Best designed concrete floor?

[Jfresh]

I need to call out the floor on my plans and I was looking for some advice in what you think would be best for my needs.

60x72 used for mostly storage Rv, Boat, etc. I would like the floor to be strong enough to support the largest loads but not overkill as I do have a budget. I would anticipate the heaviest load being most likely a fully loaded 45' Class A diesel pusher. Maybe a lift one day but at this point I do not know where I would locate it.

I am in Oregon lowest low about 20 and high around 100 degrees. It will be stick built. I always use a vapor barrier.

How many PSI?
Rebar or mesh and what sizing?
How thick?
If I use fiber can I use a densifier and still polish the floor like I have seen others do on here?
How far apart should my saw cuts be?
I want it as smooth and flat as possible. What type of finishing do I ask for?
Should I insulate and if so what do I use?
I was thinking radiant floor heat but I don't think I want to spend the money because I am rarely on the floor.

Sorry for all the questions and thanks for the advice.

 

[TLCObsession]

Find a good detail so that your garage doors close below the slab surface. Its a simple thing to do, but it will make the door seal better and eliminate wind driven rain problems.

 

[theoldwizard1]

Nothing you mentioned is really that heavy. Standard strength concrete, 4". Wire mess does not add much strength but will keep things from moving if (when) it cracks.

Someone more knowledgeable will have to comment on adding fiber to the mix.

About 53 yds of ready-mix !

Vapor barrier and 1" of rigid foam insulation is typical, but will cost you and arm and a leg. It will help. Minimum, use a vapor barrier. It will slow the concrete cure time.

Heating and/or cooling such a larger space will be difficult. Hopefully you have natural gas available. A couple of hanging furnaces should do the trick.

If you plan to build a "man cave"/office/workshop up in a raised floor (PT 2x4 sleepers and 3/4" tongue and groove subfloor. Lay down a vapor barrier and fiberglass insulation between the sleepers. This area would be perfect for a mini-split heat pump.

 

[matt_i]

I'd form with 2x6s to give a nominal 5-1/4" pour, or if the existing walls are the forms, a 5" minimum slab. Some areas are bound to be in the 4" range, others in the 6" range.

Compare that to forming with 2x4s where you have a basic range of 2-1/2 to 4-1/2. The thin spots are what worry me.

I like real, honest-to-goodness old school rebar. 1/2" or #4 bar set on 16" centers on a 2" chair. No pulling stuff up into the mix. I regard that as a corner cut by a poor craftsman, its fine the day its poured but when these people are long gone it is you who will bear the responsibility for the problems.

I regard fiber as not worth it. 3000-3500 psi mix. Add no water to the mix from the batch plant.

I would place and compact 4-6" of washed 3/4" limestone under the slab (note you do NOT want fines nor crusher run). Using water as a lubricant when compacting.

Pour under a roof structure to have the subgrade in a dry-stable condition. Also you are protected from rain which can ruin the top surface and the crew has a good amount of shade.

Use a 6 mil vapor barrier under the slab, it also has the benefit of keeping hydration in the concrete for the reaction to complete, rather than diffusing into the stone below. The bottom of the slab is in tension under tire loads so that aids strength in the most critical area.

Use a curing sealer on top of the slab as soon as its hard enough to walk on and the finishing is complete. You can of course spray extra water which is nearly free but this product will give you a finished surface similar to whats in a Home Depot or Lowes although probably not quite as durable, they use a heavier product for the large traffic as well has have some sort of maintenance program.

Note nearly every step I listed above costs extra time and money. Yet I feel like its close to a sum of best practices to get the most out of your floor.

 

[Leaflessshadetree]

A fully loaded 45' Class A diesel pusher.sounds pretty heavy to me.
I'd go 6" thick with rebar. (top of my head 1/2" on 12" grid sounds about right but I'm sure others will have better idea).
Yes fiber in the mix. IMO it's cheap and could help with fine cracks and spalling.
I try and keep relief cuts so the sections are close to square, 15' is a nice spacing up to 20' should be OK less than 10' isn't necessary. On a 60x72 inside a garage I'd make them 20'x18' (20x24, 15'x18' or 15'x14.4' would be other size I'd consider).

If you plan on heating put 2" insulation under the entire floor.

