Alchatek Blog

To backer rod or not to backer rod?  That is the question.

Alchemy-Spetec has stepped into the world of industrial floor repair.  For years we have developed products for lifting and stabilizing concrete slabs.  Now we have taken the next step and developed a couple of products for repairing and protecting the edges of the interior concrete joints.  This latest development has re-opened discussions I used to have on a regular basis about joint sealer, joint fillers, and the use of backer rod.

Let me cut to the chase.  There is a big difference between a joint sealant and a joint filler.  Joint sealants are mostly for exterior applications.  The purpose is to prevent water from entering the joints and eroding the soil beneath the slab (call me if that happens, I have the best solution for rocking slabs).  Joint fillers, on the other hand, are typically used indoors and their purpose is to protect the edges of the concrete joints from chipping and spalling.

In order for a concrete Joint Sealant to work, it has to be flexible and adhere tenaciously to the concrete.  These materials are typically silicone, polyurethane, or polysulfide based caulks.  The cured material should end up in an hour glass shape (picture an hour glass laying on its side).  This allows the material to deform and stretch in the thin part of the hour glass.  The hour glass shape is formed by installing a round backer rod pushed down in the joint so that the top of the backer rod is at a depth that is half the width of the joint.  The material is installed into the joint and then tooled so the top forms the shape of the hourglass.   

Joint Fillers, on the other hand, have a different purpose and different method of installation.  These materials are typically epoxy, polyurea, or a polyurea hybrid.  You should NEVER use a backer rod at a depth of less than two inches when using joint filler.  If you do, it will result in the material failing.  You can use a maximum of ¼” of dry silica sand at the bottom of the saw cut to help prevent the liquid material from flowing into the crack below the saw cut.  Faster set materials (polyurea hybrids) also help prevent leakage into the crack. 

Joint fillers are designed as a structural component.  They absorb the impact of hard-wheeled traffic (forklifts and pallet jacks).  They protect the joint edges.  To work properly, they should be installed to the full depth of the control joint saw cut or at least the top 2 inches of a construction joint. 

Yes, using backer rod can save you money on installation cost, but it will bite you in your hind quarters eventually.  Joint fillers do not stretch.  They are designed with low adhesive strength (aka bond strength) and low cohesive strength (aka tensile strength) so that they won’t weld the concrete together.  Saw-cut joints (aka control joints) are there for a purpose – to allow for thermal expansion and contraction of the concrete.  Joint fillers are designed to de-bond or crack if the concrete moves too much. This is not a failure of the material, but rather a built-in safety mechanism.  

If you install a joint filler properly (full depth), it will rest on the shoulders at the bottom of the saw cut and will not push down into the joint (unless you ignore my advice and use backer rod).  It will absorb the impact of hard wheel traffic and protect the joint edges.  We chose to develop a polyurea hybrid material that cures in seconds.  You can overfill the joint slightly, then shave off the top flush with the concrete in a matter of minutes.  Powerful, painless, rapid.

Quick Reference:

Joint Sealer:  Exterior use, high flexibility, installed in hourglass shape using backer rod, and prevents water intrusion beneath a concrete slab.

Joint Filler:  Interior use, low flexibility, installed full depth (normally don’t use backer rod), and protects the edges of the concrete joints from chipping and spalling.

Joint Filler Product:  AP Joint Fill 800.  Available in 10 gallon units or 22 ounce dual cartridges.

Want more information on Alchemy-Spetec floor repair products?

Finally! We are at the last basic step. Now for the fun part - injecting the polyurethane resin. If you only have one pump, be sure to flush the pump out completely with AP Flush 121 before you pump the resin (unless you like rebuilding Titan airless sprayers).

Check your safety gear - safety glasses are the most important item. Put on two pairs of latex gloves (so you can easily slip on a new pair once the outer pair gets sticky - it is tough to slide fresh gloves over sweaty hands.)

Turn the pump pressure all the way down. Squirt some resin into a cup to make sure the resin is clean. Start at the lowest port and slowly crack the valve. This is a two man job (unless it is a small job). Have your partner slowly turn up the pressure as needed. Develop hand signals if the jobsite is noisy from a generator.

