Resin, Metal and Hybrid Bond Diamonds: What Is Each One For?

The discs mounted under a grinding machine look alike at first glance: a round base with a few segments on it, or a flat pad. Yet of two abrasives with the same grit number, one may level a floor in a few passes while the other just slides over the surface and does nothing, or even leaves a deep scratch. Most of the difference lies not in the diamond grit but in the bond that holds the grits together. In this article we explain how metal, resin and hybrid bonds work, which one is chosen for which stone, how wet and dry use affect the bond, and how to tell on site whether an abrasive is working properly.

In short: Metal bond cuts and levels quickly but leaves deep scratches; resin bond works more gently and is used for refining and polishing; hybrid bond bridges the two, allowing the metal scratches to be removed with less effort. When choosing, the hardness of the stone, the problem on the surface, water use and the desired appearance are all considered together.

The Diamond Does the Work, the Bond Determines the Behavior

In a diamond abrasive, the cutting is done by very small synthetic diamond grits. These grits cannot hold onto a surface on their own; they need to be embedded in a material. This material is called the bond or matrix. The bond's job is not only to hold the diamond: as it works, it is expected to wear away gradually, releasing dulled grits and exposing fresh ones underneath. If the bond is too durable, the diamonds dull but new ones are not exposed; the abrasive glides over the stone, heats up and does not cut. If the bond is too weak, the diamonds fall out before they have finished their job and the abrasive is used up quickly.

This is why two abrasives with the same number printed on them can behave differently. The number indicates the coarseness of the grits; the bond determines how hard those grits are pressed against the stone, how long they last and what kind of scratch pattern they leave. We cover which stage the numbers correspond to in our article on diamond pad grit numbers ; here our subject is the material behind those numbers.

Metal Bond: The Heavy Worker of Leveling

In metal-bonded abrasives, the diamond grits are embedded in a hard segment made by pressing and sintering powder mixtures based on bronze, copper, cobalt or iron. The segments are usually welded or screwed onto a steel plate or a quick-change base. Thanks to their hard, rigid structure, they press directly on the stone without flexing; this is the first choice for removing height differences between slabs, stripping old coatings and adhesive residues, or opening up the top layer of concrete.

This power comes at a cost. Metal bond leaves deep, sharp scratches on the stone surface. After the first pass the floor takes on a uniform gray matte look, but within that matte finish is a dense network of scratches that the next stage has to remove. When metal bond is used carelessly, especially on soft stones like marble, it removes more material than necessary; hollowing, waviness at the edges and needless thinning of the slab can appear in a short time. If the way the stages clear these marks is not well planned, the result turns into the rings we describe in our article on the traces of poor grinding .

Resin Bond: Refining and Shine

In resin-bonded pads, diamond grits are mixed into a flexible polymer and usually glued onto a foam or hook-and-loop felt backing. Because the bond is not as hard as metal, it brings the grits into contact with the stone with softer pressure; the flexibility of the backing also lets the pad sit fully against the surface. For this reason resin pads are used to refine the scratches left by the coarse stage step by step and finally to bring out the natural shine of the stone.

The weak point of resin bond is heat. When the polymer matrix heats up from friction, it begins to soften; the resin smears over the grits, the pad glazes and stops cutting. When working dry, leaving the pad in one spot can burn the pad surface and, on some stones, leave discoloration. Although coarse-grit resin pads can serve in light leveling, they cannot replace metal bond for removing height differences; because they are flexible, they tend to follow hollows and bumps and leave the surface wavy.

Hybrid Bond: The Bridge Between Metal and Resin

Going directly from a metal bond to a fine resin pad is one of the most common mistakes on site. The resin pad struggles to erase the deep scratches left by the metal segment; the crew repeats the same stage many times, the pad wears out quickly and the marks still do not disappear completely. Products called hybrid or transition abrasives were developed to fill this gap.

In hybrid abrasives, the diamond is embedded in a mixture that uses metal powder and resin together, or in a ceramic-based bond. The result is a tool that is not as aggressive as metal bond but not as soft as resin. This intermediate material quickly removes metal marks without reopening height differences and brings the surface to a level that resin pads can easily take over. On terrazzo, dense concrete and hard stones, this transition stage often shortens the total time. Manufacturers sell their hybrid products under different names and with different mixtures; therefore two products with the same name should not be assumed to have the same hardness.

Bond Hardness Is Inversely Related to Stone Hardness

There is a widely accepted rule for diamond tools: the harder and denser the stone, the softer the bond is chosen; the softer and more abrasive the stone, the harder the bond should be. Although it seems backwards at first, the logic is simple. A hard stone like granite does not wear the bond enough by itself; a hard-bonded segment dulls on this stone, no new diamonds are exposed and the abrasive glazes and slides over the surface. A soft bond, on the other hand, releases dulled grits in time and lets fresh grits do the work.