 

[Cyberbear]

Over the years I've had several shop slabs poured and have always used 6/7 bag mix for the concrete, #4 bar @ 12" o/c, a little deeper and wider than code footings with 4 horizontal steel bars, the slab thickness was 4" and monolithic with no cold joints, the slab steel was turned down into the footings. I had them do an extra pass with the power finisher then after set up I used surface sealer to retard curing I applied myself in two coats with a garden sprayer.
This may sound like overkill, but I've never used saw cuts and never had any cracks, which I attribute to the steel and sealer. The concrete guy said over his several decades in the business he has seen the quality of the cement reduced with the usual results, which is why I opted for more in my mix. Any building is only as good as it's foundation, where you should never skimp since a slab is going to be with you a very long time.

 

[encantofred]

i built a 65x70 garage. monopour (stemwalls and floor all at the same time), i had them powertrowel it as i wanted it smooth. it is also a level floor, (not sloped). there is another thread on this forum about whether to slope or not. when you have a garage that big, even a small slope is big spread over 70 feet.

6" 3500 psi, stealth fibermesh and steel mesh. rebar was wayyy expensive. i dont need to heat, so i did nothing under the concrete. (a ton of rebar in the footings and stem walls. )

sawcuts were based on where the doors were. i have 2 doors that are 14' wide and 15' high and two mandoors.

my 45' motorhome weighs 55k lbs. and i will likely have a buddies 45' coach in occassionally to work on it.

the structure is 2x8's with tile roof and stucco outside walls and 20' ceiling

too early to tell about cracking yet.

challenge is you will get a ton of different opinions and they are all good. you just have to decide what works for you and your budget.

it is also important to get a really good concrete guy.

thats my 2 cents worth.

tom

 

[joes169]

I need to call out the floor on my plans and I was looking for some advice in what you think would be best for my needs.

60x72 used for mostly storage Rv, Boat, etc. I would like the floor to be strong enough to support the largest loads but not overkill as I do have a budget. I would anticipate the heaviest load being most likely a fully loaded 45' Class A diesel pusher. Maybe a lift one day but at this point I do not know where I would locate it.

I am in Oregon lowest low about 20 and high around 100 degrees. It will be stick built. I always use a vapor barrier.

How many PSI?

3500psi (5.5 bag) minimum, most finishers will prefer 4000 (6 bag) though, as it sets a littel faster and finishes better IMPO.

Rebar or mesh and what sizing?

That also depends on who you talk to, personally, I much prefer rebar as it's easier to handle, safer to use, easier to keep up in the pour, and will last longer when exposed to water/salt exposure at the control joints.


How thick?

5" should suffice.

If I use fiber can I use a densifier and still polish the floor like I have seen others do on here?

Skip the fibers, the standard fibers are only effective at limiting cracking due to plastic shrinkage for the first few days. There's better ways to thwart plastic shrinkage, and it's rarely an issue under a roof and over plastic.

How far apart should my saw cuts be?

Industry standard is 10' by 10' for a 5" thick slab and 8' x 8' for a 4" thick slab. Saw cuts should be made as soon as possible, but definately within 24 hours of placement. I literally carry a pair of old slippers in the back of my truck so I can saw some slabs with an hour or two of final machine pass, and my boots will still leave imprints.

I want it as smooth and flat as possible. What type of finishing do I ask for?

Start by hiring the best crew you can find, references go a LONG WAY here. Don't be afraid to ask to look at previous work either. You should ask for a power trowel finish.

Should I insulate and if so what do I use?
I was thinking radiant floor heat but I don't think I want to spend the money because I am rarely on the floor.

If you're not installing radiant heat in the floor, I doubt you will ever realize the benefit of underslab insulation, as it isn't cheap. I would consider insulating the outside 2-4' on the perimeter, as long as it's not a grade beam slab.

Sorry for all the questions and thanks for the advice.

Is this a floating slab, where the slab serves as the foundation for the building, or is there a separate foundation in place before the slab?

 

[tfinniii]

1st off make sure any soft spots under gravel are taken care of and tamp well then gravel tamping every 3" layer or so.

 

[encantofred]

building conditions are different in almost every area. since i had to raise my pad up over a foot, (50 dump truck loads), it was then compacted and compaction tested. mine tested at 117%, meaning it should provide a great base. i also had 4" of abc rock put in and compacted.

someone else said it too, but the best thing you can do is to find the best concrete guy you can. and get references. do your homework.

for a slab that big, i would never have a buddy do it. (unless the buddy was the best concrete guy i could find)

tom

 

[bggrnchvy]

In finding good concrete guys at a reasonable price, I talked to buddies who are commercial PM's and they recommended a crew of union masons who did side work. Amazing quality, reasonable (not cheap) rate and they per enough concrete to get excellent rates per yard.

