Treating Rust with Phosphoric Acid

One of the bigger projects we have in the workshop is a Burns Vista-Sonic from the early 60s. Alongside a number of other issues, it has badly rusted metal parts: particularly bridge saddles and bridge plate. Because these parts are very hard to find we’re forced to make do with the old ones… and they’ll do the job well once we treat the rust.

There are a number of ways to tackle rust, but because these parts are so badly oxidised I’m going to use a chemical solution. This will ensure all the rust will be eliminated because it can get in every nook and under loose plating.

1. Acid Bath

Ideally, we’d disassemble the parts but, because they’re so seized up, I’ve had to dunk the saddles with the height adjustment grub screws still attached. We can remove them later once the acid has had a chance to work. I’m using  a 30% solution of phosphoric acid. You can get much stronger solutions of phosphoric acid, but it doesn’t seem to have any noticeable increase in its efficacy past a certain concentration.

I’m working outdoors to minimise odour and fumes, and have also taken the precaution of wearing protective gloves. I let the parts sit in the acid for an hour. You can leave it overnight, but there isn’t much going on after a certain point.

2. Strain

I strain the acid through an old t-shirt so I can use it again. Obviously, store this stuff responsibly. Mine’s locked away in the dark in a large glass jar.

As you can see, we’ve lost a bit of the zinc plating that was hanging off a saddle. C’est la vie.

3. Disassembly and Cleaning

Now I can take it to bits a little easier. I’m using cotton buds to apply acid to areas that look like they need additional work. In this case, all the tiny machine screws need a bit of attention.

Here you can see the very badly rusted bridge plate. The rust has been made inert by the the acid.

4. Neutralising the Acid

In order to work safer and quicker, I neutralise whatever acid remains on the parts by covering everything in baking soda. Make sure everything is coated. This will help dry the parts and bring the pH level of the acid down to a safer level. There may be some fizzling and bubbling! I then, carefully, brush the powder off using an old toothbrush.

5. Clean and Wax!

I clean all the bits up with a cloth or cotton bud and a little WD-40. I don’t want to soak any of the parts, really, so go easy on it. Try to work as dry as you can and clean off any excess with paper towel.

When everything’s clean and dry, you can decided how to proceed. If you’re painting the metal you can get on with that. Ideally, we want to apply some barrier to prevent rusting in future. Especially in this case as much of the plating has gone. Paint or lacquer is one way to go, but not really ideal here when we have moving parts subject to abrasion.

A compromise is to use a wax. This provides a reasonable barrier and adds a little lustre to our dull grey surface. I rubbed in a few coats and let it sit overnight then buffed it up.

I’m under no delusion that this will prevent rust returning to this unplated metal, but hopefully the process will not be quite so rapid.

6. Inspection and Reassembly

Here’s the finished product. Rust free and ready for reassembly. Come back in a few weeks, and hopefully we should have it back on the guitar!

The assembled bridge:

Epiphone Cortez Repair Blog #3: Scrapers, glues and bagging

Hello, and welcome to the third blog in our series showing how we repaired this 1960s Epiphone FT-45 Cortez. In part two, we defretted the guitar and removed the bridge and pickguard. This time, we’ll remove the finish, and discuss hide glue and guitar humidity.

 

Preparing The Surface

We’re going to refinish the the face of the headstock and the top/soundboard. So, the first step is to remove the old finish. Both top and headstock had, at some point, been finished with shellac. Shellac is a traditional finish for string instruments, but is fairly uncommon on steel-string acoustic guitars.

The nice thing about shellac is that it can be hand-rubbed and touched up easily if needed. However, it isn’t very hard-wearing and the finish that had been applied here was thick and uneven. We’re going to refinish the guitar with authentic nitrocellulose lacquer which will give us a durable, thin coat that will, hopefully, bring out the best in the instrument.

The is the scraper that did most of the work removing the shellac. The key is to get it straight and keep a nice sharp, even burr along its edge. When scraping a large area you’ll probably find you need to hone and reburr the scraper a number of times. Keep a diamond stone handy!

The other thing to focus on is bending the scraper so you can zone in on the area you’re working on. This curve will also prevent the corners of the scraper gouging big train tracks in your wood!

The surface prep is finished with 320 grit paper and sanding blocks. I use two types: cork and rubber. The rubber block has a little more give and eases over uneven surfaces a little better than the cork block.

Our prepped top:

You can see the repaired areas under the pickguard weren’t even touched by the scraper or sanding block. The wood in this area is already thin and it seemed prudent to leave well alone. I filled the largest void to the left with small slivers of spruce just to add a little strength and some finish pooling in there (I’ll try to dig out a photo for next time).

Spruce has a tight grain which doesn’t need to be filled. The same is not true of the mahogany headstock:

This is it immediately after scraping. Mahogany has an open pore which needs to be filled if you want to get a flat finish (which we do). There are a number of good fillers on the market, but my choice for smaller areas like this is medium viscosity cyanoacrylate, AKA superglue. It is quick to work with, and leaves a perfect surface. Obviously, care needs to be taken! It probably deserves a special blog, so for now, I’ll talk about another glue I used on this project: hide glue.

Getting down to pacifics

Here’s a recent addition to the store. If you’re looking for a superb starter electric you can’t go wrong with the classic Yamaha Pacifica. Renowned for its build quality and neck feel, it’s a modern classic!

Smashing Starters!

Added a couple of great second-hand guitars ideal for learners or anyone in search of a reasonably-priced quality instrument! First, the Squier Stratocaster SE pictured: a superior Squier strat! We’ve also the ever popular Freshman Renegade: one of the best starter acoustics out there in a comfy folk size!

They’ve also both received a professional setup: so grab yourself a bargain!

Take Your Pick!

Eagle-eyed visitors and fans of browsing will have noticed we’ve added a new shop section for guitar picks. All picks can be bought individually so you have the opportunity to get a real mix of gauges and materials.

Some more second-hand bargains to come!

Epiphone Cortez Repair Blog #2: Planning & Pulling Apart

Hello, and welcome back to our repair blog covering the fix-up of this 50-year-old Epiphone FT-45 Cortez.

Last time round, we inspected the guitar for problems that we need to address. This edition, I’ll discuss the line we’re going to tread between repair and restoration. Then we’ll get started in earnest by pulling off all those bits we’re going to replace!

The Plan

Beginning a fairly big project like this we need to decide what is our goal? Are we trying to restore this instrument, as best we can, to the condition it was when it first came out the Kalamazoo factory in the 60s? Or are we trying to repair this guitar so it can live on as a working instrument?

Valuable, collectible instruments are usually restored using authentic materials, parts and methods so as to preserve the value of the instrument. This guitar, however, is destined to be a player’s guitar. So, while we will be sympathetic in our repair, we are not going to be slaves to the original design and construction of the instrument. I talked with the owner and we worked out what needs done so he can use this guitar day in, day out.

So here, in no particular order, is our action list. These are the main areas we’re going to address. More may be added as we go along, and there’s bound to be a surprise or two lurking, but this is plenty for us to be getting on with:

  1. Repair structural problems (cracks, loose braces and so on)
  2. Replace bridge
  3. Repair and re-radius fingerboard
  4. Re-fret
  5. Refinish top

That should keep us busy. Now let’s look at something we decided didn’t need to be done…