David Phillips, Hi-Tech Floors, Inc.
This is the latest in a series of "The Contractor's Soap Box", a question and answer column dealing with the insights, struggles and professional experiences facing the concrete contractor in his never-ending quest to master the sometimes changing and fickle nature of this beast called concrete. We are sure you will benefit from the positive nature of this column and hope you'll learn from some of these professionals.
In this issue, we feature Dave Phillips, President of Hi-Tech Floors, Inc., one of America's top concrete contractors with a long list of clients and positive testimonials. Hi-Tech Floors, Inc., in business since 1989, is an industry leader in the installation of shake-on (colored and non-colored) hardeners on concrete slabs for retail and industrial applications. I'm sure this list of questions and Dave's answers will hold your attention.
As Dave points out in this interview, you always have to rely on your instincts and professional experience! Nothing is set in stone as changes are the inevitable nature of this business. We thank Dave for sharing his insights and for his ongoing dedication to excellence in the concrete business!
JV: What is the maximum air content in concrete over which a shake-on hardener should be placed?
DP: Whenever we're doing a mix design, we always ask for a 2% maximum air content. In some cases, we do have a field test that will allow us up to 3% air content. If we're having an issue with the finishability, then air content becomes more important. Air content is always a job-by-job judgment call and a lot of things factor into this formula. Different raw materials from different parts of the country will cause this to vary.
JV: What slump range do you like to work with?
DP: The range we like to work in is around a 3-inch to 4-inch slump...although, with some of the super plasticizers, we're going in a little tighter than that. If super plasticizers are being added to the mix, we like to be around a 5- or 6-inch slump, because we get a better performance from our cement with the plasticizers in the mix.
JV: Do you use a set-retarding admixture in the summer?
DP: We never use a set-retarding admixture in a concrete mix that will later receive a shake-on hardener! We have done a lot of experimenting with this in the past and it has been our experience that, when using a set-retarding admixture, we end up with a concrete mix that does not have enough moisture for the shake-on hardener. A set-retarding admixture seems to dehydrate the mix, so that by the time we can get onto the slab with a machine, there's very little moisture left to wet the dry shake-on hardener. This adversely affects the placement and finishability of shake-on hardeners. In lieu of using retardants, we've found that employing more finishers on the job is the way to go. If, because of summer temperatures, you have to get on it faster and move quickly, then you need people to do that. The way I explain this is, "In the summertime our rule of thumb is: screed...spreader...float machine! It needs to be that quick!"
JV: Do you have a given water amount you generally like to work with?
DP: Generally, for the dry shake-on hardeners, we like to work around .48 to .50 water: cement ratio. That normally equates to a 5 or 5 ½ bag mix (about 520 lbs of cement) and about 32-gallons of water per yard. I also get a lot of help from guys like L&M's Phil Smith and the technical guys from the local ready mix suppliers as far as local raw materials and water quality. Everywhere we go with our crews conditions are a little different, so we rely on the experts and the local guys a lot when it comes to certain mix designs. We send our guidelines to the ready mix companies for each job, and usually rely on the guys who have a better local expertise to adjust for the local variations and guidelines.
JV: How much bull-floating to you do? And which kind of floats do you like better, wood or magnesium?
DP: For a colored shake-on hardener, we like to bull float the slab before applying the dry shake hardener. We always use wood bull floats to open up the surface to let the moisture bleed out versus magnesium floats which tend to close it up and prematurely seal up the surface. We try not to run the floats over the top of the non-colored shake-ons once they are applied if we don't have to. It seems to bury the shake in a little deeper than it actually should be. So, again, we generally only bull float before and not after the shake-on is applied.
JV: Do you find evaporation control agents helpful?
DP: We use evaporation retardants all the time! Depending on the weather conditions, it is a must! Most of the time, we apply the retardants in a 2/3-1/3 ratio (that's 2/3 during screeding and 1/3 when we apply the shake-on.) That's what the specs call for and that seems to work for us, too. When we're working in the dry, higher-altitude mountain or desert areas, we'll actually apply the retardant three times: before, after, and again after we apply the shake. On the jobs we do in the upper Midwest, we just use them as needed. In the winter, when it's really dry, we'll use them a little more.
JV: Do you use a wind/temperature chart to know when to use an evaporation control agent, or do you just go by your instinct?
DP: It almost always has to be by instinct. We carry humidity and temperature gauges. In cold weather, we also carry carbon dioxide detectors to measure heated indoor air to guard against carbonation problems. But as far as when and where to use an evaporation control agent, I almost always rely on my instincts! An old saying we use in my industry is, "Anybody can put on a good shake-on hardener on a good day." Fact is, it's hard to plan on the wind, sun and rain! Luckily, we almost never apply shake-on hardeners in the open air, but you have to constantly be concerned about the wind and the shrinkage factor of the concrete. Applying shake-ons in the hot sun and wind without a roof can be a recipe for disaster.
JV: Do you review the mix design before placing the concrete?
DP: When it comes to concrete that is to receive a shake-on hardener always, always, always...I have control! Before we do these jobs, I personally sit down with the engineer. If there's any discrepancy or arguments, this is the time and place for everyone to come to a final agreement. There's always a little wiggle room for adjustments based on regional or job conditions. Again, I try to stay away from the jobs that are outside and in the sun. Every one of our jobs gets a guideline and a review, and ultimately an approval. We are a major part of that process. When it comes to shake-ons, we need that control!
