This is the first of an occasional series of tutorials covering tips and techniques for those of us who have limited facilities for building and finishing guitars and basses but nevertheless still wish to produce results that are fit for purpose and perfectly respectable - even when pitched against those produced in fully-equipped guitar building shops.
This first tutorial covers wipe-on varnishing.
Gloss finishing of a guitar or bass can be daunting for the Bedroom Builder with visions of spray booths, compressors, burnishing wheels and high degrees of skill. With the wipe-on approach, a perfectly acceptable result can be achieved with the minimum of equipment and facilities.
What does this tutorial cover?
This tutorial aims to:
- explain the process of wipe-on varnishing
- detail some tips and techniques to produce a perfectly acceptable finish with the minimum of equipment and facilities
- explain the important differences between this and a spray finish (especially nitro) and particularly relating to the final stages and polishing
This tutorial does not:
- claim to be the best or only way of producing a non-sprayed finish
- claim that this method of finish can compete with a professionally sprayed commercial-standard finish. It can, however, produce surprisingly good results that would bear close examination before revealing its humble origins.
- represent necessarily the quickest way of finishing. Its aim is to produce an acceptable finish when faced with limited resources
What types of finishes can the wipe-on technique be applied to?
Most standard finishes can be varnished using the wipe-on technique, including:
Natural wood finish:
Stained wood finish:
Solid painted finish:
Facilities and Equipment
Do I need a workshop?
No. Wipe-on varnishing can be done in any convenient room or facility, providing that:
- there is adequate ventilation
- there are no naked flames or other high-temperature sources in the immediate vicinity
- no major sources of air-born dust are present
These are general precautions, but please always ensure that you read and follow the specific guidelines relating to the specific varnish or thinners you are using.
What equipment do I need?
The specific varnish illustrated is standard household polyurethane clear varnish, thinned with standard household decorators’ mineral spirits (white spirits). Other varnishes can be applied using the wipe-on technique, although some experimentation may be needed to optimise the proportions of varnish to thinners.
The equipment needed is:
- rubber gloves
- varnish (in this case clear polyurethane gloss varnish)
- compatible thinners (in this case white spririts)
- a mixing/storage jar
soft micro-fibre cloths for the application of the thinned varnish.
- The ones I use are low cost, budget hardware-store cloths and they work just fine. Other conventional lint-free cloths may be suitable, although ‘lint-free’ often isn't! Micro-fibre cloths – in my experience – generally are.
Additionally, and optionally, I use an additional type of microfiber cloth to remove any dust from the surfaces prior to varnishing. I use the type that are sold as window-cleaning cloths and find these much better than many commercial ‘tack rags’ that sometimes leave sticky deposits...and sometimes even leave bits.
What stage of the finishing process is this tutorial starting at?
For illustrative purposes, it will be assumed that it is a guitar or bass body that is being varnished and that it is ready for varnishing. It is therefore assumed that the guitar body:
- has been finish sanded-down to final pre-varnish levels
- where applicable, any stains/dyes or paint coats have been applied
- optionally, in the case of natural wood or stained finishes, a sealer has been applied to reduce excessive absorption of the initial varnish coats.
What are the main stages in the wipe-on varnishing process?
- Preparing the body and thinning the varnish
- Wiping on layers of varnish and periodic ‘flattening’ the hardened varnish with abrasive paper
- Final flattening and finishing coats
- Hardening period and final polishing
Stage 1 - Preparing the body and thinning the varnish
As explained above, this tutorial assumes that the body has been sanded down to a grit level ready to start varnishing. In normal circumstances, grit fineness up to P600 should be more than sufficient. Finish the final sanding ‘with the grain’ to avoid any cross-hatching.
Dust control is critical for wipe-on. Points to note are:
- for approaching the first hour after application, dust landing on the surface will tend to stick
- it is all too easy to allow dust to contaminate the cloths or the varnish
Simple precautions help, such as:
- wipe down the surface to be varnished with a lint-free cloth dampened with water, naptha or white spirit (refer to product guidelines for suitability and precautions)
- if possible varnish in a room that has had air limited movement for the previous hour or so
- varnish from each side, middle outwards – not reaching over the freshly applied varnish
- short-sleeves help while varnishing. A remarkable number of fibres are shed from shirt sleeves!
- if at all possible, don’t varnish where cats live...that fine downy fur!!!
- once the surface has been varnished, tip-toe out of the room and leave it undisturbed for at least an hour
- micro-fibre cloths do not shed fibres. However, they can collect dust. Before use (somewhere other than the room where the varnishing is going to be applied) shake vigorously to remove any dust.
Thinning the varnish is important for wipe-on. Out of the tin, varnishes tend to be too thick to work well and it is easy to be left with ridges (‘brush’ lines) in the finish. Thinning helps to avoid this. Main principles here include:
- wipe-on works at its best with multiple coats of thinned varnish. Thinned down, each coat will dry fast, allowing up to 3 coats a day
- mix the varnish and thinner in an appropriate jar (follow manufacturers guidelines relating to fumes and fire risks)
- for initial coats, up to 30% thinners is usually OK. The final coats (see later) can often be thinned as much as 50%
- Mix by gently agitating the jar. If bubbles form, let them fully disperse before using the varnish
Stage 2 Wipe-on of Initial Varnish Coats
Wiping on the initial coats is a straightforward process. However, the key to this process is multiple coats of very thin applications of varnish:
- It is best, if possible, to wipe the main applications onto a horizontal surface as the thinned varnish runs readily.
