By John Shearer

Polyurethanes: A Definition

Polyurethane coatings were invented in the mid-20th century. Plastic resins in liquid form, they are used primarily to protect wood surfaces. Their main ingredients include acids derived from vegetable oil, nitrogen-based chemical amalgams, isocyanates, and mineral spirits. Nitrogen helps keep polyurethane finishes from chipping, isocyanates make them hardier in general, and mineral spirits constitute the base that supports the other components.

A polyurethane coating cures when some of its chemical elements form powerful links with one another after reacting with atmospheric oxygen. These links allow the finish to resist damage due to external factors. In contrast, lacquer does not stand up well to strong chemical agents. However, polyurethane is prone to eventual discoloration, and its application may make light woods darker.

Water-Based Polyurethane Products

Ecological awareness has prompted several finish manufacturers to make water-based polyurethane products. The basic formulation calls for the suspension of polyurethane in water. Although these coatings are more vulnerable to wear and tear than traditional, oil-based finishes, they dry rapidly, produce almost no smell, and are water washable. They also represent less of a health hazard than oil-based polyurethanes, which should only be applied in a properly ventilated area.

Oil-Based Polyurethane Products

Oil-based polyurethane cures most efficiently when the temperature is neither too high nor too low. Not surprisingly, humidity level is the key factor when a water-based finish is curing. On average, it is necessary to apply one more coat of water-based polyurethane than of oil-based finish. Whatever the nature of the coating, sanding and cleaning the wood after each layer has dried is advisable. Oil-based coatings are inflammable and more environmentally harmful than water-based alternatives, which do not burn or yellow and can be washed with water and simple cleaning products. The wait between applying one coat of oil-based finish and adding the next may be as short as four hours or as long as 18.

How to Apply Polyurethanes

Under no circumstances should one shake a polyurethane finish prior to applying it. Agitation creates bubbles, which may later appear on the surface being treated. Gentle stirring is the recommended way to mix polyurethane. A cloth, foam brush, or fine-bristled brush may be used to apply it to a surface. When brushing, follow the wood’s grain and get rid of every bubble you see.

A day after finishing the surface in question, sand it with 320-grit sandpaper. Take care not to remove the polyurethane entirely, thus damaging the wood stain below. After the sanding process, remove the bits of material it has produced and add a second coat of finish. Uncommon shine may be achieved as follows: Sand the final layer of finish with 600-grit sandpaper, then buff it to a high gloss.

Water-Based Finishes

If a wood surface has been stained with an oil-based product, avoid using a water-based finish. The incompatibility of oil and water is widely known, but if this combination must occur, it is essential to coarsen the wood before applying the polyurethane. (A less smooth surface is easier for water-based finish to stick to.) A thick layer of water-based finish could elevate the wood grain, so make the coats as thin as possible. The first is likely to dry within two hours or so. While sanding is not essential prior to the application of a second coat, water-based finish must be layered more times than its oil-based counterpart, which only requires two or three coats.

Gravity can be a frustrating enemy when applying finish to a wall. When polyurethane begins running down the surface, a keenly sharpened blade, such as that of a razor, can be the perfect tool to remove it. Sanding whatever the blade cannot remove is also wise. The thinner your layers of finish, the fewer runs you are liable to encounter.

Acrylic Urethane Vs. Polyurethane

Without realizing it, we frequently use items made out of urethane or polyurethane – and most of us are not even painters. Many may believe that the only real difference between the two are the compounds that make up polyurethanes (if we even think as deeply as that on the subject). But while polyurethanes are made up of several different urethane compounds, there are many more differences between polyurethanes and urethanes.

Although the main difference is the compounds (polyurethane is basically a chain of urethane organic compounds, and urethane has a main functional group of compounds).

Acrylic urethane differs from polyurethane in several noteworthy ways. For one thing, polyurethane chips and stains less easily than acrylic urethane. It also stands up better to substances like alcohol. Some acrylic urethane coatings rival or even equal their polyurethane competitors, but generally the latter continue to earn their reputation as the stronger of the two. Furthermore, acrylic urethane coats fewer square feet per gallon than polyurethane and “sticks” less easily to surfaces.

Like any coating, polyurethane finish has its downsides. It dries, sets, and cures considerably more slowly than acrylic urethane, which can dry within 10 minutes. In addition, buffing acrylic urethane to a gloss is easier than doing so with polyurethane.

 

 

Both types of finish lend themselves well to spray application. However, brushing acrylic urethane is a tough job; it hardens rapidly, often producing visible brush lines. If a wall or other surface must be completely even, acrylic urethane — and polyurethane, for that matter — should be sprayed rather than brushed. Prior to finishing a surface, a contractor or homeowner may apply an epoxy primer. The primer hides imperfections that might otherwise come to light when the finish is added, especially if it produces a significant shine.