If the resin is flowing, keep pumping. If not, slowly adjust the pressure up. Here comes the art of the game. You have two ways to control the flow of the resin. The pump operator can control the pressure and the valve operator can control the flow. The more experienced technician should control the show.

If I am on the valve, I will tell the pump operator how high to turn up the pressure. I will close the valve while this is being done. Once the pressure is up, I will control the flow of the resin from the valve. Very slowly cracking it open. This way, if I feel a shear start to form, I have a split second to close the valve.

If I am on the pump and the valve operator is less experienced, I will have them open the valve and I will control things with the pump pressure. I will turn it up and down as necessary. It is better to have the valve operator control the show in most circumstances since that person is closer to the action, but hey, I am a control freak when it comes to crack injection.

When to stop? My rule is this - if resin is flowing, keep pumping. What if it starts to run out the face of the crack? Again, my rule is this - if more resin is going in than is coming out, keep pumping. You only have a few minutes to get the resin where it needs to be. As the AP Seal 500 reacts with water it starts to thicken up and becomes more difficult to push into the tighter recesses of the crack.

If raw resin comes out of the crack (amber resin, not a white foam), then it is time to stop. This resin will seal the crack, but at this point there is not much water for it to react with and it will cure slowly. Stop injecting and move to the next port because it will be slow to seal. It is better to see white foam coming out the face of the crack.

What happens if the foam travels past the next port - should I stop? No way. This is a home run. In most cases, the further along the face of the crack the resin travels, the deeper it is travelling as well. This gives you a better seal.

If too much resin is flowing out or washing out due to high water flow, you can use AP Oakum and a screwdriver to create a temporary plug (large or small) to give the resin time to react, expand, and seal the leak.

There are many more nuances about resin injection that you can read about in the leak seal section of this blog. For now, you have completed the basic training of sealing leaks in concrete structures. Here are the basic steps one more time for review:

1. Drill the injection holes.
2. Flush the injection holes.
3. Set the injection ports.
4. Flush the crack with water.
5. Inject the resin.

Congratulations! You have now completed the five basic injection steps and are ready to give it a shot on your own. Of course, many readers are as experienced as I am. If you aren’t, please feel free to call us at 404-618-0438 and ask any questions. The team at Alchemy-Spetec is here to help!

Click below to read the previous articles in this series if you missed them:
5 Steps of Concrete Crack Injection - Overview
5 Steps of Concrete Crack Injection - 1. Drilling Holes
5 Steps of Concrete Crack Injection – 1. Drilling Holes (Continued)
5 Steps of Concrete Crack Injection – 2. Flushing the Holes
5 Steps of Concrete Crack Injection – 3. Installing the Ports
5 Steps of Concrete Crack Injection – 4. Flushing the Cracks

Want in-depth info on crack injection procedures and products?

All cracks that aren’t actively leaking at the time you are sealing them need to be flushed out with water. Flushing them gives you several advantages:

1. Let’s you know whether your drill holes have intersected the crack.
2. Flushes dirt and debris out the surface of the crack so your resin has a cleaner internal surface to bond to.
3. Reveals how far you can expect the resin to travel so you know if your drilled holes are close enough together.
4. The water will help open up tight cracks that the thicker resin may not otherwise have been able to penetrate.
5. Ensures that the resin has sufficient moisture to react with.

Start at the lowest point in the crack and flush clean water through your injection ports. It is best to have at least two pumps onsite. One for pumping water and one for pumping resin. Use the same type of high pressure pump that you use for resin. You can use a smaller pump if you like, as long as it is capable of generating between 2,800 and 3,500 p.s.i.

BE CAREFUL when flushing tight cracks! The low viscosity of water coupled with the high pressure of the pump can shear the concrete. The water can push into tight cracks and capillaries and all at once split your concrete. You can also shear concrete with resin, but it is more likely to happen with water because you are testing your crack and trying to open it up.

