Levelling over concrete slab?

[freedomlives]

@Redlands Okie -- the grid comes in flat sheets. I've used it in the past, but mostly because no-one has cattle/hog/feedlot fence panels here, so I cut the reinforcement panels lengthwise and get a rusty substitute. On the slab the uncle-in-law did we put one, but I think it ended up way, way, to deep.

This one I'm doing alone, unless I can get some friend to come out here and help with the mixer. My father-in-law just ends up getting on to a drinking binge with any long project, and both he and my uncle-in-law always do things their way, which isn't always the best.

How big of a grid is fiber mesh? For walls we use a reinforcement fiberglass mesh with 1/4" holes, so I can imagine something similar for concrete, but I suppose it must have much bigger holes.

I was looking at some plastic fibers and metal fibers that can be added to concrete, but the plastic ones are quite expensive, and the steel fibers-- well, it seems like some of them would end up in contact with the surface and rust.

 

[Billrog]

Welded 1/4" grids work well and you want your re-enforcing to be within 1" ( 25mm)of the bottom.

 

[Tractor Seabee]

The fiber I am talking about is long fiberglass (there are other fibers except steel also) added to the concrete mix. Cost is not that bad,(unless you are nickel/dimeing the project) probably not any more or less than the rebar grid. Remember for this application 4,000# concrete is all you need to spend money for. The American Concrete Association (industry standard setter) has done a lot of research on this and has it as an option for reinforcement for slabs on grade that do not have a structural requirement such as bridging soft subgrade. I have both done a lot this stuff and was an inspector for such work for many years. I have never had a slab crack except at the control joints which is why you do that right after finishing. Proper reinforcement location is 2/3 of the thickness from the top elevation; any where else is a waste of time and money.

I will say no more; it is your project and your money. Only trying to be helpful and answer your questions based on my extensive construction experience.

Ron

Ron

 

[Redlands Okie]

The fiber mesh some of us are referring to are small strands. Perhaps half a inch long and diameter of a hair ?

 

[freedomlives]

I appreciate all the different input. The difficulty here-- well, there is a saying that Slovakia is 20 years behind the US. It certainly isn't true in everything, but particularly where we live in east Slovakia, it is true about construction methods. So finding more modern materials in the stores here-- some things yes, other things no. My wife went to the city yesterday, and she had called ahead to ask some store there about the vapor barrier under the concrete. No store in the nearby town had this, but one in the small city said they had it. They sold her the sort of plastic sheet you'd put down when painting-- the "heavy duty" kind, which is 2.7 mils thick.

I am convinced now about the fibers into the concrete. I was confused at first by this talk of "mesh", as I imagined something like a sheet with a grid of fiberglass. So they sell here a fiberglass product from Owens Corning that is precisely 1/2" long "hairs". Likewise there are some polypropylene fibers that meet the standards necessary to replace the reinforcement mesh.

They are more expensive than the reinforcement grid, but not too much more. And you all are right, that it will be difficult to not mess up the height of the rebar, since I'm going to be bringing the concrete in one wheelbarrow at a time from the mixer.

One more question. Given that the mixer does 1/5 a cubic yard at a time, and I'll need 2.5 yards of concrete, is there any problem with pouring 2 or 3 slabs next to each other, instead of doing it all at once? I wasn't timing myself this summer, but I know it had to take me at least 15 minutes for each loading of the mixer and emptying to the wheelbarrow 3 times. So I would estimate it will take at least 4 hours to make all of that concrete, so I wonder if that will lead to a problem, having such a time difference across the slab.

 

[Egon]

Separate slabs is a very good idea. Set them up so they would act like grooves placed for cracking. Have rebar in to conect the slabs.w

Google "Portland Cement Association". Enough information to keep you reading for a few days and it's reliable information.

A little information on slabs. Placement of the reinforcement may be surprising.
[video]http://www.concreteconstruction.net/how-to/construction/reinforcement-for-slabs-on-ground_o[/video]

Don't be too hard on us old folk. There are times a few loosening libations may be necessary to get any movement from worn out old joints!

 

[freedomlives]

Also-- other than compacting the gravel beneath a slab, is it conceivable to use a vibratory plate compactor on top of a drier concrete mix? Or when I was talking to the sales rep of the concrete additive I used this summer, did something just get lost in translation, and he perhaps understood something different from the words I used for vibratory plate compactor, when he told me that is a good idea to compact the concrete?

 

[Egon]

Also-- other than compacting the gravel beneath a slab, is it conceivable to use a vibratory plate compactor on top of a drier concrete mix? Or when I was talking to the sales rep of the concrete additive I used this summer, did something just get lost in translation, and he perhaps understood something different from the words I used for vibratory plate compactor, when he told me that is a good idea to compact the concrete?

In some cases the concrete used will be a dry or minimum moisture type. Packing it may be done.

 

[Redlands Okie]

I am not familiar with running packers over concrete in the pouring process. Street laying machines do handle the concrete really dry. Have heard of running handheld packers over concrete but have not been around it when done. I do however suggest from experience on running packers over a variety of dry base material after rains, overly weted pads, etc that if you do try to run a packer over your concrete it will likely need to be way dryer than one might suspect. I have done quite a few old style dry packed shower pans and think that even that mix might be to wet. You might be able to do a small test spot in a deep corner before you do your vapor barrier.

 

[3Ts]

As for compacting concrete - when I was younger, about 50 years ago I watched a concrete crew with a device that was essentially expanded mesh with handles sticking up vertical to the mesh. They used that as a tamper all over the concrete pad and splashed concrete everywhere! It's purpose turned out to get the aggregate settled and allow the fines to come to the top so they could get a smooth finish. Other than this, I've only heard of compacting concrete that was dry enough that it didn't flow.