spraying synthetic paint hints and tips

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dustyfog
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spraying synthetic paint hints and tips

Postby dustyfog » Thu Nov 13, 2008 8:12 pm

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

UPDATE
Flo rite is no longer available
there are two ways to get rid of silicon, one way is to use barcoat, this is a yellow quick drying isolator suitable for all types of paint on older cars. available from the internet or car paint suppliers.
alternatively: you can dry dust coat the primer you are using over the affected area to fill in the silicon craters. You will need to do this several times but make sure the primer is going on dry. Too wet and it will just react to the silicon

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

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.<br>Image<br>
Last edited by dustyfog on Mon Aug 24, 2015 2:25 pm, edited 3 times in total.


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PSL184
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Postby PSL184 » Thu Nov 13, 2008 9:34 pm

Thanks Dusty, very interesting reading....
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Postby bmcecosse » Thu Nov 13, 2008 10:16 pm

Good stuff - bit surprised at the high air pressure quoted. I've always been told to keep the air down to ~ 20 psi for celly - but I do tend to spray it on quite thinly (ie well thinned) - on the basis of many thin coats!
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Dean
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Postby Dean » Fri Nov 14, 2008 1:39 pm

Can a Mod move this to the hints and tips section please.

Dustyfog, thank you for taking the time to prepare this post.
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Kevin
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Postby Kevin » Fri Nov 14, 2008 4:24 pm

All done.
Cheers

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bmcecosse
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Postby bmcecosse » Fri Nov 14, 2008 4:55 pm

I think the idea might be to make it a sticky in the hints/tips section!
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dustyfog
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Postby dustyfog » Fri Nov 14, 2008 7:35 pm

your most welcome chaps n chapettes lol thanks for the kind comments. i enjoyed writing it if i think of any thing else i will add it


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Kevin
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Postby Kevin » Sat Nov 15, 2008 9:17 am

Changed to a sticky due to various requests.
Cheers

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brian
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Re: spraying synthetic paint hints and tips

Postby brian » Thu Apr 01, 2010 1:39 pm

Hi what size of compressor would you suggest,1.5 or 2.0 hp ,and a 24 ltr or 50 ltr tank,cheers Brian


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Re: spraying synthetic paint hints and tips

Postby bmcecosse » Thu Apr 01, 2010 10:13 pm

The bigger the tank - the better! Actually - 50 litres sounds too small for continuous spray use. And - be sure to have the compressor outside - or at least not in the same room you are doing the spraying!
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dustyfog
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Re: spraying synthetic paint hints and tips

Postby dustyfog » Thu Apr 01, 2010 10:39 pm

Hi brian , as a rule of thumb, the bigger the better. there are quite a few factors to consider when buying a compressor for the first time, if you are intending in buying a compressor ,then buy one thats up to the job from the start, that way you have a more versatile piece equiptment, i personally would stay away from small compressors under 3hp motor

insight into buying compressors

1 what do you want it to do.

having a bigger compressor from the start gives you more room to expand.

2 electric motor

personally i would choose nothing under 3 hp single phase with belt drive, belt drive are smoother than direct drive.

3 air tank

nothing below 100 ltr really as the compressor will keep cutting in and out as you demand air from the reciever

4 electric motor/ tank

the compressor output is calculated in hp for the motor and cfm for the tank

cfm means cubic feet per minute
fad means free air delivery. this is the end measurement the compressor will have once the equiptment trigger is pulled

as an example

a 3hp 14 cfm air pump will deliver 9 cfm fad with a 50 ltr tank
a 4hp 18 cfm pump will deliver 14 cfm fad with a 200 ltr tank

so ideally a 3hp electric motor with a 150- 200 ltr tank would be about right

all electric motors are single phase

these type of compressors are rated as industrial equiptment and must have ample electricty supply
usualy running on nothing less than 6mm twin and earth cable, with a rcd fuse rating between 30 -40 amps
you also need a blue 32 amp round 3 pin commando type socket and plug. these do not plug straight into the mains via a normal 3 pin plug as the current drawn on start up will melt the plug

a good source for compressors are machine mart, but this is just my opinion

hope this helps

dustyfog :roll:


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brian
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Re: spraying synthetic paint hints and tips

Postby brian » Thu Apr 01, 2010 11:41 pm

Many thanks,sounds a bit expensive,maybe e-bay will help,thanks ,Brian


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Re: spraying synthetic paint hints and tips

