A good sealer can protect flagstone and bring out its color. A sealer put on the wrong way can leave a cloudy, patchy finish that is hard to fix. Most problems come from one mistake: sealing stone that is still damp. This guide covers how to prepare the surface, when and how to apply, and how to choose between shiny and matte finishes. We stock sealers, strippers and other finishing products, including Glaze 'N Seal, and our staff can help you pick one.
Rule one: never seal wet stone
Never put any sealer on wet stone. It is a recipe for disaster. Moisture trapped under a sealer can cloud the finish and keep it from bonding. Stone holds water longer than it looks, so give it real time to dry.
Sealing is also optional. Many stones look and wear well unsealed. Sealing is most useful when you want to enhance color, resist stains in an outdoor kitchen or dining area, or make routine cleaning easier.
Prepare the surface
Pull weeds and scrape out any loose joint material before you wash. Anything left on the surface will be locked under the sealer once it cures.
- Wash the area to remove dust, dirt and debris.
- Turn off any sprinklers that could get water on the area.
- Let the stone dry for 5 to 10 days.
- Check the forecast, and wait if rain is coming.
- Sweep off any fresh dust right before you start.
Apply in the cool of the morning
Sealer can be brushed, rolled or sprayed. Do not apply it in the heat of the day. Early morning is better, when the stone is cool and the sealer has time to go on evenly.
Two coats are best. Apply the first coat in one direction, north to south. Apply the second coat across it, east to west. Crossing the coats gives you more even coverage and fewer missed spots. Follow the drying time on the product label between coats.
Work in small sections so you always keep a wet edge. Avoid puddles, which can dry cloudy. Keep people, pets and sprinklers off the area until the sealer has fully cured, following the time on the label.
Shiny or matte, and why the stone matters
Sealers come in shiny and matte finishes. Some also darken the stone for a "wet look." The same sealer can look different on different stones, because the porosity or density of the stone changes how much it soaks in and how it reads on the surface.
Tell us what you are sealing and how the area is used, such as a patio, pool deck or wall. We will help you pick a sealer that fits the stone. See wet look vs natural for more on finishes.
Think about where the stone is used, too. A high-gloss finish can look striking on a wall or fountain. On a walking surface, especially near a pool, many people prefer a lower sheen. Ask our staff about the feel of each finish underfoot.
Test first
Try the sealer on a spare piece or a hidden corner and let it dry fully before you do the whole area. It is the simplest way to see the real color and sheen on your stone. We also carry strippers if an older coating has to come off first. Browse finishing products on our supplies page.