4 Problems with Existing Epoxy Mortars

By: Andy Odorzynsk, Induron National Sales Manager

MortarChemWhile cementitious epoxy mortars are a vital step in most concrete lining projects, the epoxy mortar products available are typically fraught with problems and application challenges. 

First off, because concrete in immersion deteriorates over time, the necessity of coating these immersion substrates becomes painfully obvious. In other environments, we may simply resurface concrete with a cement mortar. But, the resulting surface would have the pores, capillaries, and surface irregularities typical of concrete. These problems  make it nearly impossible to hermetically seal a concrete structure. 

Epoxy is used to modify cementitious mortars so that the mortar is able to penetrate and seal capillaries and pores in the concrete, which creates a smooth monolithic substrate for subsequent high performance lining. The entire purpose of resurfacing is to create this smooth, consistent surface for lining. Yet, many installations fail to achieve this finish.  At best, this results in a lining system that still exposes the underlying concrete to the contents being stored. More often, however, we find adhesive failures manifesting between the existing concrete and the mortar, or between the mortar and the lining applied on top of it. Why? 

Let’s take a minute to look at why these problems occur.


These products tend to be HEAVY! Upwards of 18lbs per gallon. Nearly double that of a typical gallon of house paint. Weight matters for many reasons. Every pound has to be moved multiple times by the workforce as buckets are moved around a job site, product is mixed, transported to a work area, and installed. If you double the weight, you double the work. Conversely, lowering the weight substantially will inevitably increase productivity and make proper installation easier.  The weight of common epoxy mortars primarily comes from cheap fillers like silica. Silica is heavy and angular. Two properties that make it difficult to trowel into a smooth finish.

Induron’s Mortarchem tackled this problem using hollow ceramic sphere additives. Utilizing multiple sizes of spheres, Induron’s team of polymer scientists engineered the perfect balance of performance and applicator friendliness. The ceramic spheres provide structural reinforcement and create a light-weight, easy-to-apply mortar. It spreads like smooth peanut butter, but outperforms concrete in adhesive testing.

 Short Working Times 

Epoxy modified mortars have two mechanisms of transition from liquid to solid: the hydrolysis reaction of Portland cement and the polymerization of the epoxy. Applicators are left with only minutes from the time they mix the product until it becomes so viscous that they cannot effectively finish it with a trowel. This short work time often leads to areas where the resulting substrate looks like a pile of sand, instead of a smooth monolithic surface suitable for lining.

Mortarchem was designed utilizing a unique 100% solids water-based epoxy technology, which extends its working time significantly. In side-by-side testing with competitive products, I applied multiple epoxy mortars in the heat of an Alabama summer. With temperatures in the upper 80s, only one product was workable after 15 minutes: Mortarchem. In these summer temperatures, we were able to create a fantastic finish with Mortarchem up to 30 minutes after mixing. In fall applications with temperatures in the 50s, the product remains workable for up to an hour. More working time consistency results in far less waste, and a better substrate for lining.   

Difficult Finishing 

Anyone who has ever attempted to patch a hole in their drywall can appreciate that viscosity and consistency of your mortar matters greatly. If you have thick, chunky material, it will result in a rough patch. It’s just difficult to work with. The same is true when resurfacing concrete. A proper mortar should be thick enough to build substantially thickness without sagging and slumping on a vertical surface, but should also be workable enough to allow a wetted trowel to glide across its surface. Most products on the market simply don’t allow for both. As a result, applicators must field-modify the product by adding water.

The addition of water is a common solution to all three problems I have listed above. Dilution with water will lower the weight of the working mix. When the product begins to cure and thicken, water will make it more workable. However, the addition of water can quickly become more of a problem than a solution. 

Adhesive Failures

This brings us to the real problem: failures. Epoxy modified cementitious mortars have seen some very large, ugly failures in the past few years. These often manifest as adhesive failures, and water is at the root of many of them. 

When applying repair mortar to concrete, most data sheets require an SSD condition. A Surface Saturated Dry condition seeks to get the substrate wet, but not too wet. A difficult and subjective goal! If we do not wet the concrete at all, the slab will pull moisture from our mortar. This can result in a moisture-starved hydrolysis reaction at the point of substrate interface, resulting in adhesive failure. If we get the substrate too wet, the water will simply act as a bond breaker, stopping the mortar from truly contacting and bonding with the existing concrete. Induron recommends a scrub coat be utilized to achieve consistent adhesive results between the mortar and the substrate.

Depending on the product, the addition of water directly into the mortar is fine up to around 10% of the total volume. Beyond that, the product will have a low enough viscosity to facilitate stratification of the mix.  Applicators often view this as a good thing because as the heavy aggregate sinks into the mixture, the surface becomes smooth and consistent. However, what we have actually created is a stratification wherein our mix is cement-rich at the substrate-to-mortar interface, and epoxy-rich at its surface. This is also likely to manifest with the adhesive failures. 

When the surface of an epoxy modified mortar becomes epoxy-rich, it is visually evident. We can see a white film manifest on the surface. This is a clear sign that the mortar has either been thinned with too much water, or has been overworked to the point that the epoxy is separating from the cement and aggregates. This film can result in jeopardized adhesion between the mortar and the high performance liner installed over it. 

Mortarchem was designed specifically to overcome these challenges. The combination of our unique water-based epoxy resin and the addition of our ceramic sphere reinforcement eliminates the need for heavy thinning. Our 9.5lb/gal mortar creates a beautiful finish on a trowel. The buckets are a breeze to move around your job site. 

It really is one of those products you have to apply yourself to understand just how different it is. We would love to bring you our material and let you see for yourself. Please contact the representative in your area to schedule a demonstration.

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