10 Things Not to do with Concrete Repair Epoxy

Posted by John Bors on Thu, Aug 2, 2012 @ 13:08 PM


1.      Leave Large Quantities of Mixed Epoxy in Bulk

concrete repair epoxyEpoxies that cure at room temperature generally give off heat (are exothermic) when the two components react. Most products if mixed in quantites as small as a pint will heat up to as much as 450°F (this includes hardware store products). So, if you need a large quantity of epoxy adhesive or coating, mix only what you can use within the potlife and plan to place it on the substrate as soon as possible.


If the epoxy in bulk is not used quickly, the generated heat can be enough to boil the epoxy and some products will generate smoke and possibly ignite as well as melt a plastic pail. Should this occur, you can add dirt or sand to the hot epoxy to cool it down and prevent additional smoke—be careful!


2.      Use wet aggregate

If you want to add aggregate (or sand) to epoxy to make a mortar or grout, use aggregate that contains less than 0.2% moisture. Don’t use sand that was stored in a loose pile that could contain excess moisture or the strength and properties of the mixed grout can be negatively impacted.


3.      Mix with a stick

Two component epoxies require adequate sheer in order to properly react. With some lower viscosity products, a rotary paint mixing blade on a drill is fine. For higher viscosity epoxy coatings or pastes, a “Jiffy” type mixer is strongly recommended as it will provide shear without adding excessive air to the mixture.


4.      Use wrong proportions

Most epoxies can tolerate off-ratio proportions to 5% and some epoxies will cure with higher off-ratio mixes. To be safe, stay within 5%. Most professionals who mix epoxies by hand will purchase either disposal plastic measuring cups to ensure proper proportions or on critical projects will weigh each component separately. If you elect to weigh the components, check the proper amount of A and B as the weight ratio is often much different from the volume ratio.


5.      Apply epoxies wearing a t-shirt, shorts and sandals

The minimum proper personal protection equipment (OSHA term is PPE) for mixing epoxies generally includes eye protection (safety glasses, face shield or goggles), skin protection (rubber gloves, long sleeves and pants). In most jurisdictions, there is also a requirement to have an eyewash station available within less than a minute from the location of the work.


6.      Apply epoxies to dirty or contaminated substrate

Most professionals know that taking a shortcut on surface preparation can ruin a project. Attempting to adhere to concrete, wood or steel that has oil contamination is foolhardy and the bond will likely fail in use. Discuss the issue of contamination with your supplier and he will provide the best way to prepare for the application. In most cases, a slight removal of the surface with a grinder or shotblast with some roughening (similar to 40 mesh sandpaper) is a preferred approach.


7.      Apply epoxy over a moving crack or joint

When repair epoxies or protective epoxy coatings are used on concrete (particularly in exterior applications), the concrete will expand and contract linearly in relationship with temperature. This means that cracks or cold joints will become smaller as the concrete temperature increases and larger when the concrete temperature decreases. In some climates, the daily temperature cycle is as much as 40°F or more. In these locations, the crack will move a considerable amount each day and the repair material will crack almost immediately.


8.      Store epoxy overnight in pickup truck or outside in cold weather

If the nighttime temperature is expected to fall below 40°F, the epoxy stored in the truck will be cold. It will cure very slowly and also be much thicker and difficult to mix properly. In cooler seasons, store epoxy as close to 73°F as possible prior to use. In some cases, professionals will intentionally “condition” their epoxy by storing it at an elevated temperature so that it will cure faster and be easier to mix especially in cold weather applications.


9.      Place neat epoxy in large voids

For the same reasons as stated in item #1, epoxies in large masses can become very hot to the point where the epoxy is damaged. If it is necessary to repair a large void, consult your manufacturer for his recommendations. One solution to prevent damage from epoxy exotherm is to mix aggregate with the epoxy which lessens the exotherm effect as most of the mass is in the aggregate. We offer several low exotherm products (a low viscosity liquid epoxy and a paste epoxy) which are especially designed for this use.

 10.  Purchase the exact quantity

With the high costs of delays, manpower, shipping and mobilization, most professionals purchase excess materials for their project. For coatings, often a 15% safety factor is used and for other concrete repairs or restorations with epoxy, the factor can be 5-10%. We offer a great estimator tool and you can preset the safety factor to account for accidental losses and unforseen quantity needs (exact measurements on construction projects are never exact which is why they are often called estimates).

Please call or write us at ChemCo Systems if you need more information on concrete repair epoxy or epoxy protective coatings.

Tags: epoxy repair tips, concrete repair epoxy, epoxy coatings