Can coatings be used over impregnating sealers?
Estimated Reading Time: 3 MinutesQ. 25 years ago, our painter applied a sealant, possibly epoxy, polyurethane, or acrylic, to a new flagstone interior entry. It‘s held up beautifully. We are about to install flagstone in a small breakfast room. We want to retain the color of the stone and have a hard, protective surface with some gloss, much like we have in the foyer. Most of what I read advocates an impregnator. From what I gather, impregnators don‘t change the smoothness of the surface or allow shine. Can we apply a high-solids or resin coating over an impregnator? What would you suggest we do to get close to the results we want? The stone is here, waiting to go down, and we, including our stone mason, are stumped.
A. You're right to pause before making a move. Impregnating sealers, also called penetrating sealers, are designed to protect from within the stone. That's why they won't create a glossy appearance or change the texture of the surface. Impregnators are excellent for stain resistance and breathability, but not for creating the look you're describing.
What you have in your foyer is almost certainly a topical coating, probably a solvent-based acrylic, polyurethane, or epoxy. It has likely been applied directly to the stone, not over an impregnator. These types of coatings create a film on the surface, giving the stone that hard, glossy, durable look. And when properly maintained, coatings can last decades indoors, just like yours has.
Here's the issue. You can't apply most topical coatings over an impregnator. Impregnators leave residue in the stone's pores that prevents coatings from bonding. If you try to put a resin-based coating over your stone, you risk delamination (peeling of the coating), flaking, or uneven gloss.
So, what should you do? If your goal is to match the look and performance of the foyer, skip the impregnator entirely on the new floor. Go with a high-quality, solvent-based topical sealer or coating, such as:
- Solvent-based acrylics (easier to apply and recoat)
- Water-based urethane or polyurethane (if odor or VOCs are a concern)
- Epoxy coatings, if you want an ultra-hard finish (but be cautious because epoxies can yellow over time with UV exposure, even indoors)
Make sure the stone is clean and dry before applying anything. Apply at least two coats, using manufacturer instructions for coverage and drying times. Consider applying a compatible wax or finish coat on top if you want to add more gloss. This extra coat could also provide ease of maintenance.
If possible, find out what exact coating was used in the entry. Some companies still make those legacy sealers, or similar ones exist. Test the coating on the leftover flagstone piece first to confirm the look and bond. If you ever need to recoat, make sure you're using the same chemistry, or you'll need to strip the old coating.
In summary, your new flagstone can match the look and performance of your 25-year-old flagstone entry. Since impregnating sealers are designed to repel liquids, it follows that water-based sealers will not adhere properly. Make sure your high-solid or resin coating is solvent-based if you are applying it over any area where impregnating sealers were previously used. For the best results, hire an experienced professional stone restoration contractor to achieve the results you want. To find a vetted PRO in your area, visit www.surfacecarepros.com and click on Find a PRO.
ABOUT THE AUTHOR Fred Hueston is the Chief Technical Director at SurfaceCarePROS.com and Director at StoneForensics.com. He is also the author of Stone and Tile Restoration: The Manual, a comprehensive online manual for stone and tile restoration contractors. [Learn more about Fred.]