Postby bmcecosse » Fri Apr 02, 2010 11:28 pm

Be wary of buying something with too large a motor - your electrical supply may not cope. I've used a large calor cylinder in the past as an additional receiver (but do make SURE it's protected with a relief valve) , and this gives a huge mass of air so you can spray several panels before the pressure drops too low, even with a small compressor. In fact - I find it best now to just spray ONE panel at a time, and let the fumes subside - otherwise I start to feel ill from the fumes....... And doing it this way my small compressor from Aldi is fine - with no additional receiver. I also only spray outdoors now - on a fine/still day.
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dustyfog
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Re: spraying synthetic paint hints and tips

Postby dustyfog » Thu Apr 08, 2010 10:58 am

i did explain all about electricty supply in the post


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Re: spraying synthetic paint hints and tips

Postby bmcecosse » Fri Apr 09, 2010 8:24 pm

Yes indeed you did - I'm simply amplifying the point! Not many can rig up a suitable supply like that. I think in England you are now not 'allowed' to do your own electrical mods ???
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Re: spraying synthetic paint hints and tips

Postby 1mustard » Sun Jun 13, 2010 3:42 pm

Hi dusty,
good advice you have put on here, i have been painting my car with 2k and have had a few runs and dust in the paintwork, i have flattened these out with 2000 and soap, and flattened the rest of the panel, i was planning on using a fine compound and mopping slowly, clearly i don't want to hit the primer, do you think i would be better using a decent polish and just polishing? also how would you block for example a curved bonnet or front wings, i have no runs in these but they will need to be flattened to match the rest of the car and to lose slight orange peel? any advice would be appreciated.
cheers
Andy

dustyfog
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Re: spraying synthetic paint hints and tips

Postby dustyfog » Mon Jun 14, 2010 9:59 am

Hi Andy,

Q, I have been painting my car with 2k and have had a few runs and dust in the paintwork, i have flattened these out with 2000 and soap, and flattened the rest of the panel, i was planning on using a fine compound and mopping slowly, clearly i don't want to hit the primer, do you think i would be better using a decent polish and just polishing?

A. I personally would respray the panel that has the runs and dirt contamination in it. I would wet flat with 800 down to the primer where the run was, feathering out away from the affected area and flat off the shine on the rest of the panel., secondly when you have runs, flatting and buffing sometimes doesn’t always rectify the problem and in natural daylight the panel can look rippled where the run was because of the shine, the light will reflect high lighting the affected area.

Q how would you block for example a curved bonnet or front wings, i have no runs in these but they will need to be flattened to match the rest of the car and to lose slight orange peel? Any advice would be appreciated.

A. basically you don’t use a block, you use your hand kept flat following the body contours

When colour sanding you need to go over the whole car panel by panel checking for dirt in the panel first with you hand, isolate these dirt contaminated area’s by flatting the dirt out (only that area ) with 1500 or 2000 wet n dry with clean water either with washing up liquid in the bucket of water or a bar of soap n water, drying off each time to see if the dirt has gone.( check flat check flat etc) Once this has been done either by block or hand, then flat the rest of the panel with the same grade wet n dry so the paint gloss has gone you will see the orange peel disappear. Keep water clean, use plenty of lubricant

Buffing
Using compound you use a round sponge type, keep the sponge wet, and dip into clean water, running off the access before putting a small amount of compound to sponge, if you don’t keep the sponge wet it will cause too much friction with the paint and will burnish the top coat

If the painting has been done outside of a proper body shop, then the paint will need to cure for at lease a month, other wise it will damage the top coat

Hope this helps

Cheers dusty
:D


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Re: spraying synthetic paint hints and tips

Postby 1mustard » Mon Jun 14, 2010 7:48 pm

compounded today, used some of your tips, went well, cheers for your help.
its not perfect but is pretty good.
cheers

dustyfog
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Re: spraying synthetic paint hints and tips

Postby dustyfog » Mon Jun 14, 2010 8:55 pm

glad it turned out ok


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Re: spraying synthetic paint hints and tips

Postby kipper » Sat Jan 22, 2011 6:33 pm

Does anyone know the anser to my latest problem ? I have had a convertable now for 3 years - when I bought it in 08 it had recieved a respray ( in 2004) and was living in Bristol - just parked on the street. It always had slight pimples on the bonnet - so small it just resembled dust under the paint - hardly anything. Anyway, this year - we had to store her outside with a cover over her- but with all the snow we experienced etc the pimple condition has become slightly worse. If we had a respray would the pimples ( which I presume are bubbles due to rust - perhaps from a poor respray job in the first place) dbe treated and not re-occur for some tiome - it would really push the price up having 2 new wings and a bonnet! Any advice on this - and a rough guide to what it would cost would help -Ps the condition is still acceptable - but we were wondering about having her made better- there is no visible rust yet just slight "bubbles " under the paint.Thanks again


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