In the opposite case, sandy and porous materials consume the bond like sandpaper. On freshly poured concrete, some sandstones or old screeds containing a lot of sand, a soft-bonded segment is used up very quickly. On these materials, a hard bond preserves both service life and cutting performance. Marble stands between the two: it is soft but not abrasive; here the problem is usually not the bond but the metal abrasive being chosen too coarse.

On site, this rule can be tested with a few signs:

• Glazed segment: If the segment surface shines like glass and no slurry forms, the bond is too hard for the stone; the diamonds have dulled but new ones have not been exposed.
• Rapidly shortening segment: If the segment height visibly decreases over a few square meters, the bond is too soft for the stone and the abrasive is no longer economical.
• Heating body: A base or pad that heats up without cutting shows that friction is turning into heat rather than work; the bond choice or the amount of water should be reviewed.
• Uneven marks: If some segments leave scratches and others do not, the tooling has worn unevenly or different products have been mixed.

Choosing the Bond for Marble, Granite and Concrete

The same machine and the same crew work with three different abrasive sequences on three different materials. On marble the aim is to level without removing more material than necessary; on granite, to cut evenly even among hard crystals; on concrete, to open the surface and reveal the aggregate texture to the desired level. We explain in detail why granite requires more time and more stages in our article on granite grinding and polishing .

The table below summarizes the general use pattern of bond types on three materials; the exact sequence is always determined on a test area:

What stands out in the table is that metal bond is often not used at all on marble. Starting with a metal segment on a marble floor that has no lippage and is merely dulled and scratched produces unnecessary deep marks that later have to be removed. On granite, however, metal bond is almost always at the start of the process, because a resin pad lacks the strength to level this stone.

Wet and Dry Use

The bond type also affects whether the abrasive is used with water or dry. Water carries away frictional heat, removes slurry from the surface and keeps the diamonds in constant contact with the stone. This is why most resin-bonded pads are designed for wet use; on hard stone in particular, water is the main safeguard that keeps the polymer from softening and glazing over the grains. Pads made for dry use are built with more heat-resistant resins and ventilation channels; even these heat up when left in one spot.

Metal-bonded segments can work both wet and dry. The biggest problem with dry work, however, is stone dust. The fine dust produced on granite and concrete may contain crystalline silica, and inhaling it poses a health risk; we have covered this topic and ways to protect yourself separately in our article silica dust in dry grinding as well. If you are going to work dry, connecting the machine to a suitable dust extraction system, wearing personal protective equipment and cordoning off the area are indispensable parts of the job. The choice between the wet and dry method changes not only the abrasive, but also how the work area is protected, the duration of the job and waste management.

Reading the Marks an Abrasive Leaves

The most reliable way to tell whether an abrasive was chosen correctly is to look at the surface it worked on. After each step, the slurry is collected, the floor is wiped dry and the surface is inspected under a light held at a low angle. In a sequence that is working properly, the marks of each step are finer and more uniform than those of the previous one; if a few isolated deep scratches remain from the previous step, that step is repeated instead of moving on to the next grit.

The types of marks we commonly encounter in the field can be listed as follows:

• Deep, straight lines: These are usually scratches left over from the metal bond; if the transition step was skipped or applied insufficiently, they do not disappear in the fine steps.
• Circular rings: A large grain trapped under the pad, or a dirty pad, spins in one spot and draws a ring; the pad is cleaned and the floor is washed.
• Hazy patches: In areas where the resin pad has heated up and glazed, the gloss becomes uneven; the amount of water is increased and the pad is refreshed by dressing it on a clean surface.
• Edge difference: Because the areas along walls are worked with small hand machines, they may end up with a different finish from the center area; they are finished separately with the same bond type and the same grit.

Evaluating an abrasive at the end of its life is also informative. If one side of a segment is more worn, the machine is applying uneven pressure; if the center of a resin pad is used up while the edges remain, the pad is not sitting fully flat on the surface. These observations make it easier to choose the right tooling for the next job.

Storage, Cleaning and Service Life

Diamond abrasives are expensive consumables, and their maintenance directly affects their service life. At the end of each job, pads and segments are rinsed with clean water and the slurry is removed before it dries. Dried stone slurry clogs the pores of the resin pad, causing the pad to cut poorly during the first minutes of the next use. Pads are stored on a flat surface, without being crushed on top of each other, and away from direct sunlight; hook-and-loop backings can deform with heat.

It is also a good habit to keep tooling used on different stones separate. Hard grains trapped in the pores of a pad used on granite or concrete can leave unexpected scratches when that pad is subsequently used on marble. For this reason, many crews keep separate pad sets for marble and granite and roughly note how many square meters each set has worked on which stone.

The right bond choice determines both the speed of the job and the quality of the result; but the final decision is always made by the floor itself. To see which step you should start from on your floor and which abrasive sequence is suitable, an on-site test area is the most reliable way. You can reach us through the service request form with photos of the area and its approximate size.