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-   -   Dumb question that i should know the answer to.. shrinkage (http://www.hotrodders.com/forum/dumb-question-i-should-know-answer-shrinkage-71572.html)

beemdubya 10-07-2005 12:22 AM

Dumb question that i should know the answer to.. shrinkage
 
Ok so lately ive been noticing alot of shrinkage around my body filler areas. i dont know what causes this but i havent seen it come through my final paint until recently.. after i do my body work i prime with nason 421-17 2k surfacer. then i block sand/ final sand.. all is well until usually within a day or two rings around the filler show up (only on certain repairs).. i even tried using a sealer and the same thing. ive never had this happen to me before so i dont know what causes it. i know since i started using the nason primer thats when i started having alot more sand scratch swelling as well. maybe its just the quality of the primer?

BarryK 10-07-2005 04:40 AM

This is called mapping and from the time frame you have given
its coming from the first coat of primer.

First we will assume you mixed everything right and we know you did.

1)Trapped solvents from not letting the primer flash long enough between coats.

2) Primering over cold metal (in winter) normally in conditions where metal is 50 degree's and the shop is 70 degrees.

3) Too many coats for the primer, Some 2ks will not stand up to excess coats.

The above are your choices for the time frame you gave us.

jcclark 10-07-2005 04:47 AM

I had problems something like that when I don't let the primer
cure long enough before sanding. I always wait at least 24 hrs but
I prefer 3 days. I know most people consider that overkill but
my final paint also has less shrinkage. I guess the question is,
How long do you let the primer age before sanding?

Randy Ferguson 10-07-2005 07:42 AM

I had the same problems when I was painting. Fortunately, I'm now a full time sheetmetal shaper and don't have to worry with these problems, but anyway...When I was fighting this problem, we were using PPG K36, and although the filler was finish sanded with 320 grit prior to primer, we still got sandscratch swelling and bullseyes. We NEVER painted the same day as we shot primer. Always waited at least overnight and was assured several times that we were waiting plenty long enough. The folks at PPG assured us that 2-3 hours was plenty long enough to wait before topcoating. What a load of crap!! When doing restoration and hot rod work, I would wait at least 7 days before blocking primer, and never had problems, but you can't do that in a production shop. We fought it every way possible and still never got a handle on it. My opinion is that the base coat acts as a wick whenever fresh solvents are applied, such as spraying primer. I believe where the base is exposed due to featheredging the paint around the repair, that it sucks up the solvents in the primer and they become trapped for several days.

NOW, Just about the time I quit the body shop, I got in touch with Barry Kives at Southern Polyurethanes and we had a long discussion about this. At that time, he had a new product just hitting the market that was a fast cure 2K primer. 'Turbo 2K' I think is the name?? Anyhow, I used it on a Chrysler Voyager hood that had previously been repaired with DuPont products and still had the OEM finish. The only thing we were to repair was the rock chips, and there were several of them!! To give the SPI Turbo primer a real test, I sanded out the rock chips with 80 grit on a DA, followed by 180 and finished with 320. It should have been stripped, but what better way to test a product. We informed the customer going in that we were using it as a test vehicle and sould need to see it monthly for 6 months and if it failed, we would strip it and repaint as no additional charge. After spraying the primer, I let it set overnight, lightly sanded it with 320 on DA, followed by 600 wet. It sanded out beautifully. The paint went on super slick with no reaction to the primer and after three months, it still had no signs of sandscratch swelling. Barry assured me that the Turbo 2K primer was a 3-4 hour total cure product.
I'm completely sold on this product as well as many others I've tried from SPI.
Most primers on the marke have a 7-21 day total cure rate. The difference is monumental!!

Try it!

Randy

MARTINSR 10-07-2005 08:21 AM

HOWEVER, if you were to bomb the "Turbo primer" with too short of flash time and/or cold metal and/or applying too many coats you will still get shrinkage as with any other product. They AMOUNT of shinkage will vary but if you abuse ANY product you will get shrinkage.

And like wise if you apply even the poorest primer with care you will lessen or eliminate the sand scratch swelling/shrinkage.

Brian

baddbob 10-07-2005 08:52 AM

Another thing that can cause shrinkage problems is epoxy primer if applied too heavy without enough cure time especially if more than one coat is applied. Epoxy is a slow drying primer. If you do your work and apply epoxy then your urethane surfacer while the epoxy is too wet the faster curing urethane primer will seal and slow the cure rate of your epoxy. Just another example of bombing products on and the problems that can happen. And a reason why most collision shops won't use epoxy even though the durability is so much better than any etch or DTM urethane. IMO any restoration or show car quality jobs should be allowed more cure time than regular production/collision work-how long depends on what products are used, temperatures, application.... Give longer flash times between coats, make sure you keep the shop warm, don't apply more coats than suggested and the right thickness. A heat lamp is also a good investment if you need to speed things up-just be sure to give the primer time to purge the solvents before you apply the heat. I have absolutely no shrinkage problems.

jcclark 10-07-2005 09:21 AM

These are some good points and shows that every rule has exceptions.
To say always follow the mfg recommendations has exceptions here too.
Waiting longer is better, true they give min times usually but they like
to boast their product with fast time advertisements to lure bodyshops
into buying their pruduct. There's a lot of things you can get away with
in the "perfect world environment" as they give directions to but for most
people like me that screw things up all the time it's better to error on the
side of safety. That's why I advise letting primer set 3 days before sanding
and clear to set more than 24 hrs. There's not always time to do that
and all products are different,but waiting longer helps.

