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 Post subject: guide on paint spraying
PostPosted: Thu Jun 11, 2009 9:11 pm 
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my dad did this post on the morris minor website and i though this maybe some help to someone on here, this is a professional guide written by my dad who was a paint sprayer for 22 years

hope it helps
kyle



Spraying synthetic


Introduction
I have noticed recently an interest in spraying synthetic paint, there also seems some confusion as how to spray this type of paint, what is it compatible with?
Synthetic can be sprayed over cellulose and 2 pack paint but not the other way around unless some form of isolator is used first; this is due to the make up of each type of paint. I will try and keep this as easy to read as possible without too much technical jargon, people whishing to try and use synthetic that have never sprayed before might find this informative.

Cellulose
Cellulose is an aggressive paint due to the fact of the amount of thinners needed for the finished application normally mixed 50 parts paint to 50 part cellulose thinners or 1-1. the reason the pressure was 30 to 40 psi was the paint is thicker at 1-1 if you put a lot of thinners in celly you don't need a such a higher pressure , but this can cause its own set of problems to someone thats not used to spraying,spraying thicker paint at such a low pressure can cause its own set of problems, these can come in the form of reduced spray gun fan width, this will make the paint from the gun dryer, stop flowing correctly and it would be slower to apply, even ending with tram lines on the panel and a genral uneven coat on the surface . What i tend to do with celly is to start off with a 1-1 mix and give it 2 all over coats then on each additional coat add more thinners the final coat would be litery a colour coat of thinners

2 pack paint
2 pack has 2 main components 1 is the paint 2 is the hardner. When the hardner is mixed with the paint in the correct ratio usually 2-1 a chemical reaction occurs hardening off the paint. There are also thinners used to help with the flow and thin the mixed paint / hardner, the finished ratio is normally 2-1-10% sometimes 20% thinners
Paint 2
Hardner 1
Thinner 10% or
20%
Again with the make up
Of this paint you cannot spray this over synthetic

Starting off
Firstly look at the vehicle to be painted, what condition is it in? decide what finish you want, just a quick blow over or more of a lasting paint job. The reason I say this is it will all come down to the preparation .If the paint on the vehicle is not in too bad of condition you could just do with a wet flat, or scotch brite pad, rusty areas will require more rougher sanding working to a finer grit and filled if necessary. The other way is to use a Da sander all over using a 180 or 240 grit sanding disc I use this method myself. Please make sure before any rubbing down commences that there is no wax, oil grease or silicon on any body work as this will be rubbed into the scratches and will react to the primer / topcoat.

Spraying primer
I personally use I C I now called nexa fast build primer, this is a commercial vehicle primer that can take all types of paint mentioned above, it can be sprayed over synthetic, it’s a 1pack primer mixed with 1335 thinner in a ratio of 4-1 it also has anti corrosive properties so is an excellent primer for areas that have been broken through while sanding 2 good coats all over left over night to dry. With using the ici primer there is no needs to use etch primer before priming. Only down side to this primer is it’s only available in 5 litre tins, white and grey, same goes for the thinner in 5 litres only
Depending what paint manufacturer you use, check to see what primer / thinner is available for the synthetic top coat you choose.
You also want to ask for a data sheet for the primer and top coat as this gives all the relevant mixing information needed

After primer
A quick dry flat off with 800 wet n dry tack off then ready to paint

Thinning synthetic Top coat

Synthetic can be thinned down 3 ways

1 mixed with a mixing stick thickness depends on individual paint manufacturer
2 by viscosity / flow cup usually ford bs4 thickness as above
3 hot spray application no need for thinners

Spraying synthetic topcoat
Once the correct mixing has been achieved, start on the roof on one side with a semi tack coat not a full wet coat, go to the other side of the roof and do the same that side. Repeat this all over the car starting from the side of the roof you first sprayed including door edges if your doing them inside boot and bonnet if doing them as well keeping the spray gun approximately 12” away from the panel . Once the first tack coat has been applied you can start from the same place you first started from this time with a heaver coat working methodically around the car. One point to remember with synthetic topcoat is it takes longer to dry so it will keep on flowing on the panel for longer so be careful not to over do the wet coat, you can indeed go around the car again if needed, but wait about 10 minutes before going over again .

