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to prime or not to prime ....

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john melia 108/12/2013 18:18:21
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I asked this question over in the delta thread , but doesnt seem to be any interest over there , so I'll try here ...........

As you can see in this photo , I wasnt very happy with my original paint finish , I sprayed thinned varnish over the red , and the varnish began peeling off like sunburnt skin after a week , so I've rubbed it down , and cut the sig koverall out of the unsheeted areas because the paint started to crack , my question now is ,

 

Can I respray over the surface I have rubbed down , or will I need to prime it all again , its getting resprayed the same colour red . The unsheeted areas are going to be covered in solarfilm .

Would I need etch primer

Edited By john melia 1 on 08/12/2013 18:19:26

Depron Daz08/12/2013 19:59:20
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So long as you have removed all trace of the cracking varnish you should be ok. Go over it with some panel wipe and ensure that it is spotless. The flattened red will be fine IMO, and will make the top coats more vibrant rather than red over grey primer.

Use fine dust coats first just to ensure that the varnish is all gone.

Daz

john stones 108/12/2013 20:05:45
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use red primer first?

give you a nice base to spray finish on

Steve Hargreaves - Moderator08/12/2013 21:04:55
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Couldn't you just cover the whole top surface with heatshrink film or fabric??

Flatten down the red....panel wipe & ensure you get all the dust off & iron on the new covering. Coloured & proofed in one step....thumbs up

john melia 109/12/2013 08:38:55
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steve I was thinking of doing exactly that , but I hate shrink film , how would you approach covering it , in on large bit and cut slots in the covering for the stabs , or multiple bits .

I need to make a decision soon because I'm hoping (weather permitting) to get it flying again at the weekend . I've also pulled the elevons off as I'm going to make them bigger .

Jim Carss09/12/2013 19:15:44
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John,

You need to primer the model so that you have an even base to start with,Red is one of the worst colours for bleeding through,its nearly transparent.

As JS says use a red primer and you will get a result first time.and then the problem is fuel proofing , make sure the proofer is compatible with the paint underneath.

john melia 109/12/2013 19:40:45
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jim I'm using mipa 2 pack paint and mipa 2 pack clear from alpha paints , he guaranteed me the clear once gassed off will be 100% fuel proof .

blew a few coats of red on today and ended up with hundreds of fish eyes , lots of rubbing down yet again tomorrow .

not sure of the cause , I know its due to oil contamination , I didnt use any primer by the way , and this 2 pack covers really well

I'm going back to alpha paints tomorrow to get some panel wipe , yes I know I was told to in the above thread , but thought I might of got away with it.crook

instead I have given myself lots of extra work . hopefully I can cure the fish eye problem , because other than that the finish even without the laquer is superb .

Jim Carss09/12/2013 19:49:10
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John

Fish eyes could be oil or polish of some sort, model need a good wipe down with thinners before you spray

good luck

john melia 109/12/2013 19:58:03
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I wiped it down with cellulose thinners before I started , had the compressor in the same area where I was spraying , maybe it was that .

wonder if I need an isolator on first, will have a word with paul at alpha paints tomorrow.

Bill Brown 309/12/2013 20:17:37
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John, the reason your varnish coat cracked was because it had a different surface tension to the paint beneath it, however, I would agree with Jim to prime it all following a good wipe with thinners or panel wipe, if the fish eyes are caused by silicone polish you may never get rid in which case try a drop of starchem paint additive code PA-1 or other equivalent anti silicone drops.

Good Luck chap yes

Jim Carss10/12/2013 09:41:45
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John

Just thinking,are you using cellulose thinners to thin your 2pack,if you are then the thinners could be finding little spots of oil based varnish thats soaked into the wood and giving you the fish eyes.

As you say maybe a barrier coat is the answer

BB3 once sprayed a wing on a car and got a horrible reaction to the paint,stupid boy had wiped down the finished primer coat with a yellow duster that had been used for polishing furniture, lesson learnt

john melia 110/12/2013 15:29:45
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well this isnt goin good I'm afraid , went back down to alpha paints to see paul after my second attempt with panel wipe and scotch cloth failed , he gave me a small tin of isolater free of charge and said if this doesnt work then there is no other options .

after rubbing it all down again , panel wiping , and giving it a gomover with the scotch cloth just before spraying , I applied the isolator , now it did work up to a point , but even with this fish eyes were still evident , nowhere near as many , but still there nontheless .

Unfortunately I think once the model has been flown , it is nigh on impossible to eradicate all traces of the fuel residue . Believe me I have tried crook

so I suppose the motto of this story is to make sure the job is done properly in the first place before the model ever sees an engine

john melia 110/12/2013 15:36:39
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This is it with the isolator applied , the marks on the right are where I'm carefully sanding out the fisheyes with 600 wet n dry

Edited By john melia 1 on 10/12/2013 15:43:26

Edited By john melia 1 on 10/12/2013 15:44:43

Chris Bott - Moderator10/12/2013 15:42:44
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I think some nice profilm is the answer now John.

The more paint you can get off the better. When sticking film to a painted surface, air bubbles can get trapped because it isn't porous like balsa.

One other possibility might well be to use protrim. This has a tacky, self adhesive backing, so could at least be stuck on and smoothed out before the Iron is applied to fix it properly. Not that I've tried it over paint myself.

Chris Bott - Moderator10/12/2013 16:05:24
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Now I've seen a pic, that isolator looks OK. Well, as far as you can tell in a photo.

What are you planning to cover the open part with?

john melia 110/12/2013 16:16:24
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chris I was thinking of using solarfilm , just the stuff I've got leftover from the jodel build

Glyn R10/12/2013 16:34:44
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Posted by john melia 1 on 10/12/2013 16:16:24:

chris I was thinking of using solarfilm , just the stuff I've got leftover from the jodel build

I have used Solafilm to cover a glassed and painted model. Took me 2 days to get it off because of the bubbles its almost impossible to apply without bubbles once they are there they cannot escape. I could have spent hours with a pin letting the air out but decided removal and repaint the best option.

john melia 110/12/2013 17:18:51
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its just for the open areas on the wings glyn

Bill Brown 310/12/2013 19:50:06
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Jim, think again about who the guy was that sprayed the car wing because it certainly was not me, I managed a car body shop for 8 years during my employment and a lint laden polishing cloth would be my last choice to wipe down with prior to paint.angry

john melia 111/12/2013 08:25:36
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Posted by Chris Bott - Moderator on 10/12/2013 15:42:44:

I think some nice profilm is the answer now John.

The more paint you can get off the better. When sticking film to a painted surface, air bubbles can get trapped because it isn't porous like balsa.

One other possibility might well be to use protrim. This has a tacky, self adhesive backing, so could at least be stuck on and smoothed out before the Iron is applied to fix it properly. Not that I've tried it over paint myself.

Chris the protrim is only 9.5cms wide .

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