Varnish cracking possible reasons and solutions

[Beardie]

Hi all,

 

Over the years I have suffered now and then from varnish cracking and crazing and I think I might have figured out the reason and solution.

In the past I have put this down to incompatability of paint with varnish, poor quality varnish and various other reasons but now I think that I knew the real reason all along and never made the connection until I recently returned to painting in oils on canvas.

Put simply in oil painting the major reason for crazing of a finished oil painting is applying the varnish too soon after painting. The reason is that, if the paint isn't thoroughly cured, it will continue to move/shrink until the drying/curing process is finished and the varnish which dries cosiderably quicker will craze as it doesn't have the flexibility to stretch as the underlying paint dries.

 

This will be a particular issue with oil based enamels and thick layers or multiple coats of paint which could take weeks or even months to thoroughly cure. I think that, for myself in future I will be leaving my finished models for a period of approximately three months (in the display case) before applying varnish.

[dreadeddrew]

Hmmm.......food for thought,thanks for that Beardie. Could I suggest you put "Varnish By...." stickers on them so you don't forget??

But then maybe your grey matter isn't as......um?.....um?................forgetful!!! as mine.

Andrew

[Beardie]

Hah I Would not say that my grey matter is very.....ummmm....good, it is more like grey mush and you raise a very good point. I think I might get myself a wee notebook and keep records of completion dates so I know the earliest date for varnishing.

 

I actually suffered crazing years ago when I resprayed full size motorcycles and guitars. I never made a connection as I had sprayed metallics, then given the bodywork a day or two of good warm conditions before lacquering with clear acrylic automotive lacquer thinking that these rapid drying paints would have been fully cured. At the time I couldn't figure out why it crazed but now, looking back, I know that I gave these pretty heavy coats of paint and only gave it a day or two before lacquering. The bikes were done with automotive spray paints and the guitars were done with 'Auto Air' acrylics so it was two different types of paints and the same results. I am guessing that, if you use acrylics the time frame for varnishing won't be nearly as long as with oil based enamels but I reckon at least a week or two would be advisable for them.

[Caerbannog]

So far I was lucky and just one model crazed. Though I doubt for the reasons which are descried above. The varnish did not crack but looks like melted. Quite bizzare ad no clue how it happend. It really looks as if it got too hot. But I cannot say for sure as I cannot say exactly when this happened. I only realized one day when the damage was done.

Still your considerations are very plausible and will reduce the risk of cracking varnish. Just take care to use a very good masking tape on areas which are to be protected from varnish overspray. Or remove the mask and remask for varnishing.

Sadly (at least for me) your suggestion will also reduce the chance to finish a GB in the given time as well ;-)