Humbrol Clear, crazy paving effect in a bottle

[Duncan B]

Why did I use Humbrol Clear to gloss coat my latest kits, I knew there was something about the stuff? Now I have 2x crazy paved Bf109's that have taken absolutely ages to get to the decaling stage. I can't blame the paint underneath not being fully cured as they were painted over 2 months ago. I only applied a single thin coat by brush and it has left a lovely shiny but very crazed surface.

Any tips on how to remove the stuff without destroying the paint underneath or failing that how to seal the stuff without causing more damage?

Duncan B

[Black Knight]

Hard to give advice on this. The new Humbrol Clear is supposed to be acrylic. You could try using an alcohol such as meths, on a cotton wool ball to soften and wipe the surface. Don't use too much or rub too hard otherwise you might affect the main coloured paint.

[steve4428]

I had a look at my newly Kleared Hawk and have noticed very fine crazing when I held the model up to the sunlight! I also only used a very small amount applied by brush, over Humbrol enamels in my case, anyone know if this is the norm????

[Black Knight]

Humbrol Clear? - Yes, its the norm. They use a very volatile carrier which reacts with all the other paints.

[steve4428]

It's the first time I have noticed the crazing effect, even though I have used it before on other kits!!

[Beardie]

I don't know if this is the same thing but I had something similar to this happen in the past when I was doing some custom painting on motorbikes and guitars. I used traditional nitrocellulose paints for the colour work but then used an automotive Acrylic clear coat over the top as I couldn't find any suitable clear for Nitro cellulose and had wild crazing everywhere. Since then I have never used acrylic over anything else but acrylic. I use enamels and always coat with humbrol clear enamel varnish.

If your clear is over enamel you should be able to remove it with alcohol as alcohol shouldn't have any negative effects on the enamel.

[Duncan B]

I applied the Clear over acrylics, Mr Hobby in fact. The real annoying thing is that I tried it on my paint mule first which had only been painted with the same paints the day before and got no reaction what so ever so felt safe to go for it over the models that had been painted a few months ago, go figure?

I've checked back through my previous builds and found that I've used the same bottle of Humbrol Clear once before on another kit that had also been painted with acrylics and had no reaction at all. Dangerous stuff if it is this unpredictable, I think I'll just ditch the bottle to be on the safe side.

Duncan B

[Beardie]

Does Humbrol clear dissolve Humbrol Clear the way that Klear does? Maybe it is worth trying to give the models a reasonably liberal further coat of clear, I would suggest keeping the models reasonably cool while they dry as I am guessing that the crazing is caused by the clear shrinking as it dries too quickly, possibly the coat was too thin and dried too quickly. All the above is only a guess and I could well be wrong.

[Duncan B]

That is an interesting thought, I might have a wee test on the paint mule. It does appear though that the crazing is worst where the Clear went on thickest, i.e. in corners and joints.

Duncan B

[Mike]

My first idea would be to lightly sand it back to get rid of the worst of it, then apply some more clear by airbrush in an attempt to level things off, without filling all the panel lines - a very fine line to tread. Other than that, I think you've going to have to strip her, a thing that I've happily so far never had to countenance, despite a few close shaves

[Beardie]

Hmmm glad I use Enamels. Just been doing a little research into acrylic varnishes. According to the website for Golden Artists Acrylics ( A well regarded artists paint manufacturer in the US) all acrylics craze and they also state that it is "too thick" a coat that will craze the worst and apparently drying times affect the degree of crazing. Guess I overdid the clear coat when I was customising and I definitely shouldn't have heat cured it.

Edited June 1, 2015 by Beardie

[lesliegl]

Hi I've only used it once on a 1/35Italeri truck shelter which I did up in Nato camo using 1 Mr Hobby... 1 Tamiya and 1 Revell..all acrylics.. I applied it with a airbrush and it came up great..took a while to dry but its a hard durable finish with no crackling..

Leslie

[davepb]

Had this happen to me after finishing a Maltese Islander conversion.

[Duncan B]

Saved by the grace of Mr Color! I've just sprayed a coat of Mr Color flat over the offending patio and it appears to have covered most of the crazing and as an extra bonus hasn't caused the Humbrol Clear to react either.

Humbrol Clear will now be relegated to the waste bin and never bought again.

Duncan B

[chrismac60]

Ditto

[Black Knight]

Saved by the grace of Mr Color! I've just sprayed a coat of Mr Color flat over the offending patio and it appears to have covered most of the crazing and as an extra bonus hasn't caused the Humbrol Clear to react either.

