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Old 17th May 2018, 5:30 pm   #1
brightsparkey
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Default Repairing catalysed lacquer type finishes

On my Grundig 4070U the corners got a beating. I have finally got hold of some cellulose thinners to attempt to remove the finish on the corners so I can repair the veneers and then re-finish.

The clue is in the 'attempt' - the thinner makes no impact whatsoever on the finish, so I expect it is some form of catalysed lacquer rather than a nitro-cellulose type finish. The thinners didn't even make it tacky to the touch at all.

The finish is a high-gloss finish and where the impacts have occurred it has brittle fracture lines so its obviously quite hard.

Are there any hints and tips on how to repair this sort of finish? What can I use to remove the finish and how can I repair the finish and fill scratches etc. ?

I'd rather remove the finish on the corner with a solvent. Using abrasives is likely to damage the veneer even more than it has been already.

Any guidance gratefully received.

Kevin.
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Old 17th May 2018, 5:47 pm   #2
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Default Re: Repairing catalysed lacquer type finishes

I once restored a Grundig (or similar) cabinet - but this was a complete cabinet strip and I resprayed with two-pack urethane (ISTR) finish. The results were very good but I never want to have to do it again! The only way I was able to remove the original finish was to use a mechanical (ie. scraping) method. This was very hard work.

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Old 17th May 2018, 5:49 pm   #3
stevehertz
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Default Re: Repairing catalysed lacquer type finishes

We really need to see what you are talking about. If the lacquer cracks are not too bad, then an application of scratch cover polish will leach dye into those cracks and make them 'disappear'. Not sure if you've used or heard of it before but in most applications it is that good.

Otherwise I would make no attempt to perform a partial removal of the finish. I'd apply a lacquer, possibly with some dye content to those corners and allow it seep into the cracks. Keep re-applying and build it up until the desired effect is achieved, then fine sand and cut back accordingly. But we really need to see some photos.
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Old 17th May 2018, 10:47 pm   #4
brightsparkey
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Default Re: Repairing catalysed lacquer type finishes

Pictures to follow tomorrow, but two corners have been crushed by the courier's rough handling.

In both cases the veneer is intact but the chipboard is compressed. The vertical face bulges out and the horizontal is depressed.

My method here would be to remove the chipboard under the veneer in the affected area. Also the finish would need stripping back. Apply a metal corner to the casework with waxed paper covers to prevent adhesion. Then backfill the chipboard with sawdust and pva resin and press it in under pressure, thus returning the veneer to its flat state hopefully.

The Finnish is chipped and splintered with long glass like cracks so the corner needs stripping back.

I guess I might get the veneer flat enough to allow use of abrasives, but I fear the bits of old finish will get in the way.

What do you think? Pictures will help - there are some on the restoration thread I started.

Kevin.
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Old 18th May 2018, 7:03 am   #5
stevehertz
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Default Re: Repairing catalysed lacquer type finishes

Oh dear, another victim of shipping damage. Personally I blame the packer not the shipper. Having shipped and received literally scores of radios, videos and hifi items, I know that shippers throw these boxes the length of lorries, drop them, etc etc. Clearly that's not right, but sadly it's common, it's what happens and there's no getting away from it. My last example was a vintage hifi item received a few weeks ago. So, given that situation the packer has to factor that in. This 'bee under my bonnet' doesn't help you now of course, but hopefully it will help others.

I have successfully dipped compressed corners of wooden cabinets in boiling water to swell them back to normal. The effect is quite pronounced after dipping, and carries on for a few days.
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Old 18th May 2018, 8:14 am   #6
Craig Sawyers
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Default Re: Repairing catalysed lacquer type finishes

This is the standard fix with solid woods - a dent can be taken out by using a damp cloth and domestic iron (I actually have a cheap one in the workshop for this, and for hammer veneering).

I have no idea how well this will work with chipboard, which has a horrid tendency to absorb water and swell.
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Old 18th May 2018, 9:23 am   #7
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Default Re: Repairing catalysed lacquer type finishes

Here are a few pictures of the corners..

