I received a message in my inbox from Mr. Milan, who needed advice on renovating old terrazzo (stone, concrete) windowsill slabs. Since Mr. Milan sent photos of the original condition right away, we agreed to turn his case into an article.
I really enjoy receiving messages from you. Even though the topics sometimes repeat, there hasn't been a moment where I haven't enjoyed it.
"Hello Mr. Šáray, I was very interested in your website about grinding wheels for grinding/cutting concrete and stone. I would like to renovate the cover plates on the staircase from the terrace of my family house. I would like to order some diamond grinding wheels for the refurbishment of these plates – see pictures. I assume it is a terrazzo material and I would like to ask for your advice on which grinding and polishing wheel/wheels you would recommend I order from you and subsequently what coating or paste to use for protection after grinding.."
Detailed view of the original condition of the terrazzo windowsill slab
First, let's remind ourselves what kind of material terrazzo actually is and what its composition looks like.
Terrazzo is also called stoneware or artificial stone. Basically, it is a standard concrete mix consisting of high-quality cement mortar and specific aggregates. Most often, black and white marble chips are used, but you can also add crushed colored glass from bottles, aggregate of your choice, or even beads to the concrete mix. After full curing, the material is first ground and then optionally polished to a high gloss.
Terrazzo is a durable material resistant to wear and scratches. Its use dates back to the 15th century. It experienced its greatest popularity in the second half of the 20th century as an extremely popular architectural material.
Let's get back to Mr. Milan's situation. I'm interested in his technical equipment, knowledge, and what he expects from the result.
Between us men, I am used to a brief and factual debate. Therefore, I will try to summarize it in points:
- It would be ideal if you have an angle grinder with speed regulation available. Polishing pads require lower speeds.
- First phase - grinding. If you only need it for a one-off project, I would recommend using a cheaper concrete grinding wheel from the ECO class. I leave the diameter to you, depending on your machine. In this case, even a grinder without speed regulation can be used.
- After grinding, the material will be a nice white, but scratched with grinding marks, porous, and therefore very absorbent. It can be finished at this stage, but the material must be protected with a proper layer of impregnation. We covered the correct way to impregnate in the article "How to Protect Stone".
- I recommend using at least one or two more steps of the polishing process to better seal the surface. If interested, you can continue to a high gloss.
What is your vision?
- Do you wish to just lightly sand the surface, refresh it, and not spend too much time on it? Do you just want it to look nice, even if it lacks significant durability? Over time, dirt, dust, and smog will settle in the pores, followed by lichen and moss if not cleaned.
- Is your vision a new look with a shine similar to a granite slab? It involves a bit more work and more steps, but it will look beautiful for a long time.
In the first case, after grinding with the grinding wheel, you can use one more step to cover coarse marks—for example, a flexible polishing pad with grit #100. The material will remain white, matte, and absorbent. Therefore, it is necessary to apply a protective coating or impregnation.
In the second case, if you want a top-tier result, use grit #100 along with #400, 800, and for a nice shine, also #1500. If you wish to increase the shine even further, you can use polishing paste along with a polishing felt wheel.
You can read about how to properly seal and protect the surface in the article where we discussed this issue. For your case, I recommend impregnation with a reinforcing effect or a coating with color enhancement.
I sent my answer to Mr. Milan and waited for a reaction. What followed and what did Mr. Milan decide?
"Thank you very much for the guiding information. I won't overthink it and I'm going to order the grinding wheels from you (#30, 100, and #400). I already have an angle grinder with speed regulation. Could you please send me an offer for the wheels: #30, 100, and #400 and the impregnation with a reinforcing effect? I will place the order immediately."
Surface of the terrazzo/stoneware slab before starting work
A few days passed and a message appeared in our inbox.
After seeing the photos, I can say that Mr. Milan is a master and handled this project brilliantly. The result looks clean and brand new. Judge for yourselves. In a similar way, you can renovate floors, stairs, graves, windowsills, and basically anything made of concrete.
"Hello Mr. Šáray, well, I tried my hand at your craft over the weekend. Since I promised you photos of the work, I'm sending a few shots. I figured out many 'tricks and tips' during the grinding and polishing. I also applied the impregnation; I'll see how it looks after today's first rain. Thank you for the great advice and the kind and practical gifts included with the ordered wheels. I really appreciate it because in today's nervous and tense times, finding a helpful person is truly great. I wish you, your company, and your colleagues all the best and much success.
Best regards,
Milan K., Nemšová"
A look at the restored and treated surface. A joy to look at!
Conclusion
If you ever decide to contact me, know that I don't know how skilled the craftsman on the other end of the phone or keyboard is. Therefore, I might start by asking you "weird" questions like:
- Is it really marble? Isn't it terrazzo or granite? Correct definition of the material is key, and we mentioned it in the article "Granite or Marble?", where we help you correctly identify the material.
- What mechanical equipment do you have? You either have the necessary machine at home, borrow it from a friend or a rental shop, or buy it. There is a solution for everything.
- Do you have any experience with similar work, or should we go over it from the beginning? You've sanded wood or car bodywork? Great! Then we can handle this together too!
I communicate mainly with professionals, but I am a big fan of those who aren't afraid and want to try it themselves. There are jobs you shouldn't be afraid of, and there are those I will talk you out of. Even if you have respect for your project, don't hesitate to ask and we will go over it together. I look forward to hearing from you!
Pavol Šáray
CEO & Technical Expert at DiaSegment
I spend most of my time in the field with customers, finding the best solutions for their specific tasks directly at construction sites or in stonemason workshops. These field trips are my greatest inspiration – I subsequently process insights from practice into professional articles to help you navigate the field. Since I am often in full work mode, you might not reach me immediately, but I will be happy to devote my full attention to your questions.
✉️ Email: diamantovenastroje.cz@gmail.com
📞 Mobile: +421 903 528 039
Available on business days 8:00 AM – 4:00 PM.
If I don't answer, please send me an SMS or WhatsApp, and I will get back to you.