Alchatek Blog

Concrete is the most common building material in the world. While it has high compressive strength, it does not have much tensile strength. It is only since about 1910 that rebar has been specified. Reinforced concrete can and does still crack. So does that matter? Yes, most of the time it does matter.

Epoxies Are for Structural Repair

Epoxies are commonly and very effectively employed to “weld” these cracks back together. End of story, right? Of course not. For structural repairs epoxies are correct and necessary, but what about non-structural dynamic cracking? Well first off, why do we even care if there is a non-structural crack? Sometimes we don’t, but when this non-structural crack is the source of water intrusion action is required!

Water intrusion, besides being unsightly can cause many problems. Slip hazards are an obvious one, remember that rebar we started adding back in the 1910s? It can corrode, per NACE it can expand about 7-8 times its size, causing spalling and even complete failure of the concrete. Epoxy repair of a dynamic non-structural crack does not end well. The crack is there to relieve stress and if it is welded together with epoxy then it cannot move to relieve the stress, which causes what we call mirror cracking (this is a new crack in proximity to the previous epoxy repaired crack). Now we are back to where we started and we wasted time, labor, and materials on a failed repair.

Polyurethanes Are Ideal for Sealing Leaks

Flexible polyurethane grouts are ideal for dynamic cracks. They will waterproof the crack but still allow the cyclic movement - thus no mirror cracking, no leaks, and no corroding rebar. There are two main categories of polyurethane grouts, hydrophilic and hydrophobic. Hydrophilic grouts have more flexibility (higher tensile strength) and better adhesion than hydrophobic grouts. So, the answer seems clear, choose a hydrophilic grout. Hydrophilic grouts are the first choice for most below-grade applications, but since they form an open crosslinking when they polymerize, they can dry out in arid environments. Hydrophobic grouts have a closed crosslink and therefore are unaffected by wet-dry cycling, but have less elongation and lower adhesion strength. So, if you're new to this, it's best to consult an expert when selecting a polyurethane for your leak seal job.

Technical Support for Leak Seal Contractors

When it comes to waterproofing with chemical grouts, product selection and application techniques will make or break a job. Good technical support ensures more production and less product waste. I have over two decades of field experience. I'm happy to share that knowledge in support of all your waterproofing needs, and I am just part of the most experienced grouting tech service team out there. We pride ourselves on education and training in the field, in the classroom, and online. Please let us know how Alchemy-Spetec can be of assistance to you. Call our tech support team today at 404-618-0438.

Want more info on leak seal products and equipment?

In this post, I’m going to personally review two popular methods used to handle water leaks and infiltration. Both hydraulic cement and chemical polyurethane grouts are used in civil applications such as sewer pipe rehabilitation, tunnel or shaft construction, sealing leaking cracks in concrete structures, permeating soil to control the flow of groundwater, filling voids to stabilize soil, and handling common inflow and infiltration issues found all over the world.

This post will reveal the good, the bad, (and the ugly) when it comes to product selection and application. When considering chemical grout or hydraulic cement for your waterproofing needs, we will need to look at:

• Features
• Costs
• Applications

When it comes to waterproofing with chemical grouts, application techniques will make or break a job. There is a lot of misinformation out there, so I encourage you to carefully evaluate the content below and make the most educated decision for your upcoming projects. (For further assistance with that decision, feel free to call our tech support team at 404-618-0438.)

Before we continue, I’d like to briefly let you know who I am and what I do. My name is Charlie Lerman (a.k.a. The Grout Geek). I was the Technical Field Services Manager at two industry-leading polyurethane grout manufacturers for 18+ years before joining Alchemy-Spetec as the Director of Technical Services – Leak Seal Division. My full-time responsibility is to take care of your questions and uncertainties concerning waterproofing with chemical grout and alternative options. So when is it best to use hydraulic cement? When should you use chemical grout? Let’s compare:

What is Hydraulic Cement? Key Features

Hydraulic cement is inexpensive and easy to apply but its benefits stop there. It is a surface patch that is primarily applied to the negative side. It has a weak adhesion and thus is applied in a groove or similar cut. It can be used to shut down low-pressure leaks. Being that it is cement it has a low tensile strength which means just like other types of cement it will be brittle when it is cured.

Chemical Grout Features

There are two primary types of chemical grouts when it comes to crack injection, each unique in its composition and makeup: (1) acrylics and (2) polyurethanes.

