How do I go about blending new paint into old.

[The Ghoul]

Here is the situation I run into all the time. I need to fix a dent or rust spot. I take it down to bare metal  fix what ever do all my prep than paint. I have tried spraying a very thin over reduced final coat to blend. The wet sanding with progressivly finer grits always leaves a dull finish. I have tried a random orbit buffer with rubbing compound with no good results..
So whats the key?
Should I get a fancy buffing wheel and super fine grit compounds?
Come to think about it all my attempts at wetsanding have ended as dull gloss-less sheens. Is the buffing what I have been missing?
Or is there some type of final spray that will melt the new overspray into the old paint?

[Doc74]

Are you talking about blending new clear onto old ?
The trouble with the spots being dull is mostly because of a too coarse grit paper, you can start out as coarse as grit 180 as long as you follow each consecutive step towards grit 3000.
Ok so let's say you repaired the front fender corner, have it in primer, sanded and finished with a grit 1200 wet to make it smooth as silk.
If you can then I suggest to always sand the full panel, apply color where you need it and clearcoat the whole thing.

But that's not your question is it 
First things first, clean the panel with warm water and soap, then degrease it with a autobody degreaser (mix of water and alcohol) and then use a coarse polish to really clean up the old clear so it looks brand new.
There are tons of products and ways to do it, I use 3M products, it's a 4 step buffing job but you will actually do with two and it works perfectly.

The first step, the coarse polish is 3M perfect-it III rubbing compound, I suggest using a good polish machine, forget doing all this by hand.
Now you have a super shiny fender with smooth sanded primer on the front. Now what you need is a grit 3000, another 3M product which is called Trizact, it's a sanding disc for a rotary sander but you can do it by hand too. Make it wet but don't soak it and cover a large area around the primer, lets say the primer spot runs top to bottom on the fender front edge and is 2 inches wide, you need to sand the area around at least 10 inches, you can't really go too far because you'll be able to machine polish it in about 20 seconds ! Better sand too much with the trizact then not enough in this case.
Degrease again, tack rag it and you're ready for paint.Mask the clear coat with a big piece of paper but make sure you can rip it off without touching the fender at any time, you'll need to later.
Color the primer, depending on color this technique changes a bit. A black car is very easy to touch up, you won't see any marks easily, a silver car on the other hand will make you go a lot further to feather the color and get the metallic parts even, if you keep it too small you'll have a light or dark spot, very visible.I assume since you're tackling this that you know how to paint but if it's not clear just ask.
Try to not spray in the direction of the masking paper, if the paper touches the fender it'll leave a nasty line.

Time for the tricky part !
Get the masking paper off and let the paint cure, then rub the fender with a tack rag again to remove any dust.
Apply another masking paper on the fender to just about the dull sanded spot, do not tape it against it, leave it loose and tape it from behind so it can't touch the fender.This applies to the previous paper too, forgot 
Take your clear and apply your first coat painting in the direction of the touched up spot, back to front, it'll limit the overspray near the masking paper, apply it smooth and with fair pressure so you don't have a lot of orange peel on the edges but don't overdo it.
Apply your second layer and make it smaller so that you don't go as far as with the first coat, this will make layer two blend into layer one more easily and won't give you buildup around the edges.This is your finish so mspray it smooth as possible but don't take too many chances since you'll be sanding and buffing later anyway.

Now remove the masking paper carefully and you'll see a nice shiny fender with a very dull streak where you stopped with your clear.
You'll need a spot repair thinner, different brands use different names, with Sikkens it's called SRA thinner. The base thinner would even work but not recommended so ask in your supply store for one.

Now apply the thinner with the same airgun as your clearcoat, some first apply a 50-50 mix of thinner and clear but with todays products it's not really needed.
Again spray towards the spot repair but dust it, not full coats or you'll need a bucket to catch it. 
A few dustcoats will bring gloss to it but don't try to do it perfectly,it needs time to cure and will look a lot better within minutes. You can feather it in one coat, don't let the clear set so empty the gun, get the thinner in and spray.It shouldn't take more than 10 seconds actually spraying to give you an idea.
What you have done now is dilute the overspray mist, with good products I can make it shine so you barely need polishing.
After plenty curing you're ready to sand.If the overspray is very fine then start with a 1500 grit, then 2000 then go to the trizact, use a sander for the latter if you have one, to speed it up. If there's a bunch of dustspecs or even runs in it then you'll have to start with a coarser grit working you're way up to the trizact, don't skip any steps here or you'll still have marks and dull spots.
What you have now is perfectly blended paint, albeit very dull.

