Wood Finishing 101, Revised Edition E-Book

Bob Flexner

• Herausgeber: Fox Chapel Publishing
• Kategorie: Lebensstil
• Sprache: Englisch
• Veröffentlichungsjahr: 2022

Seitenzahl: 191

Beschreibung

Wood staining and finishing doesn't have to be complicated or confusing. It can be simplified with easy-to-follow, step-by-step instructions, and that's exactly what Wood Finishing 101, Revised Edition provides; no science, no art, just simple directions with clear photography to show you every step of the process. With this must-have guide, you'll learn how to finish common woods using widely-available finishing materials. Follow step-by-step instructions, eliminate the guesswork, and get the finished results you want every time! Bob Flexner has been writing about and teaching wood finishing to hobbyists and professionals for over 30 years. With his expertise, guidance, and easy-to-understand directions, this complete guide to everything you need to know about wood finishing belongs in every woodworker's library. This newly updated wood finishing book includes revised information on solvents and stripping agents.

Leseprobe

READ THIS IMPORTANT SAFETY NOTICE

To prevent accidents, keep safety in mind while you work. Use the safety guards installed on power equipment; they are for your protection.

When working on power equipment, keep fingers away from saw blades, wear safety goggles to prevent injuries from flying wood chips and sawdust, wear hearing protection and consider installing a dust vacuum to reduce the amount of airborne sawdust in your woodshop.

Don’t wear loose clothing, such as neckties or shirts with loose sleeves, or jewelry, such as rings, necklaces or bracelets, when working on power equipment. Tie back long hair to prevent it from getting caught in your equipment.

People who are sensitive to certain chemicals should check the chemical content of any product before using it.

Due to the variability of local conditions, construction materials, skill levels, etc., neither the author nor Fox Chapel Publishing assumes any responsibility for any accidents, injuries, damages or other losses incurred resulting from the material presented in this book.

The authors and editors who compiled this book have tried to make the contents as accurate and correct as possible. Plans, illustrations, photographs and text have been carefully checked. All instructions, plans and projects should be carefully read, studied and understood before beginning construction.

Prices listed for supplies and equipment were current at the time of publication and are subject to change.

METRIC CONVERSION CHART

TO CONVERT

TO

MULTIPLY BY

Inches

Centimeters

2.54

Centimeters

Inches

0.4

Feet

Centimeters

30.5

Centimeters

Feet

0.03

Yards

Meters

0.9

Meters

Yards

1.1

Copyright © 2022, 2011 Bob Flexner and Fox Chapel Publishing Company, Inc., 903 Square Street, Mount Joy, PA 17552.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior permission of the copyright holder.

Wood Finishing 101, Revised Edition (2022) is a revised edition of Wood Finishing 101 (2011), published by Fox Chapel Publishing Company, Inc. Revisions include updated text and photos.

Print ISBN 978-1-4971-0148-7

eISBN 978-1-6076-5924-2

Library of Congress Control Number: 2020948588202094858

We are always looking for talented authors. To submit an idea, please send a brief inquiry to [email protected].

ABOUT THE AUTHOR

Bob Flexner has operated his own furniture making and restoration shop in Norman, OK, for more than 45 years. For the last 30 years, he has taught wood finishing and restoration. His writing accomplishments include the authoritative and best-selling book Understanding Wood Finishing, now in its third edition, editing the professional trade magazine Finishing and Restoration, making the award-winning DVDs, “Repairing Furniture” and “Refinishing Furniture” for Taunton Press, and writing the long-running columns “Finishing” in Woodshop News, and “Flexner on Finishing” in Popular Woodworking Magazine.

Important Note: I have never recommended brands. Mainly because there’s so little difference between them. But also because people get used to whatever they are using, which is typically what is being sold at the store or catalogue they shop at, and they struggle when they switch brands because of different working characteristics (drying rate, color produced, etc.). Switching brands usually causes problems for a while.