Humbrol Clear will now be relegated to the waste bin and never bought again.

Duncan B

Did you do any prep or remedial work first?

[Mike]

Hmmm glad I use Enamels. Just been doing a little research into acrylic varnishes. According to the website for Golden Artists Acrylics ( A well regarded artists paint manufacturer in the US) all acrylics craze and they also state that it is "too thick" a coat that will craze the worst and apparently drying times affect the degree of crazing. Guess I overdid the clear coat when I was customising and I definitely shouldn't have heat cured it.

We're not (generally) using artists' acrylics here, and that blanket statement based on "something you heard" is somewhat misleading. I've been using various acrylic varnishes and paints since before Britmodeller was a twinkle in my eye (8+ years ago), and never once had them craze. That sort of mis-information from a die-hard enamel user isn't very helpful

Saved by the grace of Mr Color! I've just sprayed a coat of Mr Color flat over the offending patio and it appears to have covered most of the crazing and as an extra bonus hasn't caused the Humbrol Clear to react either.

Humbrol Clear will now be relegated to the waste bin and never bought again.

Duncan B

Lots of people (AFAIK) use Humbrol Clear with no problems though, so it can't be all bad. I would still be interested to know how it happened, even just to save others from suffering the same thing.

[Shane]

I applied the Clear over acrylics, Mr Hobby in fact. The real annoying thing is that I tried it on my paint mule first which had only been painted with the same paints the day before and got no reaction what so ever so felt safe to go for it over the models that had been painted a few months ago, go figure?

Duncan B

In my experience Gunze acrylics (NOT talking about their lacquers here) are highly likely to cure further for between 5 days and a month after painting depending on the weather, paint thickness and *particularly* if the surface finish is gloss.

Bear in mind that I live in Brisbane and cold is never a cause of slow curing.

The Gunze paint will be touch dry, having outgassed, but the chemical linking that completes curing will take longer. As the paint cures under a now dry clear coat, it shrinks and cracks the topcoat. I have had this happen with Tamiya, Vallejo and even Gunze acrylic clears. I have also had it happen with Future, but only after brush painting it on.

The problem is somewhat reduced by using lacquer thinner with the Gunze acrylics, which seems to speed up curing. And it's dramatically worsened by brushing the clear coat which makes it thicker and more likely to craze if the substrate shrinks

BTW, the slow curing is also the reason you will read of Gunze acrylic users having their apparently dry paint marked by Tamiya tape. In that case the glossier the paint, the worse the effect.

Incidentally, only one model was harmed in learning this. After that happened I started a three month experiment, so the results are rather more laboratory than kitchen table. And I have never had it happen with Airfix Clear, possibly because I have only used it over enamel which has dried for at least four days - your experience says that I have been wise to wait until I have time to test it.

Shane

[Mike]

Nice one Shane - so the prime suspect is incomplete and extended curing? Sounds reasonable

[Black Knight]

I used the Humbrol Clear when it first came out. I could smell the carrier very strongly. Original Klear would be touch dry in about 5 minutes at my desk. Humbrol Clear was drying faster than that. It was the carrier evaporating at a rate of knots. This led to crazy paving on my model. Actually a couple of models.

It is the rapid drying which causes the crazing; too much carrier evaporates off quickly and the main stuff [whats it called?] contracts, it doesnt have time to flow out into one smooth sheet of covering.

Crazy paving caused by a lower layer drying out faster than the top coat is noticeable if the crazing goes into that lower layer too.

[Duncan B]

For clarity (pun intended) I'll elaborate on what happened and when as I'd like to be able to a): not dis Humbrol unnecessarily and : not bin a product that is actually fit for purpose if at all possible.

To recap, the 2 models in question have been in build since this time last year (yes I normally build that slowly!). All the filling, priming etc was completed probably 6 months ago using various Gunze products ( Dissolved Putty, Mr Surfacer) and Tamiya rattle can primer decanted and sprayed through the airbrush then polished to a smooth surface.

The top coats were applied 3-4 months ago using Mr Hobby Aqueous acrylics for the top colours and Mr Color for the RLM 76 on the bottom all thinned with Mr Color Self Levelling thinners, all airbrushed of course. Last week I decided to change my usual process slightly and use Humbrol Clear instead of my usual Gunze clear coats and to try brushing the stuff on. Before going straight to the models I trailed the Clear on a test mule that had been painted with the same paints only a few days before, reasoning that if it didn't react with fresh paint my 4 month old paint would be fine. The trial went fine with only one thin brush coat applied I had a good enough surface for decaling onto so straight onto the models. One thin brush coat was applied to the models and then set aside. The next day when I checked on the kits I noticed that I had crazing, particularly on the areas where the clear coat was ever so slightly thicker. We're not talking Grand Canyon rifts here but still obvious crazing that any wash would highlight.

