Chrome plating is a process that applies a thin layer of chromium onto a metal surface to provide protection and a shiny, mirror-like finish. When chrome plated parts become worn or damaged over time, a common question that arises is whether you can simply plate more chrome over the existing layer. The answer is yes, it is possible to chrome plate over old chrome, but there are important steps and considerations to follow for best results.

Why Plate Chrome Over Old Chrome?

In some cases, it may be desirable to apply a new layer of chrome plating over an older chrome surface, including:

Restore Corrosion Protection: Old chrome that is worn or damaged may have reduced corrosion resistance. Adding a fresh layer of chrome replenishes this protection.
Repair Wear/Damage: Chrome surfaces can become scratched, pitted, or worn over time. Re-chroming can fix this damage and restore a smooth finish.
Refresh Appearance: Re-chroming an older chrome surface provides a “like-new” brilliant mirror finish and removes any tarnishing or dullness.
Salvage Mistakes: Defects in the original chrome plating job can sometimes be covered up by adding another layer.
Increase Thickness: Adding more chrome builds up thickness, which is useful for hard chrome applications needing enhanced durability.

Challenges of Plating Over Chrome

While it is possible to plate additional layers of chrome onto existing chrome, there are some challenges to consider:

Adhesion Issues: There is a risk of poor adhesion between the old and new chrome layers, which can cause flaking or delamination. Proper surface prep is vital.
Quality Variability: The quality of the re-chroming can be inconsistent depending on the condition of the original finish. Heavily worn or corroded chrome may give poor results.
Limited Thickness: Too many layers of decorative chrome can result in quality problems like cracking or nodule formation.
Labor Intensive: Prepping and re-chroming worn parts requires more time and work than plating new components. This can increase costs.
Masking Difficult: It can be challenging to mask areas that need re-chroming without damaging the existing chrome finish. Creative masking solutions may be needed.

Surface Preparation

Proper surface preparation is the most critical factor in achieving good adhesion and results when chrome plating over existing chrome. The steps involved in prepping include:

Cleaning

Use alkaline cleaners to thoroughly degrease and remove all oils, grease, dirt, residues and any other contaminants from the chrome surface. Hot tank immersion works best.
Agitate or scrub during cleaning to free trapped grime. Avoid abrasives that can scratch the chrome.
Rinse thoroughly after alkaline cleaning to prevent chemical drag-over. Use hot water followed by a cold water final rinse.

Etching

Etch the chrome surface using the chromic acid plating solution. Immerse and allow it to warm to solution temperature without current.
Apply low current density (0.5 A/dm2) for 2-5 minutes to lightly etch the surface.
Increase current density to 2.5-3 A/dm2 for another 2-5 minutes. Observe larger hydrogen bubbles being released.
Do not rinse when transferring part from cleaning to etching and plating tanks.

Desmutting

After etching, desmut in a 50% nitric acid solution for 30-60 seconds.
Rinse thoroughly with cold water and return to plating tank immediately while still wet.

Nitric Dips

For heavy build-up, hard chrome, or porous/damaged surfaces, use a more concentrated nitric acid desmutting dip.
Immerse in 70% nitric acid at room temp for up to 5 minutes for heavier etching.
Rinse thoroughly with cold water after nitric dip.

Masking

Mask areas not to be chrome plated using plater’s tape, stop-off lacquers, greases, or waxes.
Ensure masking materials are resistant to chrome solutions. Test first.
Apply masking carefully to prevent lifting existing chrome finish.

Current Density

Use a lower current density than normal to slowly build up chrome thickness.
For decorative chrome, keep current density below 40 A/ft2.
For hard chrome, use 10-25 A/ft2 initially, increasing to 50 A/ft2 maximum.
Lower currents give a finer grained deposit for better adhesion.

Chrome Plating Process Steps

Once the part has received proper surface preparation, the electroplating process can begin. Follow these best practice steps:

Loading

Use suitable fixturing to suspend and position parts in the chrome plating tank. Minimize contact points.
Ensure good electrical contact at contact points to give even plating distribution.