Like I said I use 3M for polishing and it works like a charm, start with perfect-it rubbing compound, don't push too hard but keep it firmly on the fender, make sure the machine is low rpm or you'll burn the paint or leave swirl marks.
Use a wool or hard foam pad for this, use small amounts and rub them out before turning the machine on or you'll be cleaning all day. 
Use soft cloth to rub it out.

After one go you'll have about 90% gloss back and no marks anywhere in sight, start smiling, nearly there.
Repeat this step until you find it's nearly perfect, then switch to a soft polish pad with perfect-it machine glaze.Again rub out with clean soft cloth, you'll find this second polish is more oily too and you can feel it getting smoother.
One or two runovers will you result in a perfect panel.You can go further with machine glaze and another which name slips me but it's anal, trust me.Just throw a cloth at it, if it slides over like the fender wasn't even there, you've done a good job. Or...for more fun, ask a buddy to pose and let him lean on it,when he slides off and wakes up in the dirt you got it right !     

You can apply this technique to direct gloss acrylics too, basically the same thing.
The key secret is following the sanding steps and ending with the trizact or similar product here. You can have the best polishing machine with the best products, if the paint is not fine enough you won't get the results you want.

When you wetsand with a grit 2000 and move to the trizact 3000 you'll notice something right away, it get's glossier.
Any marks or more coarse spots you see now will be visible later so follow the steps, don't go from grit 1000 to 2000,won't work, too big of a difference.
2000 to 3000 will however be perfect since grit 2000 isnearly good enough to polish and sometimes can be done without a hitch.

Polishing should be done in minutes, don't start until the sanded clear is smooth as silk and you can't see any imperfections.

When all is done, wash the fender with warm water to get any polish residue off of it.

I hope it's a bit clear, I'll try to take pics at work and show the steps to make it easier.

[The Ghoul]

hummm, seems to make sence thank you very much for all the info. It seems that ive been stopping at 2000.
Thank you very much

[Doc74]

hummm, seems to make sence thank you very much for all the info. It seems that ive been stopping at 2000.
Thank you very much

I wondered if it'd make sense, I reread it and don't have a clue....

Continuing with finer grit after 2000 will most likely solve your problem.

You're welcome

[CB]

Are you talking about blending new clear onto old ?
The trouble with the spots being dull is mostly because of a too coarse grit paper, you can start out as coarse as grit 180 as long as you follow each consecutive step towards grit 3000.
Ok so let's say you repaired the front fender corner, have it in primer, sanded and finished with a grit 1200 wet to make it smooth as silk.
If you can then I suggest to always sand the full panel, apply color where you need it and clearcoat the whole thing.

But that's not your question is it
First things first, clean the panel with warm water and soap, then degrease it with a autobody degreaser (mix of water and alcohol) and then use a coarse polish to really clean up the old clear so it looks brand new.
There are tons of products and ways to do it, I use 3M products, it's a 4 step buffing job but you will actually do with two and it works perfectly.

The first step, the coarse polish is 3M perfect-it III rubbing compound, I suggest using a good polish machine, forget doing all this by hand.
Now you have a super shiny fender with smooth sanded primer on the front. Now what you need is a grit 3000, another 3M product which is called Trizact, it's a sanding disc for a rotary sander but you can do it by hand too. Make it wet but don't soak it and cover a large area around the primer, lets say the primer spot runs top to bottom on the fender front edge and is 2 inches wide, you need to sand the area around at least 10 inches, you can't really go too far because you'll be able to machine polish it in about 20 seconds ! Better sand too much with the trizact then not enough in this case.
Degrease again, tack rag it and you're ready for paint.Mask the clear coat with a big piece of paper but make sure you can rip it off without touching the fender at any time, you'll need to later.
Color the primer, depending on color this technique changes a bit. A black car is very easy to touch up, you won't see any marks easily, a silver car on the other hand will make you go a lot further to feather the color and get the metallic parts even, if you keep it too small you'll have a light or dark spot, very visible.I assume since you're tackling this that you know how to paint but if it's not clear just ask.
Try to not spray in the direction of the masking paper, if the paper touches the fender it'll leave a nasty line.

