As in many other construction activities, taking proper steps to properly clean and prepare surfaces prior to the use of repair materials is critical to the time efficiency and long-term success of your repair. Surface preparation methods include (from gentle to aggressive) detergent scrubbing, acid etching, grinding, abrasive blasting, steel shotblasting, scarifying, needle scaling, high pressure water blast, scabbling, flame blasting, bush hammering and milling/ rotomilling.
If you are considering pressure washing, 5000 psi has been determined as the minimum pressure to provide acceptable levels of cleaning of concrete surfaces. In cases where the cementitious surface was overworked when placed or excess water was used, it is highly recommended that the paste layer be partially or completely removed for the optimum performance of the repair. Applicable specifications include: ACI 503R, ASTM 4263, ASTM 4260, ICRI 03732 and ICRI 310.2.
2. Elcometer tab pulls
Even with the best surface preparation (and a small mock-up), unexpected issues can interfere with good surface bonding. For a small investment,
This preconstruction step demonstrates that you are willing to take the extra care to ensure a quality project. This tactic is especially useful if you are planning to use a new material. Disagreements should be minimal when the actual appearance is presented before the project starts. Sometimes, you can be compensated for your time and materials.
For polymer repair mortar or grouts, many (if not most) manufacturers package their aggregate filled systems in a 3-package system which includes bags or pails of graded sands.
Unfortunately, shipping a low cost and dense product such as sand around the country or overseas is very costly and we don’t think that it is necessary. Call us when you develop a requirement for this type of a system and we’ll provide recommendations to locally source a gap graded aggregate system that can provide significant savings for you and your customer. Use only dried sand (less than 0.2% moisture) in polymer mixes.
For most of the repair jobs (not counting coatings) where epoxies and other polymeric products are used, the material cost is typically within a range of 5-10% of the total job costs which include other materials, equipment, mobilization and labor. If you estimate conservatively and your guys run short, there may be several negative consequences.
First, the guys might shortcut the application rate which might undermine the performance of the areas that were short. Second, they might run out and call you on late Friday afternoon looking for a very costly delivery by air on Saturday, or your crew might have to re-mobilize because the owner needs the area back in service while awaiting the replacement material. There isn’t much cost risk in buying a little extra as epoxies are very long-lived materials so you can use them on future projects or return them in unused condition (we charge a 15% return fee).
If you elect to buy a little extra material, you likely just saved a lot more on your most expensive cost item which is labor. Finally, if your guys discover a bit of extra work not originally noticed, you have an option for a change order without excessive costs.
Maintain copies of all SDS (safety data sheets) to be easily accessible on site. Don’t assume that because you’ve worked in the industry for 30 years that the content of the SDS is the same as in 1982—they are frequently updated and the contents are subject to change. For example, in the case of accidental ingestion of a toxic substance, syrup of ipecac is no longer routinely suggested.
In some individuals, certain chemicals can cause an allergic sensitivity that can be triggered over repeated exposures and make working in the field impossible. Encourage your employees to clean their work clothing regularly rather than allowing contaminants to build up. Finally, don’t assume your guys will think about drinking sufficient water on the hottest days—you will have to keep reminding them.
For cleaning epoxies and other polymers from tools, many field techs use acetone or MEK. If there are only minor amounts of product to be cleaned and the bulk material is uncured, you can squirt a bead of liquid dish-washing soap right on the tool surface and rinse off the blade or surface with hot running water. Many of the polymers will emulsify and rinse off if you use a little extra concentrated soap which is far less costly (and never flammable) than solvents. The same technique works on cleaning exposed skin—liquid detergent is better for your skin than acetone. Some contractors swear by using film forming liquid skin protectant creams for the times when the gloves are off or as a great secondary barrier practice.
Instead of disposing of large cardboard shipping cartons, have your warehouse guy save them and cut them into 12”x 12” (or some other favorite size) squares to use as mixing platforms for small quantities of 2 component polymers or for making small paste mixes. When the project is over, you can toss the cardboard as the epoxy scraps should be in the hardened form of a cured inert plastic.
Your project site pictures have a value far in excess of 1000 words. An absolute job requirement is that your foreman takes shots before and after every job. These are helpful in many ways: establish baseline conditions, provide visual backing for change order situations, be used in safety training, assist in accident investigations, provide evidence of quality work and project completion, are valuable for marketing, establishing credibility and to help educate new employees.
