The Advantages of Shotblasting Concrete Floors

Shotblasting concrete floors has an advantage to you and to your customer.

Concrete Floor Preparation, like any surface that is to be coated or have an overlay or screed applied has one prime requirement – Prepare it right, and it will perform.

With concrete, there is a few extra things that make adequate preparation so important when compared to other substrates.

• On a construction site, concrete often gets walked on, and may get oils, fats, grease, dirt, adhesives, plaster and all sorts of other contaminants on it before it is time to prepare the surface for coating. Where the concrete had a previous floor covering on it, there may also be membranes, sealers, glues and old floor coverings.
• Concrete can be very different from one slab to another slab. No two slabs, even on the same job done by the same layers, are the same. Even the weather or climatic conditions on the day will influence how concrete cures and how much laitance on the surface and many other factors.
• Concrete can be a minefield of moisture problems, salt, porosity, etc. These must be addressed correctly, especially moisture.

When quoting to prepare a concrete floor the first question you need to ask the customer/owner is: “What will the floor be treated with?”

• Coating?
• Membrane?
• Carpet?
• Sheet vinyl,
• VCT?
• Cementitious Screed?
• Epoxy Mortar?
• Many others.

When this is known, it can be decided what method is right to prepare that slab.
The area of the job too, will influence the logical choice that should be used. For instance, if it is only 20 sq m (200 sq ft), then a Grinder or a Scarifier may be the logical choice, but that depends on the floor treatment.

When is shotblasting it the right preparation method?

Firstly, let’s look at the advantages of Shotblasting;

• It is very fast
• It has the lowest cost per square metre of any mechanical prep method.
• It is very dust-free
• It is immediately ready for coating, priming, screed application as soon as it is done. No waiting, no vacuuming usually, just magnetic sweep and go.
• You can control the ‘Profile’ easily, fine or rough blast or anywhere in between. (Profile is a standard used to define ‘Surface roughness’).
• Shotblasters will blast every square inch (or square centimetre) equally as much as every other square inch.
• Therefore, anything that is weaker will get blasted away and you will be left with a very sound surface to accept nearly every treatment.

What are the disadvantages of shotblasting?

• The only disadvantage is that because it will remove weaker areas more than stronger concrete, the floor will be less flat than when you started.
• Shotblasters are not usually successful on glue removal although some very thin ‘hard’ glues may come of easily. Anything thick and/or sticky is highly unlikely to work.
• Removing some thin coatings may work quite well but be aware that removing thick elastomeric coatings can be difficult. Sprayed-on Road-line markings may remove quite well, but thick, multilayered or thermoplastic lines are not likely to be successfully removed using a shotblaster. Scrape 80*90% of the coating off first with floor scrapers then blasting is often the best way to remove these coatings.
• Really, there are very few disadvantages of shotblasting.

So, let’s look at some the incredible features of Shotblasters.

1. Did you know that the finer the shot the faster you can go and get a floor beautifully prepared. Because the Blastwheel can throw a certain number of kilograms (pounds) of shot per minute the finer shot contains many times the number of particles per kilogram. This means that more impacts occur per minute and a finer profile is achieved. With fine shot such as S230 and S280, you can blast a floor at low cost and do incredible areas easily. Profile can be around CSP-3
2. If you use large shot, you may not do as many square metres, but you sure can take a deeper cut out of a floor. If a big profile is required, then larger shot such as S390 or S460 is the way to go. Be aware that 6 ½” Blastwheels should never be used with S460! Profile is CSP-7
3. Medium sized shot such as S330 is a great size to use for high build coatings or cementitious screeds, epoxy mortars and anywhere that the floor is only in average condition and you need to remove a weak top layer. Profile is likely to be CSP-5
4. Here is an interesting fact: Large profile does not mean better adhesion!
   In fact, a Class CSP-2 or CSP-3 profile in most cases will deliver the best adhesion, especially for coatings or primers for screeds! Exceptions seem to be high build cement screeds of around 15 to 70mm for instance.
   This can be proven with adhesion ‘pull-off’ tests.
   It does mean that you will use more coating to fill the profile before getting the required DFT! (Dry Film Thickness). Great for paint manufacturers.
5. If you apply coatings and membranes and want the surface flat, but the assurance of adhesion, many contractors will give a floor a quick coarse grind first then shotblast lightly after. This gives the best of both worlds, flatness and adhesion.
6. Many Polished Concrete contractors use a shotblaster as the first line of attack of a concrete floor so you can blast till you are just about touching the aggregate. Use S280 or maybe S330 if there is a thick layer of sand cement on top before you get to aggregate. The great thing is this part of the floor which is the biggest unknown becomes the quickest and surest section of the job. Grinding after that (if you are using the right shot size) is fast and easy. You can reduce the time taken and your cost on any job hugely!
7. The benefit of Shotblasting is that it has minimal tendency to create micro-cracking into the surface, just like diamond grinding. Scarifiers have a medium risk, and Scabblers are very high risk.

CONCLUSION

The lesson that we can take away from this is that Shotblasters should be used far  more than they are. In fact, it doesn’t make sense not to.
Exceptions may be that if most of your work is only 10m2, 25m2 and occasionally a 50m2 and you don’t do these size job frequently, if this is the case, you would be better off with a concrete grinder.
Shotblasters are far more cost efficient, far better adhesion, easier to make the floor dust-free and ready after blasting than grinding, or any other method of Concrete Floor Preparation.