Testing ... testing ... is this thing on?
I've been starting to think a bit more seriously about how to finish the instrument. In the opening post I said something like, "
I dunno; 2k matte on body; tru oil on neck; subject to change; lalala ...". But the more I thought about it, the less I liked it.
I've done 2k finishes at home before and have a decent respirator and full-seal goggles, but it's not a full-face PAPR, so it means every time you do it you have to:
(a) get brand new organic compound filters (once you break the seal on the packaging, them wee boogers only have a functional life of 6 months as the active carbon deactivates);
(b) make sure your particulate filters are more than serviceable (usually means getting new ones to be sure);
(c) do it in a well ventilated area (and then get the fark out of there, Dallas);
(d)
shave -- because the biggest danger with non-PAP respirators is that the respirator seal against the face breaks, meaning the negative pressure from your inhalation preferentially pulls the air through the face gap rather than the filters (which have higher resistance than an open airway) and you get a lung-full of juicy isocyanates. Beards are a vacuum-breaker by design.
(e) suit up -- leaving as little skin exposed as possible.
In short: major PITA.
So I looked around for options. My original plan was simply to seal in any dye with Chestnuts' aerosol acrylic sanding sealer (notsponsored) and then finish with acrylic lacquer or cross-linking acrylic varnish of some kind over the top. As a plan, it's still on the table.
Downsides:
(a) I was planning on using water-based pore/grain-filler and, if any significant gaps needed filling, water-based wood filler. I don't
think this would cause a problem if done gradually, light and well (and the pore filler says it can work with all finishes once dry), but it would need some testing and is a risk.
(b) Acrylic lacquer. All the problems with that; particularly slow curing times and lack of resistance to certain solvents.
But still ... doable.
I then thought about Prevals and all the things you could spray on with those, and then did a bunch of research (including our very own epic 'varathane' thread) as to how feasible it was. Wasn't entirely sure I liked what I read, but it's theoretically possible, especially if you seal with water-based varnish or shellac (but the problem with shellac is that it's meths/DA-or-isopropyl-based so, in theory, could strip/raise your aniline dye -- as can water -- more on this later).
Then I came across this product (again; not sponsored):
Rustoleum Polyurethane Finish.
It appears to be a Rustoleum EU product only; there's no direct equivalent in North America, although I was wondering whether it was a rebranded version of the Varathane aerosols (which aren't generally available over here without importing). I don't
think it is as the MSDSs don't fully match, although that could just be different prohibitions on solvents between EU and US (<-- that's more clever than it first looks). I'm not sure.
I assumed at first that it was another water-based polyacrylic thingamijig masquerading as solvent-based poly, (not that I'm against those but it wouldn't solve the water-based aspect), however a few things intrigued me. One was that, while advertising itself as 'non-yellowing', the internet was full of complaints as to how much it yellowed or darkened white or light workpieces. Another is that, if you somehow manage to track down the PDS (which the manufacturer seems coy about providing, but is essentially the text on the back of the can), it says: "
Drying and Recoating: Touch Dry in 2 hours; Hard Dry in 24 hours". Those aren't really water-based numbers; they're nearer oil-based poly or, really,
wipe-on oil-based poly.
So I managed to figure out that the product is actually manufactured by Tor Coatings and I emailed them about it. I was pleasantly surprised that they took the time to get back to me relatively quickly, but they would only say that it was "solvent-based" which wasn't very helpful (so is acrylic lacquer). If anyone who's fluent in speaking MSDS could look at the
safety data sheet, that would be useful.
So, given that there are places online where you can get it for £8 (despite it being £14 at B&Q
), I decided to take a punt and try it. At first, I just thought I'd spray it on something, following the instructions, and see what it did, but then I had a better idea. Tests. Marginally-more-scientific ones.
So I quickly sanded and knocked-up a couple of boards ...
... and marked and labelled them ...
Even though they're essentially the same, they sort-of have opposite purposes. With the 'spray' board, the idea was to spray-coat the entire board in a few layers of the product, let it cure for three days, and then start applying swatches of both oil-based and water-based 'poly' at semi-regular time intervals
over the spray finish to see what it does.
The 'brush' board is the inverse. I've brushed one edge of the board in about 4 thick-ish coats of water based poly (rustins) and the other edge in 2 thick-ish coats of oil-based poly (ditto). I'm then going to spray different swatches over similar time intervals to see what, if anything, happens. This isn't just to see if the coatings are compatible, it's also to see the difference in the effect each coating has, both over / under other coatings, and on its own.
I then came up with another test which was as follows. There's not really such a thing as a polyurethane sanding sealer because you don't really need one: it's generally less troublesome to use poly itself as its own sanding sealer for compatibility reasons. One of the potential uses for the spray poly (
iff it's compatible) is to seal the dye patterns in so that you can safely come back over the top with either wipe-on or brush-on poly without disturbing the dye. Which raises a question: How many spray coats do you need to prevent the dye from running? (This might be a slightly premature question for reasons that I'll get to later, but we'll go with it for now).
