What is Diamond Grinding
Diamond Grinding is the use of diamond segments mounted on a machine that drags the segments across the surface of concrete or stone. The diamond grit protruding out of the segment abrades the concrete and aggregate to remove laitance and to remove the top layer. The aim is to achieve a good substrate and anchor pattern for coatings, overlays or glue adhesion or to create a flat surface for decorative concrete.
For Diamond Polishing contractors the process can be continued past the point of removing laitance to expose the aggregate or stones in concrete and then, by using finer and finer grades of diamond chips, it can be used to make the surface start to shine for decorative concrete.
How can I Grind Faster on Hard Concrete?
It is a known thing that every slab is different, even areas within the same slab can vary from easy to grind to Hard to grind. Here we describe what is actually happening and why we need different grades of diamonds and grades of matrix to make machines work.
If the concrete is very hard to grind the metal matrix in the diamond segments will not wear fast enough to keep fresh diamonds exposed. This can result in the diamonds rounding off and the grinding process slowing down a lot.
- Use soft bond tooling with less segments to overcome the issue – more pressure per segment helps.
- Add weight to the grinding head.
- Turn the dust extractor down, this will leave more dust under the machine and increase you chance of opening up the diamonds.
- Throw a little bit of sand onto the slab, this can increase the grit to open the diamonds, or try a misting of water.
- If you have tried Soft bond discs for a while they may be glazed over, try opening them up again by running the machine on a softer piece of concrete.
- Single segment plugs, or putting only 2 discs on a satellite can help get higher pressure per segment.
- Reversing rotation will also help matters
How does Diamond Tooling Work?
Diamond tooling uses diamond segments to engage the concrete and grind the surface. This may include not only concrete, but also laitance, old coatings, glues and high spots. Diamond Tooling has many variables that affects the rate and ability to remove the surface of concrete. These include:
- Diamond Speed – This is the one thing needed to make any diamond tooling actually work; it is governed by the machine that the Diamond Tooling is fitted to. Firstly speed is metres per minute; secondly weight per disc.
- RPM is not the critical number you need to look at. It is the number of metres per minute that the diamond segments are dragged over the surface, which is a combination of a) The RPM by the diameter of the disc, b) PLUS the cumulative speed of the main tooling head; c) PLUS the weight on the disc(s).
- The Diamond Speed and weight to do the job is dependent on the available horsepower. Many machines are mechanically inefficient, so the power left over to do the job is not much more than half of the motor power.
- Diamond Segments are powered to move over the surface and grind. The critical thing is the Diamond speed (metres per minute). The planetary discs on a multi-disc machine (3 or more discs) can be powered so they are actively driven, or be passive (floating). Passive machines rely on the main head they are attached to to give the speed of diamond over the surface. A machine with non-powered (passive) discs usually has a high main disc speed. RPM of the planetary discs does not necessarily mean high production if the final diamond speed over the surface is slow or there is not much weight on the diamonds.
- Matrix composition – Changing the alloy the matrix is made from will vary the wear resistance and the range of concrete hardness that the matrix will perform over, and will change the rate the diamond chips are ‘exposed’. How much the diamond is exposed, or sticking out of the matrix governs how effectively the segment will abrade the surface. Premium matrix alloy will work over a broader range of substrates than budget segments.
- Diamond Chip size – Changing this changes the depth of the scratches it makes on the surface and therefore the rate of removal. Creating larger, grittier, abrasive dust will help to keep diamond matrix open.
- Effect of the dust extraction, or vacuum: When we suck away all the dust from the grinding process this changes the way the segment erodes away and in turn the amount of segment poking out of the segment. By not sucking all the dust from under the machine when on hard concrete this will allow the dust to erode the matrix and the diamond will protrude out of the matrix and scratch the concrete properly creating an faster grind. In turn sucking away all the dust produced can slow the wear of your diamonds on soft concrete.
Should I clean Filters With Compressed air?
Cleaning dust extractor and vacuum cleaner filters is a messy job, and most of us at some point or another have grabbed the compressed air nozzle and given the filter a really good clean.
The filter looks like new, but did you know that cleaning filters with compressed air will most likely result in damage to the filter media?
Filters are made up of a delicate filter media, and when compressed air pushes on the particles lodged in the filter media, damage to the filter media inevitably occurs. This then allows larger and more abrasive particles to pass through the filter and travel on to the motor, causing damage and wear as they pass through, and significantly reducing the life of the dust extractor.
Because this is not something that happens straight away, many contractors don’t see the connection between incorrect filter cleaning methods and reduced dust extractor motor life. The following guidelines will help you can greatly increase the life of your dust extractor and filters.
