New concrete slab low spots

[minytrker]

I just got my 24x40 building built and was pressure washing the floor and noticed a couple spots water sat in. As soon as the spray foam is finished and painted I am doing the floors with an epoxy coating.

What causes the low spots and should I be concerned? Should I just epoxy the floor and not worry?

 

[sco44]

Low spots are normal. Not sure how low we are talking though. Shine a light low across floor and u can really see them.

 

[minytrker]

Nothing crazy, never had a brand new slab before so didnt know what to expect.

 

[Olyar15]

Just get a squeegee broom. Useful for moving the water.

 

[matt_i]

Nothing to worry about. I have some low spots 3/8" or so lower than the perimeter. Once the building is dried-in you won't worry about them any more

 

[rburke65]

Low spots are caused by a lack of concrete in that area......!

 

[readhead]

Not uncommon. Once you get in there and start working you won't even notice them.

 

[Cyberbear]

There is a cement based product used in the vinyl flooring industry that is poured on and is self leveling. Once installed and set-up, it's ready for any type of floor covering, including epoxy coating, etc. I had it done in my long and narrow bathroom floor ten years ago and it's still perfect.

 

[Jon_E]

Just had my slab poured last week and there are some obvious low spots and high spots. I found them when I flooded the floor the next day for wet curing. Nothing more than 1/4" out over 10' or so, it's really not a big deal. You can't see them when the floor is dry unless you know they're there. I wouldn't worry about it at all. Unless your finisher used a laser screed or was really a perfectionist, every floor will have spots like that.

 

[sberry]

I have 2 little high spots I want to grind, just enough that water doesn't finish drain dry from them. But I have about 1500 sq ft or so flat enough I can toss steel on the floor to build a common trailer.

 

[Joemctag]

If it’s 1/4” over 10’ they did a really good job! The concrete doesn’t level itself. And it’s heavy, so it takes experience to minimize moving it around. They don’t just pull the screed over it and it’s flat. Without experience, it’s backbreaking work and still might not be a good job.

 

[klassenl]

I have 2 low spots where I park my minivan. Right by the front doors.

 

[DFB]

I have one low spot underneath and slightly behind my basement garage staircase...would be the perfect place for a floor drain

Other than that it all pitches toward the garage door and actually works quite well.

 

[finn]

I had water getting trapped in a low spot between the door and my lift at my shop. Pretty aggravating until I figured out that rain was running down the outside of the door and into the shop rather than away from the building since the slope of the door threshold was insufficiently pitched. Ten minutes with a diamond grinding wheel on a 4 1/2” grinder to correct the pitch in a small area, and a small, shallow trench or swale fixed the issue. Water no longer pols, even though the low spot is still there, as it has relief.

Probably one reason dome prefer to pitch the slab towards the door slightly.

 

[myredracer]

Are you going to be driving in a vehicle often that would track in water from raining or snow that'll melt and drop on the floor and end up draining in the wrong direction?

Our 1800 sq. ft. garage/workshop is split into three rooms. Concrete was done be an experienced pro. company and done with a code. min. slope to the O/H door. Looked really nice when finished. One "room" is the garage for two daily driver cars. First winter we discovered that the floor sloped in the wrong direction slightly at the back and melting snow causes water to run towards the back wall. We just lay a few towels on the floor and forget about it. We have a push squeegee but find a few towels does the trick.

If there normally wouldn't be water on the floor, I wouldn't worry about it. A "slightly" wavy floor is common when using the large power trowels and normally you can't see it. After a few years and you've got oil, dirt, paint and other "stuff" on the concrete, insignificant dips won't be noticed anymore...

 

[Firebrick43]

Very few concrete guys have intelligence enough to pour concrete flat enough to have minimal low spots. Tennis courts need to be very flat and I have heard of specs such as

The court shall be flooded and no low spot shall be deeper than the thickness of a dime.

You will pay dearly for that kind of skill!

 

[brownbagg]

Very few concrete guys have intelligence enough to pour concrete

i do a lot of concrete inspection, Its 1/8 in twenty feet or if you put two nickles on top of each other and jefferson drowns, its not legal

 

[ConCretin]

I wasn't going to comment because it's a 4 year old thread and I'm pretty sure the OP has long since moved on but some of the more recent comments have changed my mind.

Even the flattest floor will manifest puddles so the question is, what's reasonable?. Honestly I've never heard of Brownbag's 1/8" in 20' standard. I don't even know where one would find a 20' straightedge. The old standard was to use a 10' straightedge. An 1/8" gap underneath was considered really good and 1/4" was considered acceptable for most uses. The reality is most residential slabs wouldn't meet either standard.

Today slabs are measured using different methodology based on Ff and Fl values. The slab is measured with a device that kinda looks like a roller blade and the result is determined by computer. Basically the Ff number measures the floors waviness and the Ll number measures the floor's overall levelness. Its a bit more complicated than that but that's the basic idea.

It's surprisingly difficult to achieve a perfectly flat slab and most residential contractors aren't very skilled at it. On the other hand, a perfectly flat slab isn't necessary in most applications. If you want your slab to drain, build in some pitch. Otherwise, be prepared to live with a few puddles.

 

[rburke65]

I’m sure there is a product that can be used to level out the low spots before you epoxy.

 

[Milzo]

There is a cement based product used in the vinyl flooring industry that is poured on and is self leveling. Once installed and set-up, it's ready for any type of floor covering, including epoxy coating, etc. I had it done in my long and narrow bathroom floor ten years ago and it's still perfect.

This is the stuff contractors use around here to level low spots https://www.ardexamericas.com/products/