Alchatek Blog

I recently provided on-site technical support on a job with Foundation Repair of Western Colorado. A post-tension residential slab had some interior settlement issues. (Post-tension slabs are constructed with embedded high-strength cables that keep them from cracking or moving.) It looked like the settlement was due to an issue with the cables, either a faulty installation or failure to properly stretch them after the install.

Are Post-Tension Slabs Dangerous?

When working on a slab containing post-tension support cables, you must be extremely careful. These cables are typically stressed to greater than 30,000 lbs tension. If you accidentally drill through or cut a tensioned cable, it can likely rip out of the concrete with a sudden whip-like motion. Consequences could include slab destruction, equipment damage, serious injury, or even death. A few years ago, I witnessed a geotechnical engineer accidentally cut a post-tension support cable when drilling through a slab for a soil boring sample. We were inside a building. The cable snapped with a sound like a massive gunshot. It shot out from the exterior of the foundation wall. Fortunately, no one was standing near that area at the time. Nor was there any valuable equipment nearby. However, serious damage was done to the slab.

How to Repair Post-Tension Slabs

While consulting on this job with Foundation Repair of Western Colorado, we used ground penetrating radar to locate the cables before doing any post tension slab drilling. The crew then marked the “no-drill” areas and was able to safely drill through the slab for polyurethane injection. In addition to locating the post-tension cables, we used the GPR system to locate rebar within the slab and check for underground utility lines.

Ground Penetrating Radar uses radar pulses to image the subsurface. It is a non-intrusive method of surveying the sub-surface to locate underground utilities such as electrical conduit, plumbing, duct work, cables or masonry. GPR can also often identify the location of voids under the slab, providing helpful information in the injection process.

This slab lifting job went very well. The crew used AP Lift 430 to level the slab. The settlement was remedied, and the customer was very happy with the results.

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As we stated in a previous blog post, Lifting Slabs in Cold Weather, there are plenty of jobs that need to be done in the winter. This is just as true for sealing leaks as it is for slab lifting. So let's take a look at those cold weather leak seal markets. We'll also review some special considerations for conditioning leak seal material and equipment. Then we’ll leave you with a few cold temperature leak seal application tips.

Cold Weather Markets

You have a variety of options for seeking jobs that are inside, out of the elements, during the winter months.  Hopefully these ideas will spark more brainstorming on your part. First up we have tunnels, both pedestrian and vehicle. Tunnels often leak, sometimes significantly enough to result in quite a big job. Aquariums are another possibility. As you can imagine, there are infinite potential leak problems in a structure holding that much water. Other possible large jobs could include mines and water treatment plants (which have plenty of interior spaces with potential leak issues). On the smaller side, there are utility vaults, lift stations, manholes and elevator pits.

If you’re still up for working outside during the winter months, you’re in luck because concrete contracts during colder weather. The contraction makes cracks open wider. Wider cracks make leaks more apparent to the property owner and make them easier to repair.

Conditioning Materials and Equipment

One important point to understand is that cold weather requires you to make an extra effort to keep your materials and equipment warm. Cold material reacts slower and gets thicker. Be sure to store your materials and equipment in a heated room the night before the job. When on the jobsite, there are many ways to keep everything warm. Use an enclosed vehicle, like a box truck, enclosed trailer or pickup truck with a camper top or bed cover. Keep as much material and equipment inside the vehicle as possible when working. Use a portable heater to maintain a warm temperature. You can also use electric pail heaters to keep your resin ready for action.

Remember that it won’t do you any good to heat the resin if you’re pumping it through cold equipment. The cold steel inside the pump and the cold hose will literally suck the heat out of the resin before it gets where it needs to be. This will increase the viscosity, making it harder to mix with the water and it will slow down the reaction dramatically. So don’t neglect the equipment side of the equation!

Cold Temperature Application Tips

If you’re using a product with an accelerator, you may need to use a faster accelerator or increase your percentage. Also, bring lots of oakum. You may have to use more if the cold temperature slows down the material or the contracted concrete has made the cracks wider.

If your job requires you to inject into a structure underwater (and the water’s cold), you can use a technique called twin streaming. In this approach, you hook two valves together in parallel fashion – then inject warm water along with the resin to kick start it reacting before hitting the cold water.

