FREQUENTLY ASKED QUESTIONS

Over the years we've had hundreds of request for cleaning and removing coatings from concrete.  And most people are not familiar with concrete and the wide variety of finishes such as "Broomed, Stamped, exposed aggregate, flat work, stained etc.  The list is extensive and there are many factors to consider before sandblasting because it will effect the final finish of your project.   The photo above is a typical porch that was coated with an exterior enamel. Prior to starting any coating removal project, we will physically inspect the project to determine several factors;  What type of coating (which is not always possible).  How thick, how many layers and the condition of the concrete, How much containment is required, what the access for our machine & equipment and what's involved in regard to clean up.  And although we determine the square footage of your project, this can only be used as a baseline for a daily production rate because every project is very individual.   

Standard concrete is made up of the same basic ingredients....Portland Cement, Sand and Aggregate. However, the specific finish, the individual concrete mix and how it was installed makes every "pour" different.  The photo above is a core sample showing the amount of sand and aggregate (small stone) for an average pour.  The top surface is smooth because during the installation process the Portland Cement is brought to the top during finishing. This smooth layer of cement (we call cream) covers the sand and aggregate.  The thickness of this layer will depend on the mix and the finisher.

The answer to that question will be based on a few things.  The thickness of the "cream" the age of the concrete and the thickness and type of coating(s) to be removed.  The coating is usually the biggest factor.  What type and how thick.  Many coatings are thin and already pealing off so a fine media will remove it fairly fast.  However, if an epoxy or urethane was applied, blasting will take longer.  The longer it takes, the more the  top layer of cement or "cream" is subjected to the blast stream.  Although very hard, Sandblasting can slowly remove that cream, exposing small amounts of sand and/or aggregate if the operator is not experienced.                                                                                               Should this occur, the exposure won't necessarily be even  because the thickness of the cream is never perfectly even, which can give the surface an uneven profile or texture.  The photo above is the same porch (still a bit wet) after wet blasting.

In regard to a surface, profiling refers to the texture or finish.  With the porch above (now dry), the coatings were removed with a medium/ to fine glass media (40/70) which is typically softer than many other media types and works well on concrete leaving a fairly smooth profile.  In this case it's comparable to 180 to 220 grit sandpaper.  All sandblasting will leave a different profile compared to an original finished trowel surface.  This includes surfaces such as stamped or broomed concrete.  Exposed aggregate concrete however, will not reflect any texture change.  it will take the sheen off the small rocks (aggregate) because once again sandblasting is slightly profiling the surface of the rocks.  

Wet blasting or Dry Blasting is a mess and there's no way around it!  Regardless of the project, some sort on containment to protect the surrounding area from the blast stream will be necessary.  High pressure media can leave the blast nozzle at 400 ft per second causing damage to anything not protected.  With this project, everything was protected including the lawn and landscape areas.  Protection is not the only issue.  All the media drop, which is the used blast media, paint chips, slurry, etc. must be contained to minimize the clean up to a smaller area. Around pool decks, the entire pool is double taped with a plastic sheet, keeping the media drop from entering the pool.

Actually yes and no.  Since water is mixed with the media, what comes out of the blast nozzle is completely dustless. The mix of media and water creates a slurry around the blast area during the process.  However, there is still media that is thrown beyond the slurry and this media can dry very quickly creating smaller particles that can become airborne.  So, if it's windy or when it's swept during clean up, these blast particles (shown above) can create dust.  A simple solution to this is to hose down the media drop with water, basically turning it back into slurry.  The first step in clean up consists of simply brushing and sweeping the slurry and media drop into sand bags for disposal.     The surface must then be thoroughly wash down to collect the remaining media and fine particles.  A final pressure wash is required to clean out the pores of the concrete.  This step is critical if a sealer or new coating is to be applied.