# leveling a large platform



## j10c3y25

Since installing built-ins requires working with unlevel surfaces sometimes I thought this post would belong here.

I have a large weightlifting platform in my garage that I built a year or so ago, together with the squat rack and plate storage it has around a 12'x8' footprint. The construction is 2 layers of 3/4 osb and then a layer with 3/4 plywood in the middle and 3/4 rubber horse stall matting on the sides to absorb the impact of the weights.

Previously it wasn't in a very level location, but the problem was somewhat alleviated by jamming cardboard under most of the gaps. The garage floor is concrete slabs with large separations and slopes that do not match at all. The new location I've chosen is so off that cardboard isn't going to work. I need a solution to level this giant platform, as well as FULLY support it. If I drop a barbell loaded to 300+ lbs from overhead and the weights hit a hollow spot, well that's that.

First I tried taking measurements and carefully ripping tapered strips, placing them every 4" apart under the front 4x4 squat rack platform. This resulted in semi-satisfactory results once the rack was sitting on top. Its not completely level, and the pieces aren't all bearing the load, but it will not be subjected to any impact, so a little flexing (1/16th?) should be fine. For the larger 8'x8' section this is simply not going to do, not to mention was a huge pain and not that successful. I can't do anything TOO permanent, but I have come up with an idea that I think may work: sand.

I edge jointed some 2'x4's, and put the jointed sides up with a level on them and am attempting to scribe them to the concrete at the edges of where the platform will sit. The idea is to get the scribe right, and then rip them to the correct width so that I have a level 8x8 frame. Then I'll fasten it together somehow, run some kind of sealer/filler around the inside edges so the sand cannot escape, and then fill and screed the sand. Then I just have to figure out how to set the 400 lb platform on it.

Does anyone have an easier method that I'm not thinking of? Also, I need to make sure that the platform doesn't move but I don't want to drill holes in the floor, could I maybe glue the frame down with something that can be scraped off later? Its not going to take much side to side forces I think so it probably doesn't have to be that strong. I'm having a rough time with this, so I would really appreciate any suggestions. Thanks.


----------



## woodnthings

*what about using sand?*

You could use a bag of sand, wet it a little so you can screed it off the highest point(s) using a long board and check the diagonals.

If the platform is too heavy to lift and move around as is then that won't work. You could blow sand under it in place using a shop vac or an air compressor. then use wedges to support it at the edges.

There is a product call "self leveling concrete" where you mix a light slurry of the product so it can flow out to a level surface. That would be worth looking into.

If you can tip it up on edge ... enough to apply a few gobs of Liquid Nails then let it settle down squeezing out the gobs until the whole unit was level, that may work.


----------



## cabinetman

This is somewhat like making a ladder type toe kick to install cabinets, making shed floors, or temporary dance floors to be used on less than perfect floors. You could be forever trying to scribe wood to level the floors.

I would start with ordinary 2x4's on edge and make your perimeter frame, and configure the grid within. Being open, you can use shims under the low spots. They are tapered, and can be tapped in place with a hammer. Use a long straightedge, like a slice off the edge of a sheet of plywood to lay across the 2x4's to check for flat. You can also get a platform that's level. Once you are happy with the grid work, screw down the substrates for the top.


















.


----------



## j10c3y25

A ladder frame sounds good, but I'd need to use an enormous amount of wood and then still fill nearly all gaps with the floor after leveling with shims. I suppose I could just jam tons of shims under it after it's set level, but to stand up to the forces generated id need upwards of 25 2x4's to build it. ANY flex in the platform is extremely noticeable on heavier pulls, it kills your momentum and really just makes for a crappy experience. This would work great for the squat rack portion but it's a lot of work (and expense) for the platform side. The abuse it has to take is far greater than any ordinary subfloor. If I were starting from scratch I would do this, it's basically an entirely different design. I think when I move I'll build my new one with that style floor, thanks for the suggestion.