So I knocked-up another board with two thick lines of dye. One dye was red (3:1 red:yellow Keda powder, 0.8g per 120ml mix) and one was darker blue (7:2 black:blue, similarly -- which is a cool colour). I then partitioned the board with the intention of spraying different amounts of the aerosol finish over it, each section having one more coat than the previous section. In this context, 'coat' means a heavy-ish mist coat. It's a a somewhat light coat in that you mist it as per normal, but you ensure that everything gets hit, which is a bit more payload than your typical mist coat.
This picture was taken as I was about to apply the last-but-one coat. It shows the gradation pretty well:
The following pic is the current situation. The 'spray' board had 2 heavy-mist coats and two heavy coats of aerosol before being left to cure for three days. It's also had it's first swatches of water and oil poly (4 coats and 2 coats respectively) after the initial 3 days of curing. The 'brush' board has had its base coats of water and oil poly (also 4 and 2, somewhat thick), and is waiting for its first swatch of spray (Thursday).
The 'how-many-coats-is-safe' board is still being left to cure, but I'll probably run the test on Thursday as well.
The one thing I've already learned (apart from the fact that my fineliner pens seem to be water-based) is that the spray itself
feels like polyurethane (it also looks like it if you compare the 'oil' side of the 'brush' board with the background of the 'spray' board). I'm pretty sure it's not straight 1K acrylic lacquer as I have decently extensive experience with that and it doesn't behave / feel the same. Most of the solvents flash-off pretty quickly (if you're doing mist coats, you can hit it again in about 5-10 minutes), which leaves a sticky surface. A couple of hours later, the molasses-sticky has gone, but it has that tacky, gummy poly feel to it, which gradually hardens over 18-hours to a day. I'm inclined to believe them; it
feels like poly and, when finally dry, feels harder than either the water-based acrylic-poly stuff or the 1k acrylic.
However: After I made the dye-protection-test board, I was researching what was 'likely' to happen and I came across a couple of sources (one was Prana Guitars on youtube -- who does a fair bit of decent dyeing -- and the other was a forum post) who attested/asserted that white spirit (mineral spirits) doesn't actually lift aniline dye that much; it's water and the alcohols (Denatured/Meths and Isopropyl) that cause the problems (which isn't surprising as they're the typical carrier solvents used with the dyes).
So I thought I'd test that, too, and I grabbed one of the old Keda Dye test boards from the other thread and rubbed at it with water and mineral spirits. It
seems, at first glance, to bear out what they were saying. You had to scrub reasonably vigorously to move any semi-meaningful amount of dye when using the white spirit, but the water moved it much more easily.
This is particularly interesting because white spirit is the primary constituent of wipe-on oil-based poly, so if it's possible to get a couple of coats of wipe-on onto the workpiece without disturbing the dye too much, the wipe-on itself will protect the work from subsequent coats.
I didn't get any pics of this step -- I was just winging it at the time to see what happened -- but it's inspired me to do
another couple of tests.
The first is that I'm going to do an actual full-ish-process sample of popping the grain and sanding it back, then colour-dyeing it and sanding it back (simple version), and I'm going to protect one half of it with whatever the protection test says is the right number of aerosol coats. The
other half I'm just going to hit with wipe-on poly and see what happens. If there's not that much difference, you might not actually
need the spray protection at all (but the number might still be useful to know for compatibility with water-based topcoats etc.).
So I've started knocking up a test board with a sycamore (maple) off-cut. This is the grain-pop stage (dark mix, 7:1 black:blue ratio, 1.2g per 120ml strength). I'm going to let this dry, sand it back, then put straight mid-blue over it. Here's a pic of the colour going on wet (it'll look different when dry):
The other test is just going to be a more formal test of {water vs. isopropyl vs white spirit vs water-based-poly vs oil-based-poly vs oil-based-wipe-on-poly} in terms of lifting the dye. I'll set that board up tomorrow night when I'm doing the blue dye on the grain-pop test. One of the the issues behind this test is that white spirit / mineral spirits is not necessarily the only solvent that's in oil-based poly (and water isn't always the only thing in water-based), so there could be a weird situation where the white-spirit itself is relatively fine in terms of dye-raising, but the final wipe-on mix might not be. That's why you have to test these things.
Oh. Last but not least ...
Returning to actual building work, I started work on the neck. Not much, but I got it roughed-out and a centre-line established (it's the lower of the two centre-lines
). I'm keeping the edge on one side for the time being as that's the reference edge and I'm going to do some layout from that side, plus I'm probably also going to rout the truss-rod channel using a fence from that edge (not fully-decided, but probably).
Anyway, that's more than enough for now. More incoming, f'shure.
You'd have many options of shwoop depending where on the surface you picked your section...
