Hay problem

I use a 1037 NH bale wagon to offload hay into a 40X80 barn with concrete floor. Problem is even with the plastic that was put down prior to pouring floor--I get moisture that molds at least 50% of crop. Very hard to keep material between floor and hay the way the wagon pushes out from under they hay.
Any suggestions?

Are you sure the moisture is coming up from down below and mot just condensation forming on the cold concrete? I have a condensation problem on my barn floor until the floor gets warmed up after the winter cold. Best to keep the doors open to let in a little ambient heat in.

I put mine on pallets (skids to some folks). Just lay them down as you go and take them up as you remove. Lets air circulate and a cheap solution.

You have to have ventilation under the hay. But if 50% of your bales have mold I wonder what else is wrong. Even piling bales on wet ground i would not expect more than the fist layer to be affected.

If you have 50% of the hay is molding, you've got more problems than floor moisture. Sounds to me like you need to wait another day before baling your hay or be treating that hay with a preservative?

I would have to agree with Cowman. Look for additional moisture sources or too high content in bales.

Was the concrete new? If so you may have some extra moisture coming from that for a while.

How dry is your hay?

I've dealt with this, if the moisture is running higher in the hay and you have a moisture issue in the building, definitely a bad combination. Is the building adequately ventilated, are the gutter down spouts or ends far enough away from the perimeter of the building ? We have a very large morton building and with the above combination of conditions of ground and trapped moisture. I have lost significant hay, way up top, mold on the top side, and this hay was very dry when baled, (I baled it). All of this was the building, I find out late that the roof vent fans were for some reason not known about or power cut off etc. Maybe that would have changed things. Dirt floor, as its a riding arena, and we put poly down, then pallets, ground moisture gutters soaking the perimeter, and even with the big doors open, the whole thing just sucks to store hay in there and is why we don't any more, other barn had roof issues, but not this problem, could not win, and you can't fool with this kind of hay with horses, made a ton of extra work dealing with it and discarding it too. Nice 2nd cut I did as a favor and knowing the well kept fields and quality crop it was, lots of clover and just some nice green hay grasses, only to spoil, way up high in the stack, as of late I don't even fool with hay any more, would like to under different pretenses, but for now, forget it LOL! Funny how the bottom tier would be fine. I've had higher moisture hay as well, knew better to put that in there, never thought I'd lose the top tier like we did that year, well it went for mulch on a pasture I replanted, no weed seed given the cutting it was, if anything any seed would have been desirable, lot of mature clover in it. Never knew a NI 215 flail type manure spreader would make a great mulch spreader, worked great actually ! So all was not lost I suppose.

I should have said I'm losing 50% of the bottom tier.
The downspouts do grain against the building.

18.5% or less. This year had Orchard Grass at 15.5%
Horse people like to do brain surgery on your bales before they buy them!

I pile my hay outside, I have about 6 inches of shale under it and have not had a problem with moisture damage. Guys here often put down gravel then shale over dirt floor barns. Generally my top limit on hay moisture when bling is 14% but it will climb a little after baling.

Old conveyor belts reportedly work well.

Second floor or loft.