Jack374 Posted April 2, 2015 Share Posted April 2, 2015 Afternoon, A couple of hours ago I set up my airbrush as usual outside as it's a nice day, and mixed Humbrol Matt Cote/HMG Enamel Thinners to the consistency of milk. This set up and mix has worked fine for me on two occasions, the most recent was Tuesday. So I started on the fuel tank of a Bachmann '66, and mid way through the first coat I noticed the test spray in the cardboard box had turned brilliant white...so I stopped. Sure enough, the 66's fuel tank was now white: Slight whiting has occurred before with rattle can varnish, but nothing this severe. I thought it might be the sun drying it too quick, so I turned the cardboard 'spray booth' round and resprayed. The whiting immediately went, but returned after around a minute. I really don't know why this has happened, as I did it with some other locos 2 days previously, haven't used the airbrush since, and haven't changed the set up at all. The only slight difference was being outside, as on Tuesday I sprayed in the garage. Any help would be much appreciated, TIA, Jack. Link to post Share on other sites More sharing options...
RMweb Premium Phil Mc Posted April 2, 2015 RMweb Premium Share Posted April 2, 2015 Hi Jack, I once had a similar experience with Phoenix Precision matt varnish, although not as severe as in your pics. The next time I saw their stand at an exhibition I asked what I had done wrong, they told me that the matting agent in the varnish does have a tendency to go white if too much varnish is applied in one go, so very thin coats allowed to dry between applications is the way to go. Luckily for me I was spraying onto some 'Turbot' wagons, so the effect I ended up with didn't look out of place! (I have even deliberately used the same technique since) I tend to thin matt varnish slightly more than other paints/varnishes for spraying, so I can see the model is 'wet' before I've applied too much actual varnish in the mix. HTH. Cheers, Phil. Link to post Share on other sites More sharing options...
Karhedron Posted April 2, 2015 Share Posted April 2, 2015 This is an effect called "blooming" and can occur with any sprayed-on varnish. It happens when moisture in the air gets trapped in the spray and then deposited on the model. The best way to avoid it is to spray only on dry fine days and avoid spraying in the early morning or evening when changing temperature can cause relative humidity to increase. One cure I have heard suggested is to rub olive oil over the affected area and then leave for 24 hours before cleaning it off. I have not tried this method myself but it might be worth a try as it is easier than stripping the model and starting again. Link to post Share on other sites More sharing options...
Jack374 Posted April 2, 2015 Author Share Posted April 2, 2015 Thankyou gents! TBH Iprobably did put too much varnish on and not thin it enough as Phil said. It's also been fairly humid today so that probably didn't help! Ah well, I'll try again tomorrow and see...as for the engine, I suppose I'll have to try re varnishing it and possibly re weather it. Thanks again, Jack. Link to post Share on other sites More sharing options...
Richard Pike Posted April 2, 2015 Share Posted April 2, 2015 Hi Jack, It could be a number of things, firstly a bad batch of varnish, or I suspect it may have been the air temperature outside compared to the varnish temperature, causes an effect known as "blooming" which is basically the chemical make up of the paint/ varnish drying at different times. Link to post Share on other sites More sharing options...
micklner Posted April 2, 2015 Share Posted April 2, 2015 Shake the can for at least two to three minutes .Then warm the can in hot not boiling water for a couple of minutes before another light coat. With luck it will disappear. It is "blooming" as already said. Link to post Share on other sites More sharing options...
Jack374 Posted April 2, 2015 Author Share Posted April 2, 2015 Thanks Richard and Nick, As I said I'll try it again tomorrow and take all of these factors into consideration, like the temperature, mix and coating. Thanks, Jack. Link to post Share on other sites More sharing options...
86902 Posted April 3, 2015 Share Posted April 3, 2015 I had the same trouble a few years ago jack, and only realised after spraying half a dozen royal coach conversions that had took months to build! I found the varnish was old, do you know how long you've had yours? Temperature I'm told can also be a factor with whiteing. Kind regards Bob Link to post Share on other sites More sharing options...
RMweb Premium Dava Posted April 3, 2015 RMweb Premium Share Posted April 3, 2015 I found Humbrol Matt varnish was prone to this but Tamiya was fine esp with warmed cans! Dava Link to post Share on other sites More sharing options...
david.hill64 Posted April 3, 2015 Share Posted April 3, 2015 I had a similar problem: http://www.rmweb.co.uk/community/index.php?/topic/83275-milky-finish-with-satin-varnish/ A hair drier made an improvement but in the end I brushed thinners over the surface and that worked. Good luck! David Link to post Share on other sites More sharing options...
