Official Luthiers Forum!

So I’m leveling my pore fill which is the 2nd coat of epoxy. Question: what about sanding scratches... I have a black headstock and I can still see scratches after leveling with 800. Will this become invisible after applying my em6000?



Sent from my iPhone using Tapatalk Pro

Yes, they will fill in and level...

I have a related question for those here with more finishing experience than I have. I've picked up the idea that sanding with fine grit (above 400, say) can introduce a risk of poor adhesion of subsequent layers. I have no idea if this applies to epoxy but I have read that it does with regard to finish. Any opinions on whether this is an actual problem for either one?

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Absolutely a problem anytime you apply a layer of finish that relies on a mechanical bond. And that would be any type of finish you put over an epoxy as it is the only bond available on epoxy. Different types of finish material have different preferences for proper adhesion but none will work well above 600 grit between coats. I almost never exceed 400 between any coats.

For prepping the pore fill for finish you must first determine if the wood is completely sealed with epoxy or are the pores filled with bare wood between? That makes a difference to as in one instance your coating must adhere to bare wood and the other is an inter-coat type situation where coatings bond solely to themselves. Normally your TDS from the coating manufacturer would cover all this in detail, but Emtech doesn't seem to be as up on this as all the other professional brands I have used.... this is all they really say

"Sand with 400-grit sandpaper to remove surface imperfections, runs, sags and contamination. Moving up to 600 or 800-grit sandpaper is recommend if a high-build finish is required. "

We typically do not want high build (thick) finishes on guitars so 400 would be if the epoxy seals all the wood and anytime between coats you need to sand. If you still have bare wood with just the pores filled that should be no finer than 320. I use 220 as my basic bare wood prep for clears.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Here is a chart that someone photographed on the wall of the finishing department at Martin. It appears to apply to bare wood and not to the finishes, but I found it fascinating that different wood are treated quite differently.

"do not sand with 320 grit on any body that receives a hand-rubbed stain"

And what is Chakte Viga?

Ed

Edit: came up with this:

https://umgf.com/ngd-martin-d-42-custom-shop-paela-wood-the-one-and-t139657.html

Is this s till the only one they have made with this wood?

Brian - Thanks a lot for your reply. I've been using 400 when I have a reason to sand between coats and on epoxy that covers the wood so it's good to have that approach confirmed. Also thanks for mentioning the bare wood prep too. I was taught not to sand above 220 for wood that's going to receive a finish.

Ed - That's an interesting chart. I wonder what the reasoning is behind the different sanding schemes for the different woods. I don't see an obvious pattern.

Fourth one down: "Tonewood"

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

As far as sanding through... which I’m assuming is generally what you don’t wanna do.....
I have some lighter places after I’ve leveled some.... it doesn’t “feel” like wood, and when wiped with naptha it disappears and looks like the rest. Is this just a super thin coat? It feels like epoxy but I don’t want to start the laquer process if it’s going to look blotchy...


Sent from my iPhone using Tapatalk Pro

You either want to sand through until you have just the filled pores remaining surrounded by bare wood, or not sand through and leave a coat that covers all the wood.

If I remember right, you are using Silver Tip epoxy. I haven't used that, but with z-poxy, any small areas of sand through or blotchiness after with leveling can be taken care of by wiping on a wash coat (z-poxy:ethanol, 1:1). I've done the final wash coat approach on Indian rosewood, ziricote, and claro walnut. It would think it would work with Silver Tip too. Someone who uses it can weigh in on it.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

How filled are your pores? A third coat may be in order.

A lot of folks do a final wash coat with the epoxy mixed with alcohol 50%.

I ended up using zpoxy for this. I may do one more coat to to make sure I got everything .
Wenge has some canyons
After that sand down I’ll do a wash coat
Thanks for the advise


Sent from my iPhone using Tapatalk Pro

Yeah, wenge. Wenge, man. I've never done a gloss wenge guitar, not sure I would. I'd be curious as to how much weight/mass is added in porefill alone. Have you ever weighed before and after to see how much finish goes on?

Not yet


Sent from my iPhone using Tapatalk Pro

Ed I have some chackte vega it/s a very orangey wood that comes from central and s america . its a dead ringer for pernambuco from brasil. except .it doesn/t age to a golden reddish brown like pernam, but gets a darker orange colour