GENERAL GUIDELINES FOR CLEANING FILTERS
The first step in any process is to gently tap the filter against a hard surface to loosen the accumulated dust. Take care not to damage the element. If your filter is washable, use a garden hose without a nozzle.
- Direct the water to the clean side of the filter first, running the water up and down the filter pleats. Do not bring the nozzle in contact with the filter media at any time.
- Repeat this process on the dirty side of the filter. Use cool to lukewarm water.
- Do not use soap! Air-dry for 24-48 hours or until completely dry before you replace it in the vacuum.
- Filters that are closed on one end can be cleaned by soaking.
- The filter should be placed open end up in a suitable tank filled with warm water (37-60 °C or 100-140 °F) and any commercial non-sudsing detergent.
- Allow to soak for 15-30 minutes, agitate the filter in the solution with a gentle swaying/rotating motion, and allow to soak an additional 10 minutes.
- Rinse the filter with clean water from the clean side until the water runs clear. Do not fully immerse the filter in the cleaning solution. Care must be taken to avoid contact of the clean side of the filter with the contaminated wash water in the tank. The cleaning solution should not be reused.
To vacuum a filter clean use a standard shop-vacuum or central vacuum supply.
- Move the vacuum nozzle slowly up and down the pleats on the dirty side of the filter only.
- Do not bring the nozzle in contact with the filter media at any time. A small brush type nozzle can be used.
- Floorex does not recommend using compressed air to clean filters under any circumstances.
- To ensure no damage is done to the filter media the pressure of the compressed air would have to be so low it would be ineffective at cleaning.
ABSOLUTELY DO NOT:
- Scrape the contaminant from the surface of the media.
- Allow dust from the dirty side of the filter to attach to the clean side of the filter during any of these processes.
- Allow dust to enter the filter box while the filter is removed.
- Disassemble the element to clean.
After cleaning in a well-lighted area, inspect the gasket for continuous adhesion and the absence of tears and cracks. In a darkened room, inspect the filter by placing a shining a torch inside the filter.
Visually inspect for weak spots or holes in the media identified by bright pin-holes of light. If defects are detected, discard the filter.
After cleaning and inspecting, permanently mark the filter with the cleaning method, the number of cleans and the date.
All sound too hard? Check out our self-cleaning filters at https://floorex.com.au/dust-collection/dm-series-dust-collectors.html
FINAL NOTE: When a reverse pulse type dust extractor is functioning properly you don’t need to take the filter out to clean it.
For machines with no compressor on board – Simply block the inlet, start the dust extractor and pulse clean the filter.
See the video tab here https://floorex.com.au/rp-1236-dustmaster-floorex.html for more detail.
Discs or Knock In Shoes?
Typically Floorex has not utilised ‘knock-in shoes’ for several very good reasons. the concept of being able to individually remove each segment sounds good; but it does have some major drawbacks in reality:
- The consumption of diamond use on newly re-installed shoes will be higher for the first while until they bed in again. You could lose up to 5-10% each time you change them
- Often, even with knock on shoes they take around 2-3 times as longer to change.
- If you want flat floors, you will achieve flatter floors with discs every time (all other things being equal).
- Once you wear a set of shoes to a certain point you cannot just add another two segments as they will for certain be a different height meaning you will have to keep sets together, You might as well have a single disc holding them together.
- By using 175mm discs on most of the satellite machines, if you were to ever have an incomplete set you can use them on hand grinders.
ShotBlasting - How does it work?
Shotblasting is a process of blast cleaning concrete or steel surfaces. The shot is thrown at high velocity at the surface by a Blast Wheel which is spinning at high revs. The shot hits the surface hard enough to do two things:
- Hit hard enough to break of concrete and anything weak enough including contaminates away from the surface.
- To bounce back up after hitting the floor, and end up back in the recovery bin and shot cleaner up near the top of the blast chamber.
The shot returns by bounce to the shot recovery, and along with the shot the dust and contaminates.
A strong airflow at this point pulls the dust and contaminates out of the heavier shot and makes the shot clean and ready to re-use.
Now the shot can pass down past the magnetic shot valve and be used over and over again.
There are several very important things that must be understood:
- The dust extractor vacuum is very important; it must have precisely the right airflow to suck out the contaminates without pulling out good shot.
- At the same time the dust collector must be able to maintain exactly the same airflow and not block up and require the filters to be pulled out and cleaned. For this reason a proper vacuum will have true reverse pulse filter cleaning to keep the same airflow hour after hour.
- Anyone using a shotblaster must have had training in the use of a shotblaster by a properly trained user. Floorex offers this along with every sale which includes:
- Training on how to set the correct flow of shot onto the blast wheel
- Training on how to replace and set-up the blast wheel and control cage.
- Training on how to be able to check and replace the wear liners.