Always start every port with the lowest pump pressure and slowly turn it up as necessary. Also, slowly crack the valve open when you are first injecting water or resin. This is a critical moment in the process. If you forget to turn the pump pressure down after each port, you risk blasting high pressure into the port all at once which can result in shearing of the concrete or blowing out the port.

Keep injecting water as long as it is flowing through the port and moving further and further along the crack. Monitor the water coming out of the crack. Notice if it is clean or cloudy. Keep injecting until it comes out clean.

If the project is big enough, you can have one technician injecting water and another injecting resin right behind. Personally, I like to do both steps myself. That way I know what to expect when injecting the resin. In any case, keep the water pump nearby. Many times you will have to pop another hole in the wall here and there to completely seal the crack with resin.

Click below to read the previous articles in this series if you missed them:
5 Steps of Concrete Crack Injection - Overview
5 Steps of Concrete Crack Injection - 1. Drilling Holes
5 Steps of Concrete Crack Injection – 1. Drilling Holes (Continued)
5 Steps of Concrete Crack Injection – 2. Flushing the Holes
5 Steps of Concrete Crack Injection – 3. Installing the Ports

Click below to read next articles in this series:
5 Steps of Concrete Crack Injection – 5. Injecting the Resin

Want in-depth info on crack injection procedures and products?

Installing high pressure injection ports is pretty straight forward, so I won’t spend too much time on this topic. Just a few quick tips.

1. Hammer In Ports. Place the port in a clean 3/8” diameter hole and hammer it in. The high quality materials our ports are made of will take a pounding. But you don’t have to hammer them in too hard. With a little practice you will begin to notice the sound changes slightly when the port is seated. Use an electric screwdriver or drill with a 5/16” socket to seat the zerk fitting into the port. Also, make sure you have a “T” handle socket for use in areas where water is pouring down on your head (so you don’t short out your electric screwdriver or drill).

You may notice that the bag of ports is wet on the inside when you get them. The water helps the ports stay resistant to cracking.

The downside to Hammer In Ports is that they only contact the concrete in a very small area and make a seal (due to the tapered nature of the port). In good quality concrete this seal will hold back several thousand p.s.i. However, if the concrete is weak or the drilled hole is out of round, you can have a problem. In which case you want to use a Mechanical Port.

2. Mechanical Ports have dropped in price dramatically over the years due to inexpensive labor and cheaper materials from overseas. There is now little price difference between the Hammer In Ports and the Mechanical Ports compared to what there used to be. I have a personal affinity for Mechanical Ports because I used to make them in my father’s shop back in the early 1980s. They have a much larger surface area to create a seal and will hold more pressure than the concrete can take.

Make sure you seat the rubber all the way inside the hole. If it is partially outside of the hole, it can cause the surface of the hole to spall, chip, and crack. Setting it in at least ¼” past the surface of the hole will give you a great seal and reduce the chance of cracking the concrete unnecessarily.

Snug the ports down, but don’t over tighten. It is easier than you think to crack the concrete by over tightening (especially if you have drilled close to the crack or at a very steep angle).

Now that you have the ports installed, you are ready to clean out the crack by flushing water through the ports. I’ll discuss that in the next section.

Click below to read the previous articles in this series if you missed them:
5 Steps of Concrete Crack Injection - Overview
5 Steps of Concrete Crack Injection - 1. Drilling Holes
5 Steps of Concrete Crack Injection – 1. Drilling Holes (Continued)
5 Steps of Concrete Crack Injection – 2. Flushing the Holes

Click below to read next articles in this series:
5 Steps of Concrete Crack Injection – 4. Flushing the Cracks
5 Steps of Concrete Crack Injection – 5. Injecting the Resin

Want in-depth info on crack injection procedures and products?

Here it is. My favorite topic. Why? Because I have seen and heard some really stupid things concerning this. It is my pet peeve. It separates the technicians who care from those who are only going through the motions. And quite frankly, it can be the difference between a successful outcome and dismal failure - or at the very least an expensive call back.

