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 the varnishes are thick (or solid) instead of thin, then they have expired, but even then the only real test is to use it and see if it fully cures. One of the symptoms of an expired varnish is that it never fully cures (stays sticky). In my mind, stains that are not also varnishes could last more than 10 years.
Mix four parts of denatured alcohol with one part of shellac in a clean jar and mix completely. Brush this concoction onto the finish, working only one area at a time. This should dissolve the old finish somewhat and cause it to be revived. Wait at least a few hours to see how well things are coming along.
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.
Old varnish and stain can be removed from wood. Sanding is one of the most frequent techniques because it cuts through varnish and stain to reveal a new layer of wood.
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.
Using sandpaper
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.
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.
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.
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.
A: Usually when varnish remains persistently sticky it's the result of application in a humid or cold environment. Sticky varnish can also be caused by too-thick application, or by re-coating an insufficiently dry layer. Traditional varnishes made in-studio (e.g. damar and mastic) are most prone to stickiness.
Shellac and Varnish - To differentiate between shellac and varnish, use a cotton swab to apply denatured alcohol (ethanol). Varnish will react slowly, but shellac will dissolve right away. Oil - Wood with an oil finish will absorb linseed oil.
Most water-based lacquers or varnishes will last for at least a year if they are stored correctly and not allowed to freeze.
The answer is a resounding yes, but it requires proper preparation. Varnish is a protective coat that shields the wood from moisture and damage, making it less porous and harder for the paint to adhere. However, with the right approach, you can achieve a beautiful and durable finish.
One of the significant drawbacks of varnish is its lack of breathability. Varnish forms a film on the surface of the wood and prevents wood from naturally exchanging moisture with the environment. This can lead to trapped moisture and subsequent wood decay.
You can chemically treat the surface with a paint stripper, or use mechanical methods such as a spatula, scraper, sandpaper or a sander. You can also use a heat gun to loosen the varnish. If the varnish is stubborn, use a wire brush or a high-pressure cleaner.
PolyVine Heavy Duty Floor Varnish. This is the hardest of all 'one pack' varnishes.
– 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.
Bonding primer: Specially formulated primers can create a strong bond between paint and varnish, even without sanding. However, these primers can be expensive and may not be as durable as a sanded and primed surface.
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.
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.
Alcohol interacts with wood surfaces, acting as a solvent when it touches wood. Solvents dissolve wood finishes, including staining and varnishes. It does so by stripping away the top layer of the furniture. This can significantly damage the integrity, aesthetics and value of the piece.
Marine Spar Varnish can be recoated in 10-12 hours at the recommended coverage rate. The varnish can be recoated without sanding up to 24 hours. Beyond 24 hours, sanding is required.