Questions and Answers
What is the primary benefit of leveling the surface with sandpaper before rubbing?
What risk is associated with the approach of leveling the surface with sandpaper?
Which technique begins with using steel wool or rubbing compounds immediately?
What is a common step that should be taken to clean the surface between grits?
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What might cause a haze on flat surfaces during the rubbing process?
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When should one use naphtha or mineral spirits during cleanup?
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What is a potential drawback of skipping the leveling phase in rubbing techniques?
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How should the cloth be used when wiping down the surface after sanding?
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Which type of finish is the most difficult to rub out to obtain an even sheen?
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What is the expected outcome when rubbing out a finish that is not fully cured?
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What should result from a proper rubbing out technique?
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Which abrasive is best suited for creating an even satin scratch pattern in a finish?
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What is the consequence of rushing the rubbing out operation?
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When using sandpaper for finishing, which technique provides the most even surface?
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What type of lubrication is recommended when using sandpaper?
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What may be necessary if you plan to cut back aggressively with sandpaper?
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What is the primary characteristic of synthetic steel wool?
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What type of finish can pumice produce when used in rubbing compounds?
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Which of the following best describes the role of lubricants in the rubbing process?
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Which type of rubbing compound produces a gloss finish?
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What is a common method for using rubbing compounds?
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Which lubricant is NOT commonly used to maintain abrasive effectiveness?
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Why does the abrasive power of a synthetic steel wool pad diminish over time?
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What is the purpose of mixing rubbing compounds with water or mineral oil?
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Surface contamination by silicone prevents lacquer from adhering to wood in some spots.
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Using 'Fish Eye Drops,' which contain silicone, is a recommended solution for lowering surface tension of the finish.
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Drips and sags in finish can occur if the spray gun is held too far from the piece.
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A ruffed finish is usually less challenging to repair than a smooth finish.
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Flattening agents can be used to adjust the sheen of a finish.
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Common flaws in a film finish include brush marks and dust nibs.
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The use of coarser abrasives will result in a higher gloss finish.
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To replicate the original sheen after repair, one should use the same grit abrasive as the original finish.
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The Ford viscosity cup is typically designated as #1 for its dimensions.
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Orange Peel is a defect caused by viscosity being too low.
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Different types of oil-based finishes include matte, satin, and gloss.
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To achieve a consistent finish, it is essential to measure viscosity after each batch of material is mixed.
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Rubbing a finish can improve its quality if done carefully.
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Viscosity has no effect on the speed of application when spray finishing.
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A gritty finish can result from a viscosity that is too high during application.
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Lacquer finishes are prone to specific defects that need to be addressed during the preparation process.
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Blush is a milky white haze caused by moisture getting trapped in the finish.
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To prevent small bubbles in a finish, it's sufficient to apply a single thick coat.
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Holding the spray gun too far from the piece can lead to overspray.
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Adding a retarder to a finish will speed up the drying time.
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Fish eyes in a coating are small depressions caused by trapped air beneath the finish.
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If moisture issues lead to blush, spraying with a retarder can help eliminate the hazy appearance.
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Cutting back and recoating a finish is a difficult repair process.
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Thin products are less likely to be over-atomized when sprayed.
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Study Notes
Rubbing Schedule Overview
- Two approaches to rubbing finishes: leveling with sandpaper or starting with steel wool/rubbing compounds.
- Leveling with sandpaper enhances quality but increases risk of sand-through and visible transitions between coats.
- Skipping leveling leads to quicker results but may leave imperfections in the finish.
Cleaning Process
- Clean the surface thoroughly between grits to eliminate dust:
- Use a vacuum or blower.
- Wipe with a tack cloth or a cloth dampened with mineral spirits.
- Wipe in the direction of the grain to prevent scratches.
- Remove sludge from lubricants using:
- Naphtha/mineral spirits for wax/oil sludge.
- Water for water-based sludge.
- Sludge can dry opaque in scratches and pores, causing a haze on flat surfaces.
Type of Finish
- Hard, brittle finishes are easier to rub out compared to flexible finishes.
- Shellac and lacquer are easiest to rub out.
