Chalky concrete

[Bpoole]

Hey guys, first post

My name is Brock, I'm building a 24x36 detached garage to work on my projects. I'm into hot rods, custom cars and trucks, side by sides, etc. Really just anything cool and motorized..
But I come here for some guidance..I recently had some concrete poured. I'm having an issue with my concrete having a chalky dust keep coming up. I haven't put the building on yet. When we poured the concrete it rained about an hour after we got it floated out. The guys covered it in plastic. Then it rained for about 5 hours hard. The guys came back the next morning with a trial machine and used it to smooth it out . It looked pretty good. It's slick and smooth .just not real dark like it is burned in alot..it has a white color and stays chalky. I even pressure washed it and after it dried . I still get dust. What could be the issue. What can fix it short of replacing it all..I plan to do some type of floor "coating" or maybe stain it once the building goes up. Any guidance you can give will be greatly appreciated..

Thanks

 

[Bpoole]

Also it's a 3000 psi mix with fiber has a poly vapor barrier under the concrete.

 

[Shea]

With the vapor barrier underneath and all the rain, the mix may have been too wet. If so, the excess water rises to the top and carries all the fine particulates with it to the surface. This can make for a weaker top layer that dusts. Does the surface gouge very easily if you take a sharp screwdriver to it?

 

[ConCretin]

The dusting you are experiencing is the result of an elevated water cement ratio at the surface of your slab, which results in a weak chalky layer that abrades easily creating dust. The vapor barrier doesn't have anything to do with the issue but the 3000 psi mix is a little lean on cement, which didn't help.

You can try a chemical hardener to see if it helps but there isn't much else you can do short of grinding the weak top layer off or replacing the whole slab. It isn't a structural issue but it's very annoying.

The only thing that could have prevented this - short of avoiding the rain in the first place- was to cover the slab before the rain hit it. This can obviously interfere with finishing, which leads to a different set of problems.

Sorry you are having to deal with this Brock

 

[dogdog]

You are talking aboot these chalky things...? Just wash it off double anything you can do... my brick work have been 10 years almost... still chalky stuff on the surface occasionally.

https://www.concretenetwork.com/doug_bannister/efflorescence.htm

 

[Chris705]

LLWillysfan - would a good sealer densifier be an option here? What are the options for a hardner...trade names?

Bpoole- have you tried applying anything to the concrete surface yet?

 

[Bpoole]

Thanks for the replies. I haven't tried to put anything on it yet. It is easily scratched. The only thing did was pressure washed it. It is still chalky. It was covered before the big rain hit, but wasn't power troweled till the next day ( kinda late I think) . How deep is the chalky surface? I think that I'm going to have to sand it. Is there anything I can put on it to help harden the top coat that won't happen to interfere with with epoxy or stain. Also would anyone recommend stain over epoxy or vise versa?

 

[Bpoole]

Does anyone know if sanding the floor would help with chalky dust? Like using the walk behind concrete sander that Home Depot rents? I'm hoping to kill 2 birds with one stone by getting rid of the chalky surface and prep for floor coating. I'm at a standstill as of right now. My building should be here soon and would like to "fix" the floor before I get the building up.

 

[ConCretin]

You are talking aboot these chalky things...? Just wash it off double anything you can do... my brick work have been 10 years almost... still chalky stuff on the surface occasionally.

I don't think the OP is experiencing efflorescence, which results from soluble solids such as lime or salts being carried to the surface by water from within. While most common in masonry, it can occur in concrete but it's not the same as dusting.

LLWillysfan - would a good sealer densifier be an option here? What are the options for a hardner...trade names?

Others may disagree but I'm not convinced any of them are all that effective with dusting. Ashford Formula is a sealer, densifier and hardener and is often considered the class of the industry. Penetrating silicate liquid hardeners are thought to be effective but I can't recommend one in particular. A simple acrylic sealer won't do anything to harden the surface but it could seal the surface limiting the dusting and work as well as anything.

Does anyone know if sanding the floor would help with chalky dust? Like using the walk behind concrete sander that Home Depot rents? I'm hoping to kill 2 birds with one stone by getting rid of the chalky surface and prep for floor coating. I'm at a standstill as of right now. My building should be here soon and would like to "fix" the floor before I get the building up.

It's theoretically possible to mechanically remove the weak layer of concrete although it will be a LOT of grinding and will probably require heavier duty equipment than you can rent at the Home Depot. The question is whether you will be left with a surface finish you can live with. You might be able to remove enough to get by with a sealer or get an epoxy to adhere.


Dusting is a common and vexing problem. I wish I could offer better solutions but I'm just not aware of any.

 

[Chris705]

Brock - grinding the floor down to “solid” concrete might be an option, it would be costly and you’d need to find a floor grinding company to come look and quote you a price.Based on the size of the job it may be very difficult to find anyone interested in giving you a price. The grinders often need large amounts of electrical power, I believe a generator could be used if large electrical service isn’t available. This won’t be cheap! On the same magnitude of possibly removing the concrete & replacing.

