More on preparation – sanding sealer and using an index coat
I’m building myself a “La Cabronita” style guitar in black, with a very nice one-piece alder body from Phil at GuitarBuild.co.uk.
I can’t stress enough the need for thorough preparation for a guitar finish to turn out well. Black lacquer is very reflective and shows every defect, so it is especially important here.
Sanding sealer
Sanding sealer soaks into end grain
The first step is to sand the body well with fine sandpaper to remove any fuzzy edges from the machining process, then to apply plenty of sanding sealer.
Alder is a very absorbent wood and you’ll see it soaking into the wood, especially on the end grain.
I sprayed several heavy-ish coats until the end grain remained wet-looking, indicating that the wood had stopped soaking up the sealer.
Once I thought that I had plenty of sealer on, I let it dry overnight before block sanding.
Sanding showed up a few low spots and defects in the wood which I needed to treat.
The worst of them were a small knot between the control holes which could be seen as the sanding dust collected in it
and a depression in the edge of the body which remained shiny and unsanded.
Depression in edge of body
I filled each of these with Ronseal 2-pack brown wood filler
Knot filled with 2-pack filler
Depression in edge of body filled
and sanded smooth.
Knot fill sanded smooth
Edge repair sanded smooth
Afterwards, the whole body was given another coat of sanding sealer and allowed to harden overnight.
Index coat
I wanted to be sure that I had sanded out and/or filled every imperfection, so decided to use a technique I learned from my car-spraying days called an index coat.
An index coat is a very fine mist coat of black (or another colour) lacquer which is typically sprayed over a primed surface.
Index coat sprayed
You can even use this on transparent finishes because you sand it off again.
The index coat highlights imperfections because as you block-sand your guitar body, it remains in any low areas such as the very slight depression around our knot
Index coat reveals unevenness
and a few tiny dings which would have gone unnoticed.
Index coat reveals small dings
I continued sanding until no black lacquer remained so I was sure that the faces of the guitar were perfectly flat and free of the tiniest of defects.
I sprayed another coat of sanding sealer and sanded to 320 grit, ready for the colour coat.
Fantastic advice thanks again Steve! Once I put the sanding sealer coat on my Jaguar body I started noticing a lot of dings and scratched that I just couldn’t see when it was bare wood, this approach sounds like it will do just the trick. I tried to solve it by sanding and just laying on more sanding sealer to no avail, so I hope my sealer coat doesn’t end up too thick, might sand it back a bit. Wish me luck!
Hi Mike, yes, don’t be afraid to sand it back so that it just fills the dips and is nice and thin everywhere else. If you sand through, just spray another coat.
These are some pretty valuable tips! I just found your blog, as I am refinishing some guitars and basses for a hobby. Will read it quite often from now on. Thanks for your tips, Steve!
Yes Steve got to agree with the other comments ,just to add I’ve sprayed 2 guitars before only as a hobby ,but without sanding sealer ,but what a difference sanding sealer makes ,on the other 2 I just put more primer on until it was flat, but sanding sealer (a) seals the guitar and (b) gets a really nice surface to add primer,colour, and clear to ,anyone thinking of cutting corners like I done in the past I recommend not to ,this paint is very good and flows nice and level to,thanks once again Steve for your great tutorials