gray spots on concrete

[Tiger Pressure Wash]

I see this every once and a while after cleaning a driveway.
What is it?

 

[Chris Dubbs]

Not sure, but a few I have done have that. To me it looked like old sealer remains.


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[snagtooth]

residual moisture maybe?? a denser spot maybe (you know how a hard troweled, smooth garage slab looks sometimes) usual a little darker than a broom finish.

 

[GrassButler]

My house looks like that too. ( more noticeable with polarized lenses )

 

[Rapid HotClean]

I think they're some sort of a fungus stain. I see them most often beneath deciduous trees.

These pics show pitch stains from Douglas Fir trees.

 

[Craig]

I see this every once and a while after cleaning a driveway.
What is it?

View attachment 27953 View attachment 27952

Magnesium staining. Very common and is usually all the way through the concrete.


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[Chris Dubbs]

Magnesium staining. Very common and is usually all the way through the concrete.


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What causes them Craig? Or are they there from the get go?


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[Craig]

What causes them Craig? Or are they there from the get go?


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They are just mineral staining that come up through the concrete. Either from the water that was used in the mix to begin with or moisture coming up through the concrete from the ground.


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[Chris Dubbs]

Good to know, thanks!


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[David Phillips]

Remember, although concrete is hard and durable, it is also extremely porous. Water and moisture can carry contaminates completely through the slab. Not only from the surface down, but also up from the soil or fill below. Always take the time to educate your customer on the importance of not only cleaning, but also protecting the substrate with proper sealer. It will add value to you and also your customer. This is true no matter if it is concrete, wood, stone, brick, pavers, etc.

 

[chrishartje]

Remember, although concrete is hard and durable, it is also extremely porous. Water and moisture can carry contaminates completely through the slab. Not only from the surface down, but also up from the soil or fill below. Always take the time to educate your customer on the importance of not only cleaning, but also protecting the substrate with proper sealer. It will add value to you and also your customer. This is true no matter if it is concrete, wood, stone, brick, pavers, etc.

Great post!


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[Craig]

Remember, although concrete is hard and durable, it is also extremely porous. Water and moisture can carry contaminates completely through the slab. Not only from the surface down, but also up from the soil or fill below. Always take the time to educate your customer on the importance of not only cleaning, but also protecting the substrate with proper sealer. It will add value to you and also your customer. This is true no matter if it is concrete, wood, stone, brick, pavers, etc.

Definitely, David. What kind of sealer would you recommend for most of these guys to use that wouldn't darken the concrete and still offer good protection?