The pictures of several brands at the beginning of many chapters are meant simply as an introduction to the instructions that follow. Some of them may not exist anymore. I just had them in my shop when I was doing the photography.

Welcome to Wood Finishing 101

Every now and then a beginning woodworker or home hobbyist asks me to recommend a book on finishing, and I always feel a little hesitant because finishing books are written for the broad audience — beginner through advanced. (It’s a marketing thing.) They’re never written just for the beginner, who wants simple finishes and step-by-step procedures. The result is, the beginner gets bogged down in information overload.

This is the missing book — the book for beginners. A step-by-step picture book focused on how to apply the most common stains and finishes.

I have included, however, brief (three pages each) overviews of stains and finishes right at the beginning to help you put all the products and procedures in perspective. There are also overviews of solvents, wood, and several other topics I hope you find informative and interesting later in the book. Otherwise, this book is “step-by-step.”

If you choose, you can skip these stain and finish overviews and go straight to the section you are interested in. Each chapter is self-contained.

Applying finishes is easy and logical. I do have one caution, however: Don’t be impatient. Stains and finishes take a while to dry, overnight in many cases. It doesn’t take much time to apply the product, but you need to allow time for drying in a warm area before proceeding to the next step. Impatience is probably the beginner’s most challenging obstacle.

The book is designed as a series of exercises, to be done on practice panels. The goal here is to give you the experience and confidence to proceed to an actual project. But applying finishes isn’t difficult, so there’s no reason not to proceed directly to the project itself.

If you do choose some exercises, you can do them on scrap wood, or you can buy a full sheet of veneered plywood or MDF (medium-density fiberboard), and cut it into smaller sections.

In the construction trade, it’s common to hear the carpenters rationalize their sloppiness with the defense, “Oh, the painters will fix it.” In the same sense, it’s the finishing of a project that makes it beautiful and a success. A poor finish is a failed project. A great finish is admired. I hope this book helps you achieve admired status.

I want to thank my son, Soren, for giving me the idea for this book and my brother, Bill, for getting me back on track. I also want to thank my wife, Birthe, for her steady support and my editors, David Thiel and Kerry Bogert, for their patience with me.

Bob Flexner

TABLE OF CONTENTS

Understanding Stains

Understanding Finishes

Preparing Wood for a Finish

Stripping Old Finish and Paint

Wiping Varnish

Oil/Varnish Blend

Polyurethane

Oil Stains and Polyurethane

Wood Conditioners

Gel Stains and Polyurethane

Water-based Finishes

Applying Water-based Stain

Solvents and Thinners

Aerosol Finishing

Deterioration of Furniture

Caring for Furniture

Outdoor Finishes

Easy Finish Repairs

Cleaning and Storing Brushes

Understanding Wood

Understanding Stains

Stains & Staining

DEFINITION

A stain is a colorant (pigment or dye) and a binder (some sort of finish) with a lot of thinner added so the excess stain is easy to wipe off. This leaves some color in or on the wood.

A stain can also be just dye and thinner with no binder added.

PIGMENT

Pigment is ground earth or colored synthetic particles, so pigment requires a binder to glue it to the wood. Pigment settles to the bottom of the can and has to be stirred into suspension before use.

DYE

Dye is a colorant dissolved in a liquid, so dye penetrates well and doesn’t need a binder. Coffee and tea are examples of weak dyes.

Pigment settles to the bottom of the can and has to be stirred.

PURPOSE OF A STAIN

There are three good reasons to use a stain:

1. To make a cheaper, less interesting (usually lighter) wood look like a more expensive (usually darker) wood such as walnut, cherry or mahogany.

2. To match the color of an existing object.

3. To create a décor you or someone else has in mind.

TYPES OF STAIN

Common categories of wood stain include:

• Oil stain (thins and cleans up with mineral spirits).

• Water-based stain (thins and cleans up with water).

One of the principal reasons to stain wood, especially lighter woods, is to make them resemble more desirable darker woods, in this case walnut (on the right).

