PTA – Scarifying – What is a scarifier used for and what kind of profile does it produce?

In this chapter of the Premium Training Academy we look at what is a scarifier used for and what kind of profile does it produce.

In this module we cover off on the profiles that can be attained with a scarifier, what kind of job this machine is used for, how a scarifier works, the different kinds of flails (cutters) that are used and the benefits and cautions that you need to know about.

First, what kind of profile can be produced, then we’ll look at where a scarifier fits into surface preparation of concrete.

Profile is the term used internationally to define “Surface Roughness”. For concrete, the profile is usually determined using the comparator method. You compare the surface of your job, with Concrete Profile Chips that are prepared to a recognised standard.

These surface roughness chips are classed like this, and the method of preparation that can achieve this roughness:

  • FLX-01 Acid Etched
  • FLX-02 Ground
  • FLX-03 Light Shotblast
  • FLX-04 Light Scarification
  • FLX-05 Medium Shotblast
  • FLX-06 Medium Scarify
  • FLX-07 Heavy Abrasive Blast
  • FLX-08 Surface Retarder or Scabbled
  • FLX-09 Heavy Scarification
  • FLX-10 Breaker Abrasive Blast

NOTE: Several prefixes for concrete profile standards are used; including “CSP” by ICRI which is commonly used internationally.

Floorex concrete profile chips are actual mini slabs approximately 75 x 75mm (3” x3”) of concrete, each one is finished from to a required standard. These are supplied from FLX-01 through to FLX-10 which are the normal surface roughness profiles used for coatings, membranes, screeds, and overlays.

These are the are surface profiles that you can achieve with a scarifier.

  • FLX-04:This degree of Scarification is often used for High Build waterproofing membranes, for Ceramic Tile preparation when a cement base is used to set the tiles into and for screed preparation when the screed thickness is significant.FLX-4 profile is commonly attained when using a Scarifier fitted with 48mm Flails.

    Note that using 48mm Flails with a few extra flails fitted (and less spacers) can potentially reduce the depth of profile and reduce the ‘furrowing’ effect that scarifiers typically produce when using pointed flails, if needed.

  • FLX-06:When a surface needs to be reduced in height because it has been poured too high, etc, this degree of Scarification is commonly attained when using most scarifiers that are out there.FLX-6 is desirable when having to install high bulk screeds (High bulk is achieved when small aggregate is added to the screed to bulk it up), and under some ceramic tile beds when the bed has to be very deep.

    FLX-6 is attained when scarifying deeply with 58mm Flails (cutters). It is possible to get a FLX-6 profile using 48mm Flails if cutting deep to reduce the height of a slab. Note once again that the overall effect and profile can be varied if extra Flails are used.

  • FLX-09:Is used in jobs such as bridge building and refurbishment.

How does a scarifier work?

A scarifier is usually powered either with an electric motor or with a Petrol (Gas) or LPG motor. Other options include hydraulic motor and air motor powered machines for special applications. This motor drives a drum via a belt which revolves at 90o to the direction of travel. The drum has a number of flail shafts on which is installed the flails with hardened spacers between each flail. The flails are free to rotate on the flail shaft, and have 2mm to 5mm oversized hole through the centre of the flail on the flail shafts, plus they must have 1mm or 2mm sideways slack. In use, the drum will spin causing the flails to be flung outwards away from centre of the drum, by centrifugal force. It is the centrifugal force that we use to do the work.

How to set the scarifier cut depth correctly!

Because the hole in the flail is oversize on the shaft, the distance of the slack is the total amount that the machine should be set at to remove, otherwise damage to the flails, drum, bearings, shafts will result! So if there is 3mm slack on the shaft, then set the machine at 3mm maximum to take off. But how do you know you have it set at a maximum of 3mm?

It’s simple!

  • Find somewhere to test and set the machine cut depth
  • Now wind the depth control to highest setting
  • Then start the scarifier up, (Hopefully the flails will not touch the floor at this time if it is set to highest setting!)
  • Without moving the machine along, now lower the drum
  • Until the flails are just tipping the surface
  • Then wind it down until the machine is taking off just the right amount of concrete
  • Lift the machine (don’t adjust the depth control) move it forward and turn off and check the depth of the ‘cut’ made to the surface that it is not too deep.

At the correct depth setting you will greatly increase the life of the flails, shafts and bearings of your machine.

Do’s and Don’ts

Do not change the depth setting again! If there is a low spot in the floor, then you don’t want to be removing any concrete from that spot! Travel slow enough for the Scarifier to remove all the material it should down to the set-depth. If you have it set to, for example 3mm, but travel too quickly, then you may only take 1mm off. Don’t change the depth setting but travel at the speed where the machine will remove the full amount.

Cutting a floor flat

If you have to scarify a floor to take out undulations (ups and downs), here is how you do it.

Now scarify the whole floor in one direction at a speed that allows the machine to take off the concrete to the full depth you have the machine set at.

You may find that there are plenty of patches where the scarifier does not actually touch the floor at all. That is fine.

A smart method is to scarify a full length, then for the next pass, miss a little less than the width of the machine, then do the next stripe, and then the next, missing out nearly the width of the machine each time. Then go over the floor removing the bit in between. This stops the machine being on a side slope and cutting on an angle.

Then secondly, without moving the depth setting, do the same thing at 90o striping the floor and cutting the floor flat.
You will end up with a floor that is much flatter using this method.

Different types of flails (cutters)

  • Pointed Flails: The tungsten fitted has a 45o point. This is the most commonly used flail; these remove the most concrete possible and give the maximum profile.
  • Flat Faced Flails: The tungsten is flat across the top and at least as wide as the body of the flail. This flail does not produce much profile (quite flat) and is a good way to remove the top of the concrete to expose the aggregate so the aggregate in the floor can be Diamond ground more quickly than trying to grind 2 or 3 mm off with a Diamond grinder.
  • Hi-Carbon Steel Flails: these have many points, often 18 points of High carbon steel for low aggression removal. These can be useful for a small line-marking removal or coating removal project. They are much cheaper than tungsten flails, but they don’t last too long. The Bush-hammer on a Galaxy is an ideal machine if you are doing regular jobs of this type.
  • Milling Flails: These flails can be fitted to a standard drum. Milling tungsten flails have a flat top that may be from 11m to 22mm wide. Great for cutting off membranes or floor coverings with little contact of the concrete floor, even for planing timber decks on Boardwalks, etc.
  • Diamond Saw blades: Mastiff Scarifiers with 3phase or petrol motors can be fitted with a special drum with diamond saw blades to create a multi groove to the surface.

By the way: a Scarifier is not a Scabbler.

They are two quite different machines/tools, just like a motorbike is not a truck.
A scabbler is often a hand-held tool with a single or triple tungsten bits, but is available as a walk-behind machine. We have covered how a scarifier works. A Scabbler is very different. It is (usually) a compressed air powered tool very similar to a jackhammer pounding tungsten bit(s) vertically onto the surface, often with multiple points or a cross called a cruciform type bit, vertically down into the concrete to remove bulk concrete. They can also be used on steel, often marine work, to remove very thick rust and marine coatings. A Scabbler is useful to take down a very high area of concrete, such as taking down a kerb to create a pedestrian cross-over for example. On concrete, a scabbler is not generally used for surface preparation because it damages the concrete left with deep micro-cracking which compromises adhesion to the substrate.