12 replies to this topic

[biker1981]

Just after some advice really.

I've been out and completely sprayed my mini from bare metal....Acid etch, high build, and finally celly.

It looks ok but feel quite rough in places as if a lot of overspray dust has landed. Also I always struggle painting the roof and have zebra style lines.... All blue just hard to keep the "wet mark" going.

Any ways I would like to give it another coat... This time reducing the gun pressure and giving a better paint to air ratio.

How best to do this.... Do I need To wet sand this all again? If I just wet sanded it the rough bits would it buff up smooth ... I have plenty of paint on any advice appreciated

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[Daz1968]

If you are going to over paint then I would flat with p800 wet, but please reconsider dropping pressure it usually has opposite effect and causes more orange peel. You may need to up pressure and change technique maybe even add more thinner to the paint

[biker1981]

Thanks for the advice... I do think it atomising to much as I didn't set the compressor it's the highest it goes

[Broomer]

If you put the celly on thick enough I would leave it and at a later date when it's dry and I mean dry (few weeks to months) then work your way over it with the compounds.

I'm not an expert but I did paint mine in celly and used the same approach. Some areas were very coarse to touch, mainly the horizontal surfaces where paint dust landed in wet paint.

[miniseven61]

If you have sufficient paint on the car you could flat with 1200 wet and dry then g7, then you can Tcut to bring the shine back up then finish with wax. If you decide to go the repaint route, flat all over with 800 w&d with a little ordinary tablet hand soap, this stops the paper clogging, wash and clean all the residue then spray 4 coats leaving enough time in between coats to flash off, the paint mix should be about 50/50 paint and thinners, but use a good quality topcoat thinner as this will dry slower and flow better when drying, also it will blend better when you have been all round the car and reach the point where you started, it should not then leave a rough edge. When you do the initial flatting make sure you remove all the rough bits as these could show up again when you re-coat.  After a couple of days you an then g7 and Tcut to bring up the shine, if you have any runs or blemishes these can be done with 1200 w&d with a little soap.if you  rub through it can locally painted in. It is a far bit of work but satisfying when it is done.

[Stu.]

As above. When spraying celly you need to colour sand and polish afterwards. You won't get an acceptable finish straight from the gun.

[minimissions]

Colour sanding is a must, this should give the finish that you want.

[spraybeater]

Back when I served my apprenticeship  we  used to flat and final coat with what was called a Piss coat

about 2thirds slow thinners , when dry it was then Burnished with Brasso and then polished with Simoniz

hard wax , all by hand!!!! 

No wonder I now hate Celly paint with a passion but sometimes it gives the best authentic  Finnish on

older cars

[miniseven61]

I had forgotten about the brasso, used to buy it by the gallon, orrible stuff!!!  G7 has got very expensive, you could forego that and just use Tcut but it would be a bit harder to do. I really depends on the finish from the gun and what sort of finish you want to achieve, it all takes time.

[bluedragon]

If the finish feels rough (as opposed to being merely flat, but smooth) then I second the advice being given about needing to flatten the finish with sandpapers. If you have enough paint you should be able to carefully flatten the finish and polish it up - this is how virtually all painters get show quality finishes from cellulose (aka lacquer) paints. They are made to be color-sanded and polished.

 

You have to flatten it even if you decide to spray a fresh coat. The fresh coat won't magically fill the valleys up the peaks of the roughness - it will more or less evenly coat the rough peaks, leaving you with a surface that is still uneven, though it might be a bit smoother.

 

As far as respraying a fresh coat and the ultimate cause of the roughness - I doubt it is due to pressure. What's the temperature you are spraying at? A vital factor when spraying cellulose/lacquer is the drying speed of the thinner used. Typically the finishing thinners for automotive quality cellulose are available in fast, medium, and slow drying speeds.

 

Fast thinners are good for cold temperatures and primers. They evaporate quicker, and some roughness is no big deal for a primer since those will be sanded anyway (and the faster drying lets you get to work sooner.)

 

But using a "fast" thinner for the final gloss coats risks it drying prematurely (i.e. while being atomized by the spray gun) and this will cause the very effect of making it look like overspray particles are all over the finish - because the paint literally dried before it hit the finish surface. This is even more likely to happen if you sprayed it in warm temperatures.

 

If the temperatures are fairly cold, you can adjust by using a medium thinner, but if you use a fast thinner under warm temperature conditions, there's a high likelihood of it drying prematurely and causing the overspray-like roughness effect.

 

Other possible causes might be holding the spray gun too far from the surface when spraying - one rule of thumb is no more than a hand's width space between the gun nozzle and the spray surface, and always keep the distance constant by locking your wrist and not using wrist action to arc the gun from side to side.

[spraybeater]

Agree with blue dragons post, another thing now is as far as I-am aware Good quality Cellulose Lacquer is

not so readily available now (might be wrong as haven't used any for about thirty years  ) not PC any

longer due to high VOC content + a lot of companies that made it have now been amalgamated some of

the older Painters! on here will remember Ault&wiborg/Glasso/ICI/Parsons/Valentine to name a few!

was mostly an ICI user myself always found it to be the best Finnish of the gun so minimal polishing

required.

A lot of the problem with painting the conditions i.e light, temperature ,dust and technique practice

makes perfect and take your time and proper prep the most important Always rewarded

[biker1981]

Thanks for all the advice guys.

 

I'm painting outside but was a relatively warm day. I am using good quality "high gloss" thinner with my celly. to be honest im going to go down the repaint route reason why is I think it has good thick paint in areas but maybe light in other areas. So I will flatt it back paint again with plenty of paint then I can can colour sand and buff.

 

Im interested in what people are saying with medium drying thinners ... ay recommendations guys?

 

I read that I should be limiting the pressure of my gun - any advice what it sould be for gravity fed. My compressor is 3hp 100 litre and its just turned up to max

 

The roof is very stripey --- im really struggling to paint the roof. I normally joined the wet mark an keep it flowing if that makes sense but just cant seem to keep it going reaching - any tips

Edited by biker1981, 16 May 2016 - 07:36 PM.

[bluedragon]

If your gun is an HVLP gun, it should be no more than ~1.5-2 bar at the gun. If you don't have a pressure gage at the gun, find one of the online references to calculate pressure drop based on the diameter and length of your air supply hose. If it's set to max, it's probably way too high. If it's a normal type atomizing gun, then 2.5-3 bar is a setting you can start with. 

 

If you don't know if your gun is HVLP or conventional, find out! If your compressor has no problems keeping up with your gun, it's probably a conventional gun (HVLP guns consume huge amounts of air volume that most 3hp compressors would not be able to deliver continuously.) 

 

You should review your technique. If the air pressure is set correctly, and you have dry spots in the spray pattern, you likely are holding the gun too far away from the painting surface. This would manifest itself most on the roof, which for most people is the hardest to spray with a constant distance from the gun to surface. My previous post on this topic has hints on good technique. If you describe how you spray, that might help figure out the problem.

 

Get a good work platform to give you the height to comfortably spray the roof with good technique. Coverage per pass should be 50% overlap over the previous spraying pass, and it of course should lay down wet from top to bottom of the pattern. 

 

Wherever you purchased your paint from should be able to offer you alternative thinners. They are rated for temperature, so all you have to do it determine roughly what the temperature range is that you'll be spraying at and pick the appropriate thinner type.