There are five common types of stain. From left to right are examples of oil stain, water-based stain, gel stain, two types of dye stain (concentrated and thinned liquid, and powder), and combination stain and varnish.

• Gel stain (thick in the can like mayonnaise but spreads and wipes off easily).

• Dye stain (a colorant dissolved in a liquid).

• Combination stain and finish (doesn’t color effectively if wiped off and is streaky with brush marks if brushed and left thick).

The primary differences in stains are as follows:

•Ease of application. Oil stains are the easiest to apply because you have plenty of time to wipe off the excess. All the other stains dry quickly so you have to work fast or on smaller areas at a time.

•Drying time. Dye stains dissolved in solvent (not water), can be coated over within minutes. Water-based stains can be coated over after about an hour. Gel stains, and dyes dissolved in water, require 4 to 6 hours before coating over. Oil stains should be allowed overnight drying.

•Grain definition. All stains provide good grain definition if the excess is wiped off, because more colorant is left in the grain. Dye stains produce slightly less definition than pigment stains.

•Color control. Dye stains provide the best control of color — that is, getting the color darker without obscuring the figure of the wood. Dye is see-through; you can apply as many coats as you want and still see the wood’s figure. Pigment hides the wood’s figure if built up.

The basic rule for applying all stains is to apply a wet coat and wipe off the excess before it dries. It’s much faster to apply stain with a cloth than a brush.

STAIN APPLICATION

The basic rule for applying all stains is to apply a wet coat and wipe off the excess before the stain dries. Unless the wood is naturally blotch-prone or you haven’t sanded the wood well enough to remove all gouges and scratches, you will always get an even coloring.

You may need to divide your project into smaller sections, or have a second person wipe as you apply, to get good results using one of the faster drying stains. It’s much faster to wipe the stain onto the wood with a cloth, wearing gloves of course, than to brush it. (I can’t remember ever brushing a stain.)

A washcoat, which is any finish thinned to about 10% solids, can be used to reduce blotching, but it also reduces the intensity of the stain’s color. On this sample, I applied a varnish washcoat (wood conditioner) to the left side of the pine panel and let it dry overnight. Then I applied a stain to the entire panel.

APPLICATION PROBLEMS

Common problems and ways to avoid them:

• The stain dries in spots before you get it all wiped off, leaving an uneven coloring. If you are quick enough, you can wipe more stain on smaller sections at a time to reliquify the stain so you can then wipe it off evenly. Otherwise, strip with lacquer thinner, acetone or paint stripper and restain smaller parts at a time (or get a second person to help).

• The color of the stain doesn’t match what you expected from the name on the label. Names are simply manufacturer’s interpretations. There are no industry standards. One manufacturer’s “mahogany” may differ from another manufacturer’s “mahogany,” for example.

• The color of the stain on your project isn’t the same as on the color sample in the store. Woods color differently. Always try the stain on scrap from your project, sanded to the same grit sandpaper, and make adjustments (add pigment, thinner or mix with another color stain) if necessary to get what you want.

• Glue from squeeze-out or fingerprints seals the wood preventing stain penetration. Sand or scrape off the glue through the stain and restain that area, or leave the splotch and disguise it by painting in the correct coloring after you have applied a coat of finish.

Stain problems such as blotching and getting the color wrong can be extremely difficult to fix. You can usually remove some of the color by wiping with the thinner for the stain. If the stain contains a binder (it isn’t simply dye), you can use a paint stripper. But nothing short of sanding will remove all the color.

CONDITIONING THE WOOD

The purpose of “conditioning” or “washcoating” wood before applying a stain is to reduce blotching, which is uneven coloring caused by varying densities in the wood. A wood conditioner (also called “stain controller”) or washcoat is any finish thinned to about 10% solids so it doesn’t fully “seal” the wood. Some of the stain can still penetrate.

The woods that blotch are softwoods such as pine, and tight-grain hardwoods such as maple, birch and cherry. There’s no point in applying a wood conditioner/washcoat to medium- or coarse-grain woods such as walnut, mahogany or oak.

