So our horse stalls are packed clay. My gelding’s stall was driving me nuts- he always urinates in one spot which constantly causes mounds. He runs around so he kicks up the base…it was just becoming a nightmare to clean. I broke down and bought heavy mats to cover the stall. Before I installed the mats, I brought in a few loads of dirt to raise the floor a bit and level it out, then laid 4x6 mats on top (straight mats, not gridlocked). I use strictly sawdust on top. After 2 weeks of having the mats, the stall is even more of a nightmare than when I started! The mats are buckling at the seams (the worst spot is the corner where 4 mats meet up). The floor is swelling up, and moisture is seeping in from below. It’s a wet mess when I lift up the mats and look underneath. Yes, it has been raining in our area for the past month, so the ground is quite saturated, but how do I keep moisture from coming in from below? I’m using quite a bit of sawdust on top of the mats. I’m putting at least a wheel barrow load full of new sawdust in each night, and within 24 hours, the stall is soaked again. I assume I need to rip out the mats and put a gravel base? Anyone have any recommendations on what size of stone/screening to use and how thick? I’m going to be doing this all by hand, so this needs to be a manageable solution. Thank you for any tips or advice!
Our barn put in mats about 2 years ago. I’m not an expert, but I watched carefully. Stalls were clay base that they pounded flat with a power plate compactor. Laid a couple inches of limestone dust, compacted, on top of that. Then laid the mats. They’ve been stable/fine ever since. I think using dirt may have caused the problem?
Yes, I’m positive the added dirt was a big mistake…and I worked so hard on it 
Yes! Your barn did it right. The ‘key’ is the power compactor. When we built our barn we did not get a power compactor and although we did everything else right, because we only used a hand compacting tool, our mats wound up with the same problems as the OP.
When we replaced the mats we used a power compactor and after many years we are just now starting to see some slight problems in s few of the stalls (and our barn does get water drainage when it rains heavily).
You can rent a power compactor or you might have to hire someone if the job is too much for you but it is really the best way IMO to get the job done right to prevent the problems that you are now having.
You want something that will pack solid under your mats, and as others have said–you want to pack it solid with a vibrating plate tamper.
Organic material like soil won’t compact and will absorb water…as you’ve found. You’ll need to remove all the organics and bring in screenings, then tamp and (VERY important) level. Then reinstall the mats.
Sorry
So the consensus seems to be I need to use a power compactor on the clay. But then, do I need to put down stone on top of that? If so, some recommendations for size and depth would be great! All these numbers I’m seeing on the stone companies website have my head spinning! No. 1’s / 2’s, No. 4’s, No. 6’s ( Washed and Non-Washed ), No. 8’s ( Washed and Non-Washed ), No. 9’s, No. 10’s, No. 57’s, No. 67’s, No. 304’s, No. 310’s, No. 411’s, TY A Rip-Rap ( 24"-30" ), TY B Rip-Rap ( 18"-24" ), TY C Rip-Rap ( 12"-18" ), TY D Rip-Rap ( 6"- 12" ), Super Berm…
You need screenings.
Screening aka diamond dust.
Compacted as hard as you can get it (basically like concrete). No stone over the top. Make sure it is level. You can do this by running a long 2x4 over it. Add more screenings to the low spots, compact more. Rinse, repeat until you have a good level and solid surface.
Then put heavy mats on top (the ones that run about $40 @ TSC have worked fine for us). Cut mats so they fit stalls edge to edge of the stall, as needed. That will help prevent shifting and keep them in place if you have an active horse.
We did just this more than 10 years ago when we built our barn and have yet to have mats curl or shift. Occasionally a bit of wet bedding may get underneath a seam. Then we just lift the mat just enough to sweep out and are good again for a very long time.
I use pelleted bedding in my stalls and not a lot, just enough to create a shallow bed for them to lay down. It’s mainly aimed at soaking up the wet, which is removed daily. After the initial fill which was I think 3 bags in a 12x12 stall, I typically end up using 4-5 bags over the course of a month to refill what has come out. (My horses are out during the day, in at night.)
Organic matter (dirt, shavings, etc) holds moisture and swells, so will continually heave your mats. The compacting is hard work at the time. (I do recommend renting a compactor, does a much better job than hand pounding). We did 7 stalls in less than a day. Well worth the initial effort.
Thanks everyone! I luckily have a friend with a power compactor I can use and a truck to go get the screenings, so hopefully this will all work out! If anyone has any suggestion as to the thickness of the screenings, that would be appreciated. Is 3-4 inches sufficient?
Sounds like after all of this, I’ll need to buy a few more mats. The stall I’m redoing is an odd size…maybe 15 x 18 and I only had mats on a 12 x 12 area. Live and learn 
also, rubber expands in heat, so if you cut them super tight in cold weather you may get buckling in summer, but conversely, if it is very hot when you install them, they will contract a bit in the winter.
In a 15x18 stall we’d use 4x7s and 4x8 mats so the seams don’t meet in the middle. You could even go with some 5 wide mats to lessen the number of mats for the job. You could get by with just 4 of the diamond plate mats for even fewer seams. But each mat is close to 300 lbs so this might present some logistical problems. You probably need to excavate the dirt and make the last 6" of limestone. That should compact nicely and the mats will never move. You can always sprinkle a bit of Sakcrete on top to help solidify the job.
Yes, rohrser, 3-4" of screenings is the right amount.
I think brand makes a difference on this one. No doubt all mats expand/contact, but the mats I have here now are SO much worse with it than mats I’ve had previously. A standard mat seems to have nearly an inch of growth/shrinkage through the seasons. It’s a real PITA :-/
(Animat brand now, unsure what I had before.)
I just want to add that mats must be installed snugly wall to wall. This prevents shifting which allow bedding to get underneath the mat and cause buckling, regardless of what you’ve done with the floor.
Around here it’s called ‘quarter by fines’ - meaning nothing bigger than a 1/4" all the way down to fine dust. 3-4".
