Questions on prep and pouring for 30x48 floor

[logan1211]

Hi all,

Excited to share pictures upon completion but am trying to finalize wrapping my head around a few things before I start getting some quotes on pouring my floor.

I have a 30x48 pole barn I had put up last year, that was excavated site and all great. This is in the Ozarks, MO. About 3" slope from one side to the other on the existing dirt floor.

I have just a few questions I was maybe looking for any past experiences or input here.

1. I put a french drain in on 2 sides, as a hill sheds water to the site. This works great and has kept things for the most part good. Recently I had a deck built off one side. Some water comes in now due to what I assume some sort of change in the way the water flows due to the deck. With a good gravel base under my slab, is the goal prior to putting a floor in making sure NO WATER EVER COMES IN...or is some water coming under the slab/gravel just something that happens and is acceptable? It's not a lot, and drains away due to the slope I suppose but on heavy rains water does show up in there now on the dirt floor. Good rule of thumb here? Kicking around when I'm trenching for lines and what not to put in a french drain on the INSIDE of the shop prior to subbase/base coming in to help mitigate any potentiail issues.

2. No heavy equipment. Planning to do 4" slab, rebar, and vapor barrier. Sound right?

3. I just assume I'll call the local rock place and ask what they would recommend for base and get that brought in...but is there anything I should know about a good base for the slab?

Thanks all for any input! Really appreciate it.

 

[theoldwizard1]

I have a 30x48 pole barn I had put up last year, that was excavated site and all great. This is in the Ozarks, MO. About 3" slope from one side to the other on the existing dirt floor.

Pole barns usually have their floor poured AFTER the barn is built. Before the walls go up, you want all sod removed down about 6" and the complete area level within 1".

1. I put a french drain in on 2 sides, as a hill sheds water to the site. This works great and has kept things for the most part good. Recently I had a deck built off one side. Some water comes in now due to what I assume some sort of change in the way the water flows due to the deck. With a good gravel base under my slab, is the goal prior to putting a floor in making sure NO WATER EVER COMES IN...or is some water coming under the slab/gravel just something that happens and is acceptable?

If you want it dry, DO NOT BUILD A POLE BARN ! Dig a foundation wall down to the frost line (at least 24") and then add a 6" curb above the level of the floor. Put your walls on top of the curb.

2. No heavy equipment. Planning to do 4" slab, rebar, and vapor barrier. Sound right?

Rebar is overkill if you are not putting heavy equipment on top. Proper compaction and saw cuts and you should not need any addition reinforcement.

3. I just assume I'll call the local rock place and ask what they would recommend for base and get that brought in...but is there anything I should know about a good base for the slab?

"Crusher run" (3/4" and down including stone dust) is good because it compacts well.

 

[matt_i]

My answers will probably differ some. If you have pooling or flowing water now, its going to be very difficult to mitigate it later on. The vapor barrier theoretically should work but the theory involves a very heavy gauge of plastic that placers, etc can't puncture as they walk around on it. I would hold off and work on grading until you have created a point lower than your slab all around it so water naturally flows and drains via gravity.

Next, I view a rebar grid as a very inexpensive insurance against all kinds of pouring and subgrade maladies. At minimum I'd go with welded wire mesh mats, but those will have to be hooked into some unknown location. With rebar you know where it sits.

Last, I will always use washed "#57 stone" same limestone as above except no fines. My view is that if you have time (months) to wet and pack the crusher run its going to be just AOK, but if on a short timeline where pouring is desired immediately after initial compaction, the fines will eventually settle very slighty more in the future (after the pour), leaving incremental gaps that are directionally wrong for your well supported slab. With the washed stone, there is nothing more to ever settle once its initially packed, unless it gets smashed into the dirt below by an overload to the slab.

 

[logan1211]

Thanks all!

Sorry if I wasn't clear. I had the pole barn built last year already.

I re-measured, and from right to left on the 48' length, there is a slope of about 4" on the existing dirt floor.

