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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 are mixed and begin react. Most products if mixed in quantities as small as a pint will heat up to as much as 450°F (this includes many hardware store products). So, if you need a large quantity of epoxy adhesive or coating, mix only what you can use within the pot-life and plan to install it on the substrate as soon as possible.

If the mixed epoxy in bulk is not used quickly, the generated heat can cause the epoxy to boil and sputter. 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 dilute the hot epoxy to cool it down and prevent additional smoke—be careful! Don't add water to hot epoxy, it can convert to steam and possibly cause more foam and splashes.

If you need a low exotherm epoxy that generates very little heat while curing, call us at 650-261-3790.


2.      Use wet aggregate

sand-1If you want to add aggregate (or sand) to a liquid epoxy to make a mortar or grout or to extend the epoxy volume, the best policy is to use aggregate that contains less than 0.2% moisture. Find or specify kiln-dried sand or aggregate in sealed bags. Sand that was stored in a loose pile could contain excess moisture -- 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 in order to polymerize to full strength. 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 (structural load bearing) they will weigh each component separately. If you elect to weigh the components, check the proper amount of A and B as the weight ratio (in lbs or kg) is often much different from the volume ratio (liquid quantities).


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

The minimum proper personal protective equipment (OSHA term is PPE) for mixing epoxies generally includes eye protection (safety glasses, face shield or goggles) and 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.

If you or your buddy accidentally spills epoxy on skin, wash immediately with copious soap and water. See ChemCo's epoxy safety tip blog for more information.


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, paint or other organic contamination is foolhardy and the bond will likely fail in use. Discuss the issue of contamination with your epoxy supplier and he will provide the best way to prepare for the application.

Many epoxies form a non-permeable barrier to moisture or water vapor. So if you apply a impermeable epoxy coating to concrete that has either subsurface moisture or contains moisture with another barrier on the opposite side, subsequent temperature cycles can cause delamination or even substrate spalling.

In most cases, a slight removal of the surface with a grinder or shot-blast with some roughening (similar to 40 mesh sandpaper) is the preferred approach. High pressure water blasting (5000 psi) which removes a slight amount of concrete surface can also be effective.


7.      Apply epoxy over a moving crack or joint

Particularly observed in exterior applications, 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. When repair epoxies or protective epoxy coatings are used on concrete in regions with thermal movement, cracking or delamination should be expected.


8.      Store epoxy overnight in pickup truck or outside in cold weatherpickup in snow

If the night time temperature is expected to fall below 40°F (5°C),  epoxy stored in a truck or outside will be cold. It will cure very slowly and be much thicker and difficult to mix properly. Some epoxies won't cure at all at this temperature.

In cooler seasons, store epoxy as close to 73°F (23°C) as possible prior to use. In some cases, professionals will intentionally “condition” their epoxy by storing it at an elevated temperature (above room temperature) so that it will cure faster and be easier to mix especially in cold weather applications.

Find more cold weather tips here. Call us if you need an epoxy for cold weather, hot weather or any weird situation: 650.261.3790.


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  or ChemCo Systems for 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, safe epoxy use tips, epoxy limitations, epoxy exotherm issues, epoxy PPE suggestions, mixing and measuring epoxy