The question remains: Which is better, polyurethane or acrylic urethane? As is so often the case when working with coatings, the nature of the project dictates which formulation is best. Acrylic urethane typically costs more than polyurethane, and its quality is less consistent across brands. On the other hand, polyurethane has a greater tendency to yellow in ultraviolet light. To prevent this problem, makers of pricier finishes — polyurethane and acrylic urethane alike — often add anti-yellowing substances to them.

{ 0 comments }

Finishing and old wood table with polyurethane

by admin on September 29, 2014

 

 

Transcription:

We’re about to do a very large scale sample on this antique furniture. The room is completely white. That’s cool on a limited basis, but it makes me feel like I’m in a laboratory if I’m here for more than 30 minutes. Sometimes when we’re working on colors, looking at samples, we’re in here for an hour, hour and a half.

I wanted something natural in this room, and this table is definitely natural. Today we’re going to put the first coat of urethane–which is a Fine Paints of Europe polyurethane clear coat. It’s part of a system.

It’s been sanded down. It’s not perfect. Some of the stain finish is still in there. I’m ok with that. There’s a little bit of rust there–I’m not going to clean that off. I’m going to leave that exactly the way it is to wow all my friends.

Let’s mix up some material to use. Poly, solvent based. I am all out right now of the solvent that’s designed to reduce this product, which is a Fine Paints of Europe high-grade solvent. It’s four times the cutting power. I’ll have to use what I have in the shop right now.

You do not shake polys–you stir them, ever so slightly.

For this first coat, we want a nice mixture that’s about 20% reducer.

This substrate has already been prepped. Dust free, dust free room.

I’m using gloves because the oil from your hands can affect the finish.

{ 0 comments }

Paint Brushes and Paint Brush conditioning

April 24, 2014
Read the full article →

All About Paint Roller Covers

March 6, 2014

Republished from Shearer Painting 2011. Spending time and energy choosing the right paint for a project makes perfect sense. What’s easier to overlook is another vital step in the process: selecting the right paint roller. A roller’s anatomy is simple: There’s a handle, a cylinder, and a cover for the cylinder. The handle should be […]

Read the full article →

Epoxy Resin for table and bar tops by System Three Resins

January 18, 2014

Mirror Coat from System Three Resins. Epoxy Clear Coat for table tops and bar tops. This high performance coating is the cost effective choice for owners and building managers for restaurant and bar counter tops because of the durability and extended life cycle between service visits. Shearer Painting uses The System Three Mirror Coat replacing other […]

Read the full article →

Huntington Beach House Painting Project

January 17, 2014

November 2012 Hunting Beach House Painting Project walk through and interview. 1:17 Fresh Start Primer from Benjamin Moore 2:36 Fine Paints of Europe Hollandlac 4:40 Benjamin Moore Paint Aura siding Paint     Transcript: John Shearer: I’m in Huntington Beach, at my friend Kent Weiss’s house. This is Huntington Beach and right next door to where […]

Read the full article →

Festool DTS 400 Review

December 3, 2013

Festool DTS 400 sander Review The DTS 400 is the must have first sander in the Festool lineup if you are prepping surfaces for stain or paint. The versatile “ironing board” shape combines surface area for productivity and pointed edges for trim details and tight profiles. We use this as our go to sander in […]

Read the full article →

Apprentice Painters; first its about protection

November 21, 2013

  VIDEO TRANSCRIPT OF PREP WORK AND MOVING:   An apprentice painter, you probably think being a good painter is all about being able to apply the paint, and it is a big part of, obviously, the finish. But there are other things we need to consider, and that’s the potential damage that we can […]

Read the full article →

Shop Finish Black Gloss Door

November 21, 2013

    VIDEO TRANSCIPT OF “Black High Gloss Paint on Front Door Shop Finish”   “So this is, uh, a front door for a home in Seattle. It’s fall right now, and we decided to shop finish this door, we wanted to restore it, take it off an old home, bring it to our shop […]

Read the full article →

Interview with Tom Hill founder C2 Paint

November 18, 2013

  This interview with Tom Hill Founder of C2 Paint was filmed at Shearer Painting in Seattle, Wa.  July 2013   Transcript Tom Hill: Do I sound like I know what I’m doing? John Shearer: Silly as I feel Tom Hill: Yeah, Yeah John Shearer: I’m going to start right up Tom Hill: Sure John Shearer: Tell us […]

Read the full article →