The best way to apply a second coat of varnish or polyurethane is to lightly sand the first coat with fine-grit sandpaper (around 220 grit) to remove any imperfections and ensure good adhesion. Clean the surface thoroughly to remove dust, then apply the second coat using a high-quality brush or foam applicator.
Yes, you can varnish over varnish without sanding if the existing varnish is in good condition. Ensure proper cleaning and use a compatible varnish type. However, for the best results, light sanding and cleaning can enhance adhesion and finish quality.
It's generally recommended to remove old varnish before applying a new one to ensure proper adhesion and finish quality. However, if the existing varnish is in good condition, you can apply a new coat after thorough cleaning and surface preparation.
Sanding Tips: No sanding is needed if you overcoat within 48 hours. Don't sand unless the most recent coat has dried for 24 hours. Use 320 grit to prevent scratches; sandpaper finer than 320 grit will not allow proper adhesion. Remove residue before reapplying.
Varnish finish
Some varnish finishes can be reconditioned with a mixture of 3 parts boiled linseed oil and 1 part turpentine. Mix this solution well and apply it sparingly to the varnish with a cloth or grade 000 steel wool. This may work - it's worth a try.
– Existing Finish: If the wood has an existing finish that needs to be removed, stripping is typically the preferred method. – Surface Imperfections: If the wood has surface imperfections, scratches, or uneven areas, sanding is more appropriate.
To remove damaged varnish, lightly roughen a small area around the scratch with sandpaper, steel wool or synthetic steel wool. Find an oil-based stain that is a shade lighter than the wood finish. Stain the bare wood with a very small amount of stain on a rag, brush or cotton swab.
Although the finish may be attractive initially, the varnish must be recoated after a maximum of two years exposure. If recoating of the varnish is not done before it starts showing signs of breakdown, stripping will be necessary, which will remove the varnish and some of the stain.
This will ensure that the new varnish has something to bond to. The bottom line is that is it far better to remove any previous surface treatment - oil, sealer, polish, or varnish before re-applying varnish.
Make sure to sand the polyurethane between coats.
Next layer applied too soon
When a new coat of varnish is applied to a surface that appears dry and is not fully dry, different minute sections of the surface interacts, and expands, differently to the solvents in the new varnish. Sand down, and depending on your visual requirement, repaint.
This method requires caution.
A heat gun can soften the varnish, making it easier to scrape off. Hold the heat gun a few inches from the surface and move it back and forth. When the varnish starts to bubble, use a scraper to remove it.
While polyurethane is water- or oil-based plastic resin, varnish is older and made from resins, oils, and solvents. Because of the higher ratio of solids, varnish is less susceptible to ultraviolet light damage. This protection makes varnish an excellent choice for projects such as outside decks and exterior furniture.
The best way to apply a second coat of varnish or polyurethane is to lightly sand the first coat with fine-grit sandpaper (around 220 grit) to remove any imperfections and ensure good adhesion. Clean the surface thoroughly to remove dust, then apply the second coat using a high-quality brush or foam applicator.
Medium Grit (80-120 Grit)
Medium grit sandpaper is the most commonly used type. It's perfect for general sanding to prepare surfaces for painting or varnishing. This grit range is typically used after the coarse grit in a multi-step sanding process.
We recommend using Zinsser Bulls Eye 1-2-3 for glossy surfaces like varnished wood. Zinsser Bulls Eye is a 'bond coat' primer that's great for hard-to-stick surfaces as it offers excellent adhesion without sanding.
Instead of sanding, use a liquid deglosser to dull the existing finish. This product helps you prepare the surface for new stain or paint without the need to strip or sand. Wipe it on with a cloth, and it removes the glossy top layer, making the surface ready for refinishing.
Gloss oil-based varnish, polyurethane and Danish oil can last 10 or 20 years, though satin finishes and stains may fail sooner as pigments and flattening agents disable the driers. Water-based coatings and paints can also be viable longer than three years. Shellac, though, can go bad in under a year.
If you plan on removing the varnish and then painting the wood, sanding can be an effective way to get rid of the varnish while prepping the wood at the same time. It's also a natural and chemical-free way to remove varnish. It can however be labour-intensive: Start with 150-grit sandpaper and sand the entire surface.
Fair the edge of intact varnish into the bare spot with 120-grit paper on a small hard block until smooth. Sand the entire touch-up area with 240-grit paper. Wipe with alcohol and seal with a 50/50 varnish-and-turpentine mix. Do this with each touch-up.
For a very durable finish and one that needs to be very tough, say on a kitchen table, coffee table or end table etc, 2 to 3 coats of varnish should be enough on the top, with 1 to 2 coats on the legs/base. For chairs, benches, chests and other such pieces, 1 to 2 coats should do the trick.
Applying more than two coats of matt or satin varnish could mean making your painting look cloudy, but with gloss varnish you can apply up to three coats. If you're using spray varnish, you could stick to two to three layers, or apply anything up to 50 coats if you're after an extra high-gloss effect.
Apply a few drops of denatured alcohol to the furniture, as shown in the photo above. Wait a few seconds; then touch the spot with a soft-bristle brush or a cloth. Shellac, a popular finish before about 1920, will soften and turn a bit sticky. If it doesn't, it's not shellac, so move on to the next test.
The traditional key to any great looking (and successful) varnish job is to build up numerous coats of the best varnish you can afford, sanding in between each coat until a flat and uniform surface appears. This is the result of many centuries of experience and knowledge gained through trial and error.
To remedy the defect, the varnish must be allowed to harden thoroughly before flatting down and recoating. Prevent curtaining by applying the coating evenly and avoid heavy coats. Plan the work accordingly so that the wet edge is kept open.