Finish Prep

[Darryl Young]

You know the old saying, "the finish is only as good as the prep work". I think it's probably true!

So would you that have finishing experience mind describing the prep steps you use prior to starting the finish? Hopefully, you can add the brand and grit of paper you use, source for your sanding blocks, etc. How do you sand around the heel of the neck? Are you essentially level sanding without the finish? Do you stop with 220g?

Thanks, and I look forward to your input!

[Freeman]

I do a fair amount of scraping before I ever start sanding. Sand with the grain from 150 to 220 at least. I just use plain old Home Depot sandpaper and their little sanding pads. Wrap the sand paper around a wood or rubber block, the pads work good around curved surfaces like the neck heel (I assume the neck is off). I tend to wrap sand paper around all kinds of things to get in corners and tight spots. I use a tack rag and a little air from my compressor to blow off the dust. (edit to add, I think it is more important to use fresh sandpaper all the time than any special brand - the minute it starts loading up I get a new piece)

Pore fill, two coats of SM paste, or now, one of Zpoxy. With paste work it in with a piece of cloth across the grain, with the Zpoxy spread and squeegie as best I can (I cut some plastic cards for this). Sand to 220 again.

With paste pore fill I would shoot a couple of wash coats of the final finish diluted 1:1. With the zpoxy I didn't need too. The wash coats will give you an idea if you've adequately filled the pores.

Stain if I'm going to - sunburst on the mandolin, I stain mahogany necks on rosewood guitars. Sand back to 220, then a couple more wash coats to seal. Scrape bindings and inlays back to remove all stain.

With SM waterbased I'd shoot a dozen or so coats of their thicker sealer, three coats a day, sanding to 220 or 320 each day before the 1st of the three. With KTM-9 I just started shooting the lacquer at full strength. Again, sand to 320 each day and shoot the mist of alcohol before the first of the three.

After somewhere around 15 coats I sand 320 dry, then 400 wet (in circles) - at this point I can tell how much more finish it will need. I buy my wet and dry paper at an auto shop - don't know the brand but that is the only place I can get grits above 800. 15 or 18 is usually enough for spruce, I normally go 24 with porous wood.

Let cure for 3-4 weeks, do all the wet steps from 400 to 2000, buff and assemble.

Finishing take me longer than all the wood work.

[tippie53]

finishing is prep. Brands are not as important as technique. I will not mix brands , I select a brand of finish and use all that the brand offers. I use industrial abrasives for sandpaper. I admit ,I do not use scrapers but that is just my technique.
I don't use a filler on the closed grained woods like Maple . Once I am ready this is my finish prep . Sand to 220 then stain , seal , fill. I use pore o paq and stain this to the color I want. Then I seal again. I will use nitro and will not use shellac . This can cause adhesion issues. Once the 2nd coat of sealer is sprayed I will spray a finish coat before the vinyl will set. I want to get a good weld in of the finish. Once I am spraying I want to build to .016 to .020 . With nitro patience is the key. I let it cure for 3 weeks and level off. Once level I spray 3 finish coats and will wet sand and buff. With nitro there are health and safety concerns , so take them serious. I use butyl acetate for a retarder and thinner.
On filling , once you think you are done , do it 2 more times. I will spend more time on finish than on building. Finish is not just prep but patience and more patience.

[kencierp]

On filling , once you think you are done , do it 2 more times. I will spend more time on finish than on building. Finish is not just prep but patience and more patience.

This is great advice!!! As a mater of fact I back it up a few steps ---- the same goes for sanding "always with the grain" Do your complete sanding routine (personally I go to 320G) -- set it down till the next day, get in some real good lighting do the complete sanding routine again ---- and yes do the same thing a third time. Remember that once a lower grit is used the entire sanding grit progression squence needs to be followed. No doubt there are those that can get it perfect with one session - that would not be me.

[Darryl Young]

Thanks for the advice!

Freeman, sounds like you've had good luck using sanding pads on the heel. I just ordered the Holey Terror sanding block that Ken C. once mentioned he uses and likes.

I'm torn on which pore filler to use. I wanted to try CA (and I still might). However, a waterbase finish doesn't pop the grain as well as some finishes...........and zpoxy really pops the grain and looks nice under a waterbase finish. I wonder if CA and shellac would look as nice under a WB finish?

[Herman]

Freemans schedule is almost the same as mine. And Johns statement that the finishing take half the buildingtime counts for me too. So I can add not much. Patience is really an issue.
I sand with 3M pads from 2000 to 20000 in 6 steps. But they sand that slow, it gives you a lame arm. I think its worth the effort. A great finish shows it all.

