smart51
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| posted on 10/3/11 at 09:01 PM |
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Paint reaction - please advise
My Suzuki Cappuccino has had a hard winter tucked up in the garage and now I'm getting it out for the summer and I've found a pair of
small rust bubbles near the rear arches. No problem, I thought. I've sanded it back a little and treated with rust converter and today I
sprayed on some filler primer. It's a Halfords aerosol of the sort I use all the time - normally without a problem. This time, before the
paint has even dried, cracks started to appear in the new paint. I've wiped it off and it has softened the 17 year old colour beneath. What do
I need to do to clean the mess up so it takes the new paint?
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markie t
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| posted on 10/3/11 at 09:16 PM |
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The reason for the reaction is that the solvent/thinners in the primer has soaked through the original paint which then softens it and gets underneath
and lifts it causing cracks/wrinkles, this is generally caused by putting the primer on too heavy. You will need to let the primer completely dry out
then sand the area that has reacted untill smooth, then re-apply the primer in light coats to prevent the same thing happening again (a heatgun or
hairdryer is also useful to speed the drying process between coats) just take your time and dont rush it, give it a good 20 mins to dry after each
coat and it should be fine.
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tilly819
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| posted on 10/3/11 at 10:30 PM |
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there is another possible cause as well you may find that the old paint is cellulose and the rattle can is synthetic, these two are awful for reacting
together, if the problem persists rub it right back and apply a coat of "barcoat" made by upol there are others about normally advertised
as isolators, since it is not the whole panel you are painting you will have to be careful with the top coat as well.
tilly
F20C Haynes roadster 440 BHP/Tonne www.youtube.com/handmadeextreme
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blakep82
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| posted on 10/3/11 at 11:04 PM |
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i've sprayed cellulose over halfords can primers plenty of times and its been fine? ^
________________________
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don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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austin man
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| posted on 10/3/11 at 11:13 PM |
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Dry and warm the area up slighty, when using cans of paint I genneraly shake them as prescribed then place in a bowl of hot water, leve for 5 minutes
than shake again and apply the pressure increases so make sure you keep a good distance away, Lighter coats are better andleave ample time to dry
before next coats
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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tilly819
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| posted on 10/3/11 at 11:21 PM |
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quote:
Originally posted by blakep82
i've sprayed cellulose over halfords can primers plenty of times and its been fine? ^
its not so much of a problem when its new its more when you have old celulose and you try to repair it with new paint over the top, its not a
certainty but out of all the automotive paints most lightly to react together they are the worst
tilly
F20C Haynes roadster 440 BHP/Tonne www.youtube.com/handmadeextreme
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r1_pete
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| posted on 11/3/11 at 08:02 AM |
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quote:
Originally posted by tilly819
there is another possible cause as well you may find that the old paint is cellulose and the rattle can is synthetic, these two are awful for reacting
together, if the problem persists rub it right back and apply a coat of "barcoat" made by upol there are others about normally advertised
as isolators, since it is not the whole panel you are painting you will have to be careful with the top coat as well.
tilly
Synthetic over cellulose is fine, cellulose over just about any other finish will cause a reaction.
Cellulose is a powerful solvent, there isn't much other than Methyl Ethyl Ketone which is more powerful.
To solve your reaction problems you are best using an etch primer, this will not attack the existing paint, but will bond well to it and any bare
metal. Barrier coats do not bond to metal. The original finish on your car is more than likely acrylic.
[Edited on 11/3/11 by r1_pete]
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stevebubs
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| posted on 13/3/11 at 07:19 PM |
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IME, tf it's the Halfords filler-type primer, it's very susceptible to ambient air temperature...want it as warm as you can...
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smart51
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| posted on 13/3/11 at 08:05 PM |
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Thanks everyone. I've been away for the weekend so its been sat in the garage for a few days to dry off. I've dry sanded it and put a
very thin coat on. We'll see what it looks like tomorrow. Sadly, there's not much I can do about the ambient temperature. Does warming
the can make a difference?
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