This was excavated down to solid clay (5' due to the hill I was on) Water run off from the slope/hill is addressed, but water coming in from the deck side is what I was worried about. Again, not a ton...but a quick deluge gets a little water on the dirt floor...due to the slope it does drain freely.

I just didn't know if come in now, bring in loads of rock, get my base ready with vapor barrier...Should I be good to pour? or is the little water that is coming in going to be a critical issue to the longevity of the slab. Some folks I've mentioned this too, said, ya...this is why you have gravel (free draining) and the vapor barrier...no worries! Some are like, IT HAS TO BE BONE DRY TO BE GOOD.

I knew I should if stem wall stick built this thing

Again, appreciate all the input!

 

[lakeroadster]

Thanks all!

Sorry if I wasn't clear. I had the pole barn built last year already.

I re-measured, and from right to left on the 48' length, there is a slope of about 4" on the existing dirt floor.

This was excavated down to solid clay (5' due to the hill I was on) Water run off from the slope/hill is addressed, but water coming in from the deck side is what I was worried about. Again, not a ton...but a quick deluge gets a little water on the dirt floor...due to the slope it does drain freely.

I just didn't know if come in now, bring in loads of rock, get my base ready with vapor barrier...Should I be good to pour? or is the little water that is coming in going to be a critical issue to the longevity of the slab. Some folks I've mentioned this too, said, ya...this is why you have gravel (free draining) and the vapor barrier...no worries! Some are like, IT HAS TO BE BONE DRY TO BE GOOD.

I knew I should if stem wall stick built this thing

Again, appreciate all the input!

You have to address the water issue now, or design the slab for a condition of poor sub-grade support = thick concrete with lots of reinforcing steel.

If water gets into the sub-grade, after it has been compacted, the water will negatively affect the compaction.

If the sub-grade compaction degrades, the loads that are supposed to merely pass through the concrete into the sub-grade will now be supported by the concrete itself.

Even if you would have built a stick building you would still need to address the water issue.

 

[logan1211]

Even if you would have built a stick building you would still need to address the water issue.

Understood. Sounds like I get to do some work then this weekend

 

[theoldwizard1]

This was excavated down to solid clay (5' due to the hill I was on) Water run off from the slope/hill is addressed, but water coming in from the deck side is what I was worried about. Again, not a ton...but a quick deluge gets a little water on the dirt floor...

IT HAS TO BE BONE DRY TO BE GOOD.

Then dig a French drain ! This is how I handled my water issue.

You are still going to have to re-level the interior. You want it +/- 1"

You still want a vapor barrier. An I would still add a 6" curb around the inside perimeter.

 

[lakeroadster]

You are still going to have to re-level the interior. You want it +/- 1"

That's pretty sloppy... +/- 1". Any variance in the sub-grade = more concrete. Look at it this way, on a 4" slab that's a possible 25% increase in concrete cost, and a possible slab thickness that is between 5" and 3" thick.

The guys that prepped the sub-grade on my barn used a 2 x 4 screed board and string lines to ensure the sub-grade was accurate.

The other advantage is this yields a consistent concrete floor thickness.

 

[matt_i]

Levelling the subgrade (crushed rock) is an excellent time to break out the rotating laser level. If it has a "coarse" sensitivity, this is the perfect use. Then switch over to "fine" mode when setting the marks you will eventually snap lines between for the concrete finishers.

 

[rburke65]

I don't know.....I have a pole barn and a finished building with a pole barn foundation and they are both dry.

 

[logan1211]

Thanks all. I ended up digging a french drain on the side that had water coming in and completely re-graded it. We had about 3" the following day and I'm happy to say water problem appears to be resolved. I even backwashed a couple hundred gallons from the pool directly towards the garage and it handled it perfectly. Very happy now. Still sore from hand digging it underneath the deck though Backhoe made quick work of the rest.

I've got the rotating level and was planning to string lines and essentially screed + compact in the necessary lifts.

 

[lakeroadster]

From the "Debby Downer" perspective... The downside to a french drain is they freeze up.... if you live in such a climate.

Looks like those cold temp's aren't usual though for your area, right?