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Complete Guide of How to Do Concrete Floor Grinding

Posted by Bruce Zhang From Diacutex on April 6, 2021

What is Concrete Floor Grinding?

Concrete floor grinding is very popular in the construction industry; it is the process of smoothing the concrete and also making them glossier by using a series of diamond tools and sealers. There are big benefits of grinding the concrete floors, it can make the concrete floors with good looking, and also make cost-effective maintenance on concrete floors.

The benefits of doing concrete floor Grinding

Durability and low maintenance

Except for the concrete grinding, there are other flooring options, like the vinyl layer on unpolished concrete floors. However, the unpolished vinyl flooring are easily gotten damaged or worn along with the rate of use, or the changes of wear conditions. While the polished floors are very durable and have high wear resistance. Due to the durable nature, there is only minimal maintenance is needed. It may take up to 10 years before doing the restoring the concrete floors.

Affordability

Just by grinding and polishing, the concrete floor will get good looking, no need the purchase and installation additional materials. Also, the polished concrete floor only requires minimal maintenance. So it is really cost-effective to do concrete floor grinding.

Necessary preparations before grinding concrete floors.

1. Get the PPE ready

Always keep in mind that “safety is the priority”. Do remember to wear the PPE (Personal protective equipment), including the dust mask, ear protection, goggle, foot and hand protection devices.

2. Check the floor

  • Measure the size of the floor to determine which grinder machine is needed.
  • To see if there are too much corners, and decide if edging is needed.
  • Check the floor conditions, and decide if crack chasing, patching is needed, also to decide if the expansion joints need to be filled or just leave open.
  • Test the hardness of the concrete, the hardness of the concrete floor is normally classified by Mohs’ hardness, generally, the hardness of concrete floor ranges from 3 to 5. On the site, we can find some substitution to the test, the keys or iron nail for instance. If we can make scratches on concrete floor by keys or iron nails, then the hardness is below 5, otherwise it is higher than. do remember to check several areas on the floor and look for different colors on concrete, because the hardness varies greatly from slab to slab.
  • Clear the floor before grinding process starts, if there is epoxy layer, use PCD tooling to remove it first.

3. Prepare the repair kits

If there are damages and cracks on the floor, then a repair kits is needed. a crack chaser blade and joint sealing material are necessary.

4. Choose Right Concrete Floor Grinder

Grinders are varies in different sizes, weight, power and direction of rotation, etc. according to the size of your floor as well as the concrete conditions to choose the most suitable grinder for your needs.

5. Choose Right Diamond Tooling

Diamond tools determine the efficiency of the grinding process; you need to choose the diamond tooling with right grit and metal bond hardness. Generally the 14 grit, 30 grit, 70 grit and 120 grit are the frequently used grit sizes on metal bond diamond tooling throughout the grinding process. When come to the bond types, it depends on the concrete hardness, if the floor is hard, the metal bond should be softer, in opposite the metal bond should be harder. After choosing the diamond tooling ,it is necessary to check diamond tooling after a pass or two to determine if the concrete is too soft causing excessive wear or if the concrete is too hard and it’s not grinding much at all

6. Hardening Agent

For starters, it is easier to achieve better polishing results with harder floors. Liquid hardeners are used to make concrete floors harder and denser. Hardening also helps to protect the floor from water penetration, staining and future damages.

The Steps Of Grinding Concrete Floor

1st Step:14 grit tooling and PCD tooling (Conditional)

If the concrete is extremely hard and there are heavy sealers on it, then the 14 grit tooling or PCD tooling is needed. However, before using the 14 grit, pls do to evaluate the concrete condition again, make sure to use the14 grit diamonds as the first step if it is absolutely necessary. Because it will take a lot of time to get the heavy scratches out left by the 14 grit diamonds or PCD tooling.

Do remember using concrete vacuum to clean the entire floor (mopping and wet vac pickup is an option for smaller floors). The key is to clean up all dust and diamond grit that drop from the diamond tooling. If you don’t clean up after each step, the subsequent grits will grind over top of residual bigger diamond grit, which will create scratches on the floor.

2nd Step: 30 grit diamond tooling

30 grit diamond tooling is the most used grit size; all of the primary grinding steps will be finished with 30# grit tooling. If you want to expose the aggregate, it must be completed by the end of this step. By running the grinder at a lower RPM, the grinding speed can be increased, then the diamonds will penetrate the floor without getting overheat.

If there is any patch or repair work is needed, then the repair work should be done after 30 grit grinding. Also, another 30 grit grinding is required after the repair work is completed.

Fix medium bond 30/40# metal bond tool to handheld grinder or walk behind grinder, Start at one side and grind from“west to east” across the entire concrete floor. Make sure to overlap the grinding pass as close as possible to the previous grinding pass.

After the grinding process is finished, clean up the floor with vacuum or scrubber.

Change the direction and go “north to south” pass after the “west to east”, still take care of the overlapping, make sure the grinding passes overlap one another as close as possible. Do the same cleaning job again.

It is better to use grind the floor in swing style, in this way, the grinding passes can be blended. Also, take care of your pace during grinding, it is great if the grinder leaves solid grinding pass. However, if there is swirl grinding passes on the floor that means you push the grinder too fast, you need to slow down. Also, there may be the occasion that the grinding speed becomes slow suddenly, it is possible that the soft top layer has been remove off, the harder concrete comes out, so you need to replace the medium hard tooling with a more softer bond. 

After the “north to south” pass completed, have a short break, check the entire floor carefully. If the exposed aggregate doesn’t meet your expectation, then go back and repeat the grinding process until get the exposed aggregate as you want.

3rd   Step: 70 grit diamond tooling

Replace the medium hard 30/40# tool with Medium hard 60/70#, grind the perimeter of the floor as you did in step 2. After the grinding is done, do the clean job again.

4th   Step: Repeat 70 grit diamond tooling

Still use the 60/70# tooling, repeat the grinding process.

The initial scratches left by the 30/40# should be removed in this step, if you still can see the significant scratches, do the grinding until all the big scratches are gone.

Remember to vacuum the entire floor area before moving to next step.

5th   Step: 120 grit diamond tooling

Change to the 120/140# diamond tooling and repeat the grinding process. Vacuum the entire floor area carefully and check your grinding job so far. Do extra grinding job if needed.

6th   Step: Use the resin polishing pucks to do transition

Use the 50 grit or 100 grit resin polishing pucks to do transition grinding, to make preparations for the polishing job in the following steps.

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