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Post by Deleted on Apr 17, 2007 10:29:06 GMT
Here's a tale of woe! ...
Cleaned up the cab and and bonnet of a truck I'm working on, primed and then went looking for a suitable can of spray paint in the stash. Found a colour I liked and sat the can it in a nice tub of warm water ready to spray. Rubbed down the cab and bonnet after priming and washed them, forced dried the parts so that they were nice and warm and after agiting the paint, gave the cab and bonnet their first mist coat coat of paint, followed by a second and then a wet coat, not a bad result so I put it all away to dry and went off to work smiling.
Had a look at the result today and nearly cried. That coat of paint now looks as though there are thousands of tiny air bubbles popping to the surface, and it's coming from below the primer coat.
All I can think of is that there is some contamination from the plastic forcing through the primer and out through the gloss coat, or the paint I was using is out of date, I had it stored from a previous model several months ago.
Golden rule, soak and thoroughly wash each part of the kit before starting construction and then again after construction before painting. At the moment, the cab and bonnet are sitting in a goo of 'Mr Muscle' oven cleaner, I hope I can salvage it, the kit is 30 years old.
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Post by The Hooded Claw on Apr 17, 2007 10:41:04 GMT
How long did you stand the primer coat for before applying the top coat? Sounds like the primer is still degassing. I must admit to using sprayed primer throught the airbrush now instead of Spraycan types as I have had similar issues in the past. You've still got an airbrush havn't you? If you have I suggest Zero One Primer from Steve Hemmings. Try this link: www.hiroboy.com/catalog/product_info.php?cPath=48_61&products_id=1050H
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Post by Deleted on Apr 17, 2007 10:45:50 GMT
Cheers Ian, what time period would you suggest from applying primer coat to applying first top coat?
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Post by The Hooded Claw on Apr 17, 2007 10:57:53 GMT
Ah now you're asking. I leave it as long as possible. Up to 7 days in some cases. I usually have other stuff to do while the body is drying so can leave it ages if nessesary. Same goes for clear coat before polishing.
H
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Post by The Detail Police on Apr 17, 2007 16:11:12 GMT
Golden rule, soak and thoroughly wash each part of the kit before starting construction and then again after construction before painting. In general I've never found any need to wash parts before construction. The solvents in plastic cement/liquid glue will cut through any residues. I only wash and clean before painting or before using Milliput filler. In my experience rushing things is the cause of painting problems. Pre heating and forced drying are things I would always avoid. You need to ensure that the primer type is appropriate for the top coat and then follow the paint manufacturer's instructions on the intervals before re-coating. You did do that, didn't you?
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Post by The Detail Police on Apr 17, 2007 16:15:10 GMT
One other question: why did you use a primer?
I regard them as a complete waste of time - unless they have some special property like anti-corrosion. I never use them (on plastic); not even with Alclad and I still get great results.
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Post by chadders on Apr 17, 2007 17:29:22 GMT
The primer tends to give the part a nice even base onto which the top coat is applied. This is especially so if a gloss coat is required. If a part for example has got some form of filler on it the gloss coat will seep into the filler creating a dull/matt patch on the part, however if the part has been primed prior to the top coat, the primer will seep into the filler so that the gloss coat will etain its shine. Primer also gives you the option to rectify any inperfections on the part prior to commiting to a top coat.
Oh, and Nick.....I'm with Ian.........a week is about right. When I used to build cars I would give the primer about 5 days, then polish it back with an old peice of denim, and leave for another couple of days just in case the poilishing back had caused some un-cured paint to be discovered. If this had happened then the results would be similar to waht you have had happen to you. I must admit, its absolutly gutting, and one of the reasons that i stopped building cars. You can hide you mistakes a lot easier on a small scale aircraft!!
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Post by Deleted on Apr 17, 2007 21:44:12 GMT
I've had a go at cutting back the paint on the cab and bonnet of the truck but eventually I resorted to Mr Muscle which seems to have gone asleep. So, the truck will be consigned to the 'Previous Ideas' department, I need a cab for a project which has been abused, looks like I've found it. That's what I like about this hobby, nothing is wasted.
DP ... I always use primer for the reasons Chadders offered, it covers a multitude of sins and gives a base for the gloss coat, and yes, you're probably correct, the problem is all down to lack of preparation and being impatient.
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Post by The Detail Police on Apr 18, 2007 8:13:27 GMT
I stand by my claim that there is generally no need for a primer. If a pre-finishing coat of paint is needed (e.g. to reveal small defects or to seal minor porosity) then use the same paint as you plan for the top coat. Let this dry fully and then sand/buff as necessary. Then apply the top coat. You can still get a superb finish and you won't have to worry about paint incompatibility.
This works for Aeromaster acrylics, Humbrol enamels, Halford's cellulose car paint and Alclad. I've not tried other paints.
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Post by Deleted on Apr 18, 2007 8:33:38 GMT
I stand by my claim that there is generally no need for a primer. Hmmm! ... let's agree to disagree shall we DP? ... each to their own eh? ... Incidentally, the paint, both primer and top coat were Halfords products although both cans were a couple of years old and had been stored in a cool, dry workshop. However, never had a problem before with this brand and will replace both cans and try again.
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Post by kiwichappers on Apr 19, 2007 10:38:36 GMT
Nick, You might like to take a dip in a synthetic brake fluid. I have used this in the past with good results as it will attack the paint but leaves the polystyrene alone, marvellous!. The preferred potion is Castrol Response DOT 4 although any one conforming to ISO 4925 spec would probably do given the usual caveat of a discreet test. I would particularly advise a test as there may be a reaction between the residue of Mr. Muscle and the brake fluid.
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Post by typhoon on Apr 19, 2007 11:41:02 GMT
Hi Nick,
Fairy Power Spray can sometimes work where Mr Muscle fears to tread - and its a bit more user friendly than oven cleaner or brake fluid.
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Post by sanguin on Apr 19, 2007 22:31:29 GMT
Hi Nick, Fairy Power Spray can sometimes work where Mr Muscle fears to tread - and its a bit more user friendly than oven cleaner or brake fluid. Personal recent experience. Mr Muscle plus stainless steel sink plus toothbrush plus inadequate clearup afterwards equals domestic grief. Perhaps Fairy Power will placate the modern housewife? Sanguin the senseless
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Post by Deleted on Apr 20, 2007 20:48:02 GMT
Fairy Power Spray can sometimes work where Mr Muscle fears to tread - and its a bit more user friendly than oven cleaner or brake fluid. Ah ... got some of that, wait til Mrs Gromit is out and I'll give it a whirl.
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Post by typhoon on Apr 21, 2007 11:30:36 GMT
Hi Nick, The usual terms apply - if the Fairy Power spray doesn't work and Mrs. Gromit gets upset and comes after me, then I shall deny all knowledge - of everything and anything (not that I have a lot of knowledge to forget in the first place)!!! If it works (and I hope it does) then I shall immediately be round for tea and medals!
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