Spray gun technique
I don’t think there is any one way I can explain this, as every one sprays in there own fashion, except that I don’t spray synthetic any different to 2pk. synthetic its not a hard paint to use
Spray gun pressure
Even with the paint mixed to the correct ratio, you will need a bit more pressure at the gun, as the synthetic will still be thicker than mixed celly. If my memory lets me, celly is sprayed about 30 to 40 psi at the gun, as where synthetic would require around 50 to 60 psi at the gun

Spray gun air cap (outer nozzle)

This all depends on what make of spray gun you are using .I use a devilbiss jga 558
With a no43 air cap for primer and n 86 for top coat. I use this set up for 2 pk as well but this is just my preference

Paint runs and sags
If you are unfortunate to get a run or sag in one or more of the panels don’t panic. If you have spotted this before the paint is dry you can was off the affected area with thinners , do not use cellulose thinners as this will fetch off the primer as well, use the primer thinner or panel wipe , all your aiming to do is to wash off the top coat . Let’s say you had a run on a wing you need to wash off the entire wing being careful not to splash any thinner on any other areas. Leave it over night to dry nib wing with 800 wet and dry mask off whole car tack off wing and respray

Dry runs
Think of synthetic paint as an egg custard, when it’s first sprayed, sort of hard on the outside but runny underneath. Synthetic paint is very much like this as it takes a lot longer to dry so making re-working much more time consuming, you cannot rush re-working synthetic
You can scrape off the run with a flat blade scraper going past the run into sound paint, this will leave a deep groove where the run was, feel with you finger to see if its still tacky, if it is you will have to leave this over night to cure, you could try wet flatting with 400 wet and dry using wet and with soap, but this only just seems to make the paint roll and then you end up with more scratches .so best leave over night to cure after you have scraped off the run, then do as above.

A word to the wise
. You must let synthetic cure over night if you have rubbed into it as the underneath needs to dry. If not the thinners from the newly applied paint will react called crazing and you will be in a worse position than before

Ambient temperature
As synthetic takes longer to dry it is also doesn’t like damp / cold if this happens then a blooming reaction occurs, this is where the paint has a white milky glaze to it . This has happened because the paint hasn’t cured before the temperature dropped. so it will need a wet flat and re spraying

Dirt contamination
Again flat to get rid of contamination then leave over night and respray

Silicon
This is a pain to get rid of as the problem usually lies in the paint underneath
The way I get rid of this is to flat the area and then I use a product called flo-rite this is actually a silicon additive in a very small bottle with a dropper that you mix with the paint just 2 drops in 1 ltr will cure the problem, but you must wash out the gun well and throw away the paint left from the pot, if you had to repaint that area again you must use the flo-rite again


Footnote

Please note!! That most of these situations were delt with in a professional paint shop environment and that is how we delt with each problem that arrived, these ideas can be used in the garage but remember that it will take longer to dry

Well I hope this helps someone out, as it was written for an insight into spraying synthetic paint

By me dustyfog who was a commercial vehicle paint sprayer for 22 years. Many thanks for taking the time to read this article

here is my transit i used to own sprayed in ici synthetic (383) hot sprayed.


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hears my morris i sprayed in 2pk


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 Post subject:
PostPosted: Thu Jun 11, 2009 10:49 pm 
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thanks :D

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PostPosted: Thu Jun 11, 2009 10:53 pm 
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yeah is good info

that minors paint is perfect :shock:


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PostPosted: Thu Jun 11, 2009 10:54 pm 
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elcy95 wrote:
yeah is good info

that minors paint is perfect :shock:


that was done in our garage i can get sum piccys of it b4 paint :D

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PostPosted: Thu Jun 11, 2009 10:56 pm 
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yeah why not would be good to see the transformation.

never thought id be asking for pics of a morris minor :oops: :lol: :lol:


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PostPosted: Thu Jun 11, 2009 11:01 pm 
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hears the before picture :D

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PostPosted: Thu Jun 11, 2009 11:03 pm 
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does this mean that you get a free paint job? :lol: 8)


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PostPosted: Thu Jun 11, 2009 11:04 pm 
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elcy95 wrote:
does this mean that you get a free paint job? :lol: 8)


oh yeh :D just have 2 pay 4 paint :D so i save about £1500 lol although i am greatful for him doing it but if he wouldn't then i'd do it myself (obvs it wouldn't be as good finish) :P

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PostPosted: Fri Jun 12, 2009 11:32 am 
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can a mod make this a sticky please :D

thanks
kyle

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PostPosted: Fri Jun 12, 2009 11:37 am 
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I will move this over to the FAQ, cheers!

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