Time for the tricky part !
Get the masking paper off and let the paint cure, then rub the fender with a tack rag again to remove any dust.
Apply another masking paper on the fender to just about the dull sanded spot, do not tape it against it, leave it loose and tape it from behind so it can't touch the fender.This applies to the previous paper too, forgot
Take your clear and apply your first coat painting in the direction of the touched up spot, back to front, it'll limit the overspray near the masking paper, apply it smooth and with fair pressure so you don't have a lot of orange peel on the edges but don't overdo it.
Apply your second layer and make it smaller so that you don't go as far as with the first coat, this will make layer two blend into layer one more easily and won't give you buildup around the edges.This is your finish so mspray it smooth as possible but don't take too many chances since you'll be sanding and buffing later anyway.

Now remove the masking paper carefully and you'll see a nice shiny fender with a very dull streak where you stopped with your clear.
You'll need a spot repair thinner, different brands use different names, with Sikkens it's called SRA thinner. The base thinner would even work but not recommended so ask in your supply store for one.

Now apply the thinner with the same airgun as your clearcoat, some first apply a 50-50 mix of thinner and clear but with todays products it's not really needed.
Again spray towards the spot repair but dust it, not full coats or you'll need a bucket to catch it.
A few dustcoats will bring gloss to it but don't try to do it perfectly,it needs time to cure and will look a lot better within minutes. You can feather it in one coat, don't let the clear set so empty the gun, get the thinner in and spray.It shouldn't take more than 10 seconds actually spraying to give you an idea.
What you have done now is dilute the overspray mist, with good products I can make it shine so you barely need polishing.
After plenty curing you're ready to sand.If the overspray is very fine then start with a 1500 grit, then 2000 then go to the trizact, use a sander for the latter if you have one, to speed it up. If there's a bunch of dustspecs or even runs in it then you'll have to start with a coarser grit working you're way up to the trizact, don't skip any steps here or you'll still have marks and dull spots.
What you have now is perfectly blended paint, albeit very dull.

Like I said I use 3M for polishing and it works like a charm, start with perfect-it rubbing compound, don't push too hard but keep it firmly on the fender, make sure the machine is low rpm or you'll burn the paint or leave swirl marks.
Use a wool or hard foam pad for this, use small amounts and rub them out before turning the machine on or you'll be cleaning all day.
Use soft cloth to rub it out.

After one go you'll have about 90% gloss back and no marks anywhere in sight, start smiling, nearly there.
Repeat this step until you find it's nearly perfect, then switch to a soft polish pad with perfect-it machine glaze.Again rub out with clean soft cloth, you'll find this second polish is more oily too and you can feel it getting smoother.
One or two runovers will you result in a perfect panel.You can go further with machine glaze and another which name slips me but it's anal, trust me.Just throw a cloth at it, if it slides over like the fender wasn't even there, you've done a good job. Or...for more fun, ask a buddy to pose and let him lean on it,when he slides off and wakes up in the dirt you got it right !

You can apply this technique to direct gloss acrylics too, basically the same thing.
The key secret is following the sanding steps and ending with the trizact or similar product here. You can have the best polishing machine with the best products, if the paint is not fine enough you won't get the results you want.

When you wetsand with a grit 2000 and move to the trizact 3000 you'll notice something right away, it get's glossier.
Any marks or more coarse spots you see now will be visible later so follow the steps, don't go from grit 1000 to 2000,won't work, too big of a difference.
2000 to 3000 will however be perfect since grit 2000 isnearly good enough to polish and sometimes can be done without a hitch.

Polishing should be done in minutes, don't start until the sanded clear is smooth as silk and you can't see any imperfections.

When all is done, wash the fender with warm water to get any polish residue off of it.

I hope it's a bit clear, I'll try to take pics at work and show the steps to make it easier.

And this guy is doing the body work on my Charger.    

[The Ghoul]

hummm, seems to make sence thank you very much for all the info. It seems that ive been stopping at 2000.
Thank you very much

I wondered if it'd make sense, I reread it and don't have a clue....

Continuing with finer grit after 2000 will most likely solve your problem.

You're welcome

I fallowed it cuz most of it is what I have been doing.

