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Author Topic: Strange things going on!  (Read 2953 times)

Mark47

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Strange things going on!
« on: November 26, 2010, 06:30:06 PM »

This may work out to be a long winded explanation of what's going on, but I'll try get to the point.

7-9 years ago I got my frigate hull. I dually prepped and painted the hull in this manner.

1,Rubbed hull down with 600 grit wet & dry (with water).
2,Washed hull with warm soapy water (allowed to air dry).
3,Rubbed again with wet & dry 1000 grit (till a perfect smooth painting surface was accomplished).
4,Washed again with soapy water (left to air dry).
5,Because of problems in the past....washed with paint thinners 4-5 times (basically every time the hull had been handled to remove any grease from hands).
6,Painted hull using airbrush (7 or 8 coats per colour until even deep looking coverage achieved, giving at least 2-3 days between coats).
7,Noticed some cracking on underside of hull.
8,Rubbed back to bear hull.
9,Repeated steps 4,5,6. Half way through step 6 airbrush packed in and splattered paint all over hull. Rubbed back with 1000 grit to get flat surface.
10,Mixed paint with thinners for brush painting, completed hull colours.

At this point work, house moves, children came along and the hull was put into loft for storage.

11,7 years later, start building again. No cracking on hull, but hull twisted whilst in storage.
12,New bulkheads added twist eventually sorted, clamp marks all over paint.
13,Rubbed back to bear hull, brush paintinted the first couple of coats (still no airbrush).
14,Hull put aside during two more house moves.
15,Hull rubbed back a little. Steps 4 and 5 repeated again (airbrush bought).
16,Spray painted hull at the weekend Crackling back. >:-o
17,Hull rubbed back to the first couple of coats.
18,Just out of curiosity hull brush painted yesterday and today with the exact same paint and mixed proportions of thinners and paint (the paint that was left in jar from weekend).

What do you know....there is no crackling of paint.

Can anyone explain to me what's happening, because I haven't got a clue.
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Tug-Kenny

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Re: Strange things going on!
« Reply #1 on: November 26, 2010, 08:04:17 PM »


Sounds like a normal week in my workshop.    ok2     I have every sympathy with you and must admit to not really being an expert.

From what I've learnt on Mayhem I would only add the word 'preparation'.  From what you have said so far you have not mentioned primer or undercoat. There is quite a mixture of chemicals now residing on your boat and over the years the formulas have changed so it could be 'back to the beginning' as you are getting a reaction in the mix.


Ken

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Mark47

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Re: Strange things going on!
« Reply #2 on: November 26, 2010, 08:17:12 PM »

Sounds like a normal week in my workshop.    ok2     I have every sympathy with you and must admit to not really being an expert.

From what I've learnt on Mayhem I would only add the word 'preparation'.  From what you have said so far you have not mentioned primer or undercoat. There is quite a mixture of chemicals now residing on your boat and over the years the formulas have changed so it could be 'back to the beginning' as you are getting a reaction in the mix.


Ken



Sorry it was primed after first washes.

I can understand what you are saying about chemicals, but as you can see with the exception of this week the hull was always taken back to bear bones. What I don't get is when sprayed crackling appeared in a specific area. When brush painted it did not. Even when using the same  (exact same) paint that was used with airbrush. {:-{ %% %% %%
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Tug-Kenny

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Re: Strange things going on!
« Reply #3 on: November 26, 2010, 08:30:06 PM »


Yes I saw that and my first thought was the brush applied paint would have been thicker and set before it had time to absorb the under surface.  (maybe    %) )

I swear by Red oxide. It sands smooth and paint does stick it rather well.

hope this helps,

ken

 
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hopeitfloats

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Re: Strange things going on!
« Reply #4 on: November 26, 2010, 08:51:31 PM »

different types of paint can do that. like enamel compatible undercoat with a lacquer top coat or visa versa. it usually cracks all over but not always.
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knoby

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Re: Strange things going on!
« Reply #5 on: November 26, 2010, 08:57:32 PM »

hi mark, is the cracking always at the same points on the hull? can you tell us what types of primer & top coat you are using? what kind of thinners are you using & at what mixing ratio?

when you brush painted the hull was it with the same paint thinned at the same ratio?

sorry for all the questions, but this sounds a little more complicated than usual 7 it would help to know all the facts in order to suggest possible causes.

cheers Glenn
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triumphjon

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Re: Strange things going on!
« Reply #6 on: November 26, 2010, 09:53:29 PM »

sounds like too much paint build up , as this sometimes causes cracking ! what was the shelf life on the paint and thinners that you are using ?
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Mark47

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Re: Strange things going on!
« Reply #7 on: November 26, 2010, 10:54:19 PM »

hi mark, is the cracking always at the same points on the hull?

Yes, exact same place, exact same mark.

can you tell us what types of primer & top coat you are using? what kind of thinners are you using & at what mixing ratio?