Conclusion

I hope this overview has helped spark some ideas on your part for finding leak seal work during the winter months. Just remember to keep your materials and equipment conditioned and you should be fine. Have more questions about polyurethane leak seal in cold weather? Call us at 404-618-0438.

Editor's Note: This post was originally published in 2019 as Polyurethane Leak Seal in Cold Weather.

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Contrary to popular opinion, as a contractor, you don’t have to put up your equipment and rigs due to cold weather. There are many jobs to be done and many ways to keep your material conditioned. Use this season to your advantage and gain valuable business.

Cold Weather Markets

Seasonal attractions such as theme parks are a great place to start looking for winter work. Many of these parks (the ones that aren’t in Orlando) shut down for the winter and this is the time they do maintenance and repairs. Think of all the concrete lifting and leveling that can be done.

Factories can be less active in the winter months with production slowing down in many industries. This is a good time for them to do maintenance and floor repairs as well.

Warehouses typically operate year round, so there is always work available. Warehouse floors are used and abused on a daily basis and will sooner or later need some form of repairs done to keep business running at a steady pace. In addition, many warehouses have dangerous voids beneath their floors that require repair.  

Exterior concrete slabs are still worth considering, even in the cold weather. These slabs experience the most wear and tear from the environment itself (think erosion) and daily traffic. You’ll need to lift concrete slabs before the ground freezes and only after your materials have been thoroughly conditioned.

Conditioning Materials

Your slab lifting equipment probably has built in heaters and a heated hose. Each brand and model of pump has different sized pre-heaters and different ∆T (∆ = Delta and T = Temperature). This sounds complicated, but is actually quite simple.  ∆T is simply the change in temperature.  Let’s say your material has been sitting in a cold trailer all night and the temperature has dropped to 40 degrees F. If the required temperature of your B side material is 120 degrees F, then your pump better be rated with a ∆T of at least 80 degrees. However, if your material is preconditioned to 70 degrees F, then your machine only has to be rated for a ∆T of 50 degrees. As I said, every machine is rated differently based on the size of the heaters. What is important to know is that there are limitations to how much heating your machine can do.

Keeping your materials conditioned in the winter months is a lot easier than it sounds. The main point is to keep your AP Lift products above 60 degrees at all times. Keeping the polyurethane at or above that temperature can be accomplished in a number of ways.

If you have an insulated rig, it should stay around 40 degrees warmer than outside temperatures. Most foam rigs have built in electric heaters that require an extension cord to a power outlet at the job site or at your facility for overnight storage. Alternately, you could buy an electric radiator heater. Other available heating devices include drum band heaters and heated drum mats (be careful not to scorch the polymers by turning band heaters up too high). For a more DIY approach, you could build a hot box around the material storage area in your rig.

Heat Sink

Another consideration when lifting cold slabs is the heat sink factor. AP Lift products come out of the gun hot and get even hotter as they react. However, cold concrete acts as a heat sink and sucks the energy out of the foam as it starts to react. This can slow down the reaction speed of the foam. If you are pumping into a void, it will have little effect because most of the foam is not in contact with the concrete. If you are trying to lift a slab with little void, it will have more of an effect because more of the foam is in contact with the cold concrete and cold soil. More volume = more energy.

Conclusion

Don’t let common preconceptions deter you from slab lifting in cold weather. As noted above, there is no need to shut down completely for the upcoming winter months if you don’t want to. Opportunities still exist and one of them may just be the job you’ve been looking for all year. There are many ways to keep your equipment and materials conditioned to efficiently work in lower temperatures. Have more questions about slab lifting in cold weather? Call us at 404-618-0438.

Editor's Note: This post was originally published in 2018 as Slab Lifting in Cold Weather.

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This article is an excerpt from Episode 9 of Alchemy-Spetec's podcast The Injection Connection, featuring Charlie Lerman "The Grout Geek". Charlie is Director of Technical Services - Leak Seal® Division at Alchemy-Spetec. The Injection Connection is hosted by Jim Spiegel: Vice President of Alchemy-Spetec and Board Member at the International Concrete Repair Institute. (If you'd rather listen, an audio version of this excerpt is posted at the bottom of the article.)

Charlie Lerman: I’m very honored and happy when people say, “You’re very passionate about this.” And I am. I do enjoy it. It’s a lot like a game to me. And you know I’m pushing 50 here and I still play video games. I’ve played video games all my life. And I just love the strategic element. Kind of like a chess game. I look at every grout job just like that. When I go out there, I know what my pieces do; what my product, what my pump, what my drill, I know what all those pieces can do. The thing is, the game is, that I can’t see into the wall or see into the substrate and know exactly what’s going on in there.

