Filling a gap between slabs inside the shop

[Captain Spaulding]

When I built my shop, we were 8 months from building a new house, so finances were a little tight. We had equipment and tools stored in the basement, at our parents homes, under tarps and at rented storage, so getting a building up was high priority even given our recent expenditures. To cut costs, I only had a 20x32 section of concrete poured, with the rest filled and ready for pouring. Several years later, we poured the rest of the floor, leaving a joint between the sections.

Over the 20 years since pouring the second slab, the joint got a bit wider. It’s about 1/4-3/8 wide and max 1/8” height difference now. Much of the height difference is because the edge of the original pour had a slightly rounded edge, and the new pour filled over it. No issue until the slabs shrank a little.

So what’s the point? The gap is an issue because several of my woodworking tools are on casters, and I pulled a latissimus dorsi muscle wrestling my table saw across the joint this morning. Hurts like hell to do anything that involves moving. Getting old.

So when I’m mobile again, and off the drugs, I want to fill the gap. Planning to do a little grinding to level some bumps, clean out the gap, and fill it. Everything I’m finding online is flexible to allow the slabs to move independently. I want a hard surface So things will roll over it. On these drugs, I will fight you if you tell me to use something rubbery . Any product recommendations? I’m not opposed to mortar or concrete, maybe with backer rod underneath.

I apologize for the length of the post. My drugged brain is very chatty!

 

[ConCretin]

How big is the total slab area? I'm assuming there's no mechanical connection at the construction joint? If that's true, there's likely to be continued movement from changes in temp, humidity, etc. Even if you grind the surfaces flush, they may not stay that way.

I'd be tempted to do the grinding and monitor the joint for a year and see what happens. A solid filler material might make moving tools across the joint easier but it won't stand up to movement. A flexible material would tolerate movement but won't make dragging stuff across the joint any easier.

 

[Fixr]

Might not be really helpful, but maybe it will: Could you put substantially bigger wheels/casters on your tools? Big wheels roll over imperfections and gaps way better than little ones. Might also be easier and cheaper than trying to make two independent floating slabs act like a single slab.

 

[Sinatra]

Consider one of those epoxy kits used to repair cracks in basement foundation walls. They dry hard and you could grind it flat if necessary. You would need to use backer foam to stop the epoxy from going too deep.

 

[Leaflessshadetree]

Would you consider cutting it to be wider then drilling each side, insert rebar pins then pour concrete to fill the channel?

 

[Captain Spaulding]

One answer without quotes. Not sure I can figure out quotes right now, though the pain has finally let me sit upright enough to read.

I don’t think there is any relative movement between the slabs. I have a set of steel bank money cabinets that I put a top on as a kind of assembly bench. I spend a decent amount of time walking around in front of that, and the gap goes right through where I stand. It’s flat there and never changes enough to notice.

Backer rod is in my plan. Epoxy is something I’ve considered, but even with backer rod it’s going to take a lot.

The thought has entered my head that melted plastic would work. Squeeze it in and grind it smooth. But that doesn’t seem to be a commercial product.

I think I could get concrete or mortar in there without cutting it wider. I’ve repaired mortar on an old driveway gate post, and the scale is similar. Just not sure what material to use. I’ve looked at some high performance epoxy grout as an option since the situation isn’t too different from two giant tiles with a 1/4” joint.

 

[Hank11]

I’d fill it with epoxy made for the purpose. You’ll need to clean it really well. Likely grinding the crack out. Follow directions in the epoxy kit and after it cures, grind it all flat. It sounds like you don’t have any vertical movement, so worst thing is you might get a little crack if it does move. You can fill that again if it does.

 

[Fixr]

Do you want a flat floor, or do you want to be able to move your stuff around without injuring yourself further? Those are two totally different questions.

 

[gimpyrobb]

I have used Sika brand self leveling sealant with great results in the past.

 

[SilverJimmy]

How wide is the area that you want to be able to move wheeled equipment across? If it’s about 8’ I think I would get myself a piece of 3/16 x 6” x 8’ strap of steel, drill a couple holes down the center of it width wise, lay it across the gap, pound some appropriate size nails thru the steel into the gap to keep it from moving and then call it done. If you wanted to get fancy you could grind a chamfer into the leading edges to help wheels roll across it. I use a piece of steel like this to span the 3” gap between the ramp door and the insides of an enclosed trailer I have, makes moving heavy tool boxes roll in and out very easy. YRMV!

 

[hobie18]

I completely sympathize with you. Hate moving some of my stuff around too. And with restrictions and back issues.....
Bigger wheels will help. As for getting rid of that crack...
Will epoxy, foam, and filler work?
3m5200?
Show a picture please.

 

[nadogail]

I have had good luck with Fix-All

 

[ConCretin]

My preferred product for crack repair is a high viscosity polyurea made by Legacy Industrial called XtremeSet-100 although I'm sure other manufacturers offer similar products. You can literally pour it into narrow cracks end it will penetrate and seal the crack. For wider joints, you can fill the joint with silica sand and then pour it in. It pours like water and easily penetrates deeply into cracks and the sand.

There is excess sand and product left on the surface but you can easily grind the surface smooth for a nearly invisible repair. I use velcro backed high grit diamond pads like those you'd use for concrete countertops for a smooth finish.

 

[racecougar]

On these drugs, I will fight you if you tell me to use something rubbery

I have used Sika brand self leveling sealant with great results in the past.

 

[Skooterj]

I would cut a channel and bridge the gap with some diamond plate. That way the slabs can still move independently, but the steel would slide over the movement. Kind of like how they build a gap between a bridge and the road on a highway. And yes, bigger casters would help.

 

[yelchevelle]

My garage started as an approximately 22x30, and years later the back wall was knocked out and an approximately 30x54 added. Where they knocked the back wall out, they filled the bottom course of block with concrete. When I got it, I chipped out the block and put a paver in it so that I could match the two slopes (that were kinda off). If you start cutting concrete, I might look at cutting it wider and doing something similar.

If it were mine, I think I like the steel plate bolted to the floor idea. That seems like the least amount of work and money.

 

[Stuart in MN]

Maybe this is a redneck repair, but I'd think about cutting a thin strip of wood to fit in the crack. It wouldn't be a forever repair, but if the goal is to provide a smoother path for casters it may work.

 

[wssix99]

I pulled a latissimus dorsi muscle wrestling my table saw across the joint this morning.

Can you share more about the size and type of casters you have on your table saw? A 1/2" gap isn't that big. I have a 500lb table saw that I move over gaps like this all the time, but I have big wheels...

Spending a lot of time and effort on making your slab fancy won't give you the payoff you really need if your casters are wrong. (Tables and dollies ship with cheap casters all the time. China is flush with them!) If you make this one gap great, you may just encounter another issue later.

For little gaps like you have, I really like the Slab Gasket product. https://www.pavepatch.com/slabgasket-c-40.html They are surprisingly stout and hold up to my table saw and vehicle traffic on a 3/4" gap! The product is flexible and there are deep options that perform like a solid.

The slab gasket is also really easy to install. You can sit back and watch some football over the next few weeks and leave the job for others to do. It makes a great Mother Daughter Project...