Varnish wood conditioners (the common ones found in home centers and paint stores) are varnish thinned with about two parts mineral spirits (paint thinner). You can make your own. The key to getting the wood conditioner to work is to let it dry fully before applying the stain — at least 6 hours, better overnight.

Understanding Finishes

Finishes & Finishing

DEFINITION

A wood finish is a clear, transparent coating applied to wood to protect it from moisture and to make it look richer and deeper. This differs from paint, which is a wood finish loaded with enough pigment to hide the wood. And it differs from a stain, which is a wood finish and a colorant (pigment or dye) with a lot of thinner added so the excess stain is easy to wipe off. The remainder just colors the wood; it doesn’t hide the wood.

A stain can also be a thinned dye with no wood finish added.

ANOTHER DEFINITION

The term “finish” can also refer to the entire built-up coating, which could consist of stain, several coats of finish (a “coat” is one application layer) and maybe some coloring steps in between these coats. For some reason, we have only one word to refer both to the clear coating used, and to all the steps used.

Usually, the context makes clear which is being referred to.

PURPOSE OF A FINISH

A finish serves two purposes: protection and decoration.

Protection means resistance to moisture penetration. In all cases, the thicker the finish the more moisture resistant it is. Three coats are more protective than two, for example. Boiled linseed oil, 100% tung oil and wax dry soft and gummy, so all the excess has to be wiped off after each application to achieve a functional surface. Therefore, no significant thickness or protection can be achieved.

Finishes decorate wood by making it look richer and deeper. The impact is less on unstained lighter woods such as maple and birch, and greater on stained and darker woods such as cherry and walnut.

TYPES OF WOOD FINISHES

• Oil (boiled linseed oil, 100% tung oil and blends of these oils and varnish).

• Oil-based varnish (including alkyd, polyurethane, spar, wiping and gel varnish).

• Water-based finish (a finish that thins and cleans up with water).

• Shellac (an ancient finish derived from resin secretions of the lac bug).

• Lacquer (the finish used on almost all household furniture made since the 1920s) and

• A large number of two-part, high-performance finishes used in industry and by many professional cabinet shops.

PRIMARY DIFFERENCES AMONG THE TYPES

Scratch, solvent and heat resistance.

• Oil-based varnishes and high-performance finishes provide the best scratch, solvent and heat resistance.

• Water-based finishes are next.

• Shellac and lacquer are susceptible to all three types of damage.

• Oil is too thin to be effective.

Color.

• Water-based finishes add no color to the wood and don’t darken as they age.

• All the other finishes add some degree of yellow-to-orange coloring and continue to darken a little as they age.

Three types of coatings: Top; just clear finish, middle; paint, bottom; stain. The bands separating the sections are left uncoated, for comparison.

The left section of this panel was finished with acrylic water-based polyurethane, which, like all these finishes, adds no color to the wood. The finish just makes the wood a little darker (compared to the lighter strip down the middle, which was covered with tape). The right section was finished with oil-based polyurethane, which, like all finishes except water-based finishes, adds some degree of yellow/orange coloring to the wood. Oil-based polyurethane continues to darken as it ages, while water-based polyurethane doesn’t darken anymore.

Drying time.

• Shellac, lacquer and high-performance finishes dry the fastest.

• Water-based finishes are next.

• Varnish and oil require overnight drying in a warm room.

Solvent safety.

• Boiled linseed oil and 100% tung oil are the least toxic finishes to breathe during application because they don’t contain solvent.

• Water-based finishes (thinned with water and a little solvent) and shellac (thinned with denatured alcohol) are next.

• Oil-based varnish thins with mineral spirits (paint thinner), which some people find objectionable but which isn’t especially toxic.

• Lacquer and high-performance finishes thin with solvents that are the most toxic to be around.

