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How to [not] patch your sidewalk.

July 19, 2011

Maybe a better way to phrase that is “WHEN to [not] patch your sidewalk”.

As a follow-up on our water main replacement project, it was our responsibility to replace/repair the concrete sidewalk. Our plumber included a quote to replace the concrete, but it was nearly $500 (for a 4’x5′ rectangle), and I decided that plumbers should be left to — plumbing, and I could do the concrete myself. I’ve done lots of small concrete projects in my lifetime.

After all, how hard could it be?

(Famous last words for any project at BAB…)

The water main replacement was on Friday, July 1st, and I decided to just dig in and complete the whole project on Sunday, July 3rd. I got to Lowe’s by 9:30am and bought a dozen 80-pound bags of concrete + a bag that had been busted open and put in a brown bag – it was half price and the Lowe’s guy said he had just bagged it and it was probably more like a bag-and-a-half.

Our plumber had over-filled the hole in the sidewalk when he was filling it with gravel; he probably just didn’t want to bother with taking any away from our site. So my first task was to remove the excess gravel so that I could end up with a 4″ thick slab of concrete.

Removing excess gravel

Just a shovel and a wheelbarrow was needed. Plus a level to put across the opening and then measure down to the gravel. (But some of you guessed

I would do that.) The bigger problem arose when I had a wheelbarrow full of gravel and no place to go. Should I throw it in the dumpster? No – I’d kick myself the next time we needed some gravel, plus not sure that that’s exactly allowed. Enter sub-project #1: secure a gravel container. I ended up with a reinforced cardboard box placed onto PTK’s handy little roll-around cart, and I wheeled-the-barrow around back to the dock to fill the box.

With no real tamper to tamp the gravel, I resorted to some of our heaviest sledge hammers, some small boards, and my feet, to pound down the gravel. Twenty minutes later and I was satisfied with it.

I checked the weather for the fourth time – there was a slight chance of rain around 4:00 in the afternoon. It was cloudy but I could see some blue skies.

The risk seemed low, so I gave myself a green light and it was time to mix some concrete.

First two bags of concrete mixed

I could only mix a couple of bags at a time – the concrete without water was 80 pounds (times two = 160) and I still needed to be able to easily mix it and move the mixture around.

So when it was fully mixed, I dumped it into the hole (though it didn’t really look like a hole now…). The I immediately started opening and mixing the next two bags, and poured it in when it was mixed.

Load #2 dropped down

My plan was to place two-bag pours at first to a level of 3″, and then add a final 1″ layer that shouldn’t take more than two pours (of two bags each).

It was right around the time I was cutting open the 5th bag that I realized I should have rented a concrete mixer. With one of those I could have poured the whole thing at once. Lesson learned. (Though a couple days ago I DID ask a few friends if they had a small mixer.)

Before each pour, I checked the weather on my phone. Forecast was the same – slight chance of showers at 4:00; but it was starting to get pretty cloudy though it was only around noon.

Another 160 pounds of dusty concrete mix goes into the wheelbarrow and within ten or fifteen minutes I had it dropped onto the sidewalk.

Fourth pour

And that’s when I felt the first drop of rain. I looked up and it didn’t look that bad. I could still see some tiny bits of blue between the dark gray clouds. Another check on accuweather, no change – so I needed to forge ahead.

Bags #9 and #10 went into the wheelbarrow, and just five minutes in the mixing, the sky opened up.

A steady hard sprinkle at first, but instead of quitting I grabbed a tarp and covered the wet concrete I’d already poured. The rain lightened up a bit about 10 minutes later and I got back to mixing the concrete in the wheelbarrow.

I had it thoroughly mixed and was about to pour it out when the rain turned into a thunderstorm.


I tarped the sidewalk again – picked up all of my tools, and moved the wheelbarrow full of at least 180 pounds of mixed concrete and rain.

I sat on the steps inside our covered foyer and just watched. Nothing else I could do.

Watching the concrete project wash away

You can see two important things in that last picture: the tarp collecting water and the wheelbarrow collecting water. At one point I found another tarp to cover the wheelbarrow, but by then it was too far diluted.

I threw in the towel shortly after – the rain wasn’t letting up – and though it was not even 1:00, accuweather still showed partly cloudy and slight chance of rain later in the day.

I lifted the tarp off the sidewalk and saw that rainwater was washing under the edge of the tarp and rinsing away the concrete I’d already dumped. Damn again. It was literally getting flooded.

The project was officially called wasted – in fact I needed to plan now how I could salvage what I could and make sure the sidewalk wouldn’t become an irreparable mess. So I scrambled to REMOVE some of the concrete already down so that I could pour at least an inch when it was time to fix this (most likely the following weekend.)

I shoveled at least a hundred pounds of soupy concrete mix from the sidewalk into the wheelbarrow. Only now – I couldn’t just go inside and take a shower, or I’d end up with a 250+ pound hunk of crappy concrete in the shape of a wheelbarrow, stuck inside of a wheelbarrow.

What to do with a wheelbarrow full of excess stuff? (Seems like I was here earlier in the day…) Would some of you dump it down the storm sewer? No – wasn’t gonna do that. What I decided was to use a bucket and scoop up a big glop of concrete and pour into giant dollops on pieces of cardboard, inside our building. That took me about ten trips. When they hardened I’d throw them away.

Time to call it quits – take a shower and forget about this concrete fiasco for a while.

A week later, time to finish it up – and the weather forecast had all sun with no clouds. But LOTS of heat and humidity – high 90’s and high humidity. Great.

