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Lacquer is cracked after polishing


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Hi I'm wondering if there is a remedy for this and what possibly caused it. I am suspecting weather being too warm. I knew there was some cracks in the lacquer but after polishing the top they were bigger and more of them than I thought. The other hollow body guitar I made also has them to some extent although the top on that one is much thicker

I suppose sanding back to wood is the best way to get rid of them but are there any suggestions?

IMG_5980.thumb.jpg.6c1f13546e4b17195709b5b7c1404b0c.jpg

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I’ve got the same. While cold and heat differences can create them, so can internal  stresses from curing. In my case I laid on the clear very thick and the outer cured faster than the inner. Once sanded, the checks appeared. I’ve not done this yet, but some form of seeping solvent into the checks may work. 

http://www.frets.com/FretsPages/Luthier/Technique/Finish/Lacquer/CheckRepair/checkfill.html

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Also, looking at your pictures it seems like the checks are actually raised? You can feel them? Mine are similar, and I stick with the ‘not done curing yet’, and sanding released stresses hypothesis. 

On a previous build, I did some relicing and intentionally created checking using a freeze thaw process. Those checks were in the clear but you could not feel them.

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Thanks for that info, he says a sudden drop in temperature can cause it and I'd say that is the reason here. I'm always spending all day sanding when I think it will take an hour or so and end up spraying in the afternoon

And yes you can feel some of them

I don't know what to do I'm so fed up with it. Sanding and sanding and I've used over half a gallon of lacquer. Its just that the guitar looks quite nice and then you see the cracks

Oh well its a good thing I'm not Eric Clapton!

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I’m going to let mine sit for a few weeks, since the top layers has been leveled and the under layers can cure more. At some point I’ll experiment with some thinner and a tiny brush, seeping it in the check.

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funny, I worked so hard to get those kind of checks on one of my builds.  It took sessions of in the freezer vs heat gun vs cold air blast from air duster... then you get them accidentally.  Honestly, you could totally leave them and it'd look great but I'd understand the desire to get rid of them.

I was just looking at a tutorial on stew mac regarding this.  There was a gal there who was using lacquer retarder and a fine paint brush to melt 'deep scratches'.  Might be worth a look, just thought I'd mention.

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  • 2 weeks later...

After sanding the top a bit I managed to get a better photo of the cracks. I think they look terrible and I don't think I could pass it off as a relic finish

I've had a go at gouging some of them out and filling with lacquer but that doesn't work. I would need that stuff in the video that Komodo posted. But there are so many cracks I've decided there are two ways of dealing with it

1) Sand back to wood and respray, or

2) Re-spray and don't polish (You don't notice the cracks with a bit of orange peel on the surface)

At this point of time I'm going with option 2 because the top is too thin to sand back to wood and make it even thinner, and its a lot of work

436562438_IMG_6125MyEScrackedlacquercopy.thumb.jpg.6606aaf8f9cc64d7974484372e64a262.jpg

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Do you have any blush remover? Like Behlen Jet Spray? It does a fairly aggressive remelt. You might be well served to spray it with that or even lacquer thinner prior to respraying. The object would be for the solvent to wick into the cracks and begin the process of melting themselves together under the new layers a lacquer.

The question remains as to what caused the cracking? It almost looks like there was some physical flexing around the f-hole. I've cause some cracking by screwing a screw in too tight. If it was something physical you can avoid that and not worry about more cracks. If it was something else, the risk of future cracking may still be with you.

SR

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12 minutes ago, ScottR said:

It almost looks like there was some physical flexing around the f-hole.

Adding to that the sudden drop in temperature mentioned higher above I'm tempted to guess that the inside of the top has swelled by condensation as there's no finish there (or is there?). For that reason laminated table tops have one layer of paper laminated on the bottom side. Problem is, how to apply any paint in the inside at this stage.

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47 minutes ago, ScottR said:

Do you have any blush remover?.....

The question remains as to what caused the cracking? It almost looks like there was some physical flexing around the f-hole

25 minutes ago, Bizman62 said:

Adding to that the sudden drop in temperature........

Haven't got any blush remover but I thought thinners would do some melting, well I thought a fresh coat of lacquer would do that but it obviously didn't, so I will take you up on your suggestion of spraying thinners first

What I intend to do is sand it back as thin as possible without reaching bare wood (a bit tricky) then spray with thinners before lacquering

Yes I think it may have been a combination of temperature drop and applying too much pressure when sanding and polishing. Something that has occurred to me from all this is I need more light on the subject while working. The reason I sanded with too much pressure in that area is because I couldn't see it very well and sanded more than necessary to make sure I'm getting the job done

Thanks for your input guys it makes me feel like there is hope!

