Since tabletops are exposed to stains and moisture, you must seal them with a strong sealant. So, how to finish a tabletop with polyurethane?
To finish a tabletop with polyurethane, sand the surface with 220-grit sandpaper, apply the undercoat (paint), sand, and then apply 3 coats of polyurethane.
Don’t apply an undercoat if you want the wood grain to show. That’s because paint or primer will cover the wood grain and prevent it from showing.
Things To Know
Polyurethane will protect tabletops from moisture (water), scratches, dents, and other damage. When dry, it forms a glossy moisture-resistant layer that prevents liquid from penetrating its surface.
Polyurethane has no paint pigments on its formula, meaning it has a transparent finish. This transparent finish will highlight the surface underneath, such as wood grain or paint. However, it will also highlight imperfections on the surface. That’s why it’s recommended to sand before applying it.
This synthetic sealant is reinforced with additives, solvents, synthetic resins, and urethane compounds. Urethane, the key ingredient, is a plastic-like compound that is flexible, durable, and weather-resistant when dry.
Polyurethane Types To Use:
For indoor tabletop surfaces, use oil-based or water-based polyurethane. For outdoor tabletop surfaces, use exterior polyurethane. Exterior polyurethane is formulated with extra additives that make its finish withstand weather elements.
Water-based polyurethane works better if used over an undercoat or washcoat. While, oil-based polyurethane works better when used over bare wood. If we compare both finishes, oil-based poly is strong and more durable because it has a higher level of additives in its formula. It also takes longer to dry, meaning the particles have more time to harden and become stronger.
On the other hand, water-based polyurethane dries faster, is easier to apply, and maintains its clear finish for several years, while oil-based polyurethane tends to turn yellow over time.
How To Finish a Table Top With Polyurethane?
Applying polyurethane to tabletop isn’t hard as long as you know the right steps.
Here are the tools you need:
- Sandpaper of different grits
- Bristled paint brushes
- Mineral spirits
- 4f pumice powder
- A vacuum or duster
- A drop sheet or nylon cover
- A paint or wood stain as an undercoat (optional)
- A shellac-based washcoat (optional)
1. Sand The Surface
First, sand the tabletop. Sanding will remove existing finishes (if any), imperfections, and dirt from the surfaces. It will also smoothen the surface, allowing the sealant to stick better and dry smoothly.
If there’s an existing finish, start sanding with 150-grit sandpaper until the finish is gone. If there’s no finish, sand with 180 or 220-grit sandpaper until the tabletop surface is smooth. After sanding, remove the dust and clean the surface.
Note: If the surface is sealed with varnish, use a paint stripper to remove it.
2. Wipe And Clean The TableTop
After sanding, clean the tabletop. Cleaning will remove dust, dirt (if any), and stubborn stains from the surface.
To remove stubborn stains:
- Damp a rag with mineral spirits.
- Use the dampened rag to clean the wood.
- Wait a few minutes.
- Remove the residue of the mineral spirit using soapy water.
- Allow the wood to dry.
3. Prep The Polyurethane
Prepping should be done based on the manufacturer’s instructions or user’s guide. For example, for spray polyurethane, shake the container for a few seconds to mix the content. For liquid polyurethane, stir it with a paint mixer or turning stick to make it flow better.
Optionally, you can thin oil-based polyurethane with mineral spirits if the flow is too thick. You don’t have to thin water-based poly.
4. Apply An Undercoat (Optional)
Polyurethane is a clear coat (with no color); if you use it over bare wood, the wood grain and wood will show. So, if you want a colored finish, mix water-based polyurethane with acrylic, or apply primer or paint to the wood.
If the tabletop is made from hardwood wood like Oak, seal the tabletop with a shellac-based washcoat. This is to stop the wood from over-absorbing the sealant. Wait 2 hours for the undercoat or washcoat to fully dry.
5. Apply The Polyurethane
Once the tabletop is clean and sanded, apply the 3 coats of polyurethane. You can apply it using a bristled paintbrush or sprayer. Wait until one coat dries, sand it, and then apply the next one. Don’t apply all the coats at the same time, and don’t sand the final coat.
On average, it takes water-based polyurethane 8 hours to dry for re-coat and oil-based poly 24 hours.
7. Buff The Finish
Optionally, you can make the finish glossier and more beautiful by buffing it.
To buff a finish:
- Sprinkle 4F pumice powder on the finish.
- Apply light oil.
- Use a clean and soft rag to buff the finish.
How Long Does Polyurethane Last On Table Tops?
On average, polyurethane will last 10 years on tabletops. However, the maintenance routine, exposure to water and dirt, and how much the surface is used all determine how long the finish will last.
For instance, the finish will last longer if the tabletop surface isn’t used as much or exposed to water. However, the finish will last less if the surface is used daily and exposed to water.
Optionally, you can touch up the finish by adding one more coat of polyurethane after a few years.
Here are a few things you can do to make the finish last longer:
- Wipe and clean stains off the finish immediately after they occur.
- Don’t expose the surface to constant water or moisture.
- Use waterproof padding.
- Buff or repair polyurethane scratches with a PU Scratchfix pen.
- Don’t use harsh cleaners while cleaning it.
In summary, you can finish a tabletop with oil, water, or exterior polyurethane. All you need to do is, clean the surface, sand it, remove imperfections, paint (optional), and apply the polyurethane.
If the table is made of hardwood, seal it with a shellac-based washcoat to prevent paint wastage.