JV: Which do you use when installing dry shake hardeners: power trowels with combination blades or trowel blades with float shoes?
DP: We always use a trowel blade with a float shoe. Generally, when we're finishing concrete, we use the float shoes for the first float and shake, then float shoes again for the second shake. Just before the first hard troweling we float again, this time with a combination blade. What we're trying to do here is to keep the slab surface open that much longer before we close it up with the troweling steps. One of the biggest issues we're faced with is that, with shake-on colors, concrete finishers have a tendency to seal the floor up too soon. That can result in blisters, popping and delaminating.
Our transition is from a real float shoe (flat and open, two passes), to a combination blade (flat), then to the finish blade (flat) and then to a final trowel pass entirely by hand. This is how we transition from blade-to-blade. Our final trowel is always done by hand when we deal with any colored shake-on hardener.
In a non-colored situation, we would normally just burnish it with a trowel blade. However, in the case of colored shakes, it is really easy to burn the surface and affect the uniformity of the finished floor. By hand-troweling the final pass, we eliminate the burns. A lot of the surfaces we do are for the retail business and they prefer color uniformity. A lot of finishers (if they don't burnish it) will pull the machine off early and, it will leave the surface fuzzy. But, as we all know, shake-on hardeners get very, very hard and the resulting fuzz can become a dirt collector and produce a hard-to-clean surface. If you trowel it to the final end so that it's tight, it will be smooth and easy to clean-but then, if they burn it, they have over-troweled it.
Troweling every square inch of these floors by hand makes the difference. A lot of finishers don't want to take the time to do this, but that's what bridges the fine line between non-slip yet cleanable floors. It also has a great effect on producing a uniform color. The important thing here is to follow this procedure step-by-step, from blade-to-blade-to-blade. Not all finishers are willing or able to do this. We do over a million square feet of shake-on floors a year, and this is what we have found needs to be done to make a floor consistently uniform.
JV: How do you apply shake-on hardeners?
DP: We always do the larger areas with a mechanical spreader. With a mechanical spreader we are able to calibrate and control the right amount of shake-on hardener per square foot. We own about a dozen of them, and we carry two of them everywhere we travel so we can use a spreader on the first application and the second. There are applications, however, where you still have to do it by hand. It takes some practice to do this and do it so you can consistently throw it on uniformly! What you don't want is to get a three-pound pile out in one spot. We train our guys to get the "feel" of it and get pretty close to the recommended coverage. After you do this for a while, they know exactly what it should look like.
JV: When a slab starts to set early and get away from you on a hot day, what's the best way to save it?
DP: Pray! Pray! Pray! Seriously, we try to "man" the slab with enough help. The first thing we do is get out an evaporation retardant like L&M's E-Con. At times, we will actually "dash" some water. I'm not talking with buckets or a hose, just a few sprinkles here and there. When we work in the heat or inclement weather, we apply the evaporation retarder with a large power sprayer on the larger areas between shakes and with a three-gallon, hand-held pump sprayer on the smaller areas. We always keep a couple of sprayers mixed and ready to go so we can keep from using that "dash" of water.
JV: What special problems do you experience with the discoloration of light colored shake-on hardeners?
DP: Again, most of the time that stems from over-troweling or over-working, or a lack of materials. The failure rate for colored shake on hardeners is extremely high across the country. But this does not have to be. Fortunately (or unfortunately) 99% of the failures on a dry-shake colored slab are due to applicator error! They are either from lack of quality control, lack of experience, too much troweling, not enough hardener on the slab...all of these factors can cause discoloration. And all can be controlled by the contractor.
JV: How do you cure a shake-on hardener slab?
DP: Generally, we do not water-cure our slabs. When we do wet cure, we let the slab set up hard before we put water on the slab. If you don't wait, you can actually end up with delamination. You can also get your slab surface a bit chalky if you re-wet it and soften it. About 90% of the time we use spray-on type membrane cures, and we try to get the cure on as soon as we can.
JV: Do you design your concrete mixes or use a lab designed mix?
DP: I can't take all the credit for this. The chemists and engineers who designed the shake-on hardeners (Phil Smith from L&M would be a good example here) have helped me over the years to come up with the mix designs. I have gotten a lot smarter, thanks to the help from a lot of other people who know exactly what this stuff can do in a laboratory. I constantly ask for help with every mix and mix change we've done over the last 20 years. Actually, it's still about the same fundamental mix as we started out with, only with a few variations here and there to meet the weather and conditions.
JV: Any final words of advice?
DP: You can't always simply bank on ACI 302. Same is true for the information found on the bag or on a container label. When unforeseen circumstances threaten your slab, experience helps. If I can help just one other contractor avoid disaster with my experience, it will make my day!
David L. Phillips, Jr.
Hi-Tech Floors, Inc.
12701 Sheridan Avenue., Suite 101
Burnsville, Minnesota 55337
In 1989 Dave, along with his father and brother, developed a floor system that was later patented as the HIGH GLOSS HARDENED CONCRETE FLOOR SYSTEM, also known as the HTP Floor System. It was during the development of the HTP Floor System that Dave's company Hi-Tech Floors, Inc. was formed and continues to evolve today. His peers, clients and suppliers recognize Dave as one of the most knowledgeable experts in the business. Dave's skills and expertise are highly sought after both in the upper Midwest and nationally. Dave is a specialist in the art and placement of shake-on hardeners.
© 2008 L&M Construction Chemicals, Inc. | ConcreteNews January 2008.