Herman

[deadedith]

Ken - so I understand: when prep sanding, you work up thru your grits on day one (using a RO, or a block?), then same on day 2, and then on day 3?
Why, on day 3, would you re-scratch the surface again with a low grit? If the theory is to sand for 3 days to eliminate the chance of missing something, how could you be sure you don't miss the scratches from the lower grit on day 3?

Just askin' - I have so much to learn.


Thanks
Dave B

[Darryl Young]

..... Sand to 220 then stain , seal , fill. I use pore o paq and stain this to the color I want. Then I seal again. I will use nitro and will not use shellac . This can cause adhesion issues. Once the 2nd coat of sealer is sprayed I will spray a finish coat before the vinyl will set. I want to get a good weld in of the finish. Once I am spraying I want to build to .016 to .020 . With nitro patience is the key. I let it cure for 3 weeks and level off. Once level I spray 3 finish coats and will wet sand and buff. ......

John, does Martin typically stain a mahogany neck when used with rosewood back and sides? I think I've read that they do stain the pore filler a darker color before applying but I wasn't sure if they stained the neck before applying the pore filler. Do you know the colors they use for staining neck (if they do this) and staining the pore filler? Even if I use zpoxy as my pore filler, I may want to use pore o paq with dark dye to make the grain of the mahogany stand out. Can one dye the neck and wipe the dye away quickly so mostly the pores are dyed dark and not the rest of the neck? If so, I guess you could do this then use epoxy pore filler and have a nice contrast.

John, are you using a vinyl sealer under the pore filler and on top of the pore filler? What are your thoughts about using vinyl sealer between rosewood and a water base finish so the oils in the wood don't affect the curing of the water base finish? KTM-SV won't cure properly if it's in contact with rosewood oils so I need some type of barrier......shellac, isolante sealer, something. I've read McFaddens Rosewood Sealer works good for this but I'm not sure it's even made anymore.....can't find it anywhere.

On the shellac adhesion issue you mentioned, is this a problem with the shellac adhering to the pore filler or an issue with the nitro adhering to shellac?

Thanks!

[Ken C]

I have only been building guitars for a couple of years, but I have built cabinets and furniture for more than thirty. I second much of what has been said. Poor prep and finishing can make a great piece of furniture (or guitar) look mediocre, but great prep and finishing can do a lot of good to a mediocre project. I only recently got into spraying water-based lacquers. For years I used wipe on oil finishes that I rubbed out. These finishes are just as dependent upon good prep as the thin lacquers.

I usually sand to 320 grit as well, but if the wood is particularly hard or I am dealing with end grain, I'll go to 400 or 600g to get out all the scratches. The harder the wood, the finer the grit needed to remove scratches. I usually do what Ken Cierp recommends and run through all my grits in a given evening. Then, the next day in a different room with different lighting, I'll check everything. If I see scratches, I'll go back to the finest grit possible to remove the scratches then work my way back to 320 or 400g. Another handy trick is to keep some mineral solvents handy. I grab a clean rag or a paper towel and moisten it with mineral spirits. I then swab the entire surface with it. This does a couple of things: 1) Any glue or other contamination on the wood surface will be readily visible; and 2) It can help identify remaining scratches. I never move to finishing until I have done this.

Regarding hand or RO sanding. Prior to bending my sides and prior to bracing the back, I'll use my RO. Once the box is assembled, I only sand by hand. Don't do any heavy sanding without a sanding block or you will end up with undulations in your surface. When using a block, be sure to sand with the block at different angles so you don't sand a trough. Still sand with the grain, but just hold the block at different angles. When using a block, avoid the temptation to tip the block on an angle to get more bite. You'll just hollow out the area. If you need more bite, switch to a coarser grit.

For the heel, I typically sand to a finer grit than the rest of the neck. Because of the end grain, this may be needed to remove scratching. The Holey Terror or a medium flexible block is great for this. I have a somewhat more flexible block that I will use as well. With the proper grit papers, the heel can be ready for finish in no time.

I do use scrapers and find them very helpful for a lot of tasks, but I don't really prep my surfaces for the finish using them. One exception is a single edge razor blade. I like to run one around all my purflings and head stock laminates to clean them up and bring out the contrast. This I do after final sanding and just prior to spraying the finish.

If you are using water based finishes from Target, their shellac and EM6000 work quite well together. I have shot base coats of amber shellac on my last several guitars. Adds some nice depth to the finish. And BTW, I disagree about water based finishes not popping the grain like solvent based finishes.

Ken

[deadedith]

Thanks Ken C - a lot of good information.
Dave B