Halfords white primer. Humbrol enamels, Humbrol thinners. Mix 60/40 thinners/paint

when you brush painted the hull was it with the same paint thinned at the same ratio?

The exact same. I took the jar off the airbrush, made it air tight to be used again. Saw the crackling and after preporation as mentioned above. Dipped brush in and painted hull. The only thing I done to the paint was shake it again to mix thinners and paint.

The only time I have seen similar marks is when a hull has been popped from the mould and not released properly. I would post a picture, but the hull is fine again after brush painting.
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Mark47

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Re: Strange things going on!
« Reply #8 on: November 26, 2010, 11:07:16 PM »

sounds like too much paint build up , as this sometimes causes cracking ! what was the shelf life on the paint and thinners that you are using ?

All tins were binned encase there was a problem with the paint, after rubbing back to bear bones all new tins were bought on all occasions. Because i thought I could not have done more in the preparation. I never mix paints companies or types. only halfords white primer with humbrol enamels. Next build I will be trying revell.
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Lord Bungle

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Re: Strange things going on!
« Reply #9 on: November 26, 2010, 11:40:12 PM »

could be it was a bit warm in room you put hull in to dry, surface dried off trapping solvents underneath
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triumphjon

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Re: Strange things going on!
« Reply #10 on: November 26, 2010, 11:51:07 PM »

this time of the year im warming my spray cans in a bowl of hot water prior to spraying , i have to paint on the balcony , but then bring the boat indoors to dry . your problem could be the fact that you are using an acrylic primer but then painting over with enamel and getting a reaction of the solvents ! how are you cleaning your model after you have wet flatted between the primer and the next coat ? maybe a little expensive but there is a product used by pro painters thats called panel wipe , its a fast evapourating solvent based cleaner / degreaser , ask a local body shop if they would mind selling you a small amount to try ?  jon
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Mark47

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Re: Strange things going on!
« Reply #11 on: November 27, 2010, 12:21:27 AM »

soapy water (left to air dry) then sometimes thinners if there is lots of sanding dust left behind. I've even went over that again on occasion with soapy water.

Funny you mention pro painters. I've heard of panel wipe. My mate is a spray painter and said enamel over acrylic should be ok, but other way round is a big no, no.

EDIT-Forgot to add he's bamboozled too.
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knoby

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Re: Strange things going on!
« Reply #12 on: November 27, 2010, 04:40:12 AM »

Hi Mark, thanks for  answering my questions. I have been a car painter for 25 years & I'm confused too  %%. I agree enamel over acrylic should be fine. My best guess is that theres a fault in the gel coat at the point where you get your reaction. probably micro pours in the surface. when you clean it with thinners it can attack the gel coat, softening it up & releasing chemicals that could react with your paint. But even as i type that I'm not really convinced, after all its not like you haven't given the hull enough time to cure. i really don't understand why it happens when you spray it but didn't when you brushed it.
personally, i wouldn't ever clean anything with thinners, as its too aggressive, I'd always use spirit wipe or a plastic cleaner ( easy for me to say cos we have gallons of the stuff at work). **** happens sometimes, glad you managed to get it sorted out. sorry i couldn't be of more help
cheers Glenn
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Mark47

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Re: Strange things going on!
« Reply #13 on: November 27, 2010, 05:31:46 AM »

I guess it's going to stay a mistery like the Burmuda triangle. Somethings going on but no one knows what. O0
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essex2visuvesi

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Re: Strange things going on!
« Reply #14 on: November 27, 2010, 09:47:10 AM »

Is there any filler under the affected area?
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Mark47

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Re: Strange things going on!
« Reply #15 on: November 27, 2010, 10:03:34 AM »

Is there any filler under the affected area?

No, not a bit.
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Mark47

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Re: Strange things going on!
« Reply #16 on: November 27, 2010, 10:06:11 AM »

If I had not used the same jar of paint that I used with the airbrush I would have said the thinner mix could be creating the problem. More thinner in mixture creating a reaction. I just don't get it, at all {:-{
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Lord Bungle

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Re: Strange things going on!
« Reply #17 on: November 27, 2010, 07:32:32 PM »

just wondering what grade of wet and dry did you use to rub it down?
it could have been flatting marks from to course a paper, but when you brushed paint on it would fill them.
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nemesis

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Re: Strange things going on!
« Reply #18 on: November 27, 2010, 08:21:05 PM »

Hello, If your hull is that old the excess chemicals (if any) in the gel coat would have gone by now. I always use plastic primer on F/glass followed by the same make of paint. Not so & sos undercoat and so & sos gloss.
 They are all formulated to match one another. Celly is hard & can crack easily, enamel is more flexible, I used enamel without thinning, keeping the airbrush bottle in hot water to lower the viscosity, hope it helps.
                    Nemesis
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