I like the idea of pouring something self leveling, but I am renting the place and adding concrete to the garage may not be an option. I have zero experience working with concrete as well, would I be able to install it in such a way that I could remove it without damaging the existing floor later? Doesn't matter if I have to destroy it to get it out as long as the base floor is unharmed.

Also, the rubber and top sheet is removable, and I just chopped off about 18" off the back to get a little more floor space. Anything less felt too small but 8' was unnecessary. That being said, the osb "slab" is still a heavy beast, but I can now pick it up on edge and move it myself. I imagine 2 people would be able to place it down gently with only moderate difficulty.


----------



## j10c3y25

*its working*

First off, thanks cabinetman, your advice with the frame helped me to get this done a lot easier than the way I was attempting to do it. I am still going with scribing a single border frame and filling it with sand, but instead of doing it piecemeal I screwed the frame together and leveled it all at once before doing my scribe. That way after cutting it would all be exactly how it needed to.

This is what I got done today:

The base is laid out (top layer is not on) in the spot it will sit








I laid duct tape around it to give me a clear line to follow for my frame








Then I carefully milled my 2x3's and leftover 2x4's from my from my first botched scribe attempt (tried to rip freehand with a circular saw, didn't cut very well) and constructed the frame. The members are screwed together with the tops flush, and I have one long piece that is squared on all sides so I can use it as a giant level, support for my rip jig, and my screed later.








I measured the thickness of my two platforms, and sure enough the big one ended up about 1/10th inch thinner than the small one. The air gap from the small platform to the highest point was about 0.4", so I added 0.1" for 1/2" at the highest point of the floor. I marked 1/2 inch down from the 2x3" in that position, and then set my dollar store compass to hit that mark, and used a little block of wood with a hole drilled in it to keep it registered while scribing. Because the frame is level all the way around I only needed to set my compass once and mark all 4 pieces








Because I planed my pieces to the same thickness, I was able to use the large piece as a support for my rip jig and get good square cuts. Cutting was a bit tricky though, some of the concrete is fairly straight despite being unlevel, but some places had noticeable dips. For these pieces I had to set the jig and make a partial cut, then reset the jig and cut the next line. Most pieces only took 2-3 cuts, and little cleanup. One piece needed a little extra work with the hand plane and rasp to get a good fit.


----------



## j10c3y25

*continued*

Here's the completed frame








Low angle shot, it came out surprisingly well








I dropped the base on top with the top sheet to see how I did








Turns out I freakin NAILED it. Sits perfectly flush with the small platform from the center all the way out to the left. To the right is a different story, but its due to the small platform sloping down from the center crack.








I can fix this by shoving a few shims underneath it, but I'm thinking that this went so well I might as well do the same thing for the small platform. I could probably get it done in less than an hour now that I've got the method down.

I bought a tube of sealant/crack filler than can adhere to wood and concrete, and I'm going to lay that down around the inside of the frame before filling with sand. The other idea I have is maybe to just staple some plastic sheeting to the inside and pour the sand on that, I just worry that it could tear. Which way is a better way to keep the sand in?


----------



## woodnthings

*nice job on the frame*

Glad to see that you are using sand as I suggested, way easier than trying to shim it in a hundred places. I would use the sealant right on the frame to keep the sand inside and to keep the frame from moving. It will pop off later if you have to move. Once the frame and sand are leveled out, just screw the top on in a few places to contain the sand. It should work out great and be able to take any abuse, but let us know! :yes:


----------



## cabinetman

j10c3y25 said:


> Turns out I freakin NAILED it. Sits perfectly flush with the small platform from the center all the way out to the left. To the right is a different story, but its due to the small platform sloping down from the center crack.
> 
> I can fix this by shoving a few shims underneath it, but I'm thinking that this went so well I might as well do the same thing for the small platform. I could probably get it done in less than an hour now that I've got the method down.