When you drill holes you create concrete dust. The hammer drill bit literally chews up the concrete. Most of it comes out of the hole and falls on the floor. However, a lot of dust is left behind inside the hole. If it is not properly flushed out then it will mix with your polyurethane injection resin and make a thick paste. This thick paste can be forced into the crack and prevent the clean resin from reaching deep into the crack where it is needed. Most of the time you won’t even realize you have a problem. But there it is nonetheless. Waiting for the right conditions to allow water to seep back through the crack you thought you fixed.

How to avoid this? Simple - flush the hole out from the back using a very cheap flexible hose that attaches to your flush pump (you did bring a separate flush pump didn’t you?). Start at the highest hole and work your way down until clean water is flowing out of each hole.

Spraying water at the face of the holes may make it look clean, but it is not. There is still dust deep in the hole. Filling a water bottle up and squeezing it so that water shoots part way up the hole is not good enough. You have to have the water exit your hose at the back of the hole. This is the only way.

Exceptions? Of course there are. If you pull the drill bit out of the hole and water gushes out behind it in a steady stream you can skip this step. Otherwise, make sure you bring a flush hose with you. It has to be small enough to fit inside your drill hole. We make it easy for you. We make one and sell it for cheap (so don’t blame us if you get to your jobsite and don’t have one).

This is so basic it is silly. However, I have seen experienced technicians do the water bottle trick and try to explain that it is sufficient. I’m happy to report that those guys are working for your competitors now. Just make sure your guys don’t get lulled into laziness and skip what just might be the most important of these five basic steps:

1. Drill the hole
2. Flush the hole
3. Install the ports
4. Flush the crack
5. Inject the resin

Next up, installing the ports!

Click below to read the previous articles in this series if you missed them:
5 Steps of Concrete Crack Injection - Overview
5 Steps of Concrete Crack Injection - 1. Drilling Holes
5 Steps of Concrete Crack Injection – 1. Drilling Holes (Continued)

Click below to read next articles in this series:
5 Steps of Concrete Crack Injection – 3. Installing the Ports
5 Steps of Concrete Crack Injection – 4. Flushing the Cracks
5 Steps of Concrete Crack Injection – 5. Injecting the Resin

Want in-depth info on crack injection procedures and products?

Let’s face it, most of the structures you drill through will be full of rebar. Rebar is the steel reinforcement that gives the structure its strength. Concrete protects the rebar by shielding it from moisture, and the high pH of concrete keeps the rebar from rusting. However, once a crack forms it allows more water and environmental gasses to reach the area surrounding the rebar. Carbonation of the concrete can now occur which causes the pH to drop and the corrosion process to begin. The rust expands and takes up 15 times the volume of the un-corroded steel which causes tensile forces to work against the concrete eventually resulting in additional cracking and spalling. Hopefully, you will be called in to fix the leaks before much of this damage occurs.

Once you are on the jobsite, this slow process of decay does not really affect you (unless the concrete is spalling off as you drill). Your issue with the rebar is that it will stop your drill bit from penetrating the crack. The cracks will often follow the rebar, especially if there is not an adequate coverage of concrete over the rebar. Shallow rebar is a huge contributing factor to cracks in concrete.

At this point, all you care about are two things. First, how do you know if you have hit rebar? Second, if you have hit it, what in tarnation do you do now?

After drilling many thousands of holes like I have over my career, you pretty much know when you have hit rebar. Here are a few things to lookout for:

1. Forward progress of drilling has stopped.
2. The sound of the drilling changes.
3. The quantity of drilling dust is reduced.
4. If you are not sure, put your hand out to catch some of the drilling dust coming out of the drill hole. Observe it for metal shavings.

1. Move further away from the crack and try again (adjust your drilling angle).
2. Move closer to the crack and try again (adjust your drilling angle).
3. Move parallel to the crack and try again.
4. Move to the other side of the crack and try again.
5. As a last resort, drill straight into the crack. This is not the ideal situation, but if you can drill deep enough to get an injection port installed, then you might be able to successfully seal the leak.

