Rossi Abrasives

Achieving the best performance from your PCD scrapers is a result of two factors: PCD pressure and RPM. The pressure exerted on the PCD bits must be sufficient to penetrate through the material being removed. The RPM must allow the PCD bits to maintain good contact with the surface without creating unnecessary stress on the bits. (Note: This article only deals with PCD scrapers. For information on regular concrete grinding tools, see Concrete Grinding Tools 101 in the June 2018 issue of CONCRETE SURFACES.)

Before we dive into the first factor, let’s do a quick refresher on PCD scrapers.

About PCD Scrapers
A PCD scraper is a diamond tool designed to remove surface materials from concrete. This could be an epoxy coating, a flooring adhesive, or an overlay. A PCD scraper is a tool that incorporates a polycrystalline diamond bit (or multiple bits) to function as scraping devices. They can have anywhere from one to four polycrystalline bits per tool and can be used for scraping a range of surface materials.

PCD scrapers are far superior to scrapers that use metal scraping bits because the hardness of the diamond cutting tip retains its shape much longer, ensuring consistent performance. Metal scrapers dull quickly and lose their performance.

Calculating Pressure
In order to determine the penetrating force a PCD scraper will deliver, you need to calculate the pressure exerted on the individual PCD bits. Two properties must be known to calculate PCD pressure:

  • The head pressure of the grinder
  • The total number of PCD bits in the set of tools

The formula for calculating PCD pressure is head pressure divided by the total number of PCD bits.

You should create a table using this formula that shows all your grinders, the total head pressure, and the PCD pressure for single, double, and quad PCD scrapers. This will provide you with a valuable reference when considering which tool will be right for your job. You can handwrite the chart or create one in a spreadsheet.

Surface Materials
Armed with your PCD scraper data, let’s see how it relates to different types of surface materials. Having a basic understanding of these materials is essential for selecting the correct PCD scraper.

High Strength (50 pounds + per PCD): The highest penetrating force will be required to remove rubberized coatings (elastomeric membranes). Use the PCD scrapers to remove 99% of the coating because it will be very difficult or impossible to grind off the coating with a traditional grinding tool. A high quality epoxy or urethane coating (over 30 mils) bonded to extra hard concrete will also require high pressure. Remove 70% to 80% of the coating with the scrapers; the remaining amount should be relatively simple to grind off with a 20-grit or 35-grit metal bond tool.

Medium Strength (25 to 40 pounds per PCD): Moderate pressure will be required to remove most cementitious overlays and epoxy or urethane coatings (over 30 mils) bonded to medium or soft concrete. It’s rarely encountered, but some very old, thick black mastics fall into this category, while most would be considered low strength. Remove approximately 85% of the material with the scrapers (95% for the black mastic); remove the remaining amount with a metal bond grinding tool.

Low Strength (11 to 20 pounds per PCD): Low pressure will be required to remove carpet, vinyl tile (and other flooring adhesives), gypsum underlayment, and flaking or poorly bonded coatings. Remove approximately 85% of the material with the scrapers, remove the remaining amount with a metal bond grinding tool.

Tool Operating Speed
PCD scrapers should be run at low RPM, normally between 1 and 4 on a grinder’s speed dial. The grinder head must run smoothly with as little vibration or jumping as possible so that the scrapers can maintain good contact with the surface. PCD scraping bits are brittle and will be degraded or broken by the unnecessary stress caused by high RPM, excessive vibration, or jumping.

To find the best RPM, start at the slowest speed and progressively increase the RPM until the grinder begins to vibrate or shake. Then, reduce the speed to the level where it is running smoothly. You should not exceed 900 RPM even if the head remains smooth and vibration free. If the floor conditions change, adjust the grinder RPM to maintain smooth vibration-free running.

Scraping vs Grinding
Scrapers and traditional grinding tools should not be used in the same way. A grinding tool should remove the surface layer of concrete and leave a new, clean surface. A scraping tool should remove 80% to 90% of the material on the surface (except rubberized coatings) and then be followed by a grinding tool.

Weigh Your Options
When selecting a PCD scraper for your project, follow these four steps:
1. Determine if the material you are removing will require high, medium, or low pressure
2. Select the PCD scraper that will deliver the pressure required
3. Establish the correct RPM for the conditions, adjusting as necessary
4. Continually evaluate the PCD scraper performance, making changes as required

Opportunity Knocks
You are now equipped with the knowledge to improve your productivity, reduce your labor, and confidently tackle any heavy removal project. PCD scrapers are an immensely powerful option if used correctly; don’t let them go to waste.

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