Sunday, November 6, 2011

Making the abstract concrete

In case you couldn't tell, I'm seldom impulsive.  I view pouring concrete as a fairly permanent action that one undertakes only after one is sure he won't want to reverse that action.  Since I've got several conduits under this section of sidewalk that was removed three years ago, I've been hesitant to bury them "permanently" until I was sure everything was installed in this area that we intend to install.  The inconvenience of not having this section of sidewalk finally outweighed my reluctance to commit to concrete.

There was some uncertainty in calculating the depth of the section, so I figured I might need slightly more than a half yard of cement.  I purchased thirty bags of mix and hoped I'd have a few left over.  Did I mention I've never done concrete finishing before?  I've seen others do it, but I definitely don't have "the touch" that would have made this job much less stressful.  However, none of those facts prevent an engineer like myself from believing he is capable of accomplishing just about anything.

Most of the internet advice I read recommended a motorized mixer for this much cement, but the hand mixing went a little faster than I anticipated, and wasn't as tiring as I feared.  As you can see in this image of the partially poured section, I was able to level and semi-finish the cement as I went along.  My goal was to match the exposed aggregate finish of the original concrete, so I wasn't too concerned about a perfectly smooth finish since it would be removed eventually to expose the gravel underneath.

Here's a shot after all the cement is poured and the finishing is almost complete.  The original concrete was treated with a retardant to make it easier to uniformly remove the top surface, so I did the same.  The retardant simply slows the curing of the concrete on the surface to which it's applied, and its depth of penetration is inversely proportional to the amount of time the concrete is allowed to set before the retardant is applied.  In my case, there was a significant time difference between when the concrete next to the building was poured compared to the last bit by the yard.  Since I'd been warned not to apply the retardant too early, I applied it in sections starting at the house so the section nearest the yard could set a bit before it was exposed to the retardant.  Even so, I think I should have waited longer.

Unfortunately, I don't have photos of the removal of the top layer.  After waiting a couple hours, I used a light spray of water and a plastic brush to gingerly remove the concrete while trying not to disturb the gravel underneath.  It didn't take long before I brushed too hard in one spot and removed more gravel than I desired.  Having learned that lesson, I tried to be more careful on the remaining areas and felt pretty good about the result.  Twenty four hours later, I used a light spray of water to rinse off the gravel that was no longer attached to the concrete and gradually increased the intensity of the spray to do a more vigorous cleaning.  Mistake.  The retardant was evidently still effective on some of the later concrete, so the water jet created a few more pock marks where the exposed aggregate had been curing nicely.  Even after reading several warnings not to be too aggressive in removing the concrete, I had to learn the hard way how aggressive was too aggressive.

A couple weeks later, the concrete was ready for cleaning and sealing.  Instead of muriatic acid, I used Krud Kutter Concrete Clean & Etch which is supposed to be a safer cleaning alternative.  I found the product cleaned the new concrete well after I learned to rinse the concrete quickly after cleaning.  The photo above shows the sealing process in progress using a lacquer-based semi-gloss sealant.

I don't know how critical it was to seal the concrete before winter, but the original concrete had been sealed soon after it was poured, so I tried to follow suit.  In the end, the finished product is not as perfect as I hoped, but it is functional, and looks pretty good from about 100 feet.


  1. What a job! We had a professional do some concrete work for us a few years back and with more than 30 years experience he still ended up with a hairline crack in the cement. I'd say you did very well for your first time out.


  2. Thanks Victoria. I'm still learning to keep my expectations low since I seem to find countless opportunities to learn humility.

  3. That sidewalk, my friend, is a thing of beauty and I'm sure it will be a joy forever:)

  4. Thanks Diane. I'd be content if it refrained from being a thorn in my side as long as I live here...

  5. We are VERY impressed Kurt! Is there nothing you can't do? :)
    Congratulations on a job well done!
    PS: Doug would like to pour a basketball court for kids...He wondered if you would do the mixin', he said he would do the pourin'. :)
    Do you hire out? :)

  6. Thanks Whitakers. Let's see, his basketball court would probably require about 35 times more concrete than I mixed for this job. That means we'll have to keep at it for about three and a half days including meals and sleep. I suggest we just call a big truck and I'll do BOTH the mixing and pouring while Doug does the finishing.