1. Acrylic grouts are free of suspended solids and have extremely low viscosity. The grouts can change from a liquid to a solid in a controllable gel time ranging from 3 seconds up to 10 plus hours. The lifespan of acrylic grouts is estimated to be between 50-300 years depending on the method and application utilized. Acrylic grouts are hydrophilic, have about 500% elongation, and are only about 20 cps. These properties make them ideal for injecting hairline cracks. Alchemy-Spetec's Spetec AG200 acrylic injection resin is NSF 61-5 certified for contact with drinking water.

2. Polyurethane grouts can be grouped into two types: hydrophilic and hydrophobic. Hydrophilic grouts are usually single component formulations that react with water and cure to an expansive flexible foam or non-expansive gel requiring a moist/humid environment after curing. Hydrophobic grouts are expansive foams that require little water to react and can easily withstand wet/dry cycles. Hydrophilic foams expand 4 to 6 times their original volume, while hydrophobic foams can expand up to 40 times their original volume and may cure flexibly or rigidly. Alchemy-Spetec offers many polyurethane resins that are NSF 61-5 certified for contact with drinking water. The lifespan of polyurethane foam is estimated to be approximately 70+ years.

Both acrylic and polyurethane chemical grouts are injected into cracks or joints and thus are not considered a negative side waterproofing even though they are often applied from the negative side. Acrylic and flexible polyurethanes are designed to shut down active leaks and, because of their high tensile strengths, they can withstand the movement of a dynamic crack or joint. Because they are full-depth repair materials, they can also encapsulate rebar and thus help prevent corrosion, spalling, and thus structural failure.

Applications: When, Where, and Why

I cannot emphasize enough how helpful it is to speak with an experienced grout consultant and/or an experienced contractor when faced with the need to stop leaks or control inflow and infiltration. If you are looking for installation recommendations, a knowledgeable grout manufacturer should be consulted to assist with proper grout selection and installation methodology. I am available to assist with your next project. Call Alchemy-Spetec at 404-618-0438 and ask for the Grout Geek!

Want more information on leak seal products and equipment?

Lifting a settled bridge approach slab with polyurethane foam requires specific knowledge of proved repair procedures for these types of structures. Here's an overview...

Look for a Hidden Sleeper Slab

Larger roads and highways will often have a hidden sleeper slab that spans underneath the pavement and the approach slab. It is designed to help transfer the traffic load from the roadway to the approach slab. If there is settling at a bridge approach you must determine if there is a sleeper slab in place. Drill through the pavement where it meets the approach slab and if you hit more concrete underneath the pavement you have found the sleeper. If there is a sleeper present where there is settling you will need to perform deep injection a couple of feet below the sleeper - just for soil stabilization. Rural roads and private roads typically do not have a sleeper slab present. Always ask the client if there are drawings available.

Deep Soil Stabilization Followed by Lifting

At least one level of deep injection is required for approach slab/pavement lifting. This is for soil stabilization. 4' spacing and 4' below the pavement is standard. Do not exceed more than 30 lbs per point at a given depth. It is advised to always have a DCP (dynamic cone penetrometer) test done in order to determine the blow counts. Low blow counts indicate weak soil zones that need to be targeted for deep injection. Lifting will be done directly through the pavement/approach slab, the same way you do standard slab lifting. Do the deep injections first and then finish with the injections directly beneath the slab.

Fill Voids with Polyurethane

Watch for voids under the approach slabs where they meet the bridge abutments. There are typically voids in this area that need to be filled. When filling them, it is good to have an observer under the bridge because the foam can fill the void up and come over the abutment, depending on how the structure is designed.

Want more info on geotech repair products?

Sealing Joints with Grout and Oakum

Whether injecting with a pump or a cartridge, it's always helpful to have AP Oakum on hand. Liquids will take the path of least resistance and oakum is very adaptable for controlling them. For example, joints are typically easier to inject than cracks, and precast joints are about as easy as they come in regards to injection work. They are also very common routes for water infiltration, whether in manholes, culverts, vaults, and tunnels. Since joint injection does not require the consistent pressure provided by electric injection pumps, you can often make these repairs with cartridges instead.

