UNDERSTANDING WOOD FINISHING

UNDERSTANDING WOOD FINISHING

How To Select And Apply The Right Finish

By Bob Flexner

WHY FINISH WOOD, ANYWAY?

Sanitation

Stabilization

Decoration

PREPARING THE WOOD SURFACE

Preparing the Lumber

Sanding and Smoothing

Sponging

Sharpening a Hand Scraper

Sharpening a Cabinet Scraper

Solvents for Removing Cured Glues

Glue Splotches

Dents, Gouges, and Holes

Wood Putties

TOOLS FOR APPLYING FINISHES

Rags

Brushes

Rubbing Pads

Spray Guns and Equipment

Common Spraying Problems

OIL FINISHES

Our Ancestors and Linseed Oil

Applying "Oil" Finishes

Oil Finishes and Penetration

How Oil and Oil/Varnish Finishes Protect

Types of "Oil

Safety and Oil Finishes

Using Wax as a Finish

Bleeding Oil Finishes

Which One Is Which?

How to Tell Which "Oil" You Have

How to Maintain and Repair "Oil" Finishes

Guide to "Oil" Finishes

STAINING WOOD

What Makes a Stain

Understanding Stains

A Guide to Stains

Using Aniline Dyes

Bleaching Wood

Chemical Stains

Ebonizing Wood

Matching Color

A Sampler of Wood Stains

Solvents and Thinners for Dyes and Stains

Compatibility of Stains and Finishes

How Woods React to Stains

Applying Stain

Applying Glaze

Pickling

Common Staining Problems, Their Causes, and Solutions

FILLING THE PORES

Filling the Pores with the Finish

Filling the Pores: Finish versus Paste-Wood Filler

Filling the Pores with Paste-Wood Filler

Using Oil/Varnish Paste-Wood Filler

Using Water-Based Paste-Wood Filler

INTRODUCTION TO FILM FINISHES

What's in a Name?

Sealers and Sanding Sealers

The Way Finishes Cure

Finishing Materials: How They Cure

Stain and Finish Compatibility

Classifying Finishes

Comparing the Three Types

Solvents and Thinners for Various Finishes

Solvents and Thinners

SHELLAC

How Shellac Performs

Shellac as Sealer, Washcoat, and Barrier Coat

Common Problems Applying Shellac

Categories of Shellac

Alcohol

Brushing and Spraying Shellac

Applying Shellac

French Polishing

LACQUER

Nitrocellulose Lacquer

Characteristics of Lacquer

Spraying Lacquer

Applying Lacquer

Lacquer Thinner

The Problem with Lacquer

Fish Eye and Silicone

Common Problems Applying Lacquer

VARNISH

The Mix of Oil and Resin

Characteristics of Varnish

Identifying Varnish Types

Applying Varnish

Brushing Varnish

Common Problems Applying Varnish

Turpentine and Petroleum-Distillate Solvents

WATER-BASED FINISHES

What is Water-Based Finish?