Now that the surface of your concrete looks like Swiss cheese, it is time to go get that bag of fast set hydraulic cement you brought along for just this purpose. Try to patch it up before you begin injection because some of those abandoned holes are libel to have hit pay dirt. If you don’t seal them up then you will have foam or resin leaking out of the holes.

Hitting rebar is not fun and can be frustrating. The key is to expect it and try to think three dimensionally. See if you can visualize what is going on behind the concrete. This is one of the keys to becoming a really good injection technician.

Click below to read the previous articles in this series if you missed them:
5 Steps of Concrete Crack Injection - Overview
5 Steps of Concrete Crack Injection - 1. Drilling Holes

Click below to read next articles in this series:
5 Steps of Concrete Crack Injection – 2. Flushing the Holes
5 Steps of Concrete Crack Injection – 3. Installing the Ports
5 Steps of Concrete Crack Injection – 4. Flushing the Cracks
5 Steps of Concrete Crack Injection – 5. Injecting the Resin

Want in-depth info on crack injection procedures and products?

I remember my first day on the job back in June of 1985. We were working nights in the MARTA subway tunnels in Atlanta, sealing leaks in the ceiling. They handed me a 30 pound hammer drill and told me to drill holes in the ceiling at a 45 degree angle. Sure, what the heck is a 45 degree angle? I put on a lot of muscle that summer drilling overhead and hauling 50 pound pails of resin all over the Southeastern U.S.

Drilling holes into concrete seems like a straight forward process. However, it must be done correctly or everything you do afterward is a waste of time. Often, contractors put their least experienced technician on the job because it is manual labor and can be taught quickly. Knowing a few of the basics can help a newbie drill like an expert.

First, you have to understand that the beginning of the hole is where the injection port makes its seal against up to 3,000 pounds per square inch of injection pressure. It is important that the hole stay round, especially when using hammer in type ports. That means you have to keep the drill bit in a straight line.

Why a 45 degree angle? This is the best way to intersect the crack halfway through the structure (which is your goal). On a 10” thick wall, come off the crack 5”, drill at a 45 degree angle and you should hit your target. Just start with your drill bit straight into the wall, give the trigger a few bumps to make an indention in the concrete with the bit, and rotate your drill so that the angle is half way between your starting position and the wall.

How far apart to space your holes? It depends on the width of the crack. Tighter cracks need tighter spacing because the resin won’t travel as far. Wider cracks can have wider spacing because the resin will travel with ease. A rule of thumb is to drill your holes no farther apart than the thickness of the concrete. Drill, flush and pump a test hole with water to give you an idea of how far the resin will travel.

Be sure to pull your drill bit out every four or five inches of penetration to clean out the drilling dust. Otherwise you are likely to bind up your drill bit, which is not fun to try to remove.

Sometimes you will have to drill straight into the crack. I always try to angle drill first, but with extremely tight cracks you may have to compromise and drill straight in. Go as deep as you can, but make sure you don’t go all the way through.

Another tip: If you stagger your holes from one side of the crack to another, be sure not to intersect a hole you already drilled. This causes all kinds of problems.

We will talk about flushing drilling dust out of your holes later, but I can’t repeat it enough. If you want a successful injection job you have to flush the drilling dust out of the holes from the back. Otherwise, the dust will form a paste that gets forced into the crack and blocks your resin from getting where it needs to be. Splashing water on the front of the hole doesn’t really help. Be sure to get a small hose to the back of the hole and flush it with clean water.

In the next article I will talk about what to do when you inevitably hit the injection contractors nemesis...rebar!

Click here to read the first article in this series if you missed it:
5 Steps of Concrete Crack Injection - Overview

Want in-depth info on crack injection procedures and products?

There are five basic steps to be done when injecting a crack in concrete that is leaking water. This is crack injection 101. Learn these steps and you will be well on your way to understanding what it takes to seal a water leak in concrete with products such as Spetec PUR F400, Spetec PUR F1000 and AP Seal 500. In future articles, we will explore every one of these steps in more detail and address the multitude of options (such as port selection, hole spacing, depth, what to do when you hit rebar, etc.) But for right now, we are going to discuss the most basic steps.