I'm on expansive clay, but it's got pretty good bearing strength. We did 6" of 3/4- road base compacted tight, 6 mill barrier, #4 bars on 12" centers, 2x2x2 piers for my ridge beam columns and a 18"x18" footing with 3 bars in it. Concrete was called out at 3500psi, but we got 6 sack at 6" thick.

 

[joes169]

In finding good concrete guys at a reasonable price, I talked to buddies who are commercial PM's and they recommended a crew of union masons who did side work. Amazing quality, reasonable (not cheap) rate and they per enough concrete to get excellent rates per yard.

I'm on expansive clay, but it's got pretty good bearing strength. We did 6" of 3/4- road base compacted tight, 6 mill barrier, #4 bars on 12" centers, 2x2x2 piers for my ridge beam columns and a 18"x18" footing with 3 bars in it. Concrete was called out at 3500psi, but we got 6 sack at 6" thick.

I'm not sure if your experience is the norm or not, but here where I'm at, you'd be hard-pressed to find union guys who did even decent work on the side. Most of them are think they're superior because they happen to labor on huge pours, and they won't take any suggestions from anyone. Their quality is generally poor as well, and seeing that they work for cash, they carry absolutely no liability or warranty...............

 

[zable9]

I'd form with 2x6s to give a nominal 5-1/4" pour, or if the existing walls are the forms, a 5" minimum slab. Some areas are bound to be in the 4" range, others in the 6" range.

Compare that to forming with 2x4s where you have a basic range of 2-1/2 to 4-1/2. The thin spots are what worry me.

I like real, honest-to-goodness old school rebar. 1/2" or #4 bar set on 16" centers on a 2" chair. No pulling stuff up into the mix. I regard that as a corner cut by a poor craftsman, its fine the day its poured but when these people are long gone it is you who will bear the responsibility for the problems.

I regard fiber as not worth it. 3000-3500 psi mix. Add no water to the mix from the batch plant.

I would place and compact 4-6" of washed 3/4" limestone under the slab (note you do NOT want fines nor crusher run). Using water as a lubricant when compacting.

Pour under a roof structure to have the subgrade in a dry-stable condition. Also you are protected from rain which can ruin the top surface and the crew has a good amount of shade.

Use a 6 mil vapor barrier under the slab, it also has the benefit of keeping hydration in the concrete for the reaction to complete, rather than diffusing into the stone below. The bottom of the slab is in tension under tire loads so that aids strength in the most critical area.

Use a curing sealer on top of the slab as soon as its hard enough to walk on and the finishing is complete. You can of course spray extra water which is nearly free but this product will give you a finished surface similar to whats in a Home Depot or Lowes although probably not quite as durable, they use a heavier product for the large traffic as well has have some sort of maintenance program.

Note nearly every step I listed above costs extra time and money. Yet I feel like its close to a sum of best practices to get the most out of your floor.

Sounds like a good plan. Thx for the share

 

[bggrnchvy]

I'm not sure if your experience is the norm or not, but here where I'm at, you'd be hard-pressed to find union guys who did even decent work on the side. Most of them are think they're superior because they happen to labor on huge pours, and they won't take any suggestions from anyone. Their quality is generally poor as well, and seeing that they work for cash, they carry absolutely no liability or warranty...............

Interesting.

My experience was definitely the opposite. Professional, tidy, great quality at a good rate.

 

[James-W]

I'm not sure if your experience is the norm or not, but here where I'm at, you'd be hard-pressed to find union guys who did even decent work on the side. Most of them are think they're superior because they happen to labor on huge pours, and they won't take any suggestions from anyone. Their quality is generally poor as well, and seeing that they work for cash, they carry absolutely no liability or warranty...............

I have no idea about the quality part, but I would be very much concerned about the part I highlighted above in red. I would like to think I had some sort of recourse if things go horribly wrong.

 

[wssix99]

To answer your questions, you first need to make some decisions:

- Are you going to apply a finish to the floor? If so, what type?
- Are you going to install any equipment, lifts, etc. that will dictate how far apart your saw cut control joints will be? (You should figure out what you WANT the spacing to be - this will dictate who you do the reinforcing.)
- How important is not having hairline cracks to you?

Once you decide on the above, you can make informed decisions on your questions.

Fibers, mesh, rebar, and saw cut joints all play a part in controlling shrinkage cracks. Once you know what you want in the final product, figuring out what you need inside the slab can be calculated.

