How to seal shop floor cracks?

[Rick Schubert]

I have a concrete floor in my workshop with some mats scattered around. I have several cracks, medium and small, in the floor.

It is humid here close to Lake Superior so I have a dehumidifier running spring, summer and fall. When I place plastic over the cracks a lot of moisture builds up under the plastic so I'd like to seal these cracks and prevent the humidity from entering my shop.

How would you suggeest doing it, hopefully without chipping a v-grove into all the cracks so the sealer will hold. Anyone used a product successfully? It does get cold here in the winter, but rarely over 80 in the summer.

Thanks, Rick

[tod evans]

rick, instead of squeezing a tube of some sort of goop into the cracks that`ll never really do the job, get caulking backer rod and beat it into the cracks with a cold chisel. concrete is itself porous so it will always permit moisture to pass through unless you take steps to seal the entire floor..02 tod

[Brad Townsend]

When I finished the floor of my shop with EpoxyShield, I used grey silicone sealant in the expansion joints. It remains flexible and doesn't defeat the purpose of the joint. I did it just to keep dirt and sawdust from accumulating there, but I suspect it would work for your needs as well.

Hint: Don't worry about being real neat when you fill the cracks. If you try and wipe up every stray bit of silicone, you will have it all over yourself.:D It's a lot easier to let it cure and then rub the excess off from around the crack with a rubber soled shoe.

[Rick Schubert]

Tod,

Will the caulking backer rod prevent air movement? I know concrete is porous, but when I put down plastic the moisture only gathers along the cracks.

Rick

[tod evans]

Tod,

Will the caulking backer rod prevent air movement? I know concrete is porous, but when I put down plastic the moisture only gathers along the cracks.

Rick

rick, if you pack it in tightly it will. or you could use plumbers oakum, the packing tamped into cast iron pipe joints prior to leading them. the reason i`m against goop in concrete joints is that concrete will most likely continue to move eventually breaking the seal. then you`ve got one mell of a hess with sealant stuck to the sides of an open joint. by packing some type of loose material into the joint you give yourself the flexability to reseal the joint down the road when the concrete moves again...02 tod

[Cliff Rohrabacher]

Everyone is correct about the flexible sealer material. The cracks will likely always re-appear if they are re-cut and filled with concrete.

Short of digging up and relaying the entire floor with a nice gravel sub and drainage (perfect world where are you?) I submit that the cracks are your permanent friends. I'd use a pourable silicone or flexible epoxy. open the crack a little (less than 1/4" preferably 1/8") to expose fresh concrete and get as much in as possible.

[Joe Chritz]

Have you taped a piece of plastic on the floor where this ins't a crack?

If not try that before you get really carried away. If you do and the plastic stays dry for a couple days then work on packing the joint. If you get moisture where no crack is present you may as well just seal the crack to keep crud out.

I'm assuming the crack has not shifted in height at all otherwise you got a real job on your hands.

Joe

[Ted Jay]

Try this stuff:
http://www.radonseal.com/

[Rick Schubert]

Ted, From what I could see on the radonseal.com site they were always referring to walls, not the floor. Have you tried their products?

Rick

[Barry O'Mahony]

rick, if you pack it in tightly it will. or you could use plumbers oakum, the packing tamped into cast iron pipe joints prior to leading them. the reason i`m against goop in concrete joints is that concrete will most likely continue to move eventually breaking the seal. then you`ve got one mell of a hess with sealant stuck to the sides of an open joint. by packing some type of loose material into the joint you give yourself the flexability to reseal the joint down the road when the concrete moves again...02 todIf the concrete is moving on either side of the crack relative to one another, than you have serious problems. There should be rebar, reinforcing mesh, or fiberglass preventing this type of movement.

Cracks will occur as a result of curing initially, and temperature cycling. I have a neighbor who is a concrete contractor; he poured a 6" thick slab with reinforcement at his own shop and still had cracking; there's no way to prevent them.

It should be OK to put in some backing rod, and chaulk over that.

[Kent Parker]

Rick,

Some of the older fish boats that haul out at the yard I used to work at had some good sized seams. We'd caulk them with oakum (stick fibery stuff) and them fill the seam with Water-Plug cement. Its a very fast curing cement so don't mix too much. Maybe 6 to 8 oz. at a time. I've used it in my shop floor cracks with very good sucess. Always worked for the fish boats and I'm sure those old wooden hulls move a bit more than the average shop floor.