Lots of muttering later and after seeking advice on here (thanks for taking the time to respond folks) i decided that I just needed to cut my loses and get these things off the bench so I decided to plough on with the final matt coat using Mr Hobby Matt Clear thinned with Self Levelling thinners. Both the models and the test mule appear to be fine after application with no reaction and the crazing is less evident (not up to show standard but will be fine for my cabinet).

If the top coats degassing was the problem then I would expect that the test mule would have suffered rather than the models as it was only painted a few days before application. I think that the problem was more likely due to the application by brush, even though I was very careful to apply a thin coat and Humbrol state that it can be brushed on. However the only other time I've used it I sprayed it on and had no problem.

The lessons are that a): if you have a working system don't change it unless you are prepared to ruin months of work. : Testing new products on a test mule is all well and good but still doesn't guarantee that those results will be transferred to the models and c): don't panic when it all goes wrong, take a timeout and seek advice.

Thanks again to everyone who offered advice and possible explanations and I hope that this thread will be helpful to others.

Duncan B

[Beardie]

Mike, I was not trying to "do down" acrylics simply stating what I had found in my attempts to research the problem, what I said was the result of having a troll (Not that kind of "troll" ) around the internet to try and find out what causes crazing as I have always wondered, in regard of my own experiences of the phenomenon, what causes it. I found that when doing custom airbrush work in the past it nearly always happened when the base colour was an oil based or nitro-cellulose type with an acrylic clearcoat. According to some scientific articles I read it is the nature of the acrylic polymer (something which it apparenty has in common with pottery glazes and other polymers that they will craze) The degree of crazing can be microscopic or clearly visible, have a read at the Wikipedia entry on "crazing" http://en.wikipedia.org/wiki/Crazing Obviously the company I quoted have an interest in promoting their own product which they claim has been developed to minimize the effects of crazing but I presume that the scientific basis for their claims must have some grounding.

I didn't intend to denigrate acrylic products although I do wonder whether they should be used over oil based enamels as I am pretty sure that drying and shrinkage are different between the two and liable to cause stressing in the finish. In my training as an artist I was always taught that oil could go over acrylic but acrylic shouldn't be used over oil.

Anyways my apologies to any Acrylic users I may have offended. I make a personal choice to use only Humbrol Enamels for all my model colouring requirements but that is not to say I have anything against acrylic or any other type of paint/lacquer.

Edited June 5, 2015 by Beardie

[mirageiv]

Duncan sorry to hear about your humbrol clear problems, heard a few issues with it including decal compatibility. If I may, I have tried numerous gloss coats and have found Revell Number 1 tinlet (not acrylic), mixed with Mr.color thinner and a few drops of Rustins Dryers gives a very hard, very glossy (no compatibility problems so far sprayed over tamiya/xtracolor/humbrol acrylics) and dries pretty darn quick with the added dryers.

I have tried pretty much all the gloss coats you can think of but that is my winning recipe atm, just my two cents

David.

Additionally if you use any enamels, I mix it into the paint and that totally avoids the necessary decal gloss phase.

[plasmahal]

I have only had the crazing issue recently when exclusivity using Mr hobby Aqueous acrylics. After a few days to cure a couple of light coats of klear/pledge via airbrush resulted in crazing the next day. Not easy to see from these photos but:

Never had an issues with Tamiya but the mr hobby paints are nice to work with just long curing time.

It has been suggested to me to try alclad aqua gloss over mr hobby. Yet to try that.

[Duncan B]

Plasmahal, that looks very much like the crazing I had although in some places it was a little worse. Thanks for posting that photo.

David (mirageiv), my favourite gloss is Mr Color's GX100 Super Clear 2, which comes in a slightly larger pot than their paint or Mr Hobby's Mr Super Clear UV Cut which comes in an aerosol but I decant into a small pot for airbrushing. Both usually only need a single coat and dry super glossy and rock hard and of course are totally compatible with the Gunze paint range which I use 90% of the time.

Beardie, my LP's and ES335 are Nitro lacquered and I've heard horror stories of the foam on guitar stands reacting with the finish and ruining it so it is a bit of a worry.

Duncan B