BarryK 10-07-2005 10:38 AM

Quote:

Originally Posted by jcclark
These are some good points and shows that every rule has exceptions.
To say always follow the mfg recommendations has exceptions here too.
Waiting longer is better, true they give min times usually but they like
to boast their product with fast time advertisements to lure bodyshops
into buying their pruduct. .


No, No and No.
A company is not going to boast their products!
The risk of this is to great, as a matter of fact its usually the other way around.
When was the last time you saw a dealership build a fender out of filler and spray 6 coats of 2K on it to start? Most of their work is two coats of primer as they are panel re-placers.

If a major writes a tech sheet for primer, its written for a Chevy dealer that has good painting conditions and the shop will not be under 70 degrees in the winter time and is going to be as close to lab conditions as your going to get.

They don't write tech sheets for spraying at home as number one we have Chevy and Ford dealers around here that spend $60,000 and up a month on paint materials, so that is their big business.

Its up to you to adjust for colder or hotter weather and size of car your doing. This is not furniture painting.

MARTINSR 10-07-2005 11:01 AM

However :) Barry, there are "Chevy dealers" with some pretty funky set ups. :)

I serviced a Ford dealer in a small town with a home made booth!

Brian

BarryK 10-07-2005 11:05 AM

Brian,

You are right! But I bet you did not see Dupont or PPG or yourself go into those places and try to buy the business with two free paint booths and a million dollar check up front for a 3 year contract to get their business either.

MARTINSR 10-07-2005 11:15 AM

No, but I'll tell you this, if they would have been in a more competitive area like Contra Costa County just west of the SF bay area they would have! I am not kidding, in that area DuPont and PPG thru so much money at shops it was sickening. A little shop like this with only $3000 or so in monthly purchases would be fought over and given $20,000 or something. It was sick.

Up where this Ford dealer was at in Lake county, DuPont and PPG didn't even send a rep up there. I got a lot of business up because I was willing to go. Those shops didn't even know about the incentive checks the big boys were tossing around.

Brian

jcclark 10-07-2005 11:21 AM

Quote:

Originally Posted by BarryK
A company is not going to boast their products!

I can't believe you said that!!!! :pimp:
Read this advertisement, if this is not boasting I stand corrected.

Thank you for viewing our website. Please click on any of our products and view their respective tech sheets. By doing so you will find that our 2K primers are ready to sand in 30 minutes at 70 degrees and do not require a sealer.

You will see that our clears can be buffed in as little as 1 hour, handled in 45 minutes, and buff good as much as 30 days after application. Our epoxy primers spray wet and slick, and all of our colors, including white, have outstanding adhesion to aluminum.

Our spray-in truck bed liner is tintable with such strength that we make counter mats out of them for our jobber stores! Let us prove to you that we believe in quality over quantity, and that we stand behind all of our products.

beemdubya 10-07-2005 11:40 AM

Well with that said.. i figured out the problem.. prolly putting on too many coats for this product to keep up.

The spi turbo 2k is great i have a gallon that ive been using on the porsche im restoring.. i plan on switching to that completly but i wanna use up the rest of this nason.. ill just stick to 2 or 3 coats and i wont bomb them on as sometimes happens. thanks guys

BarryK 10-07-2005 11:42 AM

Quote:

Originally Posted by jcclark
I can't believe you said that!!!! :pimp:
Read this advertisement, if this is not boasting I stand corrected.

Thank you for viewing our website. Please click on any of our products and view their respective tech sheets. By doing so you will find that our 2K primers are ready to sand in 30 minutes at 70 degrees and do not require a sealer.

You will see that our clears can be buffed in as little as 1 hour, handled in 45 minutes, and buff good as much as 30 days after application. Our epoxy primers spray wet and slick, and all of our colors, including white, have outstanding adhesion to aluminum.

Our spray-in truck bed liner is tintable with such strength that we make counter mats out of them for our jobber stores! Let us prove to you that we believe in quality over quantity, and that we stand behind all of our products.

*****************************************
Well, I don't know where the boasting would be?

One example 1 hour buff.
No, actually 30 minutes at 75 degrees.
Always a safety net!

Or what about the 45 minute handling?
How about at 70 Degrees handle and put in rain in 30 minutes and will be water spot free.
Always a safety net!

So if you don't know why bring it up?
Because you don't have a clue.
Respond to someone else as I'm done here.

jcclark 10-07-2005 11:49 AM

Well obviously we have a different definition of boast.


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