Bristol_Rich Posted April 3, 2015 Share Posted April 3, 2015 I had a similar problem: http://www.rmweb.co.uk/community/index.php?/topic/83275-milky-finish-with-satin-varnish/ A hair drier made an improvement but in the end I brushed thinners over the surface and that worked. Good luck! David I've experienced this and also used thinners on a cotton bud to lightly remove the majority of the bloom. However it can be a blessing in disguise as you can use it to your advantage and be used as a 'highlights' medium for weathering - assuming you are intending to weather! The Z4p loco attached pretty much bloomed all over when I used some matt varnish to tone dull the sprayed finish. It took some time to remove with careful rubbing and subsequent weathering.... its not a total loss! Good luck Link to post Share on other sites More sharing options...
Ben Alder Posted April 3, 2015 Share Posted April 3, 2015 As above with regard to temperature and humidity, but I would suggest trying Army Painter anti shine matt varnish. A wargaming acrylic spray, that I have found goes on very successfully with a clear matt finish with very little application. Never had total success with Humbrol matt varnish, although their colours and primer are fine, but that just may be me. HTH Link to post Share on other sites More sharing options...
Austrag Posted April 3, 2015 Share Posted April 3, 2015 How about putting the wife outside and spraying inside.... Link to post Share on other sites More sharing options...
Theakerr Posted April 3, 2015 Share Posted April 3, 2015 I users Testers matt varnish a lot and have had this happen twice. There 1st time I think/thought I was too close and the second time it was on a brand new can and I put my problem down to not shaking the can enough. On both occasions spraying was done indoors in my basement where temp and humidity are pretty well constant. Link to post Share on other sites More sharing options...
Jack374 Posted April 8, 2015 Author Share Posted April 8, 2015 Cheers people! How about putting the wife outside and spraying inside.... I'm 15. Nuf said. Jack. Link to post Share on other sites More sharing options...
Graham Walters Posted April 8, 2015 Share Posted April 8, 2015 It's a myth that spraying outside on a warm day is better than drying inside, warm air contains more moisture than cold air, if you think about it, it has to be so. Any form of spraying, especially varnish and enamels is best done at a steady temperature, and it's better if the varnish or paint is at the same temperature as the article to be painted. Link to post Share on other sites More sharing options...
micklner Posted April 8, 2015 Share Posted April 8, 2015 It's a myth that spraying outside on a warm day is better than drying inside, warm air contains more moisture than cold air, if you think about it, it has to be so. Any form of spraying, especially varnish and enamels is best done at a steady temperature, and it's better if the varnish or paint is at the same temperature as the article to be painted. Really ? Here is one that says as many do excess moisture in the air. http://www.craftsman-style.info/finishing/048m-varnish.htm Link to post Share on other sites More sharing options...
Scott Posted April 10, 2015 Share Posted April 10, 2015 As someone else said I've had this with Humbrol varnish, a coat of gloss over the top took it away then I changed varnish and its never happened again. Link to post Share on other sites More sharing options...
PenrithBeacon Posted April 12, 2015 Share Posted April 12, 2015 Cheers people! I'm 15. Nuf said. Jack. Wait until Mum goes out. Regards Link to post Share on other sites More sharing options...
Rumblestripe Posted April 12, 2015 Share Posted April 12, 2015 It's a myth that spraying outside on a warm day is better than drying inside, warm air contains more moisture than cold air, if you think about it, it has to be so. Any form of spraying, especially varnish and enamels is best done at a steady temperature, and it's better if the varnish or paint is at the same temperature as the article to be painted. To be absolutely scientific about this, the process is governed by both temperature AND humidity. The problem is caused by atmospheric water condensing because the evaporation of the propellent and carrier in the paint causes the localised temperature on the model to drop causing the water to condense from the atmosphere into the sprayed varnish. This graph (from wikipedia) shows the relationship between temperature and saturation fraction (how much water is in the atmosphere - humidity) So when you spray varnish (or paint for that matter) temperature drops at the point of contact with the model and if the atmosphere is saturated (for that temperature), condensation occurs. Theoretically, spraying at temperatures sub -40 would be perfect as there can be no atmospheric water at that temperature, but other problems would be triggered such as the propellant remaining liquid and not evaporating! But, this is why some of the tips on here like warming the rattle can, or lighter spraying may help. Ultimately though ye cannae change the laws of physics. I've not tried it but I suspect that running a dehumidifier before spraying would probably help? Personally, I'm fed up with spray varnish and these issues and the simple lack of a predictable result and apply using a brush! Link to post Share on other sites More sharing options...
RMweb Premium ColinK Posted April 12, 2015 RMweb Premium Share Posted April 12, 2015 Looks like its been working a china clay train! Link to post Share on other sites More sharing options...
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