You may want to experiment with a rented cup grinder in a small area to see if you can reach better appearing concrete before calling on a professional quote.

Or maybe try one of the sealer/densifiers and see how that performs before grinding. This route probably will not work well for epoxy. I believe only the full grinding will get you a surface suitable for epoxy. Grinding to a deep depth can however give you a nice looking floor suitable for a clear top seal or penetration sealer if you want to consider those options.

 

[Kaizen]

Go back to contractor. Hold off on building till it’s solved. It’s going to be a lot of work. Don’t start grinding. Get them out there to fix it


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[Armorpoxy]

We have seen many of these floors have dusting solved by using a sealer like our Armorpoxy Clear solvent based sealer. Inexpensive and super easy to apply. Two costs required.

 

[Bpoole]

Can I put regular epoxy over the sealer. Or is the sealer tintable? It looks chalky white.. I'd perfer to have a color if possible

 

[Armorpoxy]

You could stain the floor first with a concrete stain and then seal. We don’t offer to table stains by believe other companies may.


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[ConCretin]

If you are willing spend the time and money for epoxy, I'd go that route. Grind the floor to remove as much of the chalky layer as you can and then apply a good epoxy system. You'd probably want to grind the floor to prep for epoxy anyway although it might take a little more effort than normal. You just want a good surface for the epoxy to adhere to.

I wouldn't even think about stain. Most stain reacts with the concrete to create the color and I doubt you'd get a good result going over the surface you have. With regard to sealer, it would limit the dusting but you'd probably have to reapply periodically and you'd still have a weak surface layer that would abrade and scratch easily.

 

[Armorpoxy]

Another guaranteed not to fail and easy solution is to just cover over it with garage tiles like our www.supratile.com or other types. Fast, easy, can't fail!

 

[Bpoole]

Another guaranteed not to fail and easy solution is to just cover over it with garage tiles like our www.supratile.com or other types. Fast, easy, can't fail!

What would be the cost for 865sq ft.?

 

[TTnicksocal]

Sodium silicate dissolved in water (20-25%) is a great densifier that drives into the pores of the concrete and reacts with the cement to actually produce more cement in the pores of the concrete. Its commonly used in concrete floor hardening for industrial buildings. 2-3 coats without letting each coat fully dry should pack up the surface pores good. Any excess salt on the surface can be brushed with a broom and sprayed off with a hose.

I work in a research lab that makes stuccos and other cement based products. We use this solution when we have customers who applied their stucco in very hot weather and it flash dries without giving the cement proper time to hydrate resulting in weak and powdery stucco. The color of the stucco remains unchanged as long as there is no residual salts left on the surface.

You can find 50lb sacks of sodium silicate on Ebay

 

[DHC-2]

My concrete was like this when I bought my place. Drove me crazy for years. Was also pretty uneven, so I did drypack and self levelling, and then porcelain tile. I wish I had done it years ago. Hope you find an easier solution though.

 

[Bpoole]

Well guys i havent done much with my concrete floors yet. The holidays and the weather has slowed progress. But, while i was shopping online for Christmas gifts i did get a cheap concrete grinder wheel for my 4" angle grinder to test some things. I used it in a few spots to see if the loose chaulky surface was deep and hard it was going to remove. I did about four 1x1sq places at different spots. The grinder took very little effort, time, and no heavy pressure to remove the top layer. I used water to help with the dust and heat. It appears its only about a 1 or 2mm on the surface that needs to be removed to get to solid concrete. So the plan now is to sand the floor with a large sander and get it ready for coating. It did expose some of the rock in the concrete tho.

Does anyone know if the exposed rock would cause a problem? Im leaning towards a sealant for my floor coating. Id like to find a tintable sealant if possible. Maybe stain then a sealant? Im open to suggestions. Trying to stay economical as I can. I dont mind spending the money but im not made of it, just a blue collar guy that wants a nice shop. I plan on using rubber mats in the high traffic areas and the parking bays

 

[ConCretin]

Glad you are finding it manageable to remove the chalky surface. Exposing the aggregate is expected when you grind and shouldn't create any issues other than the appearance.

 

[Shea]

If you opt to stain you will need to apply a clear coating and not a penetrating sealer. Stain looks dull and lifeless until a clear coating is applied. It wets out the color and makes it pop. Applying a penetrating sealer won't do anything for the color since they are non film forming. A coat or two of a single-part polyurea coating would be a good choice and is very easy to apply.

 

[bighammer]

Interesting read. My garage did this after the pour and still does some 25 years later. Some areas have erroided away to a rough rocky layer. Been considering some product poured over it to refinish it or putting these plastic floor tiles down.