Simple and Effective Leak Seal Method

Time and time again, it is easy to look like a hero with nothing more than a cartridge of Spetec PUR F400, a handful of AP oakum, and a flathead screwdriver. Lastly, be confident. Don’t confuse high-flow leaks with high-pressure. When you're working less than 20’ below grade, you are only dealing with a few psi of pressure even if it is a high-volume leak.

Want more info on Alchemy-Spetec leak seal products?

Sealing Steam Leaks with Polyurethane

One of the most high-tech veneer manufacturing companies in the United States chose Alchemy-Spetec to train their maintenance techs to stop a steam leak in their facility. You heard that right. Not liquid water, but steam leaks! Prior to milling the veneer, they heat the logs in a bank of steam vaults. Rather than tearing down/rebuilding these cracked, leaking vaults they opted to inject the cracks with Spetec PUR F400, a hydrophobic flexible polyurethane grout. Replacing the vault would not only have been a lot more expensive, but it would also have resulted in a costly interruption to their milling process. No one likes downtime.

Polyurethane Leak Seal Training

Saturday is the one day of the week that the vaults are offline, and that is when I conducted the complimentary field training for their employees, who had never done any injection work before. Within a few hours, they understood how to handle the grout, how to use the grout pump, and how to accomplish their injection work. They can now self-perform their crack injection as needed.

Want more information on Alchemy-Spetec leak seal products?

I was a Machinist Mate in the Navy and thus almost all of my training was mechanically focused. One class I had was Electrical Theory for Mechanics. The quick summation by the Senior Chief instructor for it was "Electricity is magic and when the smoke comes out the show is over." Being on a submarine it was deemed a good thing to keep water and electricity separate. My first time ever using polyurethane chemical grouts was on a group of sixteen conduits entering a below-grade mechanical room. While electricians may understand the "magic" of electricity they often fall short as waterproofers. Combined with the fact the numerous electrical cables coming through a conduit can be notoriously hard to waterproof and it is a recipe for leaks and electrical problems. In this post, I'll share step-by-step instructions, along with a couple of photos from a recent job one of our customers completed in a San Francisco condo complex.

Oakum soakem is a kindergarten-skill level procedure that makes waterproofing these types of penetrations easy. I refer to this as fingerpainting with chemical grouts.

1. For PVC and HDPE pipe roughing the surface will increase the mechanical bond and is recommended.
2. Wet the application area.
3. Soak oakum in either Spetec F400, GT500, or GT380 resin until saturated.
4. Pack soaked oakum into pipe joint to be sealed. If necessary, pack multiple layers. Ensure it is under compression.
5. Allow grout to cure.

Often this is all that needs to be done, but it can be followed up with injection to fill the conduit if required.

1. Stab injection needle through the cured grout and oakum plug.
2. Inject grout.

Photo: Contractor on a recent job in San Francisco, addressing multiple conduit leaks with electric injection pump, a pail of Spetec PUR F400, and Oakum.

Want more info on Alchemy-Spetec leak seal products and equipment?

Sealing Leaks in Concrete with Polyurethane

Water is RELENTLESS. Leaks appear in all kinds of structures, from underground parking garages to municipal treatment tanks to elevator shafts. Everything from fine hairline crack leaks to gushers can threaten the long-term integrity of the structure and surrounding property. Fortunately, pressure injection of polyurethane grout into the crack or behind the leaking wall (depending on the application) creates a durable and rugged positive side repair. A relentless solution to a relentless problem.

A wide variety of leak seal solutions are available to address almost any type of concrete leak. (Call the Alchemy-Spetec technical support team at 404-618-0436 for assistance in choosing a product for your specific project.)

Polyurethane Leak Seal Solutions - Crack and Joint Injection

Crack and joint injection products are generally used for smaller non-gushing leaks:

Spetc PUR GT380
Activates as Foam or Gel Depending on Amount of Water Added
Ideal for Manhole Rehabilitation

Spetec PUR GT500
Most Dry-Cycle Resistant Hydrophilic Grout
Ideal for Cracks with Intermittent Leaking

Spetec PUR GT350
MDI Based Grout
For Wet Dynamic Cracks & Joints

Spetec PUR F400
Flexible Hydrophobic Grout
Ideal for Dynamic Cracks & Joints

Spetec AG200
Acrylic Injection Resin
Used in Special Situations (Contact Alchemy-Spetec Support for More Info)

