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Can You Apply Polyurethane Over Old Polyurethane?

To keep your wooden pieces polished, safe from damage, and long-lasting there is hardly any alternative to polyurethane. When applied over paint or wooden surface it seals them so that the shine and texture remain new. 

It’s so useful for furniture, wooden decors that you surely have applied it before.

But like every other coating, polyurethane to chips after some years. The coating starts to fall off and the surface stains. Then you will need to apply it again. 

While reapplying polyurethane many people wonder if they need to sand the old coatings or it can be applied over old polyurethane.

This query leads to much more information that you need to know about putting polyurethane layers over old polyurethane. Let’s dig in!

Can you apply polyurethane over old polyurethane?

You can apply polyurethane over the old coating of polyurethane. But you need to sand the previous layers of polyurethane first to give the piece a better finishing. Sanding old polyurethane before applying a new coat helps polyurethane to stick on the surface while making it smooth and durable.

Polyurethane is a plastic resin that can be both oil-based and water-based. It’s used largely to seal wooden, metal surfaces to protect the texture, color from dust, water, or stains. Thus polyurethane coatings make the items long-lasting and appealing.

You can find many polyurethanes in the market Brands like Minwax, Varathane, Rust-Oleum, etc. All of these have a variety of polyurethane such as glossy, matte, clear, or pigmented in their collection and it barely matters if you use new polyurethane over another brands’ product. 

However, whatever you choose for re-coating, you have to sand it before.

No matter how strong or durable polyurethane is, it will chip after a certain period. Since you can’t take a risk to leave your valuable properties with chipped or tarnished layers of polyurethane, you must coat it again.

To put coatings over old polyurethane you have to take off the old layers by sanding with a degreaser such as Minwax wipe on. Because polyurethane when dries, especially the oil-based ones provides silky texture on the surface that doesn’t let another coating stick over it strongly.

When you sand the old polyurethane it prepares a scratchy surface to hold coatings tightly as sanding with sandpaper or a buffer removes the silkiness. Sanding evens out the surface, abrade it thus another coating can stick to the paint.

In short, you can use polyurethane over old polyurethane coating but after sanding it. Otherwise, new layers won’t stick to the surface.

Can you apply polyurethane over old polyurethane without sanding? Can you recoat without sanding?

You can’t reapply polyurethane without sanding the older layer. Since the texture of polyurethane becomes silky and slick after drying, coating over it without removing the previous layer disrupts the paints’ adhesion.

If you sand the old polyurethane, it makes the surface able to hold the new layer of polyurethane by removing the grime, dust, paint pimple. Thus the new coat will stick to the surface properly.

Recoating without sanding the old coating is a bad idea. Because it will not give you the best result instead the surface may end up looking uneven. Moreover, without sanding you can’t clean the grease or dust nibs.

Even if you’re using polyurethane for the first time, you must sand the surface before you recoat it with the second layer. Thus the texture becomes long-lasting and smooth.

Should I sand in between old and new coats of polyurethane?

To ensure the best polish and longevity you should sand in between old and new coats of polyurethane.

Polyurethane is a plastic resin that’s used to seal the painted surface of wooden or metal material. Oil-based or water-based, polyurethane has a thin texture that turns into a smooth and silky finish when dried. 

So if you apply new coats of it over old ones, the newer layer might not stick.

Also due to the dirt and grease old polyurethane holds, it becomes tough to get a smoother polish by applying a new coat over it. But if you sand the old polyurethane layer and then recoat, the paint will be sealed properly. 

Also, the surface will look glossy, well-polished if abraded before recoat.

What happens if I don’t sand the old coat of polyurethane before applying a new one?

The purpose of using polyurethane is to make the appearance of a surface better and to give them a long life. But the result of applying polyurethane might not make you satisfied if you don’t consider sanding the old layer already existing there.

Let’s know what can happen if you recoat polyurethane without sanding:

Polyurethane will not stick: 

When you skip sanding the old layer, the surface remains too silky to hold the new coat of polyurethane. For that, the new layer won’t adhere to the surface and peel off later.

The surface will be uneven

Since the old layer of polyurethane includes grease, paint bumps, and rough patches, a new coat over it directly won’t come out as smooth as expected. It will look rough and sometimes bumpy in a few spots with too much polyurethane coat.

The paint can look dull: 

Polyurethane seals the paint so that the color remains vibrant. But when you already have old polyurethane, applying another coat over it without grinding the old one will not seal the paint. And so the paint will look faded.

How clean wood is to put polyurethane over old polyurethane?

Polyurethane needs a prepared surface to stick firmly. But if the wood isn’t clean you can’t expect the best outcome from polyurethane.

Old polyurethane over a wooden surface holds dust particles, grime, and paint bubbles. When you apply another coat of polyurethane over the old one without cleaning, you will get an uneven finish that might include dust nib, paint bump, and dull appearance.

So you will need to do the sanding. But after sanding the surface there will be dust everywhere that needs to be cleaned before you apply the coat. Otherwise, you’ll find dust particles trapped in the poly coating.

You need to clean the wood with a dust cleaner and then with a spirit damp cloth to prepare it for a new layer. Thus you will get a perfectly cleaned base for recoating old polyurethane.

How do you recoat polyurethane? How to put polyurethane over old polyurethane?

No matter what finishing you use it will decay over time.  Same with polyurethane. Polyurethane is one of the strongest That’s why it needs to be re-applied.

But you won’t have the best polyurethane finish unless you do it properly. So to put polyurethane over old polyurethane the right way you can follow the steps below:

Gather the tools:

To prepare a fine base for applying a new polyurethane coat over an old one you will need a few things.

For example:

  • Brush
  • Degreaser or solvent,
  • A pot of polyurethane,
  • Paint thinner
  • A piece of 150 grit and 320 grit sandpaper

Clean the surface:

Before you apply polyurethane over the old coating clean all the dirt, grease trapped on the surface. If needed use a damp cloth, any degreaser that cleans and lightly rubs the old poly surface.

Sand the old polyurethane coating:

You must sand against the old polyurethane layer before putting a new payer. For sanding it’s suggested to use 150 grit sandpaper at first then you can sand with a 320 grit fine-sand paper.

Use thinner:

thin some of the polyurethane to use in the first two-layer. Thus the coats will dry soon and get ready for the final coat.

Apply new polyurethane:

After the first two-layer is fully dried, apply the new layer of polyurethane without thinning it. Sand between the second and third coats for a smooth and rich finish.

How many coats of polyurethane should you put on over old polyurethane?

When your polyurethane finishing gets old and dull, the only way to save your furniture or decors is to recoat them with new polyurethane. But how many polyurethane coats are sufficient over old polyurethane is the confusion many people deal with.

The standard number of coatings you should put over old polyurethane coatings is three. You can add one more coat if you feel a lack of richness in the texture but more than four coats are highly discouraged.

But you can’t put all three coatings back to back. You need to sand in between to get the best result. Before applying the first coat and the final coat proper sanding is required.

Moreover, you have to wait and let the coat dry before you apply another coat of polyurethane.

Final Thoughts

New polyurethane can be layered over polyurethane. But you must sand the surface having an old poly coat first. This will replace the silky texture of polyurethane with scratches and holes. That way, the new layer will adhere to the surface providing you with a smooth and even finish.