Efflorescence and some botched repair efforts left an ugly floor.
Efflorescence and some botched repair efforts left an ugly floor.

Doesn't everyone have a part of their home that should look great but that, due to some fatal flaw, only serves as a reminder of lost potential? Ten years ago, when my wife and I built our home, we wanted an integrally colored concrete floor slab with radiant heat pipes embedded for the first floor. This 700-square-foot floor includes two bedrooms, a hallway, and a bathroom. Despite what I thought was good advance planning, the floor turned out less than perfect.

We specified the mix design, including synthetic fibers to control plastic shrinkage cracking, and even arranged to have the local Soff-Cut representative come in to cut the contraction joints. We also got some curing agent from the color manufacturer to make sure the surface would be well cured.

The first stage of the polishing effort involved hand grinding the edges with rough metal and diamond wheels. Note that Thomas is kneeling on a back-saving Racatac rolling work cart for the hand work.
The first stage of the polishing effort involved hand grinding the edges with rough metal and diamond wheels. Note that Thomas is kneeling on a back-saving Racatac rolling work cart for the hand work.

The first bad news came when I talked with the Soff-Cut rep and mentioned that we had in-slab heating tubes. He decided that he shouldn't cut the joints, since he might nick a tube. The finishers would have to tool the joints.

The concrete arrived on a hot dry Colorado day and set up rather quickly in the warm weather. While I was talking with the foreman about applying the curing membrane, others were deciding where the joints should be, intending that, in all but a few spots crossing door thresholds, the joints would end up under a wall. Someone decided that one of the joints should jog to stay beneath walls, creating a discontinuous joint that ended up exposed and likely to crack at the tees.

The early stages of grinding created a significant quantity of slurry.
The early stages of grinding created a significant quantity of slurry.

In the meantime, I was after the finishers to apply the cure & seal. They refused, saying they don't like to put curing agent on colored concrete. They finally just gave me their old beat up sprayer so I could apply the curing membrane myself. As I attempted to spray on the cure & seal, I found it difficult to control. First I got too much, creating little puddles, then the sprayer completely clogged. Eventually the pooled areas turned into milky spots and the uncured portions developed plastic shrinkage cracks.

We were left with a floor that looked OK in some spots but very bad in others, with milky spots, efflorescence, and wide, rough joints. Another problem was that the very rough top of the footing was visible for 4 inches at the edge in several areas along outside walls.


Over the intervening 10 years, we made several attempts to repair the floor. We tried a very toxic stripper to take off the cure & seal, but it only led to ugly splotches. I got a small hand-held scabbling tool that was ineffective on the sealer. We even got some acrylic stain—basically paint—and tested that in one area. None of these solutions was satisfactory and therefore we lived unhappily with the ugly floor.

Then a few years ago I began seeing polished concrete floors. This looked like the answer. On the advice of Tim Fisher, a former Concrete Construction editor who now runs his own decorative concrete business in Boulder, I contacted Shawn Weaver with Marblelife of Colorado. He quoted $3000 to polish the bedrooms and hallway and another $1000 for the very tight bathroom—we opted to skip the bathroom, since that part of the floor looked pretty good.


We cleared the rooms and removed all of the wooden baseboard trim. Marblelife's crew—Richard and Thomas—arrived promptly on the scheduled morning. After protecting the walls and the door jambs, they began with metal-bond diamond wheels to “clean up the concrete,” said Weaver. “We were taking the first layer off, the old coating and laitance, and getting down to new material. Once we have made the initial impact, it's all about increasing the grit so that you get the scratch pattern out, then going to the next and the next until you get to a very fine scratch that you can't see with the naked eye.”

After the first true 120-grit polishing pass, they applied RetroPlate to densify the surface. RetroPlate is a sodium silicate surface densifier available only to licensed applicators. “We also applied a spiff coat,” said Weaver. “A lot of people don't do the spiff coat, but we're pretty firm believers in getting a thin layer of RetroPlate on the surface—it makes the floor wear better.”

The next day, Richard and Thomas returned and in a series of polishing operations brought the floor up to an 1800-grit finish. The final routine was a three-step process using a chemical they called an interstage hardener, followed by a finish perfector burnished with #1 steel wool, followed by another pass with the interstage hardener.

When I looked over the floor, though, I was distressed to find several spots that still looked a bit milky—although I hadn't expected perfection, this seemed unacceptable. A call to Weaver brought him to the jobsite to reassure me that they would fix it. Although he wouldn't tell me exactly what they did—trade secret—Weaver said, “We do a lot of stone restoration so our knowledge of the stone business comes into play and we worked that into the concrete to make the variations blend.”

The final result was a highly polished floor with a bit of variation from the construction flaws, which serves to add some character. My wife, Wynne, said “I looked at those floors for 10 years and hated them every day. Now they are beautiful and I can begin to forget that one dark afternoon when I thought our dream terra-cotta-colored concrete floor was ruined forever.”


We were still left with the exposed footing tops and the roughly tooled contraction joints. After some experimentation, and touch up with an angle grinder and a diamond wheel, I tiled over the tops of the footings with a pebble-like tile that created a nice accent strip.

Since the joints tend to catch dirt and are very noticeable, I wanted them to be flush with the floor and match the color as closely as possible. This part of the project is ongoing. I have been experimenting with a Mapei Mapecem Quickpatch mix designed for horizontal work, which mixes easily and sets quickly and crack free. I've tried to add a bit of Quikcrete color—a blend of brown and terra cotta—but the pigment seems to retard the set of the patching cement and I've yet to get the color quite right. I'm also concerned with how to get the edges of this strip patch to look even.

The only other flaws are some chipped spots from construction and some plastic shrinkage cracking. I've tried scrubbing the chips to get them to approach the floor color, but so far, no luck. The appearance of the shrinkage cracking, though, I actually like—another character-builder.

All in all, the floor is beautiful and over the past five months has remained as shiny as the day it was polished. Although I continue my quest for the perfect floor, that goal now appears to be within reach.