Sugar - lots of Sugar


Old 04-19-10, 12:13 PM
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Sugar - lots of Sugar

Hopefully I'm posting this in the correct forum!

We just had a concrete porch poured on the back of our house this weekend. We discussed with our contractor that we wanted the exposed aggregate look. He told us it would be a 2-day job: Day 1, dirt work and place forms; Day 2: lay down plastic vapor barrier and then cut/tie rebar -- pour concrete in the afternoon around 1:30. Everything went according to his plan except that after the concrete was poured it had a hard time drying - partly due to the lack of sun/heat because it was late in the day. Around 10pm they began the washing process to expose the pebbles. The concrete still looked extremely wet when they started the washing process although it was hard enough to walk on without doing too much damage to the surface. By midnight they had finished and said they would be back in the morning to wash some more. When we woke up it looked awful. The contractor told me that the plastic vapor barrier kept the concrete from drying quickly enough so when they started the washing process it didn't work right and too much concrete and pebble was removed. There is a massive amount of pebble in the yard all around the patio. The guy that delivered the concrete came by the next day and asked to look at it. When he saw it he told me he though the contractor might have ruined it because he covered the entire area with dry sugar. I estimate that he threw out, by hand, approx 8-10 1lb. bags of sugar on to the 1300 sq. ft. 4in thick slab.

Now - I don't know a thing about concrete. What I've read and heard from the guy who delivered the mix is that too much sugar can ruin the concrete - or at least make it so that it takes a long time to setup. I guess my question is, based on my description above, what can be done to make it look correct. There are some areas that look fine and have a nice distribution of the pebbles and then there are other areas that looked washed out - not to mention that there are splotches of light gray-white that almost look like salt stains - I guess they are actually sugar stains. Also, the surface is not uniform as there are channels or low spots where too much water pressure was applied and the concrete and rock is wash away.

Not sure what I'm asking really - maybe just more insight on whether or not the process of applying so much dry sugar could have ruined the concrete. We had thought maybe we could cap it with a 2" layer and re-do the wash process to get a uniform exposed look. The guy who delivered the mix suggested this might not be a good idea since the underlying 4" slap has so much sugar in it that it might never setup properly.

Thanks in advance for any input!
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Old 04-19-10, 01:48 PM
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Sugar will kill the cement hydration. Many contractors carry it in case some equipment of mixers break down and need easier cleaning.

In college, we used to add sugar to other students' mixes when they were mixing. The much lower strength it contsistant through-out the concrete when you look at the broken samples. - We also did the opposite when we put rebar in the sample cyliders, but the instructor was aware and did no let them run up the load on the testing machine. It was just a casual part of learning the real life and properties on concrete.

If it was hand cast the concentration is highly variable and that is why good contractors spray on the proper chemicals and wash the next morning.

The contractor probably ordered the wrong mix or added the water. The fact that the delivery driver showed up makes it obvious that he same some things that were not done professionally.

Your contractor was either wrong or was not a qualified real contractor.

Old 04-19-10, 01:56 PM
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A patch job is not the way to fix this. He needs to remove the entire slab, prep the area, and pour a new slab. Maybe the sugar will help him eat this one .

Old 04-19-10, 06:20 PM
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I've done exposed agg using sugar before, but it was a solution of sugar and water, or even molasses and water. It was sprayed evenly onto the surface and it worked great. Some of the commercially available surface retarders are little more than colored sugar water. I've never heard of anyone broadcasting dry sugar onto a slab though, and 10 lbs would be a LOT of sugar. Far more than he would have needed had he mixed and sprayed it. Out of curiosity, had he ever done exposed agg before? If not, he may have read or heard about the sugar and misunderstood the process.
From the way you describe the finished product, a complete tear-out and re-do is definitely in order.

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