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16 minutes ago, Crusader said:

I need more light on the subject while working

More light or perhaps a pair of (or stronger) spectacles? Or rather both. This morning I noticed I could read the tiny instructions on a glue package outside in direct sunlight with my bare eyes. So light definitely improves your eyesight as there's more contrast. Also at that hour my eyes weren't too tired. Even the colour temperature may have made the difference, it was still on the cold range.

Another thing I've noticed about sanding is that my fingertips get numb, everything starts to feel silky smooth after some time.

Summarized, not only do you need light, you should also be alert, have slept well, use moisturizing drops if you suffer from dry eyes, use magnifying glasses even if you don't need them for reading, take hayfever pills in case of any allergy or even temporary irritation of dust, take a good pause every so often preferably going outside to look at far away objects like clouds to give your eyes a rest. If you're working in natural daylight, morning might be better than late afternoon. As you may have heard night time is the right time to be with the one you love, but why is that? Simply because the warm light makes her look friendlier, softer and even younger by hiding the wrinkles! Don't tell her, though, if you're not going to sleep on the sofa.

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My first question is what type of lacquer was being used? Some types need a plasticizer so when there is any flex it doesn't crack. These appear to be what ScottR implied about flex. Either from actual flex at that location or internal changes due to cold/heat or humidity changes.

Also, did you thin down the lacquer to spray it? If so what type of thinner. A fast/hot thinner can make the finish brittle.

Just my 0.02cents worth.

MK

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Thanks for replies

Last time I sprayed it from beginning I cleaned the surface with Shellite, and thinned the lacquer heaps. I think it was 2 lacquer 1 thinners. The reason for this was to try get a smoother finish off the gun and to compensate for warm weather. So maybe I should not thin. Its Mohawk Lacquer and Reducer 2255 - nothing special

There are only cracks in the top. None on the back which is also quite thin, and the same for the previous Semi-Accoustic that I made which was also sprayed with Mohawk - but not thinned. Cracks are mostly around holes. The top on this ES-137 is Maple and the other one has Qld Maple

Bizman, good one about the wife, I shall keep that In mind if ever I should find one!

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Around holes is where the wood can move the most, hence the back is not affected. Maybe, and just maybe, if you had let the guitar climatize for a longer period before applying the lacquer... Any carving can release tensions even in thicker parts like necks which is why most builders carve the necks to final proportions before fretting. A carved top being only some 5 mm thick is prone to move.

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4 hours ago, Bizman62 said:

...let the guitar climatize for a longer period before applying the lacquer...

Yes I think the problem is in this area because all the other factors are ruled out for various reasons. I keep a guitar indoors until the day I want to spray and then spend all day sanding and setting up the spray gear. I end up spraying in late afternoon then hang it in my small shed where it stays for a couple of weeks. Do you think I should keep it in the shed for a few days before spraying? (instead of indoors)

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16 minutes ago, Crusader said:

Do you think I should keep it in the shed for a few days before spraying? (instead of indoors)

It depends on your shed and possibly also on the season. I'm not too familiar about Australian weather conditions or how they differ in various parts of the country. I guess the best results are achieved when the lacquer could be let dry in the same climate where the guitar is going to be stored. Painting the inside as well might also help as there would be less difference between the inner and outer surfaces. And using wood that has had plenty of time to sort out any tensions. There's a reason why custom shop luthiers try to "salvage" the wood stocks of passed cabinet makers. Wood that has been properly piled for decades doesn't move much with climate changes. - I once met a luthier who had salvaged a few beams of a hundred years old log house. Tight grained guaranteed dry and settled pine for bracing and lining acoustic instruments.

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I think the weather in April and May is ideal for spraying but storing a guitar in a tin garden shed is not ideal in any situation. The variation of temperature from day to night can be a fair bit and I certainly wouldn't want anything out there in a thunderstorm. And by the way apparently we have a Cyclone coming down the coast due to arrive in Perth on Sunday!

Its a bit of a mixed bag here. I've heard of people having relatives over from England in summer and it rained the whole 2 weeks. And then the opposite where people come over in winter and its glorious sunshine. My grandmother used to call this "mid winter summers"

One of my Uni lecturers had a cousin over from New Zealand in the middle of winter. He got up one morning and couldn't find him anywhere in the house. Finally he went out the back and there he is sunbathing on the lawn!

