Matching Exposed Aggregates

Exposed Aggregate Concrete

As with most entries I make on this website in regards to concrete and contracting, they generally come about through my day to day experiences with projects and clients expectations.

One topic that comes up more often than not, are clients wanting to match their existing exposed aggregate concrete that they already have placed, with the new exposed aggregate concrete being placed.

It is correct to consider exposed aggregate stones in the same relative category as decorative resurfacing colours and colours for your colour through concrete. It is a natural product that is not calculated to precise measurements during mixing at the plant. Quite literally, the aggregates are mixed with the concrete by machinery and conveyor belts typically by weight, meaning, that no two loads of exposed aggregate will be exactly the same.

In saying this, you can trust (on most occasions), that when pouring a driveway for instance, where two or more truck loads of concrete are required, that the multiple loads supplied on that same day will be close enough to a match together that it is unnoticeable to both client and contractor. However, I have come across the rare occasion where we have poured a selected exposed aggregate, only to return a week later to pour the remaining part of the job, (with of course the same selection of stone), and have it look different enough that it was noticeable. The project itself still looked fantastic as a whole, but the blending of stone was different.

Now this is all well and good when we are talking about a singular project that we are completing at a given time. Even with a difference coming through, because the two parts of concrete are poured within a given time frame, along with being supplied by the same company, there isn’t a problem at all.

From here though is where we enter the problematic area. Lets say for instance you as the client, have had your exposed aggregate poured previously, for sake of conversation lets say it was 12 months ago. Now you are after some new exposed aggregate to be poured adjoining the existing slab. You’ve done the right thing, remembered who the company was supplying the stone and exactly what it is called, even with these measures in place, there is absolutely not guarantee that your new stone will be the same blended mix as the one that was poured a year ago.

Also you need to take into consideration the after a few months, concrete starts to build up dirt and mold in the actual cement, which typically starts to darken you cement within the concrete (seen between the stones). Then when we place the new exposed aggregate concrete, as normal, when cured it comes out a very white, bright colour. This will make the two sections of concrete appear different overall when looking at them together. This aspect of course will get better over time as the new concrete starts to get dirty and mold as well, so time is your friend in this case.

Now we get to the really tricky part. You’ve had your concrete poured a year ago and you’ve forgotten what company supplied it and what it’s name was…..This side of things is considered a bridge too far with matching. Yes, you can have your contractor look over your concrete and advise you what he/she thinks is the “best match”, you can also have a sales rep come out to site to also advise you on their thoughts, but at the end of the day it is a calculated guess and more often than not will be a wrong guess.

Our exposed aggregate concrete we supply comes in sections separated sometimes by 10%. For example, “Dalmation” (Salt and Pepper), concrete starts at 10% white stone and goes up in 10% intervals right up to 90%. So if we’re trying to match your existing “Dalmation” concrete and you can’t remember what percentage it was, we are basically then taking a guess at the problem. It might not sound much only being out by 20% of the white stone mix, but this will make the difference stand out dramatically when the two concrete’s are next to each other.

With all this said, I guess at the end of the day if you follow a few simple guidelines you can at least be assured that the best efforts are made to match your concrete…..

  1. Write down the name of the concrete exactly when you have it poured
  2. Write down the supplying company of your concrete
  3. If possible, try and complete all exposed aggregate at the same time

If you haven’t or couldn’t do these three steps…..

  1. Contact sales rep and contractor for their advice with samples
  2. Understand that the two concretes will look different
  3. Or….Choose a different aggregate to try and contrast rather than matching

Be reasonable with your expectations. We are dealing with natural products that are not mixed like paint through a computer, there is always room for error when matching these natural products and as with all colour and stone options, typically, the contractor should not have to take any responsibility for variations in these products.

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