A reader wants to know how to restore shine to a Caesarstone countertop. (LES HENIG)

Q: Our bathroom was renovated in late 2015. We installed a quartz vanity countertop, I think Caesarstone. When it was new, it was fairly shiny — not a full gloss finish, but the equivalent of a semi-gloss. It has dulled considerably. Any easy fixes?

Kensington, Md.

A: Rather than being cut from natural stone, so-called quartz countertops are manufactured in factories. A mixture of natural quartz particles, pigments and polymer resin is poured into a mold, compacted, vibrated, baked and given a surface finish. So when you are cleaning one of these countertops or trying to restore a finish, you’re dealing with two different components: bits of quartz, which is harder than many other kinds of stone, and the tough plastic material around them.

Sometimes when a Caesarstone countertop looks dull, it just needs careful cleaning, said Ruthie Batson, who works on warranty and technical services issues for Caesarstone, a pioneer in making quartz countertops. She recommended using Soft Scrub’s gel cleaner that contains bleach.

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Sharon Miller, senior learning and business development specialist for Caesarstone, also recommended the Soft Scrub Gel cleaner with bleach, but she said that when there is “built-up patina” that makes the surface look dull, it’s a good idea to use Bar Keepers Friend Cleanser, in powder form, with the gel cleaner.

“Begin by pouring a small pile of powder in the center of paper towel,” she wrote in an email. “Pour the Soft Scrub Gel directly over and mix the two together until toothpaste-like consistency. Gently rub in a circular motion (like waxing a car) about 4 square feet of surface at a time. Gently rub the affected area for no more than one minute.” She put “no more than one minute” in boldface and added that you should use light hand pressure. Immediately rinse off the cleaner and residue with water and dry the surface with a clean paper towel. “If you see a darker color coming off on to the paper towel, it is working,” she said.

If that doesn’t restore the shine, you’re probably out of luck on finding an easy fix, Batson said. Caesarstone offers four surface options: honed, concrete, rough and polished. Polished is actually semi-gloss, the finish you describe. A polished finish “cannot be repolished in the home,” Batson said. She said the countertop would need to be removed and taken to a shop where a countertop expert with special equipment could use a series of progressively finer abrasives to restore the original look.

When some natural stone surfaces get scratched up and look dull, it’s possible to sand them with very fine abrasives to give the surface an even look, which generally is better than one that is dull or scratched up in only some areas. That is an option with quartz countertops, Batson said — but not one Caesarstone endorses. “You may see swirls and stuff,” whether you use hand pressure alone or use a random-orbit sander or other type of powered sander, she said. “People have done it, but we would never recommend it.”

The lack of an easy fix if cleaning isn’t enough is maddening because, although Caesarstone and other manufacturers tout their materials as hard, nonporous, stain-resistant and easy to care for, a lot can dull the surface. “Incorrect cleaners, abrasive cleaners, hair spray,” Batson said. The FAQ section of the company’s website, Caesarstoneus.com, adds more, including oven cleaners, floor strippers, toilet bowl cleaners, oil soaps, tarnish removers, furniture cleaners, drain products, and cleaning products with a pH lower than five or higher than 11. Simple Green cleaners also can dull the surface, Batson said.

A homeowner could avoid all of those and still wind up cleaning with a product that dulls the surface, partly because marketing departments often tweak product names. The Caesarstone website recommends cleaning with Soft Scrub Liquid Gel, and Miller’s email said to use Soft Scrub Gel cleaner with bleach. The company’s nonabrasive cleaner is called Soft Scrub with Bleach Cleaner Gel ($2.89 for a 28.6-ounce bottle at Target).

This product comes in a green bottle and differs from numerous other Soft Scrub products that come in white bottles and have cleanser rather than cleaner in their name. The cleansers are abrasive, while the cleaner is not. “It’s very important to use only cleaners that don’t contain abrasives,” Batson said. She and Miller both said the Soft Scrub gel cleaner in a green bottle is the product to use.

There’s another puzzler, too. Dial, which owns the Soft Scrub brand, doesn’t list the pH of the gel cleaner with bleach, even on the official safety data sheet. But a customer service representative at Dial headquarters said it would be similar to the pH of Soft Scrub with Bleach Cleanser. The safety sheet lists the pH — and it’s 12.7, considerably more alkaline than the upper limit of 11 that Caesarstone says is safe to use on its countertops. Plain bleach, which Caesarstone once recommended for stubborn stains, has a pH around 12 or even higher, depending on other ingredients. The pH scale is logarithmic, so each whole number signals a value 10 times different from the number above or below. Bleach is 10 times stronger than what Caesarstone says is safe to use, and the recommended cleaner is probably even stronger.

Nevertheless, Batson said, it’s okay to use the Soft Scrub cleaner gel as long as you pour some on a paper towel, rub it on the surface, rinse with a damp paper towel and rub the surface dry. “Prolonged” contact with cleaners that are too alkaline or too acidic is what can dull the surface, she said. What’s too long? “If you let it sit for 15 minutes, that’s prolonged exposure,” she said.

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