- It is helpful if the room where the varnish is being applied is well lit, or has a natural light window, so that the surface can be viewed obliquely periodically to ensure that no areas have been missed
- Wear protective gloves – latex or nitrile allow the ‘feel’ to be maintained (nitrile is more durable against solvents than latex)
- Dip the microfibre cloth into the varnish and gently squeeze out the excess against the side of the glass jar.
- Wipe a stripe of varnish in line with the grain (usually neck to bridge / bridge to neck)
- With a centre-joined surface, there is less chance of dust contamination if the wiping starts along the midline and each new stripe of varnish moves from the middle towards one side, and then from the middle towards the other side. If there is no centre line, the application will be more even if wiping starts from one side towards the middle and then from the middle to the other side. However, doing it this way there is more chance of dust from your arms or clothing falling onto the wet varnish because you will be leaning over wet varnish for that first stage
- Do not try to wipe too wide a stripe at a time – you need ideally to get from top to tail (or vice-versa) in one smooth run
- Recharge the cloth, squeeze out and apply the next wiped strip, overlapping by 2-3mm
- As you progress, check the coverage from time to time by looking from either end of the guitar at the reflection from your light source or window – any missed areas or dust buggies will be immediately obvious.
- If you need to redo an area due to missed or uneven coverage, do so immediately on the strip concerned while it is still fluid and always wipe along the full run from tip to toe – a wiped correction in the middle of a run will show once dry
- If you see a missed area in a run that you did more than a few minutes before, leave it. It will cover over at the next application but any attempt to re-wipe varnish that has already started to harden will leave wipe marks.
- When you get to the final edge, apply a very thin wipe to the guitar sides, all the way round. Without recharging the cloth, run round the bottom edge of the sides once more to smooth out any drips that may have formed.
- Tip-toe out of the room, trying to minimise any dust movement for at least the first 30 minutes!
Once the varnish is dry (thinned varnish is usually dry enough for further coats after 4-5 hours), repeat the process.
Every 4-5 coats, check to ensure there is not excessive rippling or ‘dust buggies’. In this shot you can see that the ripples have cumulatively increased over a few coats:
If there are excessive ripples or imperfections:
- leave to harden overnight (as a minimum)
- sand the surface with 1500-2000 grit wet and dry used wet until the ripples are flattened
- wipe the surface with a clean, damp cloth
- once fully dry, continue wiping on coats
Stage 3 Final Stages
The number of initial coats depends on preference and other factors such as the amount of flattening, the thickness of each application, the absorbency of the wood, etc.. As a guide, this bass body was ready for final flattening and final coats after around 8 coats, applied over 4 days.
The final steps are important and are different to some other forms of finish application – notably nitro finishes.
The main difference is that nitro layers, and some other finishes, ‘melt’ into previous applications. These finishes "dry" through the evaporation of their carrier solvents. The solvent within each subsequent layer applied re-activates the previous layer slightly, causing both to blend into one. This allows buffing up with cutting pastes or mops down through the layers to a buffed-up shine. This approach does not work with polyurethane finishes!
Polyurethane applications harden chemically in addition to their carrier solvents (thinners) evaporating, and then allow well-bonded further layers to be added on top. The gloss is produced by the final layer of varnish. Hence buffing or cutting would remove that layer and expose previous layers, giving rise to dull finishes and contour lines or "witness marks" where the boundaries between successive layers can be seen.
Nevertheless, the final stages of wipe-on polyurethane varnishes are straightforward and – if you are not happy first time – repeatable.
The final steps are:
- Allow the varnish to fully dry. A week is a good representative minimum
- Flatten the surface with P2000 grit wet and dry paper used wet to remove any final imperfections or dust buggies
- Wipe clean with a damp cloth and ensure it dries fully
- Thin the varnish to a total of 50% thinners
- Charge the micro-fibre cloth, squeeze out and wipe on one very thin coat as with Stage 2 above
- Allow to dry overnight
This final coat is usually easy to apply. However, because it is very thin, once it is dry, you may be able to see dull patches where it had been previously flattened. If not, leave it and move to the final steps! If so, apply one more final coat directly on top of the previous one. In exceptional cases, it may need a third coat.
If you are not happy with the final coats, remember that the process is repeatable.
Once a satisfactory finish has been achieved, there remains only the hardening and final polishing stages. Small aberrations and low levels of small dust buggies will polish out at this final stage:
- Leave the final coats to dry and fully harden. A representative minimum here is 2 weeks. Longer is better.
- Polish with a quality low-cutting auto polish. Meguiers Ultimate Compound is ideal. Remember – you do NOT want to rub through the final thin gloss layer.
- Apply the polish by hand with a soft cloth and polish off with a clean cloth. It is polished by hand so that there is no possibility of generating enough heat to cut through that final gloss layer!
At this stage, you should be able to take a photo of yourself in the reflection!
Bedroom Builders - Wipe-on Varnishing by Andy Rogers is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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