a good concrete company knows what to do to keep the concrete from curing to fast or too slow."
You think contractors are not going to pour if it is to hot or to cold or work concrete to long. As far as additives, if concrete is done in reasonable weather far less additives are needed or desired. You do not want to pour when its 90 or when it going to freeze within 30 days... there is no reason for it.

"And yes get a solid contract. Read it multiple times before signing it. " excuse me, he does not have the knowledge of concrete spec or legal contracts to sign, that why an Architect/Engineer should be consulted, they have the ability to spec it out and write up a decent contract. Just go over how many GJ members have been screwed by contractors because they did not have a decently written contract.

 

[wssix99]

Another thing to make sure you have in writing is what the garage door closing surface will be.

a) You want flat and only rely on rubber seal of garage door to keep out dirt ??

. . . or . . .

b) You want notch in concrete so that garage door ledge is about an inch LOWER that makes a better seal to keep out blowing leaves, dirt, etc ??

Great point. I had one garage door with a badly-out-of-level sill and I had to grind the inside of the slab down (=not fun) and break out/replace the sill entirely.

* Talked to the builder this morning (the guy is responsive as heck). He said (1) 3,000 psi is more than enough for what I'm doing.

I think some people here are forgetting that this is a barn. 3000 psi is fine. The higher psi concrete has more cement in it, which allows for a nicer/smoother finish. If you don't care about that in your barn, then going with a higher psi is exponentially wasting money. 3000 psi is plenty strong for the 8-10 psi pressures the equipment will be putting on it. The slab will sink in to the ground before the concrete crushes.

Going with a higher psi exponentially increases cost because:
- the concrete costs more
- the higher psi concrete builds up higher shrinkage stresses - this requires more reinforcing steel to counteract shrinkage cracking

So, at 3000 psi, you'll be saving on cement and rebar. Hence - a rebar mat designed for a 4000 psi slab could be overkill in a 3000 psi application.

 

[AndyCBR]

Great point. I had one garage door with a badly-out-of-level sill and I had to grind the inside of the slab down (=not fun) and break out/replace the sill entirely.




I think some people here are forgetting that this is a barn. 3000 psi is fine. The higher psi concrete has more cement in it, which allows for a nicer/smoother finish. If you don't care about that in your barn, then going with a higher psi is exponentially wasting money. 3000 psi is plenty strong for the 8-10 psi pressures the equipment will be putting on it. The slab will sink in to the ground before the concrete crushes.

Going with a higher psi exponentially increases cost because:
- the concrete costs more
- the higher psi concrete builds up higher shrinkage stresses - this requires more reinforcing steel to counteract shrinkage cracking

So, at 3000 psi, you'll be saving on cement and rebar. Hence - a rebar mat designed for a 4000 psi slab could be overkill in a 3000 psi application.

I like upping the psi because invariably the finishers add water, and often too much.

Everyone says they don't do that and then when the concrete tickets trickle back to the office there is 15, 20, 25 gallons of water added to an 8 CY truck.

When you start out with a 3000 psi design mix, then use ash for lower cost, then add too much water you can get breaks on cylinders very low.

For $500 it is cheap insurance.

But as this threads proves, opinions vary....

OP, ultimately it is your money and you will have to decide.

 

[astrohip]

Thanks for all the feedback. I'm soaking it all in.

One concern I have is pouring the concrete in Texas summer heat. Part of me says these guys do it all the time, so they know what to do, and how to cure it.

But the paranoid part of me says "what should I be looking for?" Are there steps you guys expect them to take, and that I should expect to see?

Although at the rate we're moving, it could be fall before we pour.

 

[AndyCBR]

Thanks for all the feedback. I'm soaking it all in.

One concern I have is pouring the concrete in Texas summer heat. Part of me says these guys do it all the time, so they know what to do, and how to cure it.

But the paranoid part of me says "what should I be looking for?" Are there steps you guys expect them to take, and that I should expect to see?

Although at the rate we're moving, it could be fall before we pour.

It would be to your benefit if the pour falls in cooler weather.

On commercial jobs we pour at night for a pour of any size.

There are a lot of things you are "supposed" to do for hot weather concreting that people rarely do. Burlap covers, sprinklers, etc. They will even go so far as batching the concrete with ice in some plant work in hot weather.

For your barn the best that you can hope is they get a pump and start early so the concrete is placed when the air temperature is lowest. Of course as I stated above pouring in cooler (or not hot as hell) weather is best. The slower the cure rate the better.