Not as smooth as a sealant but does the job.:)

A tip for those future cement slab pourers.....If you lay a plastic sheeting (rather thick, not the Saran Wrap type) on smooth dirt prior to pouring cement you'll have much less a chance of cracks developing during curing. A lot of cracks in cement are caused by the slab "tripping" due to friction on the dirt while curing. The plastic makes a nice slippery surface for the slab to move on during shrinkage. (my grandfather was a Mason);)

Cheers,

Kent

[tod evans]

a bed of sand does well too, as well as expansion and control joints..02 tod

[Charlie Kocourek]

The radon seal sounds interesting. I also live in Minnesota and the road salt is eating up my garage floor. I wonder if this stuff would help?

[Vaughn McMillan]

Rick, how wide are these small and medium cracks? If they are wide enough to fit backer rod into, then I'd recommend foam backer rod followed by a tooled silicone sealant joint. A proper sealant joint should be concave on the bottom -- following the shape of the backer rod -- and tooled to be concave on the top as well. This ensures adhesion to the sides of the joint, while allowing the center the necessary flexibility to expand and contract with the slab. If you clean the joints very well, and use a good quality sealant designed for sealing concrete slabs (possibly not something they'll have on the shelf at the BORG), you should be able to expect 20 to 25 years of service. I'd recommend against a "v" groove in any case. You'll be better off with vertical sides on the joint, backer rod, and the dual concave tooled sealant.

If the cracks are too thin to fit the backer rod, they can still be sealed with a silicone slab sealant, although without the backer rod and dual concave shape, the sealant won't have as much "give" as it would in a wider crack.

There are also industrial epoxies that could be pressure injected to fill the cracks, but if your slab is still moving, the cracks will simply re-appear in another location. (Plus, the cost is likely not something you'd want to pay.)

I offer these suggestions based on designing, spec'ing, and inspecting the sealant on literally miles of concrete joints in airport apron pavement.

Barry mentioned a concrete contractor neighbor whose 6" reinforced slab still cracked. My dad (a licensed P.E. civil engineer, with 50+ years of concrete mix design experience) says there are three "laws" in the world of concrete: 1. It's gray. 2. It gets hard. 3. It cracks. ;)

HTH -

- Vaughn

[Rick Schubert]

Vaughn, Some of the cracks are 1/8 wide, others range up to 1/2. Most are pretty rough and jagged. Previous owner had widened some parts and put some type of concrete filler in, but that has mostly been forced out in chunks.

Garage is 2 1/2 car size and some of the cracks are 15-20' long.

So far the smallest size caulk backing rod I've found is 3/8" round. Does it come smaller?

Thanks for all the help so far, Rick

[Ted Jay]

Vaughn, Some of the cracks are 1/8 wide, others range up to 1/2. Most are pretty rough and jagged. Previous owner had widened some parts and put some type of concrete filler in, but that has mostly been forced out in chunks.

Garage is 2 1/2 car size and some of the cracks are 15-20' long.

So far the smallest size caulk backing rod I've found is 3/8" round. Does it come smaller?

Thanks for all the help so far, Rick
Rick, no I haven't personally used the RadonSeal stuff, a friend of mine who lived up north used it on his basement in Chicago. (We don't have basements here.) He only lived in the house 6 months after that, and moved down here, now he lives in Colorado. So he doesn't have long term experience with it.

Now if you think about it, this stuff is made for a basement, sealing only the walls in a basement would do you no good, you have to do the floor too.

It seems your problem is moisture coming up through the cracks. I think just filling it with silicone is just going to block it for a little while until it fails and you're back to square one again. You might want to look at the crack repair part of the site it's kinda interesting http://www.radonseal.com/crack-injection/basement-cracks.htm
Oh, I have no affiliations with the company either, but it does have alot of info on the website, IMHO.

I read alot of stuff online a while back as I was looking for some type of waterbarrier to paint on the inside of a 3 foot tall concrete planter in the back yard, and that's how I found their site.

Good luck,
Ted

[Rob Will]

are three "laws" in the world of concrete: 1. It's gray. 2. It gets hard. 3. It cracks. ;)HTH -- Vaughn

Vaughn,
I just poured a new shop floor last week. It is 6 inches thick over thick plastic and compacted DGA. The slab measures 32 x 48 and is reinforced with 6 ga wire mesh plus a #4 rebar in a criss-cross pattern at all perforations in the slab (posts, conduit boxes etc). There is also a #4 rebar around the perimeter. All of the steel was supported on 2" chairs. There are no control joints in this slab.

Here's my question:

As you might expect, there has been a hairline crack show up that pretty much follows a 1" plastic electrical condiut burried in the slab. You really can't feel it but it shows in the new concrete and sealer. (2 coats cure & seal).