Shotblasting is a highly effective way of preparing most floor surfaces, very efficient, very fast.
ShotBlasting - What are the benefits?
Shotblasting is highly beneficial to any contractor who needs to prepare floors to give the ultimate anchor pattern for floor coatings, screeds and indeed, smart polished concrete contractors who want to massively reduce the time taken to grind down to the aggregate.
The secret is to have had right training so you understand what the right preparation for the given job is.
Golden Rule: Use the smallest shot that will get the job done!
The reason for this is:
- Smaller shot will blast faster, much faster. You will do more square metres per hour, because there is a lot more pieces of shot per kilogram.
- You won’t take out un-necessary depth of concrete, which only wears out the blast wheel and wear liners un-necessarily, and means more coating or screed to fill it.
- In the case of a coating; a beautiful fine blasted finish will cover nicely, but an over blasted surface will increase costs to fill the profile with epoxy if you use the wrong shot.
- Obviously, if you need to create a bigger profile for any reason then bigger shot is the way to go. But still, the same rule applies; use the smallest shot that will give you the profile in the best time.
Shotblasting has the advantage that it is far faster and less cost per square metre to prepare floors and give excellent adhesion. Many coatings contractors will shot blast lightly, then diamond grind lightly, to get excellent finish and give your customer the ultimate adhesion on the job. It’s faster, quicker and less cost.
ShotBlasting - What are the limitations?
There are very few limitations that apply to shotblasting; that is why it is the ultimate preparation method – when it is done properly
- in low traffc areas such as pedestrian areas where a thin coating is to be applied,shotblasting may leave too much profile (roughness) show-through, e.g. in a car showroom, especially if the concrete is weak.
- won’t level up a ﬂoor; it will remove just as much off a high area as a low area.
- can’t remove many coatings, especially thick elastomerics and glues etc. Can work very well on many thin coatings. Thick epoxies may cause deep profling of the ﬂoor.
ShotBlasting - When should it be specified?
Sadly many projects today that ought to be shotblasted are prepared by other means; usually because:
- The benefts are not entirely understood. Shotblasting to the same depth of removal is cheaper than with diamond grinding, delivers better profile and adhesion, and assures you of removal of contaminates.
- Or maybe the specifier has had a bad experience because a previous project was damaged by overblasting, or similar problem.
- The specifer received advice from a contractor who, while he may know a lot; he has learnt his trade by default, or has only got other machines such as diamond grinders and can’t offer shotblasting.
ShotBlasting - Floor surfaces that ought to be ShotBlasted and Why!
Here is a brief list of floor surfaces that ought to be ShotBlasted and why.
- Food Factories
- Fruit Juice & Dairy Product Factories
- Chemical/Oil Bunds
Many of these factories use trolleys & pallet trucks that have hard wheels; such as cast iron or hard nylon. These wheels pound the surface as they are rolled. Any weak concrete is likely to be pulverised. Naturally, coatings bonded to pulverised concrete is going to lift.
Shotblasting removes weak concrete, because it blasts all the surface indiscriminately. Diamond grinding can leave weak areas because it only works in a ﬂattening action – below the level you have ground down to, there can be more weak areas not removed by the Diamond Grinding.
Contamination in food factories is a major problem. Food acids, animal or vegetable fats/oils must be removed. Diamond grinding has the disadvantage that contaminates are rubbed back into the surface after they are ground off. If you grind long enough, and preferably in several layers, it is possible to grind deep enough to have a reasonable assurance that contaminates are sufficiently removed, but this invariably costs a lot more.
Shotblasting breaks the top surface away and contaminates are actually removed and extracted. The shot is usually very close to contaminate free before it is reused.
Why not just Acid Etch?
For years, many concrete floors were prepared for coatings by acid etching. Often, acid etch techniques are inadequate, misunderstood and result in early coating failures.
Acid etching was commonly specified as preparation for thin film coatings up to 250 microns. Following a correct procedure is vital to achieve a surface preparation necessary for proper coating adhesion.
The process to achieve the correct result is labour intensive and time consuming and thus subject to contractor abuse by cutting corners. (Once the coating is applied who can tell what the preparation was like!)
The bond or link with the concrete is just as important for ‘cheap’ floor coatings as ‘hi-tech’ floor coatings.
The disruption for the client, the hassle and expense for the contractor and the embarrassment for the paint company can be avoided with proper concrete preparation.
What is the purpose of acid-etching?
Etching is intended to remove weakly bonded cement paste from the concrete surface and slightly profile the surface by exposing fine concrete aggregate. This promotes the penetration and adhesion of thin film sealers/coatings up to 250 microns. (e.g. thin film epoxies, urethanes, acrylic and alkyd coatings).
For more information please download the following link.
WHY NOT JUST ACID ETCH?