Can You Apply Polyurethane Over Old Polyurethane?

Can you put polyurethane over old polyurethane?
Can You Apply Polyurethane Over Old Polyurethane?

Can you apply polyurethane over old polyurethane? It sounds confusing, right? The wood was good enough with an old polyurethane finish. But now you’ve decided it’s time for a fresh coat.

Is it even possible to apply polyurethane on the wood again? This poly advice article will break down a few concerns and provide simple ways to help you polyurethane your furniture, floor, or cabinet, even if they were previously finished with a different type of polyurethane.

Let’s dive in.

Can You Apply Polyurethane Over Old Polyurethane?

As long as you use the proper steps to prepare the finish, you can put polyurethane over old polyurethane. But before you apply the topcoat polyurethane, you might have to first sand the surface lightly using a dull 120 to 150 grit abrasive screen using a heavy floor buffer.

How Do You Recoat Polyurethane?

Recoating your surface depends on some factors: 

Going against this will make the surface reject the new finish. 

Tools and Supplies for Applying Polyurethane over Old Polyurethane

Here’s what you’ll need for a perfect polyurethane recoat:

  • Polyurethane sealer (Oil-based or water-based).
  • White vinegar.
  • Water.
  • Tack cloth.
  • 5” to 3” bristle brush (natural bristles for oil; synthetic for water).
  • Roller or applicator pad with handle.
  • Extra roller cover or pad made.
  • Respirator with a vapor cartridge – if using oil-based polyurethane only.
  • 220 grit sandpaper or 320 and 400 sandpaper for finer grits.

How to Put Polyurethane over Old Polyurethane (Step by Step)

To recoat Polyurethane, follow these steps:

Step 1: Cleaning the Surface to Remove Dust

In a ratio of 10:1, mix water with white vinegar. Use a tack cloth to clean the wood surface. Alternatively, use a wood floor cleaner.

Step 2: Sand the Wood Surface

Use a 220 grit sandpaper or 320 and 400 to sand the surface. This is to ensure that there are no high spots.

Step 3: Prepare the Poly

Use a stirring stick to stir the polyurethane. However, don’t whip or shake it to prevent air bubbles from forming.

Step 4: Apply The First Polyurethane Recoat

Using the 5″ to 3″ brush, apply polyurethane to the wood edges. Use a roller or pad to apply polyurethane to the center of the surface is huge and give it 24hrs to dry.

Step 5: Sand the Surface Once More

Afterward, use steel wood (oil-based material) or an abrasive pad (for water-based polyurethane) to sand the wood lightly.

Step 6: Apply the Last Coat

Apply the last coat of polyurethane as you did in step 4. 

Step 7: Check the Finish

After it dries, check the finish for orange-peel texture. If an orange-peel texture is present, scratch the surface with moderate pressure using a coin; the finish should not peel away. If the surface flakes with moderate scratching, you might have to sand the floor and refinish it again.

Important Tip: 

Before applying a succeeding coat, the floor needs to be lightly abraded to make the new coating adhere and give you a level finish. A process called screening.

Can I Apply a Second Coat of Polyurethane Without Sanding?

The simple answer is no; you can’t. If you want your surface to be good, there is no shortcut but to first sand the surface before applying the second coat. Before sanding, give the Polyurethane enough time to dry and cure properly. Practically between 24 to 48 hours. Sanding between each subsequent coat will ensure you get the best results.

What Happens if You Don’t Sand Between Coats of Polyurethane?

Sanding between coats of polyurethane is vital to your finishes. If you don’t’ sand;

  • You risk poor mechanical adhesion when you apply the next coat.
  • The wood surface may have high spots which create bubbles.
  • You will have brush marks on your finish.
  • You risk having dust particles in your finish.

Here’s a quick guide I did on what happens if you don’t sand between coats of polyurethane.

Facts About Polyurethane

Brush across the wood grain before applying the finish.

All finishes soak on wood no matter how you apply. So why is it always advisable to brush across the grain to work the finish into the wood? Well, this makes the varnish even thicker. 

The longer you brush, the thicker the coat will become. And when the coating gets thick, brush marks will be more pronounced, compromising the smoothness of the coat.

Don’t shake the Polyurethane as it may form bubbles.

If you shake the polyurethane can before applying it, bubbles will form in the finish. And even after brushing on the surface, bubbles will still appear. The majority of the bubbles, however, are a result of brushing. Therefore, to avoid polyurethane bubbles, reduce turbulence caused by the rapid movement of the brush.

It is common to get bubbles on the coat whether the can is shaken or not. But don’t allow the bubbles to dry in the finish, even though they mostly pop out on their own.

If the bubbles get trapped, tip them using a brush, and they’ll break. Alternatively, add 5% or 10% mineral spirit to slow the drying and allow the bubbles more time to pop out on their own

Thin the first coat 50% to get a perfect bond.

Primers mostly create a strong bond for paint. This is because they have a higher ratio of binder to pigment. Considering all finishes are binders, they, therefore, bond ideally even without other products.

To attain a perfect bonding between coats, apply a thin coat of polyurethane up to 50% as the first layer and the coat will dry fast. The thinner the layer, the shorter the drying time. 

Sand between coats to get a perfect bond.

The core reason for sanding a surface before applying another coat is to create a scratched surface which gives the next layer of finish great adhesion. Besides, polyurethane dries slowly. So, before applying the next coat, sand the surface first to remove dust nibs.

Use sandpaper to remove all the flaws perfectly without creating deep scratches on the floor surface. Again, I will recommend a regular or {p} grade sander. If you choose to use a flat block, your sandpaper will possibly clog, creating deeper scratches into the finish.