The thicker the slab and the higher the PSI/cement content, the greater the shrinkage stresses will be. The greater the shrinkage stresses, the more you will need to employ fibers, mesh, rebar, saw cuts, etc. to control them and insure against unsightly cracks.

No need to worry about cracking from stress of driving over the pad. Your RV and boat are nothing and just exert a few PSI of pressure on the slab.

How many PSI?

Great advice above. Most masons will prefer a minimum of 4000 psi because it has a higher cement content and will finish nicer. If you want a perfectly smooth slab, you may want to go higher. ... But the higher you go - the more you will spend on steel/reinforcing... (So, going up in PSI makes things exponentially more expensive because the concrete costs more and you will need to spend more on steel at the same time.)

Rebar or mesh and what sizing?

Depends on how far your saw cut joints will be spaced and what kind of insurance you want against shrinkage (hairline) cracks forming. (Mesh a little insurance - rebar is more.)

How thick?

Great advice above. I'd recommend a minimum of 5" because 4" is what you will want if you ever install a lift, etc. and you'll need the extra inch for variability in the work and variability in the base material.

How far apart should my saw cuts be?

This depends on how much reinforcing you use and what kind of crack insurance you want. You WILL get cracking in the saw cuts, which is what they are for. The thing you want to manage is cracking outside of the cuts. 10' is a good standard for unreinforced slabs. Making the dimension smaller gives you more "crack insurance." Making the dimension larger will require rebar, in addition to the saw cuts, to control the cracking.

I want it as smooth and flat as possible. What type of finishing do I ask for?

A skilled concrete finisher. I suggest spending a lot of time to pick the right finisher and inspect some of their work that has been in place for at least a year.

Should I insulate and if so what do I use?

If you do radiant, yes.

I was thinking radiant floor heat but I don't think I want to spend the money because I am rarely on the floor.

You might consider installing the PEX tube and insulation now and not hooking it up to anything. It's a smaller cost for that material, compared to the manifolds and heating equipment, so you can purchase the option now. If you get to a point where you want the heat, you can make the bigger investment later.

I did this with my house and broke down in the first two months and hooked up the heater. Even if you insulate, the slab will get cold and **** heat out of the room. Even if you aren't on the floor, it makes the room A LOT more comfortable.

 

[wssix99]

there is another thread on this forum about whether to slope or not. when you have a garage that big, even a small slope is big spread over 70 feet.

If vehicles and/or gasoline are in the space, the sloped floor is a must. The idea is to have the heavier-than-air vapors escape through the garage doors. On such a large floor, one need not slope the entire floor in one direction. As long as every area of floor slopes towards a door, then all is well.

If having a flat area is a must (I still wouldn't do it, personally) I would make just one area of the floor flat - where vehicles and fuels/oils will not be stored. That area should also be the high point of the space.

 

[NZ0J]

I'd form with 2x6s to give a nominal 5-1/4" pour, or if the existing walls are the forms, a 5" minimum slab. Some areas are bound to be in the 4" range, others in the 6" range.

Compare that to forming with 2x4s where you have a basic range of 2-1/2 to 4-1/2. The thin spots are what worry me.

I like real, honest-to-goodness old school rebar. 1/2" or #4 bar set on 16" centers on a 2" chair. No pulling stuff up into the mix. I regard that as a corner cut by a poor craftsman, its fine the day its poured but when these people are long gone it is you who will bear the responsibility for the problems.

I regard fiber as not worth it. 3000-3500 psi mix. Add no water to the mix from the batch plant.

I would place and compact 4-6" of washed 3/4" limestone under the slab (note you do NOT want fines nor crusher run). Using water as a lubricant when compacting.

Pour under a roof structure to have the subgrade in a dry-stable condition. Also you are protected from rain which can ruin the top surface and the crew has a good amount of shade.

Use a 6 mil vapor barrier under the slab, it also has the benefit of keeping hydration in the concrete for the reaction to complete, rather than diffusing into the stone below. The bottom of the slab is in tension under tire loads so that aids strength in the most critical area.

Use a curing sealer on top of the slab as soon as its hard enough to walk on and the finishing is complete. You can of course spray extra water which is nearly free but this product will give you a finished surface similar to whats in a Home Depot or Lowes although probably not quite as durable, they use a heavier product for the large traffic as well has have some sort of maintenance program.

Note nearly every step I listed above costs extra time and money. Yet I feel like its close to a sum of best practices to get the most out of your floor.

Why do you say not to add water to the mix?

 

[Jfresh]

wssix99 very informative thank you