Do you need to sand before second coat of polyurethane?
: sand between coats to get a good bond. The purpose of this instruction is to create scratches in the surface so the next coat of finish can establish a “mechanical” bond. ... Polyurethane dries slowly, so there are always dust nibs that should be sanded out before the next coat is applied.
Respected finishing expert Bob Flexner suggests that sanding between coats isn't necessary for proper adhesion between coats. He (and pretty much everyone else) recommends doing it anyway, mostly in order to get rid of the dust nibs.
Sand Between Coats
Make sure to sand the polyurethane between coats. Sanding removes drips, bubbles and other uneven spots in each coat.
It's all about adhesion. When you recoat after 2 hours you get a chemical bond between layers. If you let it go longer than that, you need to wait 24 hours so it's hard enough to sand and get a mechanical bond.
Two coats of oil based Polyurethane are recommended on stairs. For added step protection and slip-resistance, opt for three coats, while water based polyurethane, you can apply four or more coats. Wait for at least 8 hours before reapplying oil-based Polyurethane and 2 hours for water-based polyurethane.
However, do not apply more than two coats in one day. 220 grit sandpaper should be used between coats to remove any air bubbles, but avoid using steel wool. Before applying additional coats, vacuum the surface and wipe it clean with a tack cloth in order to remove all dust.
Allow each coat to dry fully. 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.
Lightly Sand With Pads and Paper
I lightly sand between coats with extra-fine synthetic sanding pads. The goal is to roughen the surface a bit and rub out dust motes, hairs and drips. Pro Tip: If there are stubborn nibs that stand up to the pads, grab 280-grit and be more aggressive.
Factors Influencing Polyurethane Drying and Curing Times
For a faster-drying wood floor finish, use water-based polyurethane, which takes six hours to dry before being ready for sanding and a second finish. An oil-based Polyurethane is going to take 24 hours before being ready for sanding or touching.
Thus, it's best to wait until all coats have been applied and dried before walking through the room. After that final coat, your floors should be off-limits for 24 hours. This is the only way to avoid any damage.
Why is my polyurethane still tacky after 24 hours?
The poly simply needs to cure for a while. Even after it "dries" and is safe to work on, the solvents that keep the polymers in suspension aren't all gone; they'll continue to evaporate, and the clear coat will fully harden in time. Check the can for your particular product; it should have a full cure time.
Now, while 3 coats is better, customers can also opt to do an additional coat of poly a year or two later. Now how about more than 3 coats. Generally, more than 3 coats of poly doesn't do much good. It's really not needed nor recommended.
The average coating thickness for urethane is 0.032” to 0.058”.
Sprayed polyurethane foam: minimum thickness of layer: 30 mm. Minimum density: 35 kg/m3. Optimum thickness and insulation of the protective layer: polyurethane elastomer; polyurethane layer of variable thickness (1.5-3 mm), density 1,000 kg/m3 with coloration.
Pot Life for Polyurethane Adhesives
Full cure is generally 24 hours or more. In most cases, the critical piece of information, is not the full cure but the handling strength. Handling strength indicates is the amount of time before you can move or pack assemblies.
Sand with fine sandpaper between coats after they dry. Make sure you remove sanding residue before applying additional coats. I recommend three thin coats of paint, but it all depends on the color and consistency. After the final coat of flat paint, sand* lightly with super fine sandpaper.
Multiple coats makes the coating thicker, stronger and more lustrous. Cars have multiple coats of paint to protect the body; you paint your walls with multiple coats to ensure even coverage; you poly furniture with multiple coats to ensure durability. Don't sand to much. Use a very fine grit and just rub over it.
If you put polyurethane on a rough surface you will get a rough finish. Second, as @keshlam says, make sure there is no dust at all on the surface before you apply the finish. A slightly damp cloth can help pick up anything remaining (but make sure the wood is dry before you apply).
After applying the first coat, make sure the surface is completely dry before using the tack cloth in between coats. We recommend using the tack cloth in between all coats for the smoothest results. Once finished, if the tack cloth is full of particles, safely dispose.
With poly you really should sand between each coat unless there is a specific "no sand" time window specified in writing from the manufacturer. But I agree that random orbital sanders are too aggressive. By hand use 400 grit on wiped on finish or 320 with brushed on varnish.
Is it better to use sandpaper or steel wool between coats of polyurethane?
Using steel wool or sand paper allows you to create a uniform surface for the next coat of polyurethane, which generally looks nicer, more professionally, etc. In my experience, assuming the finish is dry, there isn't a difference other than the coarseness of the sand paper or steel wool.
How to Apply Polyurethane: When working with any finish. Use natural bristle for oil-based finishes and synthetic filament (polyester, nylon, or a blend of the two) for water-based and water-based oil-modified finishes. Don't use rollers or foam brushes—they create bubbles.
