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Technical Article

How to grind and polish floor, how to calculate the cost?

Grinding and Polished concrete is fast becoming the ultimate flooring finish as it gives superior durability and performance.

As a contractor it’s important you understand the process and use the right diamond polishing pads to achieve the best results. We have developed this useful guide to help you select the correct diamond polishing pads and other diamond grinding tools to get your project done on time and in budget.

Standard Procedure 

This is a guide to the standard procedure involved in polishing concrete, including exposed aggregate concrete surfaces with concrete grinding disc and using diamond polishing pads .

The procedure is virtually the same with terrazzo and other natural stone products. Note this is quite different to creating a polish effect by grinding and then coating concrete floors with a clear coating, such as epoxy or

polyurethane. This process is referred to as a‘grind & seal’, you can use the diamond grinding disc, diamond grinding shoes, diamond grinding plates and other diamond grinding tools, not polished concrete.

Firstly, a very important point: - no two slabs are the same, even on the one job. Therefore you cannot predict what the slab will look like -whether the aggregate is going to be evenly exposed, or patchy. Different techniques in concreting will give different results. The great thing you can tell the customer before you quote the job is that,

“your slab will be totally unique to you.”

Cannot predict how much of the surface will need to be ground of to expose the aggregate.

Cannot predict how hard the concrete will be to polish. Use a diamond grinding tools to complete a test patch before you quote to give you some idea on both how hard and how much may need to come of. This can change dramatically depending on how porous the floor is due to water being added to the mix when pouring, rain affected or from not being suffciently vibrated.

Make sure you talk to the experts before you buy diamond polishing pads, diamond grinding tools and other polished concrete floor grinding tools.

The Grinding Stage

The FIRST CUT is grinding of the required amount from the surface to expose the aggregate, you use the diamond grinding tools first; some customers output for the ‘salt and pepper’ look with the aggregate partially exposed, while others may prefer a full stone exposure.

The first grinding is always completed in several passes and at an even speed so no part of the floor is overground and forms an ‘ocean wave’. The first cut is done with a coarse concrete grinding disc or other diamond grinding plates, diamond grinding shoes with 30-60 grit is the most common, however 25 and 16 grit are also used to do the first pass.

In practice, the amount that is removed is often 2- 3mm and is removed in 0.5mm per pass. This means that if 3mm is

removed, this will be done in 6 even passes to ensure flatness.

So to quote a six-pass floor properly, you need to quote on grinding 6 times the floor area. A shot blaster in the hands of a skilled operator can drastically reduce both the cost and time to remove the surface; especially if the concrete slab is steel trowelled or heavily burnished. Coarse diamond grinding tools are more expensive than fine diamond tools.

The SECOND CUT: Following the first grinding it is best to do a finer grind with 60-80 grit concrete grinding disc or other diamond grinding tools to remove all score marks from the coarser discs before you move to the final 120 grit metal bond grinding.

Guide to quoting: So far in this example you have taken 8 even passes to do the job. If you charge at $8 per m² for a single pass grind, this job is 8 passes x $8 per sq m = $64:00m² for this stage.

The Hardening Stage

Following the final grinding stage, the floor is ready for the polishing and the hardening stage. You will need to make an inspection at this point to decide what products you will require.

If the floor is very dense, with little or no porosity in the matrix, then you may be best to start polishing with 80 grit then 200 grit resin bond polishing pads,skipping the 50 grit pass. This will harden the surface and help to ‘close’ the surface and create sheen as you move further into the polishing process. In the case of a particularly dense slab,polishing can come up well without any treatment, but the surface usually won’t be as well closed of.

If the floor is porous and not really a hard matrix, it may be better to apply a generous application of the resin bonded floor polishing pads before you begin the polishing process with finer polishing pads. 

Now you can use the 400 grit diamond polishing pads,and then the 800 grit diamond polishing pads. Many people will at this point have a pump bottle or pressure garden sprayer with them and when doing the 800 grit process (and finer grades if you like) will spray a small amount of hardener on the surface as they go. This wetted surface helps to further close over the surface and develop a higher sheen. With 800 grit,you should have a nice ‘60-70%’ sheen,and if you need/want to go further, the 1500 grit, 3000 grit and Buff grades will give exceptional levels of sheen.

As a guide, the various steps from 50, 100, 200, 400, 800, 1500, 3000 and then ‘Buff pads’ to produce the polished finish will take at least as long as each pass with the first cut grind.

This means that it takes 4x the time to polish the floor to 800 grit grades, and six times the amount of time to get to ‘Buff’. This is where most contractors come unstuck; they forget to allow for every step.

Interesting sales point: Grinding and Polished concrete is very good value for money; if you charge $120 to $160 per m², this is not a lot different to a good quality vinyl, including the cost of installation. The difference is that it lasts forever, it is easy to maintain, it looks great and it is unique to the customer - ‘no-one else in the world has got a floor precisely the same as you.’

To buy diamond grinding tools and diamond polishing pads to help you complete the job, contact MasterCut right now!