Exposed Aggregate - excess salt.

[Vili]

Hi all, I'm after a bit of advice/combined concrete knowledge. I've just had my driveway concreted. 8 cubic metres layed, dark grey/brown/black exposed aggregate. During the curing period, it became obvious that there was a significant salt/efflorescence issue. To make matters worse, the concrete was delivered in 2 loads and the first load is the only area that is affected. Now this is where I'm guessing because my chemistry knowledge doesn't go much further than burning stuff with the bunson burner in yr 9, however, I do believe that salt makes things dry faster. This would explain why the 2 serperate loads have very different levels of exposure ie contractor was unable to blow the top off the 1st load (no sexual puns intended). So not only do I have extreme salt staining (unable to be washed out even with acid wash) on the 1st load, it also has a relative smooth finish and less aggregate exposed. The supplier has tried telling me that it's the contractor's fault, however they can't offer any explanation as to why he only stuffed the first load, when the whole lot was layed and treated at the same time in the same manner. Any advice as to 'what to do next before legal action' would be greatly appreciated.

[Exador]

Hi all, I'm after a bit of advice/combined concrete knowledge. I've just had my driveway concreted. 8 cubic metres layed, dark grey/brown/black exposed aggregate. During the curing period, it became obvious that there was a significant salt/efflorescence issue. To make matters worse, the concrete was delivered in 2 loads and the first load is the only area that is affected. Now this is where I'm guessing because my chemistry knowledge doesn't go much further than burning stuff with the bunson burner in yr 9, however, I do believe that salt makes things dry faster. This would explain why the 2 serperate loads have very different levels of exposure ie contractor was unable to blow the top off the 1st load (no sexual puns intended). So not only do I have extreme salt staining (unable to be washed out even with acid wash) on the 1st load, it also has a relative smooth finish and less aggregate exposed. The supplier has tried telling me that it's the contractor's fault, however they can't offer any explanation as to why he only stuffed the first load, when the whole lot was layed and treated at the same time in the same manner. Any advice as to 'what to do next before legal action' would be greatly appreciated.

The first question is "how much do you want to spend?" The process of proving fault may well be significantly more expensive than the slab! The manufacturer will have good QA records on all raw materials, including sand and aggregate, although there is no guarantee that any particular load of sand has been tested, and they will also have batching records. That means that the onus of proof is on you to show that the product that was supplied was faulty. The first step is to have an independent engineer arrange for some samples to be taken from your slab (this will leave holes of at least 12mm, probably nearer to 25mm, from both the dodgy and good parts of the slab and may require some compressive strength samples which would be at least 50mm diameter, probably nearer to 100mm. That means that you will have damage that can at best be disguised, regardless of the outcome of any litigation. Even after the samples are taken, you must then have them tested for all chemical properties, including sulphate and chloride content and you may have other issues such as faulty cement (inadequately slaked lime is an immediate candidate) that the test will not show up. You would also need to sample the sand that the slab was laid on to ensure that it was not the source of the contamination.

Sad as it may be, if the concretor is denying liability and the concrete supplier is standing on its digs, you probably have very little redress available.

[Terry1]

Hello Vili,I agree with Craig on this problem.I don't know about your area but here in Wagga the town is still small enough to engage tradesmen that you know personally and usually that means that if something goes wrong someone will fix it (myself included,I'm a bricklayer)But having said that I recently waited for twelve months for a concretor to accept that he would have to cut up and replace half a front driveway that was done in exposed agg.It was a big job but he also owns a diamond wet cutting service here and they had it out (bobcat)carted away and prepared on the first day and then repoured the next morning.But he did (after some debating)admit to responsibility for the rough work and of course that is the key to your problem ,no-one is taking the blame.I don't know how they couldn't pressure wash the agg unless they mistimed the procedure, it does seem a bit unusual to me.I wonder if fair trading would have a look at it as they do here.That would be a very last resort in the rural areas but maybe not down your way .
Regards
Terry

[julianx]

Could you post some pictures, not that I could help, but some one else here might.