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I forgot about this, I enquired at a guitar repair shop and this is their reply

"Hi Doug,
From what I can see, it is unlikely that you are pushing too hard. These paints have a fair amount of flex and would normally be able to cope with sanding. It may be a contaminant or issue with surface preparation"


So surface preparation is a factor to consider and I did have issues with the ES-137 top and resprayed several times. I may have caused a problem with the surface preparation on it (sanding too fine?) However I have cracks in my other semi accoustic pictured here (I call it the "OSLP") btw there are a lot more cracks than this and they are not all associated with holes. In fact there are none around the volume controls

1974989170_IMG_6202OSLPcrackscopy.thumb.jpg.64882d8f06bbdac9862198e4e9c558a8.jpg

 

So to summarise all my thoughts on this I'm looking for common factors between the two guitars

*Both are semi accoustic - Both have cracks only on top = a clue

*Top material - OSLP Qld Maple, ES-137 Rock Maple = no conclusion

*Holes - Both have cracks no where near holes = no conclusion

*Flexing - OSLP thick top, ES-37 thin top = no conclusion

*Pre-spray Sanding - OSLP to 400, ES-137 to 800 = doubtful possibility

*Colour - OSLP none, ES-137 yellow stain = doubtful

*Type of Lacquer - both sprayed with same brand of lacquer = no conclusion

*Issues with spraying = Bad finish on initial coats on both = no conclusion

*Lacquer thinned - OSLP not thinned, ES-137 was thinned = no conclusion

*Sanding and polishing - OSLP not sanded or polished, ES-137 sand+polish = no conclusion

*Conditions when sprayed - OSLP 8th April 2018 25C degrees, ES-137 11th March 2020 30C degrees = no conclusion

*Spraying - Both sprayed by me (Mr Impatience) - initial coat too thick? = possible reason

*Time when sprayed - OSLP 6:00pm, ES-137 3:51pm - Both late afternoon = possible reason

*Storage - Both stored in little tin shed with no insulation = possible reason

 

So going by the things I have concluded as a possible reason I think I should;

Sand back to wood up to 400, apply stain, wait for good weather, keep guitar overnight in place where will be stored, start spraying in morning with a light coat and let dry for 20 minutes, apply more light coats with intervals and finish by about 10am. Store in ventilated place with good insulation where temperature is constant

 

That's what I would really like to do and if anyone has other comments or suggestions that would be great

Edited by Crusader
re-word conclusion
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That's an impressive list of potential culprits and conclusions!

One thing to add:

The cracks are more or less linear and even adjacent and mostly follow the grain. To me that sounds like movement in the wood rather than an issue with spraying. That may be related to the holes as the inner balance of the wood has changed by removing some of the material. An empty space has no counteracting force! If the initial coat had interfered with the following ones there'd be checking to all directions - something that was discussed as a desired relicing effect in another recent thread.

As nerve wrecking as it is, sanding back and letting the guitar hang on the wall where it sill be store for a year might release all tensions. Playing it is recommendable as it makes the top vibrate. A light protective temporary coat to prevent staining might be good. Actually, for the same result with less effort simply leave the current cracked finish until no new cracks appear, then sand it back and refinish it.

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5 hours ago, Bizman62 said:

....To me that sounds like movement in the wood rather than an issue with spraying...

Okay good theory but what about the other guitar? The top is as thick as a Les Paul but its on a hollow guitar. And it has a crack right down the thickest part of the top, and doesn't meet up with any holes. Very hard to take a photo of that one

...But I like y0ur thinking "just leave it" I want to get it strung up and play the confounded thing!

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2 hours ago, Crusader said:

what about the other guitar? The top is as thick as a Les Paul but its on a hollow guitar.

No matter how thick the top is (within standards) if you have done structural changes like longitudinal holes to it. A big round hole may not be as finicky, possibly because the tensions are affected on a wider area around the sound hole and the change is gradual and symmetric - and an acoustic top has been cut to thickness. Tops carved to an arch are most prone to moving as there's lots of material taken away. A chambered body with a top carved on the outside can also fall into that category as there's no support under heavily carved areas.

Why controller holes are affected on your thinner top may just be reflections of a larger movement.

As a final comment to this pondering, it may well be that the woods you've used haven't been dry enough for a hollow guitar. Kiln dried wood will live for quite some time especially if the climate changes radically. It really takes years in a climate controlled storage and even then you may be less pleasantly surprised.

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Thanks for your explanations, yes it makes sense. It reminds me of something I heard years ago

When they demolished the 100 year-old wool stores in Fremantle they sold off the timber and a guy bought some of the massive Jarrah beams to make pool cues

He cut them into 1 inch square lengths and some of them stayed straight while some of them came out bent and twisted

I can perceive the same principles with carved tops. You’re messing with the natural structure of the wood

I was already thinking along similar lines, as if the timber is under tension, like if it was being bent, or curved. I ruled that out because it’s not being curved, it’s carved. But now I think about it, it all amounts to the same thing

By the way when I read my previous comments I thought it sounded a bit “snappy” Sorry I didn’t intend it that way

Well you’ve convinced me of what I should do and thanks again for your helpfulness

cheers

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  • 1 month later...

Ummm... The water used for wet sanding isn't that much colder than the surface. Even if you had ice cubes in the water it would warm up on the surface.

The more liable culprit is that the moisture gets into the wood from the sides of the holes, making the wood swell and the lacquer crack. Even more so if the wood hasn't thoroughly dried, as it will live more with moisture.

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