Step 1: Drill holes. Use a hammer drill to drill holes in the concrete that intersects the crack. These holes are usually drilled at a 45 degree angle to intersect the crack halfway through the structure so that the resin is forced towards the front and back of the crack.

Step 2: Flush the holes. When you drill, you create concrete dust. If you don’t flush this dust out of the holes, it will be forced into the crack during injection and may clog the crack, preventing resin from getting where it needs to go. Put a flexible hose all the way to the back of the hole so that water flushes the dust from the back of the hole to the surface of the concrete. Flush until clean water is flowing.

Step 3: Install your injection port. The port is what seals the hole and gives the injection pump a direct connection to the crack.

Step 4: Flush the crack. Unless water is pouring out of the crack, you will need to inject clean water through the injection port and into the crack. This serves several purposes:

• Cleans the crack of dirt and other contaminants to allow resin to flow freely.
• Gives you an idea of how far and how easily the resin will flow into the crack when you start injecting the foam.
• Helps to open areas that the resin wouldn’t otherwise flow. Water is thinner than resin and will penetrate deeper and into tighter areas.
• Ensures the resin will have enough moisture to react with.

Step 5: Inject the resin. Always use the lowest pressure that will continuously feed resin into the crack. Slowly turn up the pressure as necessary to get the resin flowing. My rule of thumb is to keep injecting even if resin starts to flow out of the crack. As long as more resin is going in than is coming out, you are improving your chances of success. When the resin isn’t moving further along the crack, move to the next port.

Sounds simple, right? Well it is and it isn’t, as we will discover in the next several chapters of this blog series...

Click below to read next articles in this series:
5 Steps of Concrete Crack Injection - 1. Drilling Holes
5 Steps of Concrete Crack Injection – 1. Drilling Holes (Continued)
5 Steps of Concrete Crack Injection – 2. Flushing the Holes
5 Steps of Concrete Crack Injection – 3. Installing the Ports
5 Steps of Concrete Crack Injection – 4. Flushing the Cracks
5 Steps of Concrete Crack Injection – 5. Injecting the Resin

Want in-depth info on crack injection procedures and products?

Product

AP Lift 475 is a two-component polyurethane chemical grout resin system (1:1 ratio) developed for the reinforcement and stabilization of loose bulk ballast stones on railway tracks.

Procedure

AP Lift 475 is mixed together, then poured on the ballast stones to increase the rigidity and stiffness of ballast. When applied, this product is a weather resistant solution that reduces vibrations and provides a buffer zone from the concrete slab track to the ballast track. AP Lift 475 helps to reinforce the ballast, reduce loose stones and dust, as well as prevent pulverization. The AP Lift 475 also provides an excellent binder for stabilization of the ballast, so when excavation is needed under the ballast and the tracks, for applications like Micro-tunnelling, AP Lift 475 will bind the ballast together to prevent cave-ins from occuring.

Solution

For rail infrastructure, compliance of Polyurethane Stabilized Ballasts may be favorable due to the strains that can be tolerated under the loads distributed from the superstructure down through the substructure. Large differences in mechanical behavior of clean ballast before and after polyurethane stabilization indicate that the introduction of Rigid Polyurethane Foam to ballast creates a geocomposite, referred to herein as polyurethane stabilized ballast, with different and generally superior mechanical properties to that of clean ballast, recycled ballast, and fouled ballast. Excerpted from “Mitigating Ballast Fouling Impact and Enhancing Rail Freight Capacity” by the National Center for Freight & Infrastructure Research and Education.

Want information on Alchemy-Spetec soil stabilization products? 

We are pleased to announce that Spetec PUR H100 and Spetec PUR F400 are now made in the United States! 

Old Packaging
24 Pails Per Pallet

The Same Product You Used to Get in These Metal Pails 

• Same quality.
• Same consistency. 

New Packaging
Available Now
36 Pails Per Pallet

Advantages

• Can see the amount of product in container.
• Room for up to 10% catalyst in the pail.
• 2” opening allows room for 1.75” mixing paddle.

Want more information on Alchemy-Spetec leak seal products?