After the building is up I plan to recoat the floor with a colored Epoxy or something similar. So....with all of the rewire and rebar in this floor (on a solid sub grade), will it ever move enough that hairline cracks will be a problem? The remaining uncracked slab is about 32' x 32'.

Any suggestions?

Rob

[Vaughn McMillan]

Vaughn, Some of the cracks are 1/8 wide, others range up to 1/2. Most are pretty rough and jagged. Previous owner had widened some parts and put some type of concrete filler in, but that has mostly been forced out in chunks.

Garage is 2 1/2 car size and some of the cracks are 15-20' long.

So far the smallest size caulk backing rod I've found is 3/8" round. Does it come smaller?

Thanks for all the help so far, Rick
Rick, I don't recall seeing any backer rod smaller than 3/8". Most of my experience was with bigger diameter stuff...5/8" and 3/4" as I remember. I'd use the backer where you can, and in the cracks where it won't fit, I'd just go for a bead of sealant, tooled concave on the top.

Ted brings up a good point about water infiltration from below. The sealant should hold back condesation, but if there's any appreciable hydraulic pressure from ground water, the sealant can fail. especially with rough edges on the joints. I don't have any experience with waterproof coatings like RadonSeal, but if you are dealing with hydraulic pressure, that's probably a more permanent fix.

The fact that the previous owner's patches have been popping out of the slab indicate the slab is indeed moving a bit, but as long as you don't see anything drastic, or any changes in elevation from one part of the slab to another, it's likely just the typical movement from temperature change. Because of this movement, whatever solution you use will need to be flexible.

HTH -

- Vaughn

[Vaughn McMillan]

Vaughn,
I just poured a new shop floor last week. It is 6 inches thick over thick plastic and compacted DGA. The slab measures 32 x 48 and is reinforced with 6 ga wire mesh plus a #4 rebar in a criss-cross pattern at all perforations in the slab (posts, conduit boxes etc). There is also a #4 rebar around the perimeter. All of the steel was supported on 2" chairs. There are no control joints in this slab.

Here's my question:

As you might expect, there has been a hairline crack show up that pretty much follows a 1" plastic electrical condiut burried in the slab. You really can't feel it but it shows in the new concrete and sealer. (2 coats cure & seal).

After the building is up I plan to recoat the floor with a colored Epoxy or something similar. So....with all of the rewire and rebar in this floor (on a solid sub grade), will it ever move enough that hairline cracks will be a problem? The remaining uncracked slab is about 32' x 32'.

Any suggestions?

Rob

Rob, from what you've described, I don't think you have anything to worry about. Sounds like a stout slab, and you did everything right as far as reinforcement, assuming your DGA subgrade isn't sitting on Jello Pudding or something similar. :) Hairline cracks happen in nearly all slabs.

The crack following the conduit is a classic concrete move -- following the path of least resistance when it cracks. By their nature, concrete slabs try to break into roughly square pieces. A 10' by 20' solid slab will almost always crack into two 10' squares. (Or in your case, 32' squares. ;) ) Control joints provide the path of least resistance, but in their absence, the slab will make its own. A 6" slab would typically want to make itself into about 12' squares under most circumstances. A conservative rule of thumb is to take the thickness of the slab (in inches), double it, then space control joints that number (in feet). A 6" slab would have joints at roughly 12'...I've been involved in a lot of 9" slabs with 18' to 20' control joints. You can space them farther apart, though...like I said, that rule is conservative. You can saw-cut control joints in the slab, but it's probably not worth it for a shop floor. The epoxy finish will likely hide most if not all the hairline cracks that eventually show up.

Like I said, I think you don't have anything to worry about.

- Vaughn

[Joe Chritz]

Cut expansion joints.

Concrete is going to crack so it is best to make it crack where we want it too.

If the slab wants to move you probably couldn't do much to stop it anyway. My garage is just like what you have only smaller and not so thick. I have a hariline crack that has been in for a few years with no movement.

My slab is poured on (ready for this) almost 5 feet of sand fill. If one was going to shift it would be mine I'm sure.

You will love the epoxy coat.

Joe

[Vaughn McMillan]

...My slab is poured on (ready for this) almost 5 feet of sand fill. If one was going to shift it would be mine I'm sure...
Actually Joe, if the sand was placed and compacted at the right moisture, it can be a very stable subbase for a slab. Native (uncompacted) sands can give you problems, but sand fill's usually like a rock once it's in place. I can think of a lot of worse things to have under your slab.

I agree with you about cutting the control joints -- the concrete's gonna crack anyway -- but don't know if it's really worth the money for a painted shop floor. (Under tile, for example, might be a different story.) I also agree about the epoxy floor paint. Great stuff.

- Vaughn