11 replies to this topic

[digitalfriction]

Hi,

sprayed a bonnet a couple of weeks ago, colour sanded, compounded and polished. Now when I look, some areas have got a very fine cracking effect in the paint. I assume this is some sort of reaction, but I havent had it before, and havent changed how I do anything. Any ideas?

Andy

[joe90]

this normaly ocurs when you have paint saturation (been painted to many times before) the paint build up starts to move around underneith & cracks! Can happen with 2k paint as well only way to get rid is to strip all paint & do it again
hope this helps.
joe

[digitalfriction]

this normaly ocurs when you have paint saturation (been painted to many times before) the paint build up starts to move around underneith & cracks! Can happen with 2k paint as well only way to get rid is to strip all paint & do it again
hope this helps.
joe

Sort of makes sense, I dont know how many layers the panel has got, the paint it had was in good condition, jus the wrong colour, so all I did was key the surface and primered etc. I will strip back to metal. Just out of interest, when stripping back to metal is it better to use abrasion, as in sanding back to metal, or chemical, such as nitromors, or does it not make a difference?

Andy

[joe90]

It dose not really make any differance just that paint striper makes more mess & burns when you get it on your skin, ouch!!
joe

[Leewallbank]

It dose not really make any differance just that paint striper makes more mess & burns when you get it on your skin, ouch!!
joe

Only problem with sanding though is if you put too much heat into the panel it'll warp - with such a small panel it'd be better to paint stripper.

[Mr Joshua]

[Only problem with sanding though is if you put too much heat into the panel it'll warp - with such a small panel it'd be better to paint stripper.

Utter Rubbish!

I take my prep back to bare metalwith 80 grit. There is no chance in hell that you can put that much heat into a panel through hand sanding or useing a DA not a chance!

[Cooperman]

You don't need to strip it all back. Buy a tin of isolator (typically 'Barcoat'). Rub down the cracked paintwork, clean it with panel-wipe and spray two coats of isolator, When that is dry, don't rub down. Apply a couple of coats of primer, lightly nib-down and spray top coat. if it is celulose, allow a lot of time for each coat to dry. Current 'industrial' celulose takes longer to harden than the old automative celulose. Finally flat and polish.

[digitalfriction]

You don't need to strip it all back. Buy a tin of isolator (typically 'Barcoat'). Rub down the cracked paintwork, clean it with panel-wipe and spray two coats of isolator, When that is dry, don't rub down. Apply a couple of coats of primer, lightly nib-down and spray top coat. if it is celulose, allow a lot of time for each coat to dry. Current 'industrial' celulose takes longer to harden than the old automative celulose. Finally flat and polish.

Unfortunately by the time i have read your post I have stripped back to bare metal. I used chemical, and then cleaned up with abrasion. I have now also read that I will get problems with high-build primer, as I have textured the metal to give it some grip, and then sprayed high-build celly primer on, apparently this will flake off and I should have used etch primer.

How long are you thinking I should leave celly between coats? I normally leave it overnight, unless its a hot day, when 2-3 hours normally seems ok.

[Mr Joshua]

Thats utter rubbish Too! Where do these people get their info from

You only need etch primer when your painting Ally period! Celly primer adhears just fine to bare metal. You have done the correct thing in taking back to bare metal I have just done the same to my boot lid and metal flip front. now that you have put the primer on you need to guide coat it in order to locate any pits, pin holes or dent's do this by dusting on back paint from say 2ft away this way you will know where you have flatted back I would recomend 800 grit wet and dry 600 at the limit for flatting the primer, it may take a while but you have to get the prep done right.

You only really need wait 24hrs for the primmer to be ready for sanding and accepting top coat if you dont have an oven.

When you apply your top coat start thick then go light by that mix it 60/40 paint/thinner then 50/50 40/60 30/70 20/10 then finish with fog of 100% thinners. You dont have to follow that guide exactly but you get the picture. when dry the finish will be like mottled glass! when you cut it back you will see your smile in it from 5ft away!

My tip for polishing cellulose is wait for atleast 2-3 weeks (when its hard) before cutting it back. The paint is still moving even though it is touch dry and will only go dull if polished prematurely.

Remember its the prep that will give you the shine get the prep bang on and the top coat finish will make you proud.

Any other questions PM me some of these peeps annoy me!

[midridge2]

20/10, think you made a mistake there. lol

[Mr Joshua]

True 20/80

[Leewallbank]

[Only problem with sanding though is if you put too much heat into the panel it'll warp - with such a small panel it'd be better to paint stripper.

Utter Rubbish!

I take my prep back to bare metalwith 80 grit. There is no chance in hell that you can put that much heat into a panel through hand sanding or useing a DA not a chance!

Thats utter rubbish Too! Where do these people get their info from

You only need etch primer when your painting Ally period! Celly primer adhears just fine to bare metal. You have done the correct thing in taking back to bare metal I have just done the same to my boot lid and metal flip front. now that you have put the primer on you need to guide coat it in order to locate any pits, pin holes or dent's do this by dusting on back paint from say 2ft away this way you will know where you have flatted back I would recomend 800 grit wet and dry 600 at the limit for flatting the primer, it may take a while but you have to get the prep done right.

You only really need wait 24hrs for the primmer to be ready for sanding and accepting top coat if you dont have an oven.

When you apply your top coat start thick then go light by that mix it 60/40 paint/thinner then 50/50 40/60 30/70 20/10 then finish with fog of 100% thinners. You dont have to follow that guide exactly but you get the picture. when dry the finish will be like mottled glass! when you cut it back you will see your smile in it from 5ft away!

My tip for polishing cellulose is wait for atleast 2-3 weeks (when its hard) before cutting it back. The paint is still moving even though it is touch dry and will only go dull if polished prematurely.

Remember its the prep that will give you the shine get the prep bang on and the top coat finish will make you proud.

Any other questions PM me some of these peeps annoy me!

WOW! I take it that everything you say on here must be right then?? I can guarantee you now that you can warp a panel by machine sanding too much - I've seen it plenty of times. If you don't etch prime bare metal, be it steel or ally, then no paint manufacturer will guarantee it. How do I know this? I actually work for a rather large bodyshop, where we paint over 40 cars a week. I don't post *melon* - only when I know I can help.