Questions of the Week #3
Posted by Rothko and Frost on September 17, 2014
We've got a lengthier than usual QOTW for you this time, with some detailed answers regarding contour cutting decals, blooming, fillers and polishing. It would be fair to rename this edition QOAT (Questions of All Time), as they are some of the most frequently asked and important questions about decals and finishing. If you're new to finishing then we hope you'll find the info useful.
9) Do I need contour cutting for my waterslide decals?
Probably not. Contour cutting is where we pre-cut your decal to shape for you, with the shape of it following the 'contour'of the printed design. There are two circumstances in which we would recommend having your decal contour cut:
A) If you also select the Aged Coating, and are creating a true vintage style guitar where the decal sits on top of the finish (i.e., you don't lacquer over the decal once applied). The coating is required to give the inks at least a hint of protection. This is how decals were originally applied to Fender guitars in the 50s. Please note that not lacquering over the decal once applied leaves it far more prone to damage even from gentle knocks, and unless you are specifically looking to achieve this 50s effect is not recommended.
B) If you are ordering in large quantities, then having them contour cut can save you time when applying.
Our decals are exceptionally thin, and the edge is very easily hidden under only a few coats lacquer, even under thin finishes such as nitrocellulose. Once lacquered over the cut outline - and therefore the shape - of the decal vanishes, so the specific shape you cut it to is irrelevant. Hence, aside from the above outlined circumstances, contour cutting is unnecessary.
10) What's the difference between Wood Filler and Grain Filler?
Wood Filler and Grain Filler are different products which serve different purposes. They are not interchangeable.
Wood Filler is for repairs, for filling gaps and gouges where wood is missing due to snaps, knocks or breakages. It should only be used to fill these voids.
Grain Filler is for preparing open-pored wood (ash, mahogany, etc.) prior to finishing. It fills the wood's pores and natural ruts in the grain in order to give a flat surface onto which sanding sealer or primer can be applied.
11) I've sprayed clear lacquer and it has gone cloudy as it has dried, what's happened?
This is called blooming. The cloudiness is where moisture has been trapped in the lacquer as it dries, so instead of drying clear it dries to a translucent cloudy white finish. Nitrocellulose lacquer is especially prone to this when sprayed in damp conditions, or on a humid or cold day.
To help prevent blooming we recommend thinning the clear nitrocellulose lacquer using Premium Anti-Bloom Thinners. These thinners contain some Cellulose Retarder which slows the drying time of the lacquer, giving any trapped moisture time to escape before the lacquer dries. There is only so much that using Anti-Bloom thinners can do, however, and if conditions are cold or humid enough then blooming will occur.
This is not the end of the world. Blooming looks disastrous, and if you haven't seen it before then quite severe panic can set in rather promptly, but there's an easy fix. Blooming occurs because moisture is trapped in the finish. To fix it, this moisture needs to be released.
Nitrocellulose lacquer dries through solvent-evaporation, i.e. once sprayed the thinners evaporate and leave behind the nitrocellulose resin as the finish. The lacquer doesn't 'cure', it simply dries. As such, if more solvent is applied the resin re-dissolves. When you spray a new coat of nitrocellulose lacquer over an existing coat the solvents in the new lacquer you spray on slightly dissolve the coat beneath ,so the two coats melt together and then dry again as a single (thicker) continuous coat. This is in contrast to modern catalysed (2K) lacquers which when cured are not dissolved by their original solvent, so new coats layer up like the rings of an onion.
Back on topic, this feature of nitrocellulose lacquer - where dry nitro can be re-dissolved by nitro thinners - is what makes it simple to fix blooming. Once the bloomed coat has dried sand it very lightly with 600 grit paper, then spray a new coat on top. The new coat will slightly redissolve the last, which will release the moisture and now when this new coat dries it should dry clear, with no lasting evidence of the original blooming. This assumes that the problem which led to the blooming originally has been eliminated.
12) Can I use your RF3, RF5 and RF7 liquid polishing compounds to get a gloss finish instead of wet sanding?
No. Our Liquid Polishing Compounds should be used after wet sanding to achieve a high gloss finish. They form the final stage of the polishing process. The process of polishing a gloss lacquer makes it appear shiny by removing the scratches and unevenness in the surface. The smaller these scratches, the glossier it looks. To achieve the highest gloss possible requires using a very, very fine abrasive.
Abrasive coarseness is measured as 'grit'. If a sheet of abrasive is imagined as a backing with abrasive particles on it, then the grit is a measure of how many abrasive particles there are in a particular area, for example particles per inch. The lower the rating, the fewer particles fill this fixed unit of measure, therefore the larger each particle is in order to fill the space. Abrasives remove material from the surface - the coarser the abrasive, the more material it removes, the greater its 'cutting power'. While a surface may feel smooth to the touch, all abrasives leave behind scratches, the depth of which are determined by the grit of the abrasive used. A coarser abrasive leaves larger scratches.
How does this relate to our polishing question? Well, if a clear coat has initially been sanded with 600 grit wet/dry paper then it has '600 grit' scratches in it. To make it shinier these scratches need to be removed. Using a lower grit will get rid of them but introduces even larger scratches, so that's no use. Instead you need to use a higher grit. However, if you go too high then the abrasive will be so fine in comparison to the scratches that it does not have the cutting power to remove them, the result being that some areas will be shinier, but the surface will still be littered with these larger scratches. Thus, in order to achieve a perfect glossy finish it is important to move methodically through the grits, gradually getting finer, with each stage removing the scratches of the one before. 800 will deal with 600, 1000 will sort 800, then 1200, 1500, 2000 and finally move on to the finer liquid polishing compounds.