New varnish on acoustic guitar - tone changed

Nyj

I think I've made a newbie error.    I left my 1995 Takamine acoustic with my wife when I went on tour, and when I came back some heavy-handed friend at a party had used a metal pick and damaged the top.   So I sanded it down and re-varnished it.   It now sounds a lot duller than it used to.   Duller tone, and less sustain.    Is this because I used aerosol varnish from Homebase?   Does it make a difference to the tone?

ICBM

Yes, very much - especially on an acoustic. It's somewhat more debatable on an electric but I'm one of those who think it does. In my opinion it's the thickness and hardness of the finish that matters, more than the chemical make-up of it.

If you want to get it back to sounding as it was, there's probably no alternative to a professional refinish with a thin, hard polyester finish, which is what I think the original is.

I'd probably look into replacing the wife too.

SteveRobinson

This is why I never invite Brian May to parties at our house

Funkfingers

If you sanded through all of the original finish, you have probably removed some of the soundboard wood too. This is bound* to change its resonant characteristics.


* A thousand apologies for this terrible pun. 

Nyj

Well, thanks for all the insight - and the laughs     I did indeed go right down to the wood.   Brian May had dug a horrible divot by the top e string.  I had to tidy it up, so I [thought I] had to sand some of the surrounding wood away.    I thought it was necessary to get all the old finish off.  Such is the penalty for listening to the youtube expert.  And it was a long job, the coat seemed to be very thick.  So I thought I had to put down many layers, and did.  
Oh well ... every day is a school day.    Down the hardware shop to get another 100 sheets of sandpaper.

Nyj

I'm wondering what's the best way to get rid of the new finish.   Not looking forward to another week of sanding.   But it appears that the 'best' so-called paint stripper, Nitromors, is pretty much useless.    It didn't seem to touch the original varnish.   Is there a better product for removing varnish?

ICBM

Nitromors wouldn’t touch the original polyester because nothing does, really - but it should shift typical spraycan varnish.

Corvus

Depends what your new coat is but as ^^ if it came out of a rattle can Nitromors may work, even though it's so poor compared to what it used to be. Also chances are the new clearcoat will wipe off with pure cellulose thinners or acetone. But with any of these ways it'd be easy to damage the finish on the sides. Masking doesn't totally help because pure solvent will eat the edge. Maybe masking up onto the top edge would help, then scrape & sand edge areas left over after doing the main area of the top.
Going over carefully with a cabinet scraper first would give any method a head start.

Bodyshop paint stripper takes off both 2k (typical guitar paint since the 70s, catalysed urethane in the US) and catalysed polyurethane, and eventually polyester; DIY strippers were emasculation by EU regs, but 'trade' or 'bodyshop' strippers do have the missing DCM (dichlormethane) and are easy to buy, just not on DIY shop shelves.
Putting tin foil over it helps a bit, slows the DCM evaporation down. Usually still takes 2-3 goes but gets there eventually.

I have stripped bodies & necks with it but honestly most of the time would rather sand.

Andyjr1515

I'm assuming you will eventually go for just a light 'dusting' coat once you've got the thickness of the coating off?

If so, if it was me, I would use a sanding block and something like 320 grit sandpaper and sand down to a thin 'sealing' coat and stop short of sanding down further into the wood.  

I think you will find that the Halfords out of a can spray varnish will sand off very easily.  If you do it this way, replace the paper frequently to avoid lumps of varnish sticking to the paper and rubbing grooves into the top.

I would then treat that thin remainder as my priming coat.  But first, I would string it up and try it.  If the sound is back to what it was originally, then I would give it the thinnest of finish coats just to get the colour back and leave it at that.  

For such a final finish, personally, if I was after gloss, I would use Ronseal Hardglaze thinned by about 20% white spirits and wipe it on with a soft microfibre cloth.  I have never had reaction with other finishes with Ronseal (but I am specifically talking about Hardglaze - the original bog standard clear polyurethane varnish and NOT the myriad of later alternatives).  

If the finish is Satin, then I would use Osmo Polyx 3032 Polyx Clear (small tin available from Wood Finishes Direct), again wiped on (unthinned, in the case of Osmo but the tin must be stirred before use).  Ditto, I haven't suffered incompatibility issues personally with Osmo either.


In both cases, I would give it a single thin wiped coat, let it dry, see what it looks like and, at the most, give it a second coat. 


If, on the other hand, the sound is still muted, then it isn't the thickness of the finish that is causing the problem.


Did you try new strings, by the way?  Before doing ANY of the suggestions, it's worth a try.  Someone Brian Maying with a metal pick strumming like a whirling dervish could easily knacker a set of strings in a single sitting...

Nyj

Thanks again to everyone for the expert advice.  @Andyjr1515, yes I've changed strings.   I think the offender was doing something a lot less subtle than Brian May ... he was essentially slamming down on the guitar, hitting only the top string or two and doing it 16 times to the bar ...  

I'm really very grateful for all the advice, I'll do what you suggest  

Funkfingers

Lend your Takamine to Tommy Emmanuel. He'll soon have the new finish off it.

the_butler

I'd consider taking it to a classical guitar luthier & have him strip the whole soundboard & then french polishing it.
If it had a thick finish on before it would probably sound better than ever once all the gloop had gone

hywelg

Paint Panther is much better than Nitromors nowadays. 

hollywoodrox

I don’t know if this is pertinent to the discussion but I bought some nitro finish in a can off northwest guitars for a tele bass headstock once they probably do poly as well if it’s not suitable 

Nyj

Thanks to all for the advice and comments ... 
@hywelg - I would hope that Paint Panther is better ... I can't think of anything less effective than Nitromors!