[Vili]

Thanks for the replies guys. The supplier(largest in Australia, no names mentioned) came and saw the driveway 2 weeks ago an said they would send me the batch reports for the two loads the next day, as even they were surprised at the amount of efflorescence. 2 weeks later, many unreturned phone calls, no batch reports, I'm thinking they might have a problem.
At the moment I have half a driveway that is perfect, and half that is not. The base material from top to bottom of drive is the same(crushed rock), so if that was the culprit, you'd think it would affect the entire area, not just the first load. As for the contractor, I trust that he did everything he could to get more exposure on the 1st load without causing further damage. I was home during the entire process and watched as he initially treated the entire area the same. Exposing chemical was left on overnight, then the top blown off the next day with petrol gerni. After the initial acid wash, the true extent of the problem revealed itself. Further acid washing did nothing except start to affect the good part. A bit more acid on select test spots and pressure cleaning has been like trying to wipe off poo with teflon tape. Oh well, could be time to put on the boxing gloves. Your advice is appreciated.

Vili.

[Vili]

I have photos, just working out how to put them on.
Vili.

[Vili]

So here's a piccy of the drive. The steep section is the unaffected area, and just also happens to be the second load. Run off of the treating chemical has been ruled out as the there are sections of the first load(spoon drain) were pooling would occur if it did occur. The symptoms are even, right across the entire 1 st load of concrete.

Vili.

[Exador]

Thanks for the replies guys. The supplier(largest in Australia, no names mentioned) came and saw the driveway 2 weeks ago an said they would send me the batch reports for the two loads the next day, as even they were surprised at the amount of efflorescence. 2 weeks later, many unreturned phone calls, no batch reports, I'm thinking they might have a problem.

Having thought a bit more about it, I'd be seeking release of those batch reports. The most likely scenario that I can come up with is that you were supplied with an excessively strong mix. An N32 brew should reach 25 MPa overnight and there ain't no way you're going to wash that off with a gerni. Did your concretor specify that it was to have an exposed agg finish? If not, the dispatcher may have sent you a batch that was cancelled from somewhere else or simply made a mistake in batching the cement, realised it was over and figured he was doing you a favour! On that note, it would be worth checking batching and delivery times on your docket. I can't explain the efflorescence with that scenario, though, so I suspect that it's a different issue altogether. I can't tell much from your photo. Would it be possible to get a close-up of some of the worst patches?

[Terry1]

Hello Vili,Im just wondering what are the concrete supplier saying when they are blaming the concretor.(your first post)The whole process of placing and exposing the concrete seems to be a bit different here than what you are describing .I'm on my way to work now but will have a think about it later.
Regards
Terry

[Exador]

Hello Vili,Im just wondering what are the concrete supplier saying when they are blaming the concretor.(your first post)The whole process of placing and exposing the concrete seems to be a bit different here than what you are describing .I'm on my way to work now but will have a think about it later.
Regards
Terry

I agree, Terry. Up here, exposed agg is broomed off as soon as the slab has become firm enough to walk on, pretty much. Down in the cold country that could be a bit different, of course, but I've never had anything to do with that sort of finish down that way. Just as an aside, I ran all the testing on the Tarcutta Range section of the Hume (including the Wagga turn-off) and the Kilgowlah section, just south of Tarcutta. Lived at Adelong for a year. it's a very pretty part of the world.

[Vili]

Here are the close ups. No need to tell you which one is which. The difference in textures is even across both loads. At the time of pouring, 2nd truck pulled in as the other one pulled out, so there was no issue in relation to the 1st load having longer to set. From the aggregate that is exposed in the 1st load, you can see that its the same stuff. The cement/sand mix though has to be questionable.





Vili.

[kpp]

Looks like an inconsistent exposure of the concrete.

What retarder (chemical) did your installer use?

We are about to load our new exposed aggregate concrete website and one of the information pieces you'll be able to download is our Best Practice Placement Guide. Essentially this is a quality system for laying exposed aggregate concrete written for the consumer with loads of photos.

The exposed aggregate website should be up in the next couple of weeks -
http://www.concretewa.com.au

[tman]

when doing the method of exposed agg where it is washed off the next day, the timing when spraying the chemical is critical. as the chemical stops the cement from going off, if hit to early the mix will over expose and blow outs can occur, to late and it wont expose enough.
i would say the first load had dried to much befroe the chemical was applied.

also, has the driveway been sealed, this may take away the white patches..