So I have to take my knowns and then rule out things that aren’t working or figure out why something is working. It’s a big game. And then, on the other side of that is I’m the hero. When you come out there and you help somebody with a project or something that they’re having trouble with and you’re successful, everybody is happy to see you, they’re buying you lunch. So, it’s a great thing because first off, it’s just mentally stimulating and you’re solving an issue the proper way. And then everybody is happy about it. So to me, it’s just a win-win all the way around with that.

Listen to the audio version of this excerpt...

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I don’t know what it is about this time of year but for some reason at the beginning of fall we receive the most tech support phone calls from slab lifting contractors. Some of it is related to the changing weather, but this past week several things happened that made me want to address a specific topic – the compressed air system of the polyurethane foam rig.

It’s easy when discussing a trailer or box truck rig setup to focus on what type of plural component machine you are running. We all want to know whether you have a PH-2 or an E30 for example, or maybe an air powered Boss proportioner. What is often overlooked and neglected is the compressed air system in the rig. For a slab lifting contractor, it’s likely your air system is working harder than any other component on your rig. If you have had the joy of standing next to the compressor while it is running, you can’t deny that.
I want to highlight the main components of the compressed air system; describing their purpose and offering a few tips for keeping them running like they’re supposed to.

These components include:

• Air Compressor
• Coalescing Filter and Moisture Separator
• Refrigerated Air Dryer

Air Compressor

The majority of slab lifting rigs we see have reciprocating air compressors, also known as piston air compressors. These are identified by having a tank, and they are in a horizontal or upright configuration. They can be either gasoline or electric powered. There are also rotary screw compressors out there which don’t have a tank but still need to be maintained. If you have a compressor with a tank, that tank needs to be drained of the moisture it collects. Some have automatic drains that pop open after the unit shuts down; others must be drained manually.

Last week we worked with a contractor who had an air powered proportioner. His machine could build up pressure, but once he started injecting poly the flow would slow down to just a trickle. He would then shut off the gun and the proportioner would pressure up again. Turns out the air compressor tank was almost completely full of water so he would exhaust the remaining air supply right away when shooting the foam. A good policy is to drain the tank every day at the end of the shift. If it doesn’t drain automatically then there are typically valves that are easy to access. I actually like to start my compressor up the next shift with the tank valve open because it will always blow some more water out when it fires up. Then I shut the valves and things pressure up per usual.

In addition to draining the tank, you need to check and change the compressor oil per the manufacturer’s guidelines. This is for all compressors. If you don’t have a manual on board the rig to tell you when to change the oil or what oil to put in, this info can easily be found on the internet or hopefully from your rig provider.

Filters and Moisture Separators

You can usually find the moisture filter and separator mounted on the wall, often combined with the regulator and air pressure gauge. These filters have a housing below them that collects moisture that is coming from the air compressor. This is the first line of defense (after the air compressor) from keeping moisture out of your transfer pumps, so make sure to open the little valves at the bottom and drain these filter/separators daily. I do it at the end of the day and once again at the beginning of the shift when I am checking my air pressure upon startup.

Refrigerated Air Dryers

The refrigerated air dryer is the last line of defense before the compressed air is sent over to the transfer pumps. I have seen these mounted in various places in a rig from on the floor to up on the wall. First, do not pile tools and other rig items on top of and around the air dryer. These units work nonstop, and they need airflow to do their job without overheating. Take care not to block them in. Second, I believe most of these air dryers also have filters and coils that need to be cleaned occasionally. Check the manufacturers guidelines for your model and keep those items clean so that your unit can run more efficiently and for a longer life.

Conclusion

Your compressed air system is vital to your plural component machine running on ratio and making good polyurethane foam. Components that remove moisture from the air are critical for keeping your transfer pumps running like they are supposed to without breaking down or losing pressure.

Always keep these critical points in mind:

• Drain the tank
• Change the oil
• Drain the filter/separator units
• Don’t block in your refrigerated air dryer, and keep the unit clean

These essential maintenance tasks don’t take but a few minutes, and they can save you hours of frustration and head scratching.

Want more information on Geotech material and equipment?