Solution

Maintain chromic acid plating solution according to supplier’s specifications.
Check solution concentration, temperature, pH, contaminants, etc. and make adjustments as needed.
Use filtration, agitation, and tank covers to keep solution clean.
Use any proprietary additives as directed to improve performance.

Parameters

Follow chrome plating bath manufacturer’s recommended parameters for amperage, temperature, pH, etc.
Target lower current densities and longer plating times than normal.
Monitor the deposit quality and adjust parameters accordingly.
Use proper anode-to-cathode ratios for even plating thickness.

Plating

Bring plating current up slowly to avoid burning or lack of adhesion.
Plate to desired thickness based on application requirements and recommendations.
For hard chrome, plate up to 0.005-0.02” thickness. Limit decorative chrome to 0.001-0.002” max.
Check part frequently for plating distribution and quality. Remove defects via brushing or stripping and re-plate as needed.

Post-Plate Finishing

Remove plated parts from tank, rinse thoroughly with hot and cold water spray rinses.
Remove masking materials carefully to avoid damaging new chrome deposit.
Perform any required post-plate processes like grinding/polishing, buffing, or adding topcoats.

Keys to Success When Plating Over Chrome

Follow these tips to achieve the best results when applying chrome over existing chrome:

Consult experts: Get guidance from experienced platers and chrome finishing specialists before attempting re-chroming jobs.
Perfect surface prep: Spend time thoroughly cleaning and etching the chrome surface prior to plating. This is the most vital step.
Start with quality chrome: Re-chroming heavily pitted, corroded or badly worn chrome generally gives poor adhesion. Focus on parts in better condition.
Go low and slow: Use lower than normal current densities and plate slowly to get a fine-grained, smooth deposit that adheres well.
Monitor progress: Watch for plating quality issues as the layer builds up. Make timely adjustments to prevent problems.
Limit decorative layers: Build up hard chrome thickness as needed but restrict decorative chrome to less than 0.002” to avoid cracking or nodules.
Post-plate finishing: Proper grinding, polishing, and buffing removes defects and enhances the chrome’s luster.

Troubleshooting Common Chrome Plating Over Chrome Issues

Problem	Cause	Solution
Streaked or Dull Deposit	Contaminants in plating solution, overheating, high current density	Maintain plating bath, adjust parameters to spec
Rough Deposit	Poor surface prep, plating too fast, old chrome porous/damaged	Improve cleaning and etching, lower current density
Poor Adhesion	Inadequate surface prep, plating over corroded chrome	Thoroughly clean and etch before plating, avoid badly pitted chrome
Flaking/Blistering	Contaminated substrate, plating too thick, hydrogen embrittlement	Eliminate contaminants, limit decorative chrome thickness
Burned Deposits	Current increased too rapidly, plating solution too hot	Bring up current slowly, maintain bath temperature
Cracking	Internal stress, excessive thickness, chromic acid concentration too high	Lower current density, limit thickness, adjust solution chemistry
Nodule Formation	Impurities in bath, overheating, high current density	Filter & maintain bath, ensure proper temperature & current control
Plating Build-Up on Low Current Density Areas	Different current densities on part surface	Use proper racking, shielding, anode placement to equalize current
Uneven Plating Distribution	Poor part racking or solution agitation	Optimize part racking, use solution agitation, maintain proper tank geometry
Brittle Deposits	High internal stress, hydrogen embrittlement	Reduce current density, avoid entrapped bath chemistry

Applications and Examples

Chrome plating over existing chrome layers can be useful in many situations:

Restoring Car Bumpers and Trim

Older chrome automobile bumpers and trim pieces often suffer from corrosion, pits, and worn plating. Re-chroming can restore these parts to a like-new finish. Careful surface prep and masking is needed to avoid damaging good chrome areas. Decorative chrome thickness should be built up slowly.