The top rear corner is shown and this is the most noticeable (at least its at the back). There is very little missing veneer and the top veneer is intact. The second photos shows the crazed finish which goes some distance from the damage.

The lower back corner (last pic) will need more reconstruction as there is some material loss of both veneer and substrate. But its not very noticeable as its at the bottom and the back, so I can get away with more there.

Steaming dents on solid wood usually works wonders, but on chipboard, I'm afraid I'll end up with weetabix.. The sides already have a bulge.

Maybe I can re-level the surface with the finish as it is and then use a scraper and sander to clean up the finish. That would be a much bigger task, as likely that most of the sides would need re-finishing.

To be fair to the seller, he did try to do a good job, but Hermes, the courier really tried hard to break it. The seem to have a particular reputation for being hooligans, and I would not recommend them to anyone (it wasnt my choice..)

Kevin.
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Old 21st May 2018, 6:01 am   #8
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Default Re: Repairing catalysed lacquer type finishes

It is very annoying that sort of damage. You are right, a lot of it is in the packing because you can be sure when you ship something that:

"Every stage in the shipping is equivalent to throwing the item down one flight of stairs"

One option you could consider rather than repairing it is to consider a cabinet corner to cover it, that you could make, or buy and coat a dark brown color. Cabinet corners both in 2 and 3 hole fixing types are readily available, here are some from AES:

https://www.tubesandmore.com/product...e-34-thickness

A very good type of lacquer, if you are opposed to polyurethane, is nitrocellulose in spray cans, these are sold by the Luthier's suppliers, but you can find it on Ebay, this gives the amazingly shiny finish you often see on electric guitars etc.
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Old 21st May 2018, 7:30 am   #9
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Default Re: Repairing catalysed lacquer type finishes

The original finish will be a 2-pack type and it sets like an epoxy. There usually isn't any solvent which will work on it, so lacquer removal is limited to mechanical means, meaning abrasives. The usual way of breaking down epoxies chemically use hot strong mixed acids, and there would be serious difficulty in not damaging the cabinet itself.

I'd do the job in stages.
1) repair the corner, trying to get some adhesive soaked into the underlying wood to toughen it up.
2) remove the lacquer (left on it helped hold the wood together for stage one) Hard fiddly work with very fine abrasives.
3) fix the veneer.
4) Make sure the cabinet is absolutely free of any wax (or worse) silicone polish.
5) Mix and spray matching 2-pack clear lacquer ('Clear-over-base style for cars)
6) Immediately clean your gun or airbrush, you don't want this stuff setting in it
7) give it a few days and use progressively finer grades of rubbing compound to smooth and blend in the overspray region where the new lacquer has a finish like sandpaper.

Cellulose lacquer is a lot easier to use. It's a lot softer but this also makes it difficult to blend against the original 2-pack as you try to blend in a feathered edge onto the original varnish.

It'll be a lot easier to varnish the entire cabinet.

Some of these operations are very difficult to undo. Make sure you're really happy with each stage before going on to the next.

Take precautions against breathing 2-pack mist.

David
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Old 22nd May 2018, 7:07 pm   #10
brightsparkey
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Default Re: Repairing catalysed lacquer type finishes

Looks like you might be on the mark there - tried di-chloro-methane and that doesn't touch it either, so as you say it must be a 2-pack curing film. Most irritating - mechanical methods only, which means re-finishing the whole cabinet.

In that case (no pun intended) I will need to remove the speaker panel and the scale-glass. The lower edge trim seems to be stapled in - removing staples from chipboard will be fun (or rather getting them back in will be)

I will proceed as you describe, once I've got the thing apart.

For the veneer repair - in the past I've used coloured waxes for fixing missing chips in veneer - will this work under 2-part or will it just dissolve?

There may be a delay of some weeks while I get my workshop sorted out as I have no spray facilities at the moment. In the meantime there will be some light music (the radio plays well now, so I'll listen to it before it undergoes surgery..)