 

[wssix99]

For $500 it is cheap insurance.

But, it's not. It's more than that.

Going up in the 1000 psi on the concrete will increase the steel reinforcing costs by approximately 8-10%. If you go up in the concrete strength and don't add steel, then you are actually increasing your chances of cracking.

 

[AndyCBR]

But, it's not. It's more than that.

Going up in the 1000 psi on the concrete will increase the steel reinforcing costs by approximately 8-10%. If you go up in the concrete strength and don't add steel, then you are actually increasing your chances of cracking.

I would not change the reinforcing design when going from 3000 psi to 4000 psi.

My point on why I would up the psi is to end up with at least a 3000 psi break even if the finishers add too much water to the likely ash-laden concrete. Additionally the durability of the finished surface is better.

They can, and will, add excess water especially in warmer temps during placement. The dilution due to excess water can result in low breaks when tested.

 

[astrohip]

A neighbor and good friend (also my hay guy) has a son who does land work. Grading, slab prep, ponds, roadwork, you name it. I've known the son a while, and had forgotten that was his business. He's well regarded locally. In fact, one of his current jobs is putting in an airstrip with two 25,000 sqft pads for hangars. He's got a huge backlog of work now, and I probably couldn't get him for months, except his dad and I are close. When he was younger, he used to help his dad cut the hay on our property.

He does site prep for barns all the time, and knows what to do. How to grade, fill, compact, yada yada. He even suggested coming out and helping us pick the exact spot for the barns, since he's familiar with drainage issues, and can also help figure the best layout for the roads to the barns.

I asked him about the slab specs. He said for a typical barn, they are more than enough. 3,000 psi on a 4" slab with rebar, assuming good site prep, will be fine. I asked about going 4,000 psi, or maybe a thicker slab, and he said it would be a waste of money. His biggest concerns were the pour, because of the heat, and site prep. He said bad prep work causes more problems than bad concrete ever will (in this area).

So I am going to stick with the builder's specs. And it looks like I found a land guy. Although even with our relationship, he said it would be early September before he could start work.

Which given the speed that we're moving on the plans, will probably work out well.

 

[tomshep]

Thanks for all the feedback. I'm soaking it all in.

One concern I have is pouring the concrete in Texas summer heat. Part of me says these guys do it all the time, so they know what to do, and how to cure it.

But the paranoid part of me says "what should I be looking for?" Are there steps you guys expect them to take, and that I should expect to see?

Although at the rate we're moving, it could be fall before we pour.

I am further south and my slab was poured in August as I recall. Had I known the cracks I got, I would have poured in November or December. The contractor poured it and literally finished it and left it for the day. Needless to say, it baked over the next few days and immediately started cracking.

I would wait...

tom

 

[astrohip]

I am further south and my slab was poured in August as I recall. Had I known the cracks I got, I would have poured in November or December. The contractor poured it and literally finished it and left it for the day. Needless to say, it baked over the next few days and immediately started cracking.

I would wait...

tom

Thanks. I am going to ask lots of questions about this, if it appears we will pour before cooler weather.

Further south... in Texas?

 

[dogdas]

4000 psi, no less.
Fiber reinforced.
Fiber expansion strips at all vertical walls. Have them apply them to the walls with urethane of equal adhesive one day prior to the pour.
Complete plastic heavy mil vapor barrier over the sand.
Flat sheets of sidewalk mesh with chair carriers. (NO ROLLS)
5" thickness.
Hand trowel finish.
Cement saw control joints 10' O.C. and from exposed corners. No deeper than 1"
5' from walls out to be flat. (if you are putting in drains)

If you have poor compaction of the sand base you will be screwed no matter how or she you do. If they have to bring up the grade like I had to make sure that the lifts are no more than 6" between compaction. Make sure that the sand is moist when they compact also. Prep work is you biggest issue that you need to pay attention to. If you are unsure about the compaction a soil testing company will do a gamma ray test and see if you meet the 95% compaction standard. It may cost you a few bucks but that will seem like chump change if the same starts sinking.

Mesh is cheaper than rebar and accomplishes the same thing and that is to keep the slab from separating. Concrete always shrinks away from itself and that is where the control joints come in. Compaction, compaction, compaction and there will be no problems.

