- Polished Concrete Information
- Polished Concrete Pictures
- What is Polished Concrete
- Polished Concrete Cost
- Design Ideas for Polished Concrete
- Polished Concrete Maintenance
- Why Choose Polished Concrete
- Benefits of Polished Concrete
- Comparison Chart: Polished concrete versus other flooring materials
- Common Questions about Polished Concrete
- Can All Concrete be Polished?
- Is Polished Concrete Slippery?
- What are Polished Overlays?
- Polishing Products and Equipment: An overview of basic equipment and supplies needed
- Related Information
- Information About: Concrete Floors
- Concrete Contractors: Find Concrete Polishing Products and Suppliers
- Design Ideas: Polished Concrete Info
Concrete Polishing 101 x2A step-by-step guide to taking your polished concrete floors to the next level with designs and graphics
Bob's step-by-step polishing process:
- Chase cracks and contraction joints
- Fill cracks and contraction joints
- Shave/grind flush cracks and contraction joints
- First pass soft bond 40 grit metal bond diamond
- Second pass soft bond 80 grit metal bond diamond
- Third pass soft bond 150 grit metal bond diamond
- Switch from rigid plates to flex plates
- Fourth pass 100 grit transitional hybrid resin diamond
- Apply design and then saw cut
- Vacuum floor
- Fifth pass 200 grit resin bond diamond
- Vacuum and damp mop
- Apply Decorative Concrete Institute water based dye
- Clean dye residue
- Sixth pass 400 grit resin bond diamond
- Application of lithium based densifier
- Clean the surface
- Seventh pass 800 grit resin bond diamond
- Eight pass 1500 grit resin bond diamond
- Ninth pass 3000 grit resin
- Application of topical Guard
- Burnish Guard with high speed burnisher and dip pads
Back in July, a large independent company here in Georgia who manufactures high inertia motors, gears and generators consulted with us on the basics of polished concrete. Our guests mentioned they had several 500,000+ square foot buildings that they were considering polished concrete for and that a company came in and produced a mock up for them. Since they were not familiar with polished concrete and they felt that that their job site representative mockup was marginal at best, they decided they wanted to learn the entire process, as they put it, the right way.
I asked if they had pictures of the sample of which they did not. During their training here at our shop, I wanted them to show me what their floor looked like in terms of gloss when we went through each step. At the 200 grit is when they proclaimed, “That’s it, that’s what our floor looks like.” For you professional polishers, you know that the 200 grit produces a very hazy matte finish and it’s my guess that the person demonstrating for them was either not experienced or really cut corners. The fact that this company who is not involved in the industry and was wanting to self-perform all of their work due to some of the budgetary numbers they obtained could be a story in itself however, it was the after effects of their class that spawned the idea for this article.
Right adjacent to our group's training area was one unsightly panel that stood out like a sore thumb. This section had virtually every polishing consideration ranging from stains, cracks, chips, pits, joints not to mention finished polished concrete on three sides. Unfortunately, our slab exhibited cracking in one section 6 years ago when it was placed. To address them we started off by chasing the cracks in preparation for filling them with a colored metallic epoxy. Normally on commercial projects contractors fill cracks with a very rapid setting clear low viscosity epoxy enabling them to get back on the floor within minutes. In our case, of course we had to make it decorative which is why we used metallic pigments suspended in very slow setting epoxy. When filling cracks and joints it is important to monitor the level while filling since the low viscosity of these materials tend to absorb and can end up lower than the finished surface. For this reason, it’s best to slightly over fill these areas so after the initial grinding, they end up flush. Once the cracks were filled, the contraction joints were filled with colored polyurea and then shaved flush roughly 45 minutes after application.
The next day we started with hand grinding the epoxied cracks flush since it is not a good idea to run the walk behind grinding machines over these very rigid raised areas. One of the challenges on the cracked sections was that they abuted right up to finished polished concrete. This meant having to address them by hand since the grinding and honing stages using an HTC 800 could not overlap onto the finished sections, which leads me to our next consideration, which is transitioning from new to finished polished concrete. When done properly, it is really quite easy; however, I have seen multiple contractors really mess up when it comes to this important step. What’s crucial is that if you are terminating that days polishing at a sawed joint, the grinding/honing should extend at least 2 additional feet further. This allows you enough room to start working your way back to the previously polished section overlapping with each successive grit. In our case, the previously polished panels were not extended far enough into the unpolished sections which meant that there was only roughly one foot to complete 8-9 steps of transitioning. The first grit was with a soft bond 40 grit metal diamond used for hard concrete. One other very important consideration for polishers, is to know the type of surface you will be working with such as soft, medium, hard or ultra-hard concrete. This can be achieved with the Moh’s hardness scratch test kit as a starting reference. Our concrete scratched at a 6-1/2 to 7 which was the reason for the soft bond diamonds. Once the first pass with the 40’s were complete, soft bond 80 grit metals were used overlapping roughly 1” closer towards the finished polished concrete panels. 150 soft bond metals were then run in the same fashion. It is important to run each pass in opposing directions such as north/south and then east/west for example.
