Feb 19, 2011 3:27 pm
G'day all, first time viewer, first time poster. The wonders of Google in the time of need! Great thread folks, good work to whomever created it!
Just some background, prior to commencing works here at my house in the Northern suburbs of Adelaide, I contacted many concreters, requested many quotes and asked mates in both the know who was reputable in the local area. I only had two requests of them all, the job had to be 25mpa concrete and a minimum of 72 mesh. After many frustrating weeks sorting through quotes and listening to recommendations we went with a company who have a 20 + year rep in the local area. Not only that, this company was also pretty cheap in comparison to many! So we went with our gut for the 160Sq/m pour (20m driveway, paths and pergola area).
Soil here in the local area is clay, the stuff sticks to everything like the proverbial to a fan. That said, old mate and his trusty crew arrived 10 minutes early, good sign and proceeded to box and reo the job site. Boss said they'd be back in a week to commence the pour in three stages that would take about a week to complete. Had a look at the reo and the boxing and was pretty happy, although I was a little worried there was no plastic under the reo. (concern number one, question number one: Should plastic be used under concrete?)
Day one of the pour, ol' mate and his trusty sidekicks turn up 10 minutes early, which was awesome, I like punctuality, something that you don't see a lot of these days. Truck turns up half an hour later and they begin the pour. Quite happy that my concrete is finally getting laid, I watch and learn and keep my mouth shut watching as my 1.5x 15m slab gets poured. Concrete truck guy adds no water (was watching him as I'd heard this was bad juju in large doses) to the mix and was quite chatty and told me that the company that I'd chosen had a great rep and had been around longer than he recalls. Another good feel to the day, the gut feeling must have been good this time (not always the case). Day one concludes with a nice looking slab, no issues.
Day two, had to go to work and leave friends at my house to allow access to the contractors, again turned up early, prepped everything and watched as they hosed water over the reo and underlying clay base. (The base was laser levelled by another mate with a bobcat prior to the reo and boxing). Watched them string line an appropriate fall into the boxing and place plastic hats under the reo before I left. When I got home the job had been completed, looked awesome, was really happy. (question one still applies to this, pergola area was 6x9m, no plastic under the reo).
Final day (Friday), again, had to work, friends at home to allow access, ol mate and crew arrive early - day was going to hit 35 deg at 1:00 o'clock, weekend was going to be a scorcher 43. Got home, whole job looked bloody fantastic, had no issues. Spent the next few days lightly misting the job in its entirety as I'd read that concrete needs hydradtion to cure, I tried to pool water around the whole job, keeping the ground moist, whilst misting water over the slabs.
About two weeks later, I noticed there were a few dog prints on the concrete and decided to hose (not jet blast) the area, clean it up a little. everything went well until a quarter of the way through I broke through the concrete surface and noticed a piece of aggregate covered in what looked like dry sand/dry clay. Quite ** off about my perfect looking pergola slab now had an imperfection, I continued on with attitude. By the time I finished hosing, a total of 10 pockmarks had appeared, all the same as before, all no bigger than a five cent piece in diameter.
Called the concreter who came out the next day, didn't get upset, just asked him why this happened and how can this be rectified. He told me that there were two scenarios to this quandary. One, that prior to screeding and trowling someone must have walked clay into the job and trowled it over, and second, that the concrete provider has failed to wash the agg properly, resulting in contamination. He told me that he's only seen this happen 3 times in 20 + years he's been in the job. He also told me he could patch the issues and within a few weeks to a month we'd not notice the repairs, however told me to wait two weeks before he came back, just in case any more appeared. If so he'd then get the concrete company involved to try to work out why this occurred...
It's been three weeks since he's been here, 5 weeks since the job's been completed. I now have about thirty pockmarks in all three areas (all separate pours), the worst is in a section of 3x3m where there's about 15 pockmarks (scaling) in a highly visible area of our pergola. On three separate pours, the pockmarks appear on all slabs, 5 on the driveway, 2 on the first pour and the majority on the pergola. The backyard and all job sites were exposed clay, no crushed rock, blue-metal or sand anywhere. I've also noticed a rather long (1m) fine stress looking crack on the corner of a path. Not overly concerned about a stress crack, so long as it doesn't get any wider.
Also, when I wet the concrete, when wet it looks marbled, what looks like tiny cracks all over the entire surface, yet when dry, apart from the pockmarks, looks fantastic.
As much as I tried to do the right thing in respect to after-care, is there anything in your opinion that should have happened that either he, or I for that matter, could have controlled?
a. Should plastic have been used under the mesh/reo? This was a 160sq/m job
b. Can clay be walked into a job and contaminate the concrete? If so, he should have known this right?
c. How common is this condition?,
d. Will this get worse over time?
d. if I have these areas patched, what's the likelihood they're going to pop again? and will the repairs be noticeable?
Thanks for your time, I'm really concerned this is going to work out badly. Any advice you can offer, including how this should be repaired (product advice) is very much appreciated.
BTW, the contractor has been bloody awesome, couldn't and wont fault him yet. All round nice guy, his employees worked like Trojans, were courteous and well mannered (no swearing) and punctual, which in today's climate is a hard thing to find.
Re: New concrete pockmarked2
Feb 19, 2011 4:34 pm
A. depends. its good to have it, not always necessary tho. A layer of crushed metal or sand should have been used.
B. yes. more so if no sand or gravel base was used.
C. ive seen it once. not to the that extent tho.
D. sounds to me like it couldn't get any worse.
E. depends how well they are fixed up to begin with. I think you will always notice them.
The tiny cracks are called crazing, its normal and happens to all concrete.
If it was unwashed aggregate your case will not be isolated, all concrete placed from that plant during that period should have the same problem. Just got to find out what other jobs were done. Your contractor should be able to chase that up.
Re: New concrete pockmarked3
Feb 26, 2011 11:26 pm
I've seen driveways poured right onto clay and it amazes and confuses me. I thought that concrete should always be poured onto a thick bed of compacted sharp rock. I remember watching as a child - the bottom of the bed should be large broken rocks, followed by medium sized rocks, and finally smaller size rocks. Then the concrete. Perhaps a different building practice
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