 

[astrohip]

4000 psi, no less.
Fiber reinforced.
Fiber expansion strips at all vertical walls. Have them apply them to the walls with urethane of equal adhesive one day prior to the pour.
Complete plastic heavy mil vapor barrier over the sand.
Flat sheets of sidewalk mesh with chair carriers. (NO ROLLS)
5" thickness.
Hand trowel finish.
Cement saw control joints 10' O.C. and from exposed corners. No deeper than 1"
5' from walls out to be flat. (if you are putting in drains)

If you have poor compaction of the sand base you will be screwed no matter how or she you do. If they have to bring up the grade like I had to make sure that the lifts are no more than 6" between compaction. Make sure that the sand is moist when they compact also. Prep work is you biggest issue that you need to pay attention to. If you are unsure about the compaction a soil testing company will do a gamma ray test and see if you meet the 95% compaction standard. It may cost you a few bucks but that will seem like chump change if the same starts sinking.

Mesh is cheaper than rebar and accomplishes the same thing and that is to keep the slab from separating. Concrete always shrinks away from itself and that is where the control joints come in. Compaction, compaction, compaction and there will be no problems.

Appreciate the feedback. Multiple people, with a vested interest in making sure I'm ultimately satisfied, have repeatedly said 3,000 psi is more than enough for a tractor barn. Additionally, rebar is the standard for slabs in Texas. No way will I tell the builder to use mesh; if there is a later problem, who gets the blame? The owner who told him to use mesh.

Agree on the compaction. I've come to understand site prep is more critical than any other stage.

 

[wssix99]

I think some are forgetting that this is a

(I'm not sure you'll get the full enjoyment/value out of spending extra money to get a perfectly smooth and pretty floor.)

No way will I tell the builder to use mesh; if there is a later problem, who gets the blame?

This is wise. If you have a company that has had success locally with a spec and has examples of where it has worked well, then that is the best thing. Messing with the spec and not adjusting for the other variables (cement ratios, water ratios, aggregates, reinforcing, local conditions, etc.) could produce unintended results - and you'll be on the hook for them!

 

[astrohip]

This is wise. If you have a company that has had success locally with a spec and has examples of where it has worked well, then that is the best thing. Messing with the spec and not adjusting for the other variables (cement ratios, water ratios, aggregates, reinforcing, local conditions, etc.) could produce unintended results - and you'll be on the hook for them!

I agree totally. This guy has built metal barns for 30+ years, all over southeast Texas. Including several six-figure horse barns for good friends. They are universally happy with this guy. I've seen them, and they are good barns. Every time I ask a question, he gets back quickly, and talking to him, he is full of info and feedback on my ideas.

I'll still ask a million questions, but that's more from my innate curiosity than any specific concern. And reading all the posts in this thread has made me aware of what to look out for, and where not to cut corners (site prep!).

Thanks again.

 

[astrohip]

I spent half an hour today talking to the builder about these barns, and a lot of it was on the site prep. Especially since that's the one area he's not directly responsible for. He had a couple of interesting comments:

* Unless it's a cut and dry simple site prep, where everyone agrees there are no issues, he recommends a compaction test after the dirt man is finished. And since my site is not level, and will require over 18" of elevation change (either up or down), he said I should get one regardless. With slabs of 50x70, and 42x95 (horse barn), they are long enough that site prep becomes critical.

* If the dirt man can't get the soil the way he wants it, he would drill some piers first.

A good portion of the balance of our conversation was on ventilation. This Texas summer heat scares me. My barn is open on three sides now, so I get some breezes. With an enclosed barn, venti becomes job one.

 

[LifeLongWNYer]

I've been reading about concrete floors, and saw something in this thread that raised a question in my mind. So in a concrete mix, what is the advantage/disadvantage of ash?

I am almost ready to pour a floor, and am ordering with fiber, but wonder about ash.



JBP

 

[ConCretin]

I've been reading about concrete floors, and saw something in this thread that raised a question in my mind. So in a concrete mix, what is the advantage/disadvantage of ash?

I am almost ready to pour a floor, and am ordering with fiber, but wonder about ash.



JBP

You are obviously doing your due diligence to dredge up a 6 year old thread. Good for you. I believe you are referring to fly ash. Fly ash and it's cousin, blast furnace slag are by-products of industrial processes that are finely ground and used as a substitute for cement when making concrete. They alter the properties of the concrete somewhat but work pretty much the same way as cement.

Most ready mix suppliers use some form of alternate cementitious material depending on what is available locally. It's probably not worth the effort to ask them to change their standard mix designs.

While you are reading up on concrete slabs, check out my Guide to Floor Slabs in the link below. Good luck with your project and keep learning about the process. The more knowledgeable you are the better chance you have of avoiding the infamous "my slab is a disaster" threads we see so often on the GJ.