We offer several primer solutions for bonding, repairing or coating green concrete including QuikPrime which even works underwater. You can generally use CCS Coating, QuikPrime 24 hours after concrete placement.
Don’t attempt to fix delaminated concrete without confirming and mapping the extent of the problem. Bring a sounding hammer and test the area to be repaired. A heavy steel chain can also be used. Cracks and spalls will sometimes be caused by poorly bonded topping slabs or old repairs which have disbonded or never bonded over the original damaged substrate. Concrete can debond from the steel deck in elevated slab on pan installations. If the concrete is delaminated in areas, fixing the cracks without repairing the underlying delamination is a waste of time. Be prepared to consider the cause(s) and offer a fix for the delamination as first steps in the repair.
There are many techniques for heating which include: heat guns, warming blankets, pre-heating the cans of epoxy before use, warming the substrate with local baseboard heaters contained with temporary walls of plastic sheeting, etc. It’s best to use temperatures below 300°F (150°C) for speed curing (this includes heat guns). Since epoxies react by giving off heat (in an exothermic reaction), the thicker you apply an epoxy, generally, the faster it cures. Conversely, if your summer temperatures are very hot, the amount of useful life of epoxy mixes may be too short for practical use. In this case, cooling the separate components before use in an ice bath or air-conditioned area will help extend the mixed life.
If your epoxy is too thick, preheat the components before mixing. Store the epoxy containers overnight in a closet with a portable heater or put them in the cab of the truck with the heater turned up when it’s cold outside. Some field technicians mount a light bulb inside their epoxy injection pump to warm the epoxy in the reservoirs. An epoxy with a viscosity of 1000 cPs at 50°F might have a viscosity of only 150 cPs at 80°F. Don’t forget that useful (mixed) lives and cure times are also affected by temperature.
Epoxies and other polymers have a curing property that is rarely discussed. When A + B components are mixed in proper proportions, most polymers exhibit both linear and volume shrinkage upon cure. This is because the newly formed cross-linked polymer takes up less space than the separate unreacted components. Shrinkage is factor that must be considered when the use of repair polymers might involve a thick cross-section of cured material.
How thick is too thick before you will develop a problem such as internal stresses in the repair? The answer is that it depends on the specifics. There are some tactics which include the use of installing multiple lifts, low exotherm and/or low modulus resins and aggregate filled epoxy systems which help alleviate problems when thicker cross-sections of repair materials are needed. Please call us for advice.
16. Polymers move more
Standard practice for concrete floor construction today is to install a vapor barrier between the structural slab and underlying compacted earth or engineered fill. This practice is relatively new, so what can be done with older concrete floors which don’t have a vapor barrier? Today, if your moisture test shows 3 lbs/1000 sq. ft/24 hrs or more of moisture vapor transmission (ASTM F18690), don’t even think about installing an impermeable coating or flooring material without first using an epoxy vapor barrier.
We make a great product for this purpose called MVR Coating. When properly used, it will reduce the vapor drive to a safe level and can be topcoated in about 12 hours.
Surface ports have become a popular tool to use with
When your project is complete, don’t automatically react off your leftover A and B components to dispose of partial containers of epoxy. Most epoxy products are relatively stable and can be used for extended periods if kept within a reasonable temperature range and sealed. We say that most of our epoxy products can be safely used within 3 years of manufacture. There may be some settling (particularly for coatings) but the products will still perform if the separate components are mixed well individually before use. Caution: moisture sensitive materials such as polyureas or polyurethanes may have a much shorter shelf life.
Say you have a sound substrate with a myriad of different tones or slight cracks or chips that disturb the smooth face. What can be done? Consider sacking, a repair technique that involves pre-wetting the substrate and then hitting the surface a burlap sack containing fine aggregate of the same color as the concrete along with some Portland cement. A fine wet cement-based slurry can also be applied by heavy brush. This trick can also rid the substrate of the dark crack “shadow” following epoxy crack injection on architecturally sensitive surfaces such as light precast panels—call us for more information.
On all of our data sheets, we include the separate
We organize free training sessions in structural concrete repair and epoxy injection two or three times a year—they take a day and a half. It includes hands-on practice and technical lectures. Call (650.261.3790) or email us if you’re interested.