Can you Apply New Varnish over Existing Varnish?
When you need to touch up or restore a piece of furniture people often wonder if it is possible to apply new varnish over an existing varnish, but can you do this?
26/12/2022
The question of whether you can apply new varnish over old varnish is one that pops up all the time. Surely it is easier to refresh a piece of furniture simply by applying a new coat of varnish over the existing varnish, but is that the right thing to do? Some DIY enthusiasts will argue that there is nothing wrong with applying new varnish over old as long as it is in good condition, while woodworkers and carpenters will tell you not to do it. The bottom line is that it depends on why you want to apply new varnish over old. To cover this in more detail, we look at some common queries regarding varnish.
What is the purpose of varnish?
Varnish is a surface finish that sets hard, one that is applied to protect and enhance the natural beauty of wood. This surface treatment. a combination of oils and resins in a solvent carrier. Varnish has been used for centuries as a protective finish for all types of wood and once applied, varnish hardens into a durable, waterproofing finish that seals and protects the wood from damage. Despite the introduction of polyurethane, a synthetic water-based surface treatment alternative, varnish remains the trusted solution for woodworkers as a finish for timber projects.
Why bother with varnish?
When working with wood and wanting a professional, hard-wearing finish, varnish is the first choice. Polyurethane is an easier solution as far as the application is concerned, but the fact that polyurethane is water-based and contains plastics, it does not hold up well against heat, excess moisture, or harsh chemicals. The proper preparation procedures (fixing, sanding, and cleaning) should be performed before applying varnish to ensure a successful and long-lasting bond between the surface and the varnish.
When to consider the re-application of varnish
Varnish has a reasonably long lifespan but, due to the fact that wood is never static and undergoes constant movement, there will always be cases where the varnish may crack and expose areas where moisture gains access and damages the wood. UV, humidity, salt air, and temperature all have an adverse effect on wooden furniture and fitting and while varnish offers the most amount of protection, it is not perfect. When there are signs that the varnish is failing, perhaps after several years of wear and tear, it will be necessary to remove and re-apply varnish.
Can you varnish over existing varnish?
The most direct answer to this question is no. If the varnish is already showing signs of failure and the piece needs restoration, the worse thing you can do is to apply more varnish on top of the damaged varnish. If you do decide to go ahead and apply new varnish over the top of old varnish, make sure that the existing varnish is scratch-free and do give the old varnish a light sanding using 120-grit sandpaper and wiping away any dust. 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.