Patio slabs mottling

Liverpool85

Hi, I was wondering if Anyone has experience of this?
 We had cheap basic 60x60 patio slabs laid (one a hardcore compact base, then concrete bedding each one, and silica sand brushed between the gaps) 

The slabs had a bit of an uneven colour at the beginning (March) but it’s more noticeable now. It’s on some slabs but not all. It’s not just around the edges or on circled like I’ve seen on some. It’s darker patches. Less noticeable when they are wet. 

Any idea why and what I could do to get rid of it? Or cover it? Is there anything? 

Our previous patio didn’t have such variations, though was a darker grey and more aged

thank you

FreeBear

It may well be efflorescence - Basically, salts in the concrete are coming to the surface when the ground is wet, and then drying to a white when the sun is out.

You could try some acidic brick cleaner - Read the instructions carefully, always add to cold water if diluting, never add water to the acid. Wear googles (or better still, a full face shield), rubber gloves (Marigold type) and old clothes that you don't mind getting ruined. Have a bucket of clean water to hand (optionally with a good dose of bicarbonate of soda mixed in). If you splash any acid on bare skin, douse it with the cold/clean water immediately.

Try cleaning a small spot in a hidden corner first, just to see what difference it makes. Scrub the surface with a stiff brush, then hose down. Leave to dry before making a decision.

Liverpool85

Thank you. It seems to be more darker bits on light rather than white bits, but I do wonder yes if it could still be effervescence. There seems to be no pattern to it, they were laid over a few days and all areas are similarly effected. I wonder if it’ll look different if we get a long hot spell

Liverpool85

To be fair just looking at the slab online makes me wonder if my expectations are just too high and it was always going to look like this. I just look at other simple concrete patios and they don’t all look like this

stuart45

Looks like trowel burning. Effloresance is usually white, although there other colours. Cheap slabs are less likely to have an even colour.
Acid does attack OPC products, so if you do ever use it soak the slabs first.

EssexExile

Liverpool85 said:

To be fair just looking at the slab online makes me wonder if my expectations are just too high and it was always going to look like this. I just look at other simple concrete patios and they don’t all look like this

I think you're right there. Give them a couple of years and they'll be fine.

Rosa_Damascena

stuart45 said:

Looks like trowel burning. Effloresance is usually white, although there other colours. Cheap slabs are less likely to have an even colour.
Acid does attack OPC products, so if you do ever use it soak the slabs first.

Trowel burning? Implying the wrong equipment was used when installing?

stuart45

Rosa_Damascena said:

stuart45 said:

Looks like trowel burning. Effloresance is usually white, although there other colours. Cheap slabs are less likely to have an even colour.
Acid does attack OPC products, so if you do ever use it soak the slabs first.

Trowel burning? Implying the wrong equipment was used when installing?

It's not the installers fault, as the slabs are like that when they arrive on site.
Trowel burning is when a steel trowel is rubbed over the concrete when it's a bit too dry causing darker patches on it. You get the same on brickwork in the mortar joints when the metal jointer is used on the joints a bit late and the mortar turns black.
There are other reasons for dark patches on concrete such as more water in one mix than the others. Most people in this country aren't too fussy with concrete work, compared to the USA where concrete finishing is a 3 year apprenticeship.
The slabs also look like they're got chatter marks on them, which is the sign of poor trowel work. 
It depends how the slabs were made. Many are made with hydraulic press machinery, but there are smaller firms with less sophisticated equipment.

twopenny

If they are reconstituted doesn't it depend what from?

And mixing more than one type/colour or remixing ground down is going to have marks and shading I'd have thought.

"Concrete, or reconstituted stone paving, is formed by moulding a mix of stone, sand, cement and water before being left to cure."

It's not the current trend for smoothed to within an inch of it's life and all the same shade but I then it costs a tiny fraction of some stuff.

I think with some terracotta pots filled with colour, some garden furniture and it would look just fine. A bit of imagination needed. Don't see it as a feature to be admired. Use it as a base for something beautiful.

Liverpool85

Thanks everyone some good thought. Reading through the reviews of those slabs I can see others have done the same patterns so I’m assuming it’s the slabs. We just wanted cheap and basic as the kids will be chalking on them and budget was limited.
I can see how they weather otherwise am looking at options for sealing or painting. Though with furniture and pots it may not bother me down the line as advised! 

Rosa_Damascena

stuart45 said:

Rosa_Damascena said:

stuart45 said:

Looks like trowel burning. Effloresance is usually white, although there other colours. Cheap slabs are less likely to have an even colour.
Acid does attack OPC products, so if you do ever use it soak the slabs first.

Trowel burning? Implying the wrong equipment was used when installing?

It's not the installers fault, as the slabs are like that when they arrive on site.
Trowel burning is when a steel trowel is rubbed over the concrete when it's a bit too dry causing darker patches on it. You get the same on brickwork in the mortar joints when the metal jointer is used on the joints a bit late and the mortar turns black.
There are other reasons for dark patches on concrete such as more water in one mix than the others. Most people in this country aren't too fussy with concrete work, compared to the USA where concrete finishing is a 3 year apprenticeship.
The slabs also look like they're got chatter marks on them, which is the sign of poor trowel work. 
It depends how the slabs were made. Many are made with hydraulic press machinery, but there are smaller firms with less sophisticated equipment.

Seriously? You could get a PhD in that time!!