The choice of a polyurethane material provider for your geotechnical contracting business is a critical decision with far-reaching consequences. In addition to top quality concrete and soil repair material, a premier provider will offer reliable high-performance equipment, rock-solid tech support, extensive training resources and even marketing assistance.

Polyurethane Materials

All polyurethane materials are not created equally. Make sure you ask around the industry to see which materials are the most reliable.

Characteristics of High-Quality Materials

• 100% virgin (do not contain recycled polyurethane).
• Easy on your reactor (does not create high-pressure that wears out your equipment).
• Unlikely to catch fire (yes, some sub-par materials out there will char or catch fire while setting up).
• Capable of bonding to concrete.
• Strong and durable after they set up.
• Approved for contact with potable (drinking) water after curing.

Rigs and Equipment

The quality of your geotech rig is not something you want to compromise on. A premier provider will offer state of the art rigs set ups, customized to fit your exact needs. You’ll want multiple door options (side door, choice of barn door vs ramp door), multiple power outlets and slide-out equipment options. These features allow for maximum flexibility in all types of job situations. In addition, a well-insulated rig allows for operation in a wide variety of climates.

Your pumps, air compressors and slab lifting guns need to be reliable as well.

Characteristics of High-Quality Equipment

• Easy to use (not overly complicated).
• Easy to maintain (easy to clean, not a lot of complicated parts to replace all the time).
• Reliable, reputable brands.

Tech Support and Training Resources

A major differentiator separating serious material manufacturers from the rest is the availability of on-the-job technical support and service. A premier provider will offer field service to assist customers on challenging jobs. Phone support should readily available as well, with support techs ready to answer questions when you need the answers. You will also want to look for comprehensive training resources on material installation, equipment use and maintenance, and estimating/billing jobs. A good combination of online videos and articles, training literature and live events is the sign of a manufacturer dedicated to educating their customers.

Marketing Assistance

Look for a provider offering robust marketing assistance. Geotech contractors have many marketing needs, including website content (illustrations, photos, descriptive text), videos, vehicle sign design, advice on lead capture, etc. A manufacturer willing to go the extra mile in this department can help give you an edge of the competition in your market.

Do Your Own Research, Make Your Own Choices

Did we just describe Alchemy-Spetec in the paragraphs above? Of course we did. This is the Alchemy-Spetec blog after all. That being said, we encourage you to do your own research and contemplate your own needs in a material provider. Ask around in the industry. Seek out users of different brands and find out all you can about their experiences. If you think we missed anything in this article, let us know. We’d be happy to hear from you.

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The INJECTR Series single cartridge houses grout and accelerator in two separate interior compartments. The grout and accelerator are thoroughly blended when injected through the static mixer. This cartridge is compatible with standard caulk guns. Spetec PUR F400 and Spetec PUR HighFoamer are currently available in this format.

Benfits to Contractors

• Same top-line product in a smaller package for smaller jobs
• Quicker in and out - less labor
• Faster set up
• You don’t have to bring in a full crew and a pump
• Use with standard caulk gun (no special guns needed)

Spetec PUR F400

• Concrete crack leaks
• Pipe penetration leaks
• Hairline cold joint leaks

Spetec PUR HighFoamer

• Gushing leak control
• Void fill in wet conditions
• Semi-rigid tolerates movement

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As a consultant on many deep soil geotech jobs over the years, I have found myself recommending one critical piece of equipment repeatedly: The Dynamic Cone Penetrometer (aka the DCP). I highly recommend this tool as an essential part of your Deep Lift® rig set up. As Jim Spiegel explained in his blog post on this subject, this device is used to measure the strength of subgrade soils, and can be utilized to identify weak layers of soil within a soil mass. As you can see in the video below, a hydraulic pump drops a 30kg (60lb) hammer, driving the measuring rod into the ground.

To measure soil strength, the operator counts the number of blows it takes to drive the steel rod in 10-centimeter increments. Good soil requires 10+ blows to drive the rod 10 centimeters. Anything less is typically indicative of weak soil conditions.

DCP testing is a widely accepted means of in situ testing. Due to the common acceptance of DCP testing, many municipalities and agencies are willing to pay for this service.

Here is a hypothetical scenario for DCP use:

Soil strength data is needed under a concrete parking lot before a Deep Lift® job. Multiple tests would be performed, spread out evenly over the area. For thorough testing, each DCP test would be executed to a minimum depth of 15 – 20 feet or refusal (when the hammer blows no longer cause movement.) The test results can then be compared and analyzed to find where potential weak soil conditions may be present. This allows for accurate and effective application of the polymer to address the weak layers.