Polyurethane Leak Seal Solutions - Curtain Grouting

Curtain grouting products are generally used for gushing leaks or multiple smaller leaks in proximity:

Spetec PUR H100
Semi-Flexible
Ideal for Structures with Some Movement

Spetec PUR H200
2,050 psi Compressive Strength, Fastest Cure Time­­
Ideal for Soil Stabilization

Spetec PUR Highfoamer
50x Expansion
Cost Effective for Large Voids

Spetec Boom! Seal
Two-Component, High Expansion (35x), Hydro Insensitive
Used in Special Situations (Contact Alchemy-Spetec Support for More Info)

Want more information on polyurethane leak seal solutions?

Alchemy-Spetec's AP Fill 700 and AP Fill 720 are one-component polyurethanes used for filling voids in supporting soil surrounding a structure.  Situations in which these materials might be used for void fill include soil adjacent to retaining walls, basement walls, seawalls, and infrastructure boxes.  

Benefits of One-Component Void Fill Foams

• Their slow reaction time allows for the material to travel farther from the injection point, fill more voids, and permeate more soil before curing.
• They're ideal for encapsulating underground debris (decaying organics, roots, buried construction waste).
• On small jobs, they can be installed with a very small, portable pump that can be lifted and transported by hand. 

Differences Between AP Fill 700 and AP Fill 720

• AP Fill 700 features very low viscosity, making it ideal for permeating fine soil with small voids.
• AP Fill 720 is extremely rugged and durable when cured, while still retaining some flexibility. Its high expansion rate makes it ideal for filling larger voids.

Want more information on Alchemy-Spetec geotech products?

A contractor in Atlanta was recently called in to seal off a rain-induced ceiling leak in a new construction high-rise penthouse suite. Sealing off the water intrusion from the roof above was not an option, due to the rooftop swimming pool directly above the penthouse. So, they had to get into the ceiling from the interior of the suite and repair the leak from the underside.

Powerful Polymers

The crew on this job injected Spetec PUR F400, a water-reactive, hydrophobic, flexible, single component polyurethane resin. This product is ideal for sealing off active leaks in cracks.

Painless Procedures

Leaking concrete structures can be permanently repaired with concrete crack injection & curtain wall procedures using water-activated polyurethane foam. Pressure injection of these liquid polyurethane resins forces the material into leaking cracks or behind leaking walls depending on the application. After the polyurethane injection is complete, the polyurethane resin rapidly reacts with water to form a watertight seal.

Rapid Results

In this case, the leak was shut down in less than two minutes. This all went down literally right before the new tenant was scheduled to begin moving in. (No pressure there!)

Want more information on polyurethane leak seal repair?

What Causes Leaks in Concrete?

Imperfect Construction
Concrete construction is by no means a perfect science. New construction often requires Leak Seal treatment follow-up work. If the initial construction isn’t properly sealed at the time of construction, leaks are bound to appear sooner rather than later.

Weather and Wear
Concrete naturally decays over time. Exposure to extremely hot temperatures and extremely cold temperatures can take their toll over time. Even structures located in mild climates will begin to decay purely due to the aging process.

Unstable Soil
Unstable soil can undermine the integrity of concrete structures and cause cracks to appear. Loose soil has four main causes: soil erosion, poor compaction, freeze/thaw cycles, and biological decay. If soil is the main culprit, additional stabilization and slab lifting treatments may be required in order to prevent further cracks from appearing.

What is Curtain Grouting?

Curtain grouting is the process of injecting water-reactive resin behind the leaking wall in a grid pattern (from the negative side). The water on the other side mixes with the grout and cures to a solid mass covering the surface of the wall on the other side (positive side). In addition, you don’t have water pressure dislodging external “patches” over time, as can be the case with other methods.

Curtain grouting is often required when there are gushing leaks, multiple leaks in proximity, cracks cannot be identified, the walls are made of material that does not respond well to crack injection (such as masonry, stone, and CMU), or previous leak seal methods have failed.

The most well-known Alchemy-Spetec product for this application is Spetec PUR H100, a one-component, closed-cell, hydrophobic, water-reactive, solvent, and phthalate-free, low viscosity resin. If there are large voids involved, Spetec PUR HighFoamer (a similar product with a higher expansion rate) may be a more cost-effective option.

Want more information on curtain grouting?