Exposed aggregate concrete

[EmilyH]

Have you any experience of insitu concrete slab with washed to expose aggregate finish? We want to pour a concrete slab of cheap aggregate with a surface pour of decorative aggregate, and are generally concerned regarding the feasibility of doing this over a large area (5m wide pathway). ie. how is the surface pour spread without disrupting the base slab? I'd be very grateful if you could tell me of some examples of where this has been successfully done so we might go through the process with the contractor?
Thank you, Emily

[Tony McC]

You'll have noticed that I moved your post - don't post questions to the Site Agent's Office: that's purely for admin issues!

I was involved in a very successful in-situ exposed aggregate project covering over 2,000m² about 3 years ago. See the Exposed Aggs page.

[EmilyH]

I looked at your very detailed explanation of achieving exposed aggregate concrete - but have you ever poured such a large area as a two-layer construction which achieves a monolithic slab?

[Tony McC]

From memory, the largest area we covered using a face-mix type method was around 200m² on a driveway near Chester about 15 years ago. The agg that was exposed was quite expensive - around 230 quid per tonne, ISTR - so we placed a C30 ready-mix as a 100mm base and then immediately topped off with 25mm of site-mixed concrete using the expensive agg and washed off later the same day or first thing the following morning for early evening pours.

I can't recall any major problems. The base mix was placed as per normal, vibrated and rough-tamped, and then the face mix was spread, levelled, lightly tamped (but not vibrated) and floated smooth there and then.

I last saw the surface when it was around 6 months old and it seemed fine. I was never called back, so I assume all went well!