The dull and shiny spots in your hardwood floor indicate that your installers did not apply the finish correctly. Dull spots in polyurethane floors usually indicate that the finish was not applied carefully, the applicator had a dry spot on it, or the finish was thinned out with a solvent such as mineral spirits.
A wet sander can be used after sealant, varnish, or polyurethane has been applied to smooth out bumps, scratches, or imperfections on the surface. In addition to making scratches less visible, the water gives better control over the thickness of the finish.
You should use an automotive polishing compound and a buffer for big areas. Small areas will have to be polished by hand unless you have some funky buffing tools. Make sure the poly has cured for a minimum of 4-5 days at 70f. Do not try to polish an uncured film.
*How Do I Remove Brush Strokes from the 3rd Coat of High Performance Polyurethane? Sand down the final finish with a 220-grit foam sanding pad, and then add another layer of General Finishes High Performance PolyurethaneTopcoat. Apply liberally than you did previously without heavy back-brushing.
For a truly smooth finish, sand lightly between coats with a pole sander using 100-grit sandpaper. Then use the vacuum and tack rag again with care before adding another coat of finish. Don't sand the final coat — just appreciate how it reflects the light and know that you have a finish that will last for years.
Water takes a long time to penetrate PU, which is why PU works as a waterproof coating. However, if there's enough moisture in the environment, water will eventually saturate the PU coating and go into and through the fabric, causing the coated fabric to leak.
In general, I do not advise sleeping in your home after a polyurethane application, regardless of whether you are using an oil-based or water-based finish. The fumes from the polyurethane can be toxic and may cause eye and respiratory irritation.
Polyurethane glue can be used to bond wood, metal, leather, tile, glass, rubber, brick and concrete. It isn't effective with plastics like polyethylene, polypropylene and chemically-created materials like Teflon.
How do you fix polyurethane that won't dry?
If you have already applied the polyurethane and it isn't drying, you can try applying heat—for example, from a heat lamp or blow dryer.
Let the finish cure – Cured finishes buff up better and faster than finishes that aren't fully cured. The longer you wait the better. Shellac, solvent and water-based lacquers and two part finishes should cure at least a week. Oil-based varnishes and polyurethane should cure at least two weeks.
It's one of the most durable coatings for wood protection against scratches, spills and more, and is a clear coat. It can be used on both finished and unfinished wood projects, and is available in a variety of sheens. The fast-drying formula allows for quick recoats in 4-6 hours.
Depending on many factors, like your lifestyle and type of finish, polyurethane can last between three to six years.
I like to dilute poly 50-50 with mineral spirits on the first coat, and subsequent coats diluted 2-1 or even 3-1. It makes the finish go on smoother and without bubbles or wrinkles.
Since Rust-Oleum Varathane Triple Thick Polyurethane is a thicker coating, you want to apply in the direction of the wood grain with one, thick smooth uniform coat. Applying too thick of a coating can hinder the drying process, not allowing the coating to dry from white to clear.
If your stain is not fully dry, you run the risk of your first coat of finish not drying for days. Wait at least the amount of time recommended or more if the temp is low or the humidity is high. The first coat of finish does not bond to stained wood well if it's applied to soon after the wood is stained.
Varathane® Triple Thick Polyurethane is 3X thicker than a traditional polyurethane. It is an advanced self leveling formula that allows projects to be completed in one coat while offering excellent scratch and stain resistance.
This finish protects your floors, but polyurethane is not waterproof. It will make your floors water-resistant, though — the coating repels water and helps prevent water absorption.
Generally, more than 3 coats of poly doesn't do much good. It's really not needed nor recommended. Each additional coat needs to be buffed so you are kind of buffing off half of the previous layer. So 4 coats is more like 3.5 coats.
How thick should a layer of polyurethane be?
The average coating thickness for urethane is 0.032” to 0.058”.
Apply thin coats. Thick ones take longer to dry and are more likely to drip or wrinkle. Sand between coats. Using 220-grit paper helps ensure good adhesion and smooths away imperfections.
Depending on many factors, like your lifestyle and type of finish, polyurethane can last between three to six years. However, if you see damage on your floors, it may be time to reapply a fresh finish to your hardwood.
The best option is to use a varnish or lacquer to give the wood a high gloss finish. While varnish can be sprayed or brushed on, lacquer is best applied by simple spraying. Spraying makes the surface seem finer than painting as it doesn't leave any strokes behind.
It doesn't matter except if you're using water-based poly. If so, the water will rust the steel wool fibers that end up stuck in the pores of the wood and cause rust spots. I prefer steel wool because it lasts longer and conforms to whatever curves you are smoothing.