[hotrod98]

I manage a body shop for a delaership and we use the 3M Perfectit III system and the 3M Trizact system also. We love it. The cars that we buff look like a mile deep when we're through. We spray PPG 2021. It lays down so nice that we usually start with the 1500 grit trizact on a da sander. Some of the guys do this step dry, but I prefer to use water and tip the da up lightly to prevent trash from building up under the paper. You have to watch closely for trash since it will leave deep da marks if you're not careful. We go straight to 3000 from there and then buffing's a piece of cake. The biggest mistake is not buffing long enough to really move the clear around. We don't stop at just glossy, we spend a little more time in the buffing stage using a 3M wool pad and then switch to a 3M black waffle pad with buffing compound and then to a clean 3M black waffle pad with polish. All of the musclecars cars that we paint are consistent winners at the local car shows. It's not enough to just do a nice paint job, you have to know how to do the final steps to make it all worthwhile.
As for buffing blends, the only thing that I can add is to always buff from the new clear to the old clear. If you buff towards the new clear it can peel up the edge if you're not careful.
Another handy tip is to buy one of those silicone looking squeegees that detailers use so that if you're wet sanding, you can remove the water quicker for your inspection. It saves a lot of time over using those black 3M rubber squeegees. All of my guys keep one on their buffing carts.

[Doc74]

And this guy is doing the body work on my Charger.

Heehee thanks for the compliment. 

Lotsa welding will be done this saturday, weather should be a tad better too, we hope. If you wanna drop by we'll be there all day and you can always give me a call to be sure we're not out for lunch or anything.I'll have my cell with me.

I manage a body shop for a delaership and we use the 3M Perfectit III system and the 3M Trizact system also. We love it. The cars that we buff look like a mile deep when we're through. We spray PPG 2021. It lays down so nice that we usually start with the 1500 grit trizact on a da sander. Some of the guys do this step dry, but I prefer to use water and tip the da up lightly to prevent trash from building up under the paper. You have to watch closely for trash since it will leave deep da marks if you're not careful. We go straight to 3000 from there and then buffing's a piece of cake. The biggest mistake is not buffing long enough to really move the clear around. We don't stop at just glossy, we spend a little more time in the buffing stage using a 3M wool pad and then switch to a 3M black waffle pad with buffing compound and then to a clean 3M black waffle pad with polish. All of the musclecars cars that we paint are consistent winners at the local car shows. It's not enough to just do a nice paint job, you have to know how to do the final steps to make it all worthwhile.
As for buffing blends, the only thing that I can add is to always buff from the new clear to the old clear. If you buff towards the new clear it can peel up the edge if you're not careful.
Another handy tip is to buy one of those silicone looking squeegees that detailers use so that if you're wet sanding, you can remove the water quicker for your inspection. It saves a lot of time over using those black 3M rubber squeegees. All of my guys keep one on their buffing carts.

Agreed with all that's been added ! 

If one ever does have an edge in the clear they should stop immediatly and let it cure longer, if possible use IR drying.
Afterwards there's a very good shot that you'll be able to buff it out since it can be one of the reasons why it has the edge in the first place.
What I do is use IR after I sand it and it's ready for polish. Never hurts but do make sure it's cooled off before you start polishing.

The waffle pad is the one I meant for the second stage, the softer pad. Being from waffleland you'd think I'd get the name !   

Hotrod you're not near Detroit are you? I'll need a job once I get there...

[hotrod98]

Hey Doc74,
I'm a little south of Detroit, actually a lot south of detroit. The dealership that I work for is in Fort Smith, Arkansas. We're down here enjoying this 70 degree weather. I actually got my 71 cuda out for a drive on Sunday. I like living in this part of the country. There are still a lot of undiscovered mopars in the area. I just bought two 69 Roadrunners today. One is a 383 4 speed coupe and the other is a 440 hardtop. The coupe will be an easy resto and the hardtop is a little rough but still restorable.
If I decide to start the resto thing full time, I might be calling you.

[Doc74]

Hey Doc74,
I'm a little south of Detroit, actually a lot south of detroit. The dealership that I work for is in Fort Smith, Arkansas. We're down here enjoying this 70 degree weather. I actually got my 71 cuda out for a drive on Sunday. I like living in this part of the country. There are still a lot of undiscovered mopars in the area. I just bought two 69 Roadrunners today. One is a 383 4 speed coupe and the other is a 440 hardtop. The coupe will be an easy resto and the hardtop is a little rough but still restorable.
If I decide to start the resto thing full time, I might be calling you.

Arkansas...that's a serious commute...    But call anyway, I believe I had a job to do somewhere in Ohio, not sure what tho', some beyond repair 68 charger...

Mmmmmm runners, I'd like to have one of those one day. Got any pics?