SEALING WOOD

The first coat of any finish seals the wood — that is, stops up the pores in the wood so the next coat of finish (or other liquids) don’t penetrate easily. This first coat raises the grain of the wood making it feel rough. You should sand this first coat (with just your hand backing the sandpaper) to make it feel smooth. You don’t need a special product for this first coat unless you have one of two problems you want to overcome.

• Alkyd varnish and lacquer gum up sandpaper when sanded, so manufacturers of each provide a special product called “sanding sealer” with dry lubricants added to make sanding easier and speed your work. Sanding sealers weaken the finish, however, so you should use them only when you’re finishing a large project or doing production work.

• Sometimes, there are problems in the wood that have to be blocked off with a special sealer so they don’t telegraph through all the coats. These problems are resinous knots in softwoods such as pine, silicone oil from furniture polishes that causes the finish to bunch up into ridges or hollow out into craters, and smoke and animal-urine odors. The finish that blocks these problems (“seals them in”) is shellac and should be used for the first coat. Notice that, except for resinous knots, the problems occur only in refinishing.

A finish can have an infinite number of sheens depending on how much flatting agent is added. Here are three typical examples: from left to right — gloss, semi-gloss and satin.

SHEEN

Oil-based varnishes, water-based finishes and lacquers are available in a variety of sheens, ranging from gloss to flat. All sheens other than gloss are created by the solid-particle “flatting agents” manufacturers add to the finish. The more flatting agent added the flatter the sheen. These flatting particles settle to the bottom of the can, so you have to stir them into suspension before each use.

FINISH APPLICATION

Oil, wax, wiping varnish and gel varnish can be applied with a cloth or brush, then wiped off. The other finishes are applied with a brush or spray gun.

Brushing is very intuitive — essentially no different than brushing paint. Spraying is also intuitive, but spray-gun care and tuning is more complicated, and spray guns and their sources of air (compressor or turbine) are considerably more expensive than brushes.

You can get any sheen you want by pouring off some of the gloss from a can in which the flatting agent has settled (don’t let the store clerk shake the can) and blending the two parts. Or you can mix cans of gloss and satin to get something in between. You will need to apply the finish to see the sheen you’ll get after the finish dries. It’s the last coat you apply that determines the sheen (there is no cumulative effect), so you can experiment with each coat.

APPLICATION PROBLEMS

Common problems and ways to avoid them:

• Brush marks. Eliminate these by thinning the finish 10% to 30% so it levels better.

• Runs and sags. Watch what is happening in a reflected light and brush out the runs and sags as they occur.

• Dust nibs. Keep your tools, the finish and the air in the room as clean as possible.

• Bubbles. Brush back over to pop the bubbles, or thin the finish 10% to 30% so the bubbles have more time to pop out.

No matter what the problem, you can always fix it by sanding the finish level and applying another coat.

Preparing Wood for a Finish

The reason you have to sand wood before applying a finish is to remove machine marks. All machine tools leave cuts or impressions in wood that are highlighted by stains and finishes — especially by stains. Before machine tools came into use in the mid-19th century no sanding was needed. Indeed, there was no sandpaper. Wood was smoothed with hand planes and scrapers.

You can still use hand tools to smooth wood, but few people choose this route because machine tools are much faster and easier to learn to use. The price, then, for using machine tools alone for smoothing and shaping wood is that you have to finish off with sandpaper to take out the machine marks.

It helps to remind yourself of this. Sanding is the price you pay for the increased efficiency of substituting machine tools for hand tools.

With a stain applied you can clearly see the cuts and impressions left by the machine. These have to be sanded out to get a good final result.

Sandpaper is measured by the size of the grit that is glued to the paper. The lower the number the coarser, or larger, the grit size. The higher the number the finer the scratches. Typical sandpaper grits used for sanding wood are #80, #100, #120, #150, #180 and #220.

RULES FOR SANDING WOOD

Here are some general considerations for sanding wood.

• Always sand in the direction of the wood grain (from end-to-end of the board) when possible. Sanding cross-grain (across the board) or diagonally to the grain tears the wood fibers, leaving more obvious scratches that then require more work to sand out.