Characteristics of Water-Based Finish

Glycol Ether

Brushing and Spraying Water Base

Applying Water-Based Finish

Common Problems Applying Water Base

CONVERSION FINISHES

Characteristics of Conversion Finishes

Applying Conversion Finishes

CHOOSING A FINISH

Appearance

Protection

Durability

Ease of Application

Safety

Disposing of Your Solvent Waste

Reversibility

Rubbing Qualities

How to Choose

Guide to Finishes

FINISHING THE FINISH

Factors in Rubbing a Finish

Rubbing with Steel Wool

Synthetic Steel Wool

Leveling and Rubbing to a High Gloss

CARING FOR THE FINISH

Causes of Finish Deterioration

Causes and Prevention of Finish Deterioration

Preventing Finish Deterioration

Applying Paste Wax

Furniture Polish in Brief

Applying Liquid Furniture Polish

How to Choose

REPAIRING FINISHES

Repairing Superficial Damage

Applying Padding Lacquer

Repairing Color Damage in the Finish

Compatibility of Colors and Binders

Touching Up Color

Repairing Color Damage in the Wood

Repairing Deep Scratches and Gouges

Using a Burn-In Stick

FINISHING DIFFERENT WOODS

Pine

Pine with Brushing Lacquer

Gel-Stained Pine with Satin Varnish

Toned Pine with Satin Polyurethane

Oak

Oak with Satin Lacquer

Oak with Walnut Oil/Varnish

Pickled Oak with Satin Water Base

Pickled Oak with Satin Lacquer

Oak with Contrasting Pores and Lacquer

A Gallery of Finishes

Walnut

Walnut with Oil/Varnish

Walnut with Orange Shellac and Wax

Mahogany

Mahogany with Wiping Varnish

Stained and Glazed Mahogany with Lacquer

Stained and Filled Mahogany with Rubbed Lacquer

Hard Maple

Maple with Water Base

Maple with Wiping Varnish

Dyed and Glazed Maple with Oil/Varnish

Cherry

Gel-Stained Cherry with Oil/Varnish

Toned Cherry with Rubbed Lacquer

Ash, Elm, and Chestnut

Toned Ash with Satin Lacquer

Soft Maple, Gum, and Poplar

Dyed Poplar with Water Base

Aromatic Red Cedar

Birch

Dyed Birch with French Polish

Oily Woods

Rosewood with Wax

STRIPPERS

Stripping Solvents and Chemicals

Stripper Safety

Using Oxalic Acid

Using Strippers

Choosing Which Stripper to Use

Common Problems Using Strippers

Breaking the Code-An Overview of Strippers

SOURCES OF SUPPLY

INDEX

Why Finish Wood Anyway?

Why do we finish wood? It's an extra step, or steps, that most woodworkers don't find at all enjoyable. It's smelly and messy, and all sorts of things can go wrong. In addition, most woods look pretty good unfinished. Why bother? There are three good reasons for finishing wood: to help keep it clean, to help stabilize it, and to decorate it.

SANITATION

Wood is a porous material. It contains countless holes of various sizes. These holes can accumulate dirt and grime from handling, atmospheric contaminants, and food. Grimy wood is unattractive, and it can be a health hazard, providing a breeding place for bacteria. A finish seals the porous surface, making it less susceptible to soiling and easier to clean.

STABILIZATION

Besides being porous, wood is hygroscopic: It absorbs and releases moisture. Moisture within wood is called moisture content- moisture in the environment is either liquid water or water vapor (humidity). Wood responds to changes in the level of moisture around it. If you put very dry wood in water or in an area of high humidity, the wood will absorb moisture and swell. If you put wood that has a high moisture content in a relatively dry climate, the wood will release moisture and shrink.

These dimensional changes, commonly called wood movement, do not occur consistently throughout a piece of wood. The surface of wood, for instance, responds more readily than the core. Wood swells and shrinks mainly across the grain; that is, in the width and thickness of boards, not appreciably in the length. And wood swells and shrinks more around the annular rings than it does perpendicular to the rings. The result of these different responses is that wood movement generates great stresses in wood and on the joints that hold pieces of wood together. The stresses cause splitting, checking, warping, and weakening of the joints. A finish slows moisture exchange, thus reducing the stresses and stabilizing the wood.

As a general rule, the thicker the coating of finish, the better it limits moisture exchange. This is the reason you should coat all sides of a piece of furniture-top and bottom, inside and outequally. Another important understanding is that moisture exchange in wood does not have to be in the form of liquid water. It can be, and usually is, water vapor. Water-vapor exchange causes much damage to otherwise sheltered wood furniture and woodwork. It just does this more slowly than in wood subjected to liquid-water exchange.

Splits, Checks, and Warps

To better understand how moisture exchange causes splits, checks, and warps, look at Figure 1-1. A solid piece of kiln-dried wood is clamped securely so that it can't expand in width. Then it is saturated with water. The cell walls swell and try to expand but are constrained by the clamps. So the cell walls compress, changing from cylindrical to oval in shape.

If the board is released from the clamps, the cells don't return to their cylindrical shape: They remain flattened. When the water evaporates and the cell walls shrink to their previous thickness, the board shrinks, becoming narrower than it was originally. The amount of shrinkage is as usual, but the starting point is now the clamped width rather than the width the board would have swollen to without the clamps. If the board is reclamped and made wet and dry again, it will shrink further. This phenomenon is called compression shrinkage (also compression set). It explains why nails and screws work loose in wood, and why the wooden handles of hammers and hatchets loosen over time, after becoming repeatedly wet and then dry.

Compression shrinkage also accounts for splits developing in the ends of a board, checks in the middle of a board, and cupping (a type of warp) on the si