New Shop Floor

[ctjstr]

I've scoured a few sites but would appreciate anyone's ideas. We're just starting on our new shop building. Its essentially a 30 x 36 pole building with a concrete floor. Here's my question.

Around here, especially this time of year it takes forever for concrete to really cure. Cure enough so it will pass the plastic on the floor test. I've not used a vapor barrier before under a concrete slab. Does that help with drying out the slab and/or preventing moisture wicking up through the floor in the future?

Part two is, has anyone had good luck with any type of floor paint or epoxy etc on a concrete floor that might still be a little green? On our last shop, at the suggestion of the concrete company, we used a seal coat shortly after pouring the concrete. Looked great for about a month.

After reading a bunch, I'm inclined to try the vapor barrier (although I'm still not totally convinced that it doesn't help trap moisture in the slab) and use an epoxy of some sort.

If anyone has had particularly good experiences or bad in their projects, I'd appreciate the advice.

 

[EddieWalker]

You want moisture to stay in your slap as long as possible. The faster it dries out, the weeker it will be. But just the oposite of that, the dryer the concrete when you pour it, the stronger it will be. So for the very strongest pour, you want the mud at the point of being very dificult to work with, and then keeping it wet for an extended period of time.

The vapor barrier, or plastic sheet under the pour is there to keep the moisture in the concrete. If you have very dry soils, sand or gravel under your pour, it's likely that the moisture in the concrete will seep out of the mix and into the soils. This leaves you with a pad that has different moisture content, and inconsistant strength.

It's just a myth that water and moisture will travel upwards against gravity and through concrete to form a puddle on the floor of the pad. The moisture people see on concrete floors is formed by condensation. It's just like the water droplets that form on a glass or can that you might be drinking. When the humidity levels are right and the tempatures change enjough, some surfaces will become wet. Metal roofs are famous for this, and will sometimes "rain" on the inside of a building. This will also leave a wet concrete floor, but has nothing to do with a plastic vapor barrier. The plastic is strictly for keeping water "IN" the concrete while it's drying.

It will be dry enough to walk on and work on after a day. A week after you pour it, you can park a car or tractor on it. The process of drying and hardening is based on a chemical reaction, and will continue for years after you pour it. They say Hoover Dam is still drying, and that's been decades!!!

Eddie

 

[Red55]

I know things are different in Texas but in the northeast we use plastic under the slab to keep moisture out. The concrete will wick moisture into the building. Most masons use a layer of sand on top the the plastic so they can work the concrete. Once again with the hot texas sun that probably is the reverse (keep all the moisture in to be able to work the mud). Eddie is right about the drier the mix (referred to as "slump") the stronger the concrete. And curing the concrete is critical to it's strength. Remember reading (in high school) that the Answar Dam in Egypt has A/C tubing running thru it's 100 ft thick walls to "cure" the concrete and to keep it from cracking. If drying time is an issue the concrete company can add an accelerate to the mix. It is usually some type of salt which will speed up the setting of the concrete. Also been told that if you add soda (something with sugar in it) it will slow down the setting of the mud. Good luck Ed

 

[Farwell]

Depending what your end use for your building is and if you live in cold climate, you might consider putting 2" rigid foam board under your slab. The foam will keep the slab warmer and will slow the moisture from condensing on your slab.

 

[BB_TX]

Part two is, has anyone had good luck with any type of floor paint or epoxy etc on a concrete floor that might still be a little green? On our last shop, at the suggestion of the concrete company, we used a seal coat shortly after pouring the concrete. Looked great for about a month.

I have plastic under mine and as Eddie said, under the right weather conditions (temp and humidity) it will get wet due to condensation. It is a metal building 8 yrs old, but fully insulated.
As far as the floor, I painted mine with floor paint. Looks good and has lasted pretty well but I don't live on the property and am not in the building too much. But it will chip fairly easily if you drop something on it. I park my 16' utility trailer in the building. Normally not a problem. But I did park it there one time with some mud on the tires. Next time I pulled it out, up came the paint under the tires.
Just glanced at the epoxy stuff at HD the other day. Looked like it was something like $65 for a kit to cover 250 sq ft. That would be a few hundred to do my building.
I am curious what they use in manufacturing plants and stores like HD and Lowes. Our plant and many retail buildings I have seen appear to use a clear coating of some kind directly over the concrete. And they seem almost impervious to heavy usage. Anyone know what process they use to finish those floors?

 

[Erik_in_Hoyt]

for our basement, we put down vapor barrier on top of the compacted gravel, then as soon as recommended by the instructions on the can we sprayed acrylic concrete sealer on the green 'crete to keep moisture in it to help it cure stronger. It's been through an entire year now - and no puddles, condensation or otherwise, despite the lack of HVAC or tight air seal on the construction project.
don't remember what the sealer cost - but it was a 5 gallon bucket and we only used about 3 gallons of it on our 32x44 floor. thought about a second coat, but water would bead up on it just fine before we put on the upstairs, so didn't see the need. Oh, and the acrylic will destroy your garden sprayer, so use a cheap one!

 

[ctjstr]

I appreciate the thoughts. We tried the accrylic application recommended by the concrete company on the last shop floor we built, and it was a disaster. Started peeling about 6 months or so after application and eventually 90% of it came up. That's what prompted my question about what other stuff folks might use. I'm inclined to use something like an acrylic paint, so I can repair chipped or flaked areas easily.

I've had all sorts of suggestions about a vapor barrier, including, doing nothing, plastic under the concrete, or plastic covered by some pea gravel and then concrete. I'm leaning towards plastic directly under the concrete, I guess because I did nothing last time and we had moisture on the floor lots of times.

I think it essentially boils down to, you can't mess with mother nature and if moisture is going to wick up through the concrete, or condense on it..its gonna happen. You can minimize it, but I think that's about it. Unless of course you want to keep it heated all year long.

 

[em14]

I used an industrial floor finish on my concrete shop floor. I would reccomend that you contact the industrial side of the paint company you plan to do business with and ask them to look at your floor and advise you. I used Sherwin-Williams on mine and the tech came out and gave me some very good advice not only about which type product to use but also how to prep the floor. Just my $.02 ... Almost forgot ... I also used plastic under the concrete for a moisture barrier ... I have no moisture problems ...
Leo

 

[Danno1]

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I used Ben Moore industrial epoxy (M70 is the product #) on my (unheated) garage floor 3 years ago. I tend to doubt that the POs used a vapor barrier under the slab as tools left on the floor for a period of time tended to rust. Yet the tape down the plastic/alum foil test showed nothing. Anyway, this stuff was recommended to me by a friend who owns a machine shop. He tried the $60 HD Rusto kit and it peeled in short order. Tried some other epoxy that didn't last either. This stuff is as tough as nails. But very expensive too.

But if it ever was to chip I could repair it with a filled two part epoxy such as WEST System too.

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