Marine
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.
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.
Make sure to sand the polyurethane between coats.
It is generally not recommended to paint over varnished wood without sanding or priming first. Sanding ensures the paint adheres properly, while priming helps with paint coverage and durability. Skipping these steps can result in peeling or chipping paint.
Sand the wood
This will help the varnish stick and will give you a smooth finish. If you removed the previous coat with sandpaper, you don't need to do this step.
Liquid sandpaper is also referred to as deglosser and wet sanding. The advantage of using liquid sandpaper instead of regular sandpaper is that it's easier to apply and safer to use. You just rub liquid sandpaper over the object you wish to paint, wait a set amount of time and wipe off.
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.
A varnish brush applies the film at the right thickness. After your first coat of paint is dry to the touch, it's safe to recoat typically three to four hours. A good rule of thumb is to wait at least three hours to recoat, if it's water- based.
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.
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.
In general, you can apply TotalBoat Gleam 2.0 marine spar varnish on top of almost all stain products, However, the Minwax stains do not work well with Gleam 2.0, and we do not recommend applying Gleam 2.0 over Minwax stain.
The main reason people sand between coats of paint is to achieve a perfect, silky smooth layer of paint. For most drywall interior painting projects, sanding is not necessary.
– 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.
Waterborne polyurethanes usually require a minimum of 3-4 coats to be effective. Although there is some evidence that too many coats can result in a plastic-like finish, waterborne polyesters are thinner than other types and therefore require several more coats to provide the same protection for hardwood floors.
Use 180-grit sandpaper and work the wood until the varnish is no longer glossy. For corners and other tight areas, use a sanding sponge or a bit of sandpaper. It is not necessary to remove all traces of the varnish, but it is critical to remove as much of the glossy finish as possible.
To give the subsequent poly layers something to bond to, sand lightly between coats with 320-grit sandpaper wrapped around a hard block. Note: The first coat needs the most sanding to appear smooth; don't worry if it doesn't look as flawless as you'd like at first.
Polyurethane is a reactive coating - it will not re-dissolve once it is cured. Any coating that is applied on cured poly is a gamble, and in most cases will fail. Naturally, the best way to go is to strip it, and refinish it.
Sanding between coats of varnish is important because it achieves two things: First, it knocks down the “high spots” and second, but more importantly, it provides a tooth for the next coat to adhere to. Otherwise, the subsequent coats can delaminate and lift off in large sheets.
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.
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.
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.
Liquid sandpaper, a.k.a. deglosser, is a chemical that can be used to rough up existing paint on walls and other surfaces by removing the gloss, making it possible to paint over what's left on the wall after use. This is good for hard to reach places or an object that you may feel would be awkward to sand.