After a while, varnish gets old, and you need to re-coat it. So, can you apply varnish over old varnish?
You can apply varnish over old varnish, but you must sand and prime the old coating first. Varnish, when dry, forms a thick and glossy layer that repeals any type of liquid, including sealants and paints.
If you don’t sand it, the new coat won’t stick properly and will slide its glossy finish. Sanding will create tiny holes where the new coat can stick. So, re-varnishing wood is possible. You just need the right steps, and that’s what we will explain.
Do You Need to Sand?
You can seal a varnish coating without sanding, but you must apply a coat of primer. The primer creates a smooth surface and allows the new coat to stick better.
Whether you should sand the old varnish depends on how much of the old layer is remaining. If there isn’t much left on the surface, you don’t have to sand it. However, if the old varnish still has a thick and glossy layer, you must lightly sand it.
Unlike traditional finishes, varnish doesn’t need to penetrate the surface to stick. Varnish is a topical finish that sticks over the top layer of paint. However, making it stick over a glossy finish is tricky. The sealant won’t be able to stay still over a glossy finish and will slide off. That’s why sanding is important.
Sanding removes the glossy layer of the previous coating, removes imperfections, and helps the new varnish stick better. Once the glossy finish is off, the new coating can stay over the surface and will stick.
However, priming can be an alternative to sanding. The primer will cover the glossy layer and allow the new varnish to stick without sliding off.
Related Read: How To Apply Varnish With a Roller?
How To Apply Varnish Over Old Varnish?
You can apply varnish over varnish, but you need the right steps. Here they are:
1. Clean And Sand The Surface
First, you must clean the surface. Use a clean rag and wipe off the dust from the old coating. Dust prevents the new coat from sticking but can also block some parts of sandpaper.
Once the surface is clean, sand it. To sand varnish, use 220-grit sandpaper. You can use rougher sandpaper if its glossy finish isn’t coming off. You can use a power sander instead of sandpaper if it’s a large surface.
Sanding will produce a lot of dust, so once you are done, you must remove the dust off the surface. To remove dust, use a damp rag with water and use the dampened rag to wipe the surface.
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2. Add A Coat Of Primer
If the paint underneath the old coating is oil-based, the new coating won’t stick without priming.
To know if the paint underneath was oil-based, use rubbing alcohol; dampen a rag with rubbing alcohol and wipe the surface. If the paint comes off, it’s water-based. If the paint doesn’t come off, it’s oil-based.
However, priming can be useful for water-based paints too. So, apply a water-based primer before you apply the varnish. To apply primer, use a paintbrush and apply 2 coats. Wait until the previous coat dries before applying the next one.
Once the premier dries, clean the surface.
3. Choose The Varnish Gloss
Choose the sheen of finish you want to use. You can use high-gloss, semi-gloss, or satin varnish. The high-gloss sheen offers the best moisture-resistant features. It protects the wood underneath best and has a shiny finish.
The satin sheen doesn’t have a shiny finish and doesn’t protect the material underneath from water. However, it gives you a rough and dry textured finish.
4. Apply The Varnish
Once you choose the sheen, apply it over the old varnish. To apply varnish, use a paintbrush and apply light coats. You must apply 2 coats. Also, you must sand between coats, but you shouldn’t sand the final coat.
Water-based varnish takes 6 hours to dry enough for a re-coat. While oil-based varnish dries within 24 hours.
Sanding The Final Coat
You must sand varnish if you apply more than 1 coat. Varnish, when dry, forms a glossy finish that won’t allow the next coat of stick. Sanding removes the glossy finish and allows the new coat to stick.
However, you shouldn’t sand the final coat because it has a thick and moisture-resistant layer that protects the material underneath from any liquid. The glossy layer also protects the material from scratches and prevents dust or dirt from getting through.
So, if you sand it, the final coating will lose its glossy finish and won’t protect the surface underneath. However, you can sand the final coating with fine-grit sandpaper to remove small imperfections and bumps.
Changing The Color
You can apply dark varnish over light varnish. However, you must sand the light coating (to remove the glossy finish) and apply at least two coats of dark varnish.
You can skip sanding if the light coating is water-based. That’s because water-based sealants don’t have a thick and glossy finish, and you can apply another coat over it without sanding.
However, you must apply at least 2 coats of dark varnish over a light coating to prevent bleed-through. If you apply just one coat, the light varnish might bleed through and mix with the dark finish. So to avoid this, apply 2-3 coats. You can also apply primer to prevent bleed-through.
If you want to apply light varnish over dark varnish, you must apply 2 coats of primer or remove the dark finish entirely. If you don’t apply primer, the old dark varnish will bleed through.
Related Read: How To Paint Over Varnished Wood?
You can apply varnish over old varnish, but you must sand and prime the old coating first. However, to get the best result, you have to remove the old finish and apply a new coating.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,