Repairing Motorcycle & Bicycle Components

Chrome-plated parts on motorcycles and bicycles like handlebars, mufflers, shocks, rims and forks can be re-chromed after years of wear and weathering. This is often cheaper than replacing expensive components.

Refurbishing Antique Fixtures & Hardware

Chrome and nickel-plated antique bathroom, kitchen and door hardware from the 1920-50s era can have their worn finishes renewed via re-chroming. This restores both appearance and corrosion resistance.

Salvaging Improperly Plated Parts

If decorative chrome plating on new automotive or motorcycle parts shows defects like pitting or thin spots, re-chroming can add thickness to mask flaws, avoiding costly part rejection and re-manufacturing.

Restoring Industrial Molds, Rolls and Dies

Re-chroming adds hardness and abrasion resistance to worn or damaged industrial tooling like molds, forming rolls, stamping dies and drawing punches. It saves the cost of tooling replacement.

Upgrading Hydraulic Components

Hard chrome layered over existing chrome on hydraulic cylinders, pistons and rods reduces friction and wear in high pressure applications. It also prevents leakage and extends service life.

Adding Durability to Machine Parts

Re-chroming shafts, cams, bushings, slides and other machine components with thicker hard chrome adds surface durability to withstand repeated use and abrasion in industrial machinery.

Improving Food Manufacturing and Processing Equipment

Food handling machinery often uses re-chroming to meet FDA standards and prevent bacterial contamination. Hard chrome provides a non-porous, easy-to-clean surface.

Conclusion

Thorough preparation of the existing chrome surface is vital for adequate adhesion. The plating process itself requires careful control of parameters like temperature and current density to optimize results. Consulting experienced chrome platers is advisable when first attempting to plate chrome over chrome.

When done properly, putting new chrome over old can restore corrosion protection, repair wear damage, refresh appearance, and increase thickness on all types of metal components and parts. The automotive, motorcycle, antique, industrial, food processing, and manufacturing industries in particular can benefit from quality chrome plating over existing chrome layers. With some expertise and care, the process can provide repaired and renewed chromed parts at reduced cost compared to replacement.

References

Surtech Research Services, Inc. “Successful Chrome Plating Over Old Electroplated Chrome Deposits.” Chrome Plating Over Old Chrome. https://www.surtech.com/chrome_plating.php
MacDermid Enthone Industrial Solutions. “Plating on Hard Chrome.” https://industrial.macdermidenthone.com/processes/plating-on-hard-chrome/
Aalberts Surface Treatment. “Rechroming.” https://www.aalberts-st.com/processes/rechroming
Columbia Chemical. “Chrome Plating Over Old Chrome Deposits.” https://www.columbiachemical.com/PDFs/Chrome%20Plating%20Over%20Old%20Chrome.pdf
Atotech. “Hard Chrome Plating.” https://www.atotech.com/products/equipment/chromium-plating/hard-chrome-plating/
Michelle Perkins. “The Ins and Outs of Plating on Chrome.” Products Finishing Magazine. https://www.pfonline.com/articles/the-ins-and-outs-of-plating-on-chrome
Kunze, Ulrich and L.M. Calle. “Chrome Plating for Engineering.” in Modern Electroplating, 6th Edition. https://onlinelibrary.wiley.com/doi/book/10.1002/9781119300487
Sifco Applied Surface Concepts. “Technical Information: Chrome Plating Over Old Chrome.” https://www.sifcoasc.com/wp-content/uploads/2018/08/TI-Chrome-Plating-Over-Old-Chrome-1.pdf
Industrial Plating Company. “Chrome Plating (Over Old Chrome Plating).” https://www.industrialplatingcompany.com/finishes/chrome-plating-over-old-chrome-plating/
Advanced Plating Technologies. “Chrome Plating Over Existing Chrome.” https://www.aptplating.com/chrome-plating-existing-chrome/