Started early again – but now, the sun was beating down on this area intensely – after ten minutes of working there I thought I should rig a tarp up to create some shade. The B.A.T. (Big Ass Truck) just happened to be in a fortunate place so I took advantage and attached a tarp between it and the B.A.B.

Rigged up shade canopy

The day before, I hosed off the entire sidewalk area to prep the concrete and wash away debris. After careful inspection, it looked like there were areas of cement that had settled into dense powdery pools, most likely from the big rain a week ago.

I chiseled and scraped away the powdery parts and loosened anything that was willing to give way. The debris was so thick and accumulated so much that I went inside and grabbed the shop vac and vacuumed the sidewalk.

Last week's mess ready to be finished.

One thing I knew from… hmmm, either my professional experience or from previous concrete projects… was that you shouldn’t have separate concrete pours (where the first pour has had time to cure) WITHOUT adding some kind of bonding coating to help the new pour of concrete bind to the old concrete.

Concrete bonding adhesive - looks like glue

I’d purchased a bonding adhesive in advance, and there were several options for using it. I chose the direct-apply method with a brush – it had the most convenient “dry time” before pouring new concrete.

Bonding adhesive being painted on.

It wasn’t that hard to apply – but the key was to get it into all of the nooks and crannies without getting too thick. I think I used about half a bottle on this 20sf area.

While waiting for it to dry (took about 15 minutes) I got back to the task of mixing concrete.

Did I rent a mixer?

No – now I only had about 3 or 4 bags to mix so it didn’t make sense.

I figured I could pour this all in two batches – it was only about 1″ thick after all.

The first pour went smoothly – for a screed I was using a long 2×4 that I modified years ago when I laid brick pavers in the garage of our old house. It also made a good pour stop.

Hopefully second-to-last pour of concrete...

There was literally no chance of rain so I was in no hurry; I could take my time to make sure the fresh concrete was the same level as the surrounding sidewalk. The second pour (just a bag and a half) went down just as easily.

The next step was to screed the concrete level – I used the 2×4 and moved it back and forth – sorry np pictures – sometimes I get into the project too much and forget to document.

Once I was satisfied with the level or amount of concrete, I needed to wait a few minutes for the concrete to slightly set – then I could float the surface.

I had both a magnesium metal float and a wood float – and both were salvage finds. The wood float came from Bob Vavra’s metal workbench purchase, and the magnesium float was from an undocumented visit to the estate sale of the “Pig Man”, who was well known in Saint Louis.

But the right tool for this part of the job was to use the wood float – it would leave the surface of the concrete “rough” enough so that air bubbles could rise from below and create paths for excess water to rise to the surface and evaporate. (Had I used the magnesium float, it would have created a fine smooth surface that would prevent the air/water evaporation, better for indoor concrete finishes.)

Wood float used to smooth the surface.

After the concrete had set up some more, it was time to use the concrete “edger” to round the edges and create the typical “smooth” flat border. Rounding the edge of the fresh concrete helps prevent it from chipping too.

It was fairly simple – just took some careful control and patience.

Edging tool smoothes the edges

Though I am seriously bummed that I had to buy this tool NEW, when just a few weeks ago, at the Pig Man estate sale, I passed up a concrete edger for two dollars.

So once the edging was done, you could call the concrete patch complete. And it would look fine if it was either all by itself or was in a field of recently poured concrete. (“Recently”, being relative, means about 20 years in this situation.)

Sidewalk patch complete - for most people...

But most of the surrounding sidewalk had some level of exposed aggregate. Aggregate (little rocks or pebbles) in concrete can become exposed over time from years of abrasion and rainwater, as well as acid rain. But there’s a way to cheat time and expose the aggregate in fresh concrete immediately.

Which is what I decided to do.

So after a couple of hours the concrete had set up enough that I could lightly run a broom over the concrete, and at the same time put a light spray of water on the concrete. This would dissolve the lighter cement particles but leave the tiny pieces of rock/stone embedded in the concrete below. I could then lightly hose the fine cement & sandy paste away.

New concrete with exposed aggregate

In addition to the utilities marks spray-painted on the sidewalks, it looks like there are some moldy and dirty areas surrounding the new patch. We are hoping that within the next few months we can borrow someone’s power washer and take care of ALL of the concrete stains in front of our BAB.

6 Comments leave one →
  1. Patrice Petrich permalink
    July 30, 2011 11:17 pm

    I have a power washer and tamper if you need for your next project.

  2. rick permalink
    July 20, 2011 3:10 pm

    Next time I need concrete work done I’ll call you.
    Looks good. sorry it took you so long to get it done.

  3. Darcy permalink
    July 20, 2011 8:59 am

    Beautiful job, Tom! Not sure if it’s worthy of a blog post, but I sure would like to know more about “Pig Man”….

  4. Dan Conery permalink
    July 20, 2011 4:10 am

    I feel you pain around the concrete setting in your wheelbarrow. I did fire hydrant replacement work for a couple of summers while in college. I had just picked up 2 yards of concrete and one the way back to the job site managed to burn out the clutch in the truck. By the time the tow truck came and picked me up and got the truck back to the yard it concrete had set. Spent the better part of the next day with a jack hammer in the back of a truck. Must have been a funny sight for everyone but me 🙂

    • Tom permalink*
      July 20, 2011 11:37 pm

      Yikes! That’s probably one of those never-will-forget events for your entire life.

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