The success of arriving at a flat stable platform with the conditions you have is how you've done it so far. Forget the sand. I've tried that with shed floors and it doesn't hold up. It's compressible and will displace under pressure. Doesn't matter how it's captivated, you need solid support with shims in the low spots. It doesn't take many.

As I described with the ladder analogy, the tops of your frame will be even with each other. When the frame is down, tapping in some shims will prevent the frame from moving, and the tops will remain on the same plane. If you are using 2x4's, their overall flatness in mass is self supporting. Once it's all together, it will take very little solid support underneath to keep the tops all flat. 

You don't want to find out after you cap off the whole deck that you have movement in places because of what you used to support it.


















.


----------



## j10c3y25

I had this pretty much done Monday, but I took about a week off from reality to binge watch all 4 seasons of the walking dead. I can't stop thinking about zombies now :blink:. Anyways...

I went ahead with the same frame process for the small platform, but it was much more difficult than the large one. The concrete was even worse and the pieces were so small that I ended up having to do a lot of adjusting, including gluing a small strip on where I cut too much off.









After getting the fit I wanted I needed a way to hold down the pieces that wasn't totally permanent, so I came up with using carpet tape. I laid down strips and just stuck the frame pieces to it.









Then I used this sealant to put a bead around the inside and keep any sand from escaping through the bottom, and big globs in the cracks as well.









Then I poured the sand and screed it level









I decided that this is not moving again until I move, so I had two choices: Make it possible to disassemble for repairs, or seal it up as tight as possible and forget about sustainability. I figure I'll be here another 3-4 years max, so I just put a fat bead of construction adhesive on top and set the platform on it. The squat rack helped as a natural clamping system.


----------



## j10c3y25

The big one took a few more bags of sand than I thought, something like 6 or 7, but I took a few more precautions with it as well.

I found several interesting research papers and articles about the strength and behavior of sand with cyclic loading, penetration tests, reinforcement with geotextiles, etc.

Takeaways include, but not limited to
1. Sand has a period over which it "settles" and then all but stops deforming under cyclic loading (needs to be well compacted or my platform will sink over time)
2. Can be reinforced by a grid material that helps transfer shear stress and stop motion
3. Sometimes has an epoxy poured into the top layer to form a stiff crust (keeps sand from spreading and improves strength)

There are many more strategies for increasing the strength of a sand based foundation, but I decided to apply these three with what resources I had on hand. After taping down the frame and applying the sealant, I just stapled together and taped down these scrap strips in a manner I thought would help to prevent any migration of the sand over time.









I poured the sand and screed it, then I took a piece of scrap plywood and placed it on the sand, and then jumped on it as hard as I could. I did this around the entire bed of sand and then added more and screed it again. It made an immediate and considerable difference, I'm glad I didn't skip that step. 

I didn't have any epoxy, but I did have this craft adhesive stuff around, so I just sprayed a bunch of it on the surface and laid leftover pieces of landscape fabric on top. The fabric stuck to a thin layer of sand with glue on it. It serves to help lock the top layer in place a bit.









The pieces of PVC pipe were there so I could lay the platform down on top and then move it around easier. That way I could put my glue on with it down instead of trying to carefully set the giant thing down on it. After setting it on the rollers, I laid my construction adhesive and then pulled the pieces one at a time, guiding it into place.









I had plates on top at first, but I realized it wasn't squeezing the adhesive out, so I went around the perimeter installing screws to pull the platform down to my frame and get rid of all the gaps. I trimmed my mats back to fit and now everything is in place.









I did a few clean and jerks and drops from overhead and let me tell you what, it is a joy to use this platform now. Its completely solid, no give, no flex, no rocking around like before. Now that I'm done I'm thinking I might just go ahead and add trim on the edges to make it look good. It would also help keep the mats in one place, and if I leave the top edge proud; keep the bar from rolling off the platform. Other than that I need to add some kind of system on the sides of the squat rack to accept heavy bands so I can do band squats, but I haven't thought of anything very noteworthy yet.


----------