DCP testing can also be utilized prior to bidding any Deep Lift® job to develop effective injection plans, as well as accurately estimate material usage on projects. With that said, it’s not always possible or practical to perform pre-bid testing. When pre-bid testing is not performed, it would still prove highly beneficial to perform DCP testing prior to injection. I have personally encountered many situations where injection plans have been drastically altered after test results were analyzed (injection depth was added or subtracted, the weakest layers were identified, etc.) The Dynamic Cone Penetrometer is a portable tool which can easily be used in many locations where other testing methods are not feasible and it provides valuable insight into the soil conditions that need to be improved.

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When two adjacent slabs are touching, there is a high likelihood of them being bound. This is definitely something to look out for on slab lifting jobs for a variety of reasons.

Bound Slab Basics

If you try to lift a slab that is bound to an adjacent slab, you could end up:

• Lifting a part of the slab that you did not intend to lift.
• Cracking the slab.
• Lifting the adjacent slab unintentionally.
• Wasting valuable extra material trying to lift a slab that is stuck.

Even if a seam between two slabs or a control joint (a joint meant to break when the slab is under pressure in order to prevent cracking) is already loose - it's still best to run a saw through it just to be sure before attempting to lift. A concrete saw blade is 1/8-inch wide. When you cut between slabs, you are giving them a 1/8-inch gap to ensure smooth movement.

Pros and Cons of Two Types of Concrete Saws

There are two types of concrete saws to choose from when stocking your arsenal of slab lifting gear. Here are the pros and cons of each…

Circular Saw

Photo Courtesy of STIHL.

PROS

• Fast cutting rate.
• Low operating cost.
• Easily sourced blades.

CONS

• Requires overcuts (the blade typically extends 4 to 6 inches past the edge of the slab).
• Requires a wide berth. Cannot cut up against edges of walls and structures.

Concrete Chainsaw

Photo Courtesy of STIHL.

PROS

• Doesn't require overcuts.
• Can cut up against the edges of walls and structures.
• Can cut up to 12 inches deep.

CONS

• Has a high operating cost (chains and bars tend to be expensive).
• Low cut footage per bar and chain compared to circular saw blade.

Want more information on slab lifting products and procedures?

As the Director of Technical Services for the Leak Seal division at Alchemy-Spetec, I often find myself assisting customers with some interesting jobs. Such was the case when I was called in to consult with a contractor who was sealing a leak in a historic district below-grade, multi-course brick wall. As is often the case with below grade, historic spaces, water infiltration was unsightly, gave off a musty odor, and was damaging to finishes. This was a very old brick wall, approximately 8 x 15 feet in size and at least three courses thick. The owner wanted to find a way to waterproof this vintage brick structure while at the same time preserving its unique appearance. In addition to the water flow issue, the leaks were causing mold/mildew on the walls.

We proposed injecting Spetec PUR AG200, a high-strength elastic acrylic injection resin, into the cementitious grout between the bricks where the water was migrating through. In order to monitor the efficacy of this leak seal job, we employed the QP Factor® leak seal testing and quality control system. As stated on our website, “The QP Factor® system offers quantifiable water flow, pressure, and flow/pressure metrics before and after leak seal injection that will provide clients, contractors, and design professionals the industry’s first patented method for proving Leak Seal® success.

The method of testing requires additional drill holes to be placed at pre-determined locations along the crack, joint, or substrate being sealed. Prior to injection of chemical grouts such as Spetec PUR F400, Spetec AG200, or Spetec PUR GT500, the test hole is connected to a digital touch-screen device that is calibrated to provide water pressure, flow, and flow/pressure information that is extractable in excel format from a convenient USB port.”

We ran the QP Factor® system on three test areas in the wall before beginning the injection process. This revealed to us the amount of water that was flowing through the wall. After injecting Spetec PUR AG200 into the existing cementitious grout around the bricks in two of those test areas, we ran the QP Factor® tests again and realized that wouldn’t have to inject the third area due to the efficacy of the Spetec PUR AG200.

Screenshots from the QP Factor program...

In addition to stopping the water flow, sealing the leaks made it possible for the bar owner to keep the walls clean in appearance. See the treated area of the brick wall vs a non-treated area.

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