How Do You Restore a Polyurethane Finish?

Restoring a polyurethane finish is so easy. However, the procedures do differ depending on the damaged surface. So, let’s see how you can restore the polyurethane finish on various surfaces.

Cabinets

Where the cabinets are doesn’t matter. Whether in the bedroom or the kitchen, cabinets get exposed to excess moisture or cooking oil, which damages their finish. Whenever you detect oil or water spots on the surface of your cabinet, use Miniwax Wood Cabinet Cleaner to wipe them off.

After cleaning,  apply Miniwax Wipe-On Poly. Use the wet sanding technique to ensure no scratches on the cabinet surface.

Furniture

Most of the furniture today has clear coats of protective finish like Polyurethane. Unfortunately, with time, the furniture wears and tear, leaving scratches on the surface. To fix this, use the Minwax Wood Finish Stain Markers. These products are available in your local store in up to eight colors.

The product will remove minor blemishes without spending a lot of money on costly refinishing. However, for deeper scratches that require filling, you might have to use Minwax Blend-Fil Pencil. They fill the holes on the surface of the furniture and restore the wood’s original color.

Wooden floors

Every day, your floor undergoes wear and tear due to the grit on the sole of your shores. You can reduce this by strategically placing doormats. Alternatively, regular cleaning and vacuuming with Minwax Hardwood Floor Cleaner minimize wear and tear of the floor surface.

For refinishing, you can learn how to apply water based polyurethane to wood floors.

Rooting wood

Water is the worst enemy of wood. It softens and causes decay even in the toughest hardwoods given enough time. So if you come across any softened wood, use a screwdriver to get rid of the rotten wood fibers.

Allow the area to completely dry and apply a liberal coat of Minwax Wood Hardener. Give it time to penetrate the wood grains and harden the wood fibbers. Next, fill the remaining cavities with Minwax High-performance Wood Filler.

Nail holes

Whether the nail holes are in trim work or furniture, quickly fill the holes using Minwax Wood Putty. Next, apply this product to the nail hole and whip off the excess with a soft cloth.

How Do You Fix Streaky Polyurethane?

In the process of applying Polyurethane, you might end up with a streaky poly. To fix streaky and wet polyurethane, first clean up the wood with a damp piece of cloth to check if the surface is even.

If the poly is thick, sand the surface once more. If the poly is not thick, add another coat of Polyurethane. Check again if you have achieved an even sheen and buff it with wax.

Why Did My Polyurethane Turn White?

Suppose you apply a quick-drying finish to a surface with high humidity; chances are high the finish will turn milky. This is because the finish hardened before the moisture which got trapped in the finish fully evaporated. 

However, this is never the case with Polyurethane. Not even the water-based one. Polyurethane turns white because of the accumulation of zinc oxide—an element used as a flattening agent.

Polyurethane manufacturers add zinc oxide to create a satin finish and as a flattening agent at the same time. Zinc oxide is of service as it helps in cutting the gloss out of the sheen. It also helps dispense reflected light.

As a rule of thumb, stir the poly well before use as Zinc oxide tends to settle at the bottom of the can.

To fix the white spots, sand it down if it is a high spot and draw out the moisture.

Ways To Prevent the Recurrence

If you want to solve the issue with cloudiness in your Polyurethane, consider these tips:

  • Stir: Stir your varnish thoroughly. This should be done until you no longer see white residue on the stirring stick.
  • Let the wood dry well: Ensure that the wood is completely dry before applying a new coat of Polyurethane. If you’re not sure that the wood is dry, use a few drops of water. If the water doesn’t soak in fast, then the wood surface is not dry to paint
  • Never build up coats: If it’s a must that you build up coats using a gloss material, then use satin for the last two coats. 

What Is the Best Applicator for Polyurethane?

You can brush, roll, wipe or even spray polyurethane. 

For brush lovers, bristled brush is known to offer a perfect finish. 

But you are also not restricted to one type of brush. For example, form brushes, even though expensive, work perfectly for flat surfaces.

How Do You Polish or Smooth the Final Coat of Polyurethane?

After applying your desired number of coats, you might want to spray aerosol Polyurethane to the final coat and allow it to cure overnight.

Using a 1500 grit sandpaper, remove any dust nibs and smoothen the last poly coat before applying automotive paste wax, giving the floor a perfect shiny finish. You can wax using either a soft cotton rag or a polishing pad.

You may want

Polyurethane over Polyurethane FAQs

1. Can You Put Too Many Coats of Polyurethane?

Many coats of Polyurethane won’t do much good. So it is generally not recommended. Applying up to four layers of Polyurethane will compromise the beauty of your floor.

2. Is One Coat of Polyurethane Enough?

For outstanding results, you might have to use two to three coats. But before applying the next layer, you will have to wait for quite some time to allow Polyurethane to dry and cure well.

3. Can You Use a Roller to Apply Polyurethane?

The simple answer is yes, and you can use a paint roller to apply Polyurethane. Using rollers eliminates brush lines and helps you apply the right amount of Polyurethane.

4. Do You Sand the Last Coat of Polyurethane?

Yes, you can but slightly. If you must sand, you might have to use 600 grit sandpaper. Although this practice is not highly recommended as it leaves a scuffed-looking surface on your finish.

Final thoughts?

Can You Apply Polyurethane Over Old Polyurethane? The answer is yes.

This sealer plays a critical role in protecting wood surfaces, and the end result of recoating poly will always be awesome.

Be sure not to leave any bubbles on your finish. Check out our quick guide on how to apply water-based polyurethane without bubbles.

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