The slab was in poor condition with stains and scrapes that needed to be addressed, cracks and joints that required chasing, cleaning and filling, as well as serious pitting.
The cracks were filled with a gold metallic epoxy. It is important to slightly over fill the cracks and joints. Notice the small black spots. This is molding clay (putty would work as well) to act as a dam preventing the epoxy from running on to adjoining sections.
A gray based microtopping was applied to eliminate the pitting. Notice the careful transitioning taking place (Note: there are still 5 steps more to go in this small area). If done properly, this produces a level nice looking alternative.
Once the 150’s were complete and after the rigid plates on the machine were changed to flex plates, we chose to skim coat the entire section with a gray cement-based microtopping because the slab had excessive pitting probably due to the manufactured sand used in the concrete. Although, the skim coat worked great, you may want to consider using a grind and fill product which is spray applied in front of the grinding machine usually somewhere around the 80-150 grit. This type of product develops a paste which fills most voids and small cracks. Most commercial specifications require you to fill these unsightly pin holes and voids anyways. Roughly 4 hours after the skim coat application, 100 grit transitional hybrid resins were used to remove the scratch pattern from the 150’s in addition to a thin layer of microtopping residual.
It is important to vacuum after the saw cutting step. Dog is optional.
Here is where the “x 2” comes in to play. After this last grinding step a decorative design was laid out and then saw cut in to the floor. Note that if the floor is brought up any higher in terms of grit, your design layout probably will not stick to the floor (assuming you are drawing or chalking) because of the smoothness. The design was cut using a 4” angle grinder using a continuous diamond blade. Make sure to vacuum in between steps especially after decorative saw cutting to remove any chips that could otherwise end up scratching the floor. Now that the floor was clean, we switched to 200 grit resins.
Always inspect every tool as you attach it to the machine checking for gouges or knicks that can also scratch the floor. In one case while consulting on a project, I was watching the equipment operator’s mannerisms once starting a new grit sequence. Experienced operators will immediately look down at the floor once they start and even take their foot and rub the dust off the floor (assuming they are grinding dry) checking for scratches as opposed to just looking forward. In this case, I let him make one pass before stopping him and pointing out all of the scratches that were not there prior to this pass. After a brief inspection of the tools, a determination was made that one diamond was chipped creating the scratches. There’s no telling if he would have caught it potentially doing an entire section!
Once the 200 grit resin was complete and after damp mopping, it was time to add color. This is an often debated subject as to when to apply color. In our case, we were working on hard concrete and chose to use water based dye because of the detailed pattern requiring hand brushing. One other very important consideration once your coloring is complete is to be very thorough about cleaning any dye residue off of the floor especially if there are un-colored sections as part of the design. I’ve heard horror stories of color smearing when running the next sequence of diamond tooling as a result of improper cleaning. Because of the detailed design on this floor, we used multiple buckets of water and a tile sponge to carefully clean. On large projects, contractors typically auto scrub and vacuum up dye residue with either walk behind or ride on equipment.
Water based dye is applied making sure not to brush the color over the epoxy since I have seen the color stain the epoxy before. After the color has been applied, it's time to carefully remove the dye residue trying not to contaminate the un-colored or gray sections.
Pre-guard average readings of 68. Post-guard average readings of 84.
Once the floor was dry, the next step was to run the 400 grit resin bond diamond keeping in mind that we were now roughly only 2”-2-1/2” away from the finished polished concrete sections in terms of transitioning. It was at this phase of the project we applied a lithium based densifier to help lock in the color. You also need to be equally as thorough as cleaning the dye residue to make sure you clean any crystalized densifier residue from the surface. If not cleaned, this residual can load up on the diamonds and create swirls or scratches. A couple of ways to check if the floor is clean after this step is while the floor is wet, it should not have a slimy feel to it and if dry, it should not have a gritty texture to it. Fortunately for us we had neither, which meant it was time to move on to the 800 grit resin bond diamond. Next was the 1500 grit which can now technically overlap into the finished adjoining section without damaging it; however, in our case we had one dominant joint that was substantially higher than the other panel which meant we could not overlap without damaging the diamonds. Most polishing contractors stop at this grit however, I wanted to run one additional 3000 grit to see if there was a difference in gloss readings from the 1500 of which we did get about 5 points higher by running the 3000’s. After a cleaning of the floor, an application of topical guard was applied at the rate 1500 square feet per gallon. Twenty-five minutes later, the guard was burnished in using a high speed propane burnisher with 3000 grit dip (diamond impregnated pads) producing a stunning floor with excellent distinction of image as well as gloss. Gloss readings were taken pre-guard with average readings of 68 and post-guard with average readings of 84.
The finished project burnished with guard. You can see the filaments form the overhead light bulbs reflecting in the floor.
Remember, before you consider taking your polished concrete floors to the next level including designs and graphics, refine and perfect the basics discussed in this article. Avoid cutting corners or skipping steps. After all, there is no substitute for doing a job the right way.
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