This article explains how to choose the right metal bond tool for your walk behind planetary floor grinder. The same principle applies to single discs and hand grinders.

Diamond tools are expensive. Therefore, it’s not possible to stock all the different varieties that are available in the market. When there are so many different shapes, different bond hardness and different grits. How do you know which one to keep in stock and/or buy.

Only with experience, you will be able to make the best decision for the type of concrete that you are grinding and what works best with your particular machine.

Grit Size (the smaller the number, the larger are the diamonds)

Choosing the grit is quite simple. The larger the size of the diamonds, the deeper is the scratch and the more material you are going to remove.

But not that simple.

Smaller diamonds tend to be sharper than bigger diamonds. So depending on the weight of your machine and the surface area of the segments, the 30# may remove just as much and just as fast as the 16#. For this reason we don’t bother stocking the 16#. If you need something larger to remove paints and adhesives, use PCDs.

Depending on your machine and the concrete, you may also be able to use PCDs for the initial grind to get the job done faster.

To do a grind and mechanical polish, start with a 30# to remove the top layer and expose the aggregate. Continue with a 60# to remove the scratches left behind from the 30#. Grout with 120#.

To do a hone and seal, start with a 30#. Then proceed depending on the slip resistance and finish required.

Bond Hardness (the harder the concrete, the softer the bond required)

Keep in mind that the diamonds do the grinding and the metal is there to hold the diamonds.

You need to choose a metal bond that wears slowly so that the diamonds remain exposed. But does not wear so fast so that your wasting your money. The softer bond will wear faster than the a harder bond. Therefore, sometimes you may like to start with a metal bond that is harder than what you think you may need. Move to a softer bond, if you find that the harder bond becomes glazed and stops working.

Too much friction will cause the metal to overheat and expand, covering the diamonds. Your tools will then slide over the concrete instead of grinding it.

The tell tail signs are :

1. When pushing the machine you can feel it through your hands whether it’s grinding or sliding.
2. The machine is drawing less amperage then it would normally do.
3. No dust left behind on the floor
4. Glazing on the surface of the segments and
5. Burn signs on the tools and the tools are too hot to touch

To remedy this problem, you will need to use a softer bond and/or a slower speed and/or decrease the weight. To remove the glazing, run the machine on the opposite direction and/or throw some sand in front of the machine. Adding water helps to cool the segments thus keeping them sharp. If you are struggling to expose the aggregate, add water.

With new slabs that have been laid for the purpose of grinding and polishing, the aggregate should be evenly distributed and the hardness of the concrete should slightly increase as you expose more of the aggregate. The soft mortar that’s holding the aggregate will help keep the tools sharp. Therefore on concrete that has been recently laid (1 to 2 weeks depending on weather) start with a hard bond. On older concrete (3 to 4 weeks) start with a medium bond.

Old slabs are a completely different ball game. The hardness of the concrete will vary as you grind. This is more prominent in older slabs. If the concrete is well trowel, there will have a very hard crust which is not even, maybe revealing a soft mortar underneath. This hard crust will not wear evenly so you may create hard and soft patches and to complicate things, the machine may dig into the soft patches. You will eventually expose the aggregate which will be harder than the mortar holding it together. But to further complicate things, the hard aggregate will not be evenly distributed. I wish you good luck. A bigger machine with a higher number of tools will help to keep the floor level.

The following table will help you choose the required bond harness.

Bond Hardness	Concrete Hardness
		Mohs Scale	Scratch with
Hard Bond	Soft concrete	3-4	Copper Coin (3.5)
Medium Bond	Medium concrete	4-6	Knife (5.5)
Soft Bond	Hard concrete	5-7	Steel Nail (6.5)
Super Soft Bond	Very hard concrete	6-8
Super Extra Soft Bond	Super hard concrete	8+	Masonry Drill Bit (8.5)
Super Extra Soft Bond Plus

Shape, alignment and surface area of the segments

Taking into consideration that the diamonds do the grinding and the metal is just there to hold the diamonds, does the shape make a difference?

When grinding

I believe that it is the surface area that makes a difference, not the shape. The greater is the surface area, the more diamonds you have grinding the concrete so the faster you will grind. However; the greater is the surface area, the less is the pressure/mm². The less pressure /mm² you have, the slower you will grind. But remember that as you increase the pressure, you are increasing the friction and therefore potentially overheating your segments.

Choosing the right tools is a bit of a balancing act that takes into consideration the following:

1. The hardness of the concrete
2. The number of tools on the machine (if you use 6 tools per plate instead of 3, you are doubling the surface area but halving the pressure/mm²)
3. The weight of the machine
4. The power of the machine (from my experience, machines from different brands, with the same kW will perform differently)
5. Does your machine have variable speed?
6. Are you grinding dry, wet or using a bit of spray water to cool the tools?

Only with experience, you will be able to decide which tools work best for your situation.

The following table lists the surface areas of the grinding tools that we offer.

30# ZZ Single	30# Rhombus Single	30# Rhombus Double	60# Single	60# Double	120# Bar Single	120# Bar Double
240mm2	399mm2	798mm2	352mm2	704mm2	480mm2	960mm2

Use the 30# single ZZ with a small single phase planetary machine or where you are struggling to cut the surface with the single Rhombus.

Use the 30# single Rhombus on a single phase or small 3 phase planetary machine , or where you are struggling to cut the surface with the double Rhombus. The double Rhombus are for the heavier 3 phase machines.

The 60# are used to remove the scratches of the 30#. Use the singles for the lighter machines, the doubles for the heavier machines.

When grouting

You are trying to push the grout into the pores and cracks. We believe the shape, alignment and surface area does makes a difference. That’s why our 120# are only available in the large bar shape and aligned in such a way that imitates the movements that you would make if you are using a hand trowel.

Because of the greater surface area of our 120#, and the change in hardness of the concrete after the 60#, especially if you densified at that stage. You will need to use a bond softer than the one you used previously with the 60#.

The small single phase planetary machines struggle when grouting. With these machines try using the single Super Extra Soft Bond Pluss (SESB+). If you find that this wears out too fast, next time you can try using a slightly harder bond. To help with the process you may need to throw some dust or cement in front of the machine together with the liquid grout.

For the larger machines we have the single and double in the Super Soft Bond (SSB) and the Soft Bond(SB). You will need to choose the one that best suits your machine.

When trying to remove adhesives, paints and other coatings

With a small light planetary machine you may struggle. You may be better off using a single disc machine with 3 or 6 tools. A large heavy planetary machine where you can adjust the pressure and speed, will be so much more efficient.

For soft brittle adhesives (like a tile adhesive) you can use a 30# in a hard bond. The Split PCDs are good for removing paints and epoxies. The PCDs are good for removing thicker coatings and sticky adhesives.

Conclusion

There are many different machines on the market and each floor that you encounter will be different from the previous floor. The information supplied here will give you an idea and a place to start. With experience you will be able to make the best choice for you circumstances.