- Varnish (including polyurethane) and waterborne finishes are the most challenging for achieving an even sheen.
Thoroughness of Cure
- Ensure the finish is fully cured before rubbing out to avoid uneven scratch patterns and splotchy sheens.
- Proper rubbing should produce a dry powder, avoiding gumming up the abrasive (referred to as "Corning").
Choice of Abrasives
-
Sandpaper:
- Used for cutting back and leveling; effective at eliminating surface irregularities (orange peel, brush marks, dust nibs).
- A sanding block promotes a more even surface.
- Liquid lubrication improves results, requiring careful selection of dry or wet/dry sandpaper.
-
Steel Wool:
- Utilized to create a uniform satin scratch pattern; available in natural/synthetic options.
- #0000 or #000 steel wool suitable for satin finishes; must be used with a lubricant.
- Synthetic steel wool consists of nylon fibers with abrasive coatings that wear off during use.
-
Rubbing Compounds:
- Composed of fine powders in paste or liquid form; can achieve higher sheens than #0000 steel wool.
- Common types include pumice (satin finish) and rottenstone (gloss finish); various grits are available.
Lubricants
- Lubricants enhance the rubbing process:
- They help float away grit and abrasives, maintaining the effectiveness of abrasives and reducing dust.
- They can also minimize the size of scratches.
- Options for lubricants include:
- Mineral spirits, naphtha, wax, oils, and commercial preparations.
Possible Causes of Finish Issues
- Surface contamination by silicone may occur from furniture polish, leading to poor lacquer adhesion on wood.
- Drips, sags, and runs can result from moving the gun too slowly, holding the trigger while stopping, or incorrect aircap orientation.
- A milky white haze or “blush” appears in finishes due to moisture trapped in the coating, commonly during high humidity conditions.
Possible Solutions for Finish Issues
- Remove silicone contaminants by washing wood with mineral spirits, TSP & water, or ammonia & water before finishing.
- Mist on light coats of lacquer to seal in silicone, then apply a wet coat for final finish.
- For drips/runs, sand, chisel, or scrape off the affected areas and respray.
- Address blush by adding a retarder for slower drying, waiting for less humidity, or adjusting temperature to prevent condensation.
Rubbing Out a Finish
- Flaws in film finishes include brush marks, orange peel, dust nibs, roughness, uneven sheen, and incorrect sheen.
- "Finishing the finish" involves leveling and smoothing the surface, while adjusting the sheen by creating fine or coarse scratches.
- A flattening agent helps regulate sheen but requires even distribution; a ruffed finish can facilitate easier repairs using the same grit abrasive as the original.
Viscosity in Finishing
- Viscosity measures a liquid’s thickness and internal resistance to flow, varying with type and temperature.
- Flow rate is a common method to assess viscosity; the time for a cup to empty indicates viscosity levels.
- Various viscosity cups (e.g., Ford, Fisher, Zahn) exist, with the #2 Zahn and #4 Ford cups being the most prevalent for measuring.
Importance and Measures of Viscosity
- Proper viscosity affects transfer efficiency, application speed, and finish quality; overly high viscosity can lead to orange peel, while too low can result in runs or a gritty texture.
- Always measure viscosity after mixing each batch to maintain consistency.
Addressing Overspray and Attendant Issues
- Overspray issues can arise from incorrect spray distance or material consistency; reducing the distance or thinning the product can mitigate overspray.
- Repair methods include cutting back and respraying; final coats may require knocking off dry particles with sandpaper.
Small Bubbles and Pinholes
- Small bubbles form over large pores in wood when finishes dry too quickly, trapping air.
- Solutions involve dusting on several thin coats before a wet application or filling pores in the wood before finishing.
- Difficult repairs may require cutting back the finish and reapplying thin coats followed by a wet coat.
Fish Eyes
- Fish eyes refer to small depressions in the finish and are common during refinishing.
- These can be caused by contamination or improper finishing techniques.
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Description
Explore the processes involved in surface rubbing, including essential techniques such as leveling with sandpaper and using steel wool or rubbing compounds. Understand the implications of time and quality on the final finish, as well as potential risks like layering and ghosting effects.