Many thanks for the tips,

Kevin.
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Old 22nd May 2018, 8:59 pm   #11
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Default Re: Repairing catalysed lacquer type finishes

If you can get it and its not too much money or borrow a cup full , I would try a little Benzyl Alcohol on it. Might save you hours of prep, im sure there will be a chemist on the forum that could advise.
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Old 25th May 2018, 1:32 pm   #12
ColinTheAmpMan1
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Default Re: Repairing catalysed lacquer type finishes

I haven't tried it, but another organic solvent that might do the trick is tetrahydrofuran. It is miscible with water and a pretty powerful solvent, if you can obtain it.
Colin.
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Old 26th May 2018, 9:37 pm   #13
Phil G4SPZ
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Default Re: Repairing catalysed lacquer type finishes

I've found methyl ethyl ketone or MEK to be very effective as a solvent for many types of paint, varnish or other difficult-to-shift surface contaminants. Cheap and readily available, too.
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Old 26th May 2018, 10:15 pm   #14
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Default Re: Repairing catalysed lacquer type finishes

From everything I've read here, David's correct - if it's a 2-pack epoxy or urethane coating, it's effectively a fully cured, crosslinked, thermoset polymer - none of the readily available consumer solvents will dissolve it.

At 'best', you might find a solvent that'll 'swell' & partially degrade the coating - leaving what I suspect would be a 'mess', needing even more work to clean up. As a chemist, I'd advise to use a mechanical, abrasive, method here.

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Old 27th May 2018, 5:43 pm   #15
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Default Re: Repairing catalysed lacquer type finishes

I once had a chemist friend who managed to get some epoxy on his best suit. I can't remember exactly what he used to remove it but "dimethylformamide" springs to mind. No idea where you'd get any unless you can find a friendly chemist.
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Old 27th May 2018, 5:56 pm   #16
stevehertz
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Default Re: Repairing catalysed lacquer type finishes

Have a read of this corner restoration where I fitted in a new section of veneer.

https://www.vintage-radio.net/forum/...d.php?p=768253
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Old 30th May 2018, 9:25 pm   #17
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Default Re: Repairing catalysed lacquer type finishes

Quote:
Originally Posted by bluepilot View Post
I once had a chemist friend who managed to get some epoxy on his best suit. I can't remember exactly what he used to remove it but "dimethylformamide" springs to mind. No idea where you'd get any unless you can find a friendly chemist.
I wasn't aware of it previously, but yes, diethylformamide, a common industrial solvent, is said to soften and swell epoxy. Unfortunately, it appears not to be 'clean' dissolution, so it would, I think, be very difficult to produce a tidy edge of sound resin to which to work the new finish.

It's worth bearing in mind, though, for items one wishes to 'unpot'
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Old 5th Jun 2018, 10:10 am   #18
brightsparkey
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Default Re: Repairing catalysed lacquer type finishes

Thanks for all the helpful replies on this subject. The veneer replacement looks like a nice job. You needed two sheets because veneers have gotten thinner over the years - modern veneer is 0.6mm thick, whereas in the 1950's usually about 1/32" or 0.8mm-ish

I've ordered some benzyl alcohol as a last attempt at solvents. Don't want to mess with anything nastier.

The first issue to address is damage to the substrate. The impact has squashed the chipboard on the top face and its then bulged out on the side. My plan is to undermine the veneer in that area until its flexible enough to be reshaped. I'll then press some right angle steel plated gentle onto the case and then inject a mixture of resin glue and sawdust into the voids.The resin used will be the foaming type. By applying a clamp to the back face the foaming adhesive should push the veneer surface against the steel with a bit of luck so that the corner will be square again.

In order to do this I will need to remove some of the shards of finish which would otherwise obstruct the reforming. If I can't dissolve then I will have to put up with gentle removal by mechanical means.

I'm hoping that the veneer will be presentable enough once straightened out in which case I can remove the finish in the general are, re-finish and rub back flat.

Its going to be a slow process, and I really need to get my workshop finished first. I'll be back in some months time! Thanks for the hints so far.

Kevin.
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