BASECOAT ADHESION

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Garrett1984

Promoted Users
I have done a lot of reading on this forum and have noticed many people have applied a reduced mixture of epoxy to serve as an adhesion promotor, only to be bummed out their basecoat still has a faulty chemical adhesion. People on this forum have suggested that the “solvents of the epoxy got trapped and couldn’t escape the barrier of basecoat and clear coat, thus, creating a microscopic uncured weak link between the two layers”. Makes sense to me.

The following statement is understood:
“Before I apply a basecoat, I shall first apply a 1:1:1 mixture of SPI epoxy to the substrate to achieve excellent adhesion of the basecoat. Let this mixture flash off and I can apply my basecoat of choice”.

What I don’t understand is why would it not be adequate to apply 2-3 coats of SPI epoxy mixed at a ratio of 1:1… sand to perfection while the epoxy is still considered to be “green”…clean substrate…then apply basecoat within 7 days?

The reason I am confused is because I have the understanding SPI epoxy is still “green” up to 7 days after application. Possibly up to 14 days. If the SPI epoxy is still “green” during the 7 day window… then I believe the basecoat can still have adequate CHEMICAL adhesion if it was applied within 7 days of top of the SPI epoxy. This method of approach will give the epoxy more time to gas off.

Thoughts?
 
Crashtech, yeah, I have came across some pictures and conversations in this forum about faulty adhesion and it has got me paranoid and nervous now. Do you think my method would be another way to "skin a cat" and still achieve adequate chemical adhesion?
 
Garrett1984 said:
What I don’t understand is why would it not be adequate to apply 2-3 coats of SPI epoxy mixed at a ratio of 1:1… sand to perfection while the epoxy is still considered to be “green”…clean substrate…then apply basecoat within 7 days?
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That's what I and many others do on a daily basis, works great, it's more than "adequate"
it's a common procedure.

The advantage of a sealer coat is you don't need to sand it or wait very long to go ahead and paint it.

I don't think thicker epoxy. or more coats increases adhesion much,
(Barry can correct me if I'm wrong)
 
Garrett1984 said:
Crashtech, yeah, I have came across some pictures and conversations in this forum about faulty adhesion and it has got me paranoid and nervous now. Do you think my method would be another way to "skin a cat" and still achieve adequate chemical adhesion?
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What we don't see are the thousands of successful applications of the sealer technique. You might have a mistaken impression of the amount of failure, and even among the posts where users are complaining, it may not necessarily be a fault of the technique, but of the person applying it. So we still are not agreeing on the premise in your OP.

That said, I personally find that applying basecoat directly to sanded epoxy that is inside the recoat window to be a perfectly valid technique, but it's NOT going to give superior adhesion to the base on sealer technique, nor is it the SPI recommended procedure.
 
I'm with Crash, I don't recall "many people" on here having the issue you describe. Could you cite the threads pointing to this? Usually if there is an issue it's 99 times out of 100 operator related, not product related.

Sealing something is done to get a uniform colored substrate as well as to provide "chemical" adhesion. You can sand unreduced epoxy and apply base, several here favor that method, but if you have small sand throughs, either to metal or poly primer, 2K primer, or even a different color epoxy you would ideally seal it to allow it to have a uniform substrate and actually better adhesion than with sanded epoxy alone.

Epoxy mixed as sealer cures at a different rate and "gassing off" is not an issue, either with epoxy mixed as a sealer or epoxy applied days earlier provided it's properly applied and proper flash and wait times are observed.
 
The only time I've heard of loss of adhesion is when base is rushed and solvents trapped after clear. I actually painted a truck about 5 years ago where clear was peeling and as I took the clear off with air nozzle I could still smell the reducer someone had used in the base.the reducer has a particular smell and I recognized it because I had used it in the past.Truck had been painted for several years if I remember correctly.
 
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Are you talking about Shine and that mystery job where the paint was coming off in sheets? That is still a mystery but a sealer coat of reduced epoxy then base coat is the way to go and done every day.
 
It's all in the control of the painter. Mix with solvents appropriate for conditions, do not apply base too heavily, and use correct flash times. Patience is a virtue, but timers are even better. Timers and infrared thermometers, and a careful recording of what was done.
 
Knock on wood, after all these years I have only had adhesion issues one time and that was due to me taping on cheap ass nason too soon..
 
Hello everyone. I have been snooping on here for over a year and I can't recall exactly where in this forum I have seen issues of some folks with delamination issues.
However, let's say for some reason the posts I came across in the past was strictly from painter's error (no further discussion needed of course). But, I was hoping there may be someone on here that has good adhesion results by applying 2 coats of SPI epoxy primer in a 1:1 ratio...coming back 24 hours later and wet sanding with 400 grit for a solid color...then coming back 24 hours later and applied base?

For some reason I have it in my head I am more comfortable doing it this way. I have restored antique aircraft and solvent trapping has been an issue. Of course, this was nitrate/buterate dope...but I have since been nervous and like to play it safe when it comes to "letting the paint gas off".
 
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Garrett1984 said:
Hello everyone. I have been snooping on here for over a year and I can't recall exactly where in this forum I have seen issues of some folks with delamination issues.
However, let's say for some reason the posts I came across in the past was strictly from painter's error (no further discussion needed of course). But, I was hoping there may be someone on here that has good adhesion results by applying 2 coats of SPI epoxy primer in a 1:1 ratio...coming back 24 hours later and wet sanding with 400 grit for a solid color...then coming back 24 hours later and applied base?

For some reason I have it in my head I am more comfortable doing it this way. I have restored antique aircraft and solvent trapping has been an issue. Of course, this was nitrate/buterate dope...but I have since been nervous and like to play it safe when it comes to "letting the paint gas off".
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I have painted directly on sanded epoxy that is less than 7 days old many times. I ALWAYS activate the base for maximum flexibility and adhesion. It can be done, and I haven't had any comebacks due to this procedure yet. There are reasons why I do this sometimes, but none of them have to do with being scared that it will peel off later.

It's not considered "best practice."
 
Garrett1984 said:
Hello everyone. I have been snooping on here for over a year and I can't recall exactly where in this forum I have seen issues of some folks with delamination issues.
However, let's say for some reason the posts I came across in the past was strictly from painter's error (no further discussion needed of course). But, I was hoping there may be someone on here that has good adhesion results by applying 2 coats of SPI epoxy primer in a 1:1 ratio...coming back 24 hours later and wet sanding with 400 grit for a solid color...then coming back 24 hours later and applied base?

For some reason I have it in my head I am more comfortable doing it this way. I have restored antique aircraft and solvent trapping has been an issue. Of course, this was nitrate/buterate dope...but I have since been nervous and like to play it safe when it comes to "letting the paint gas off".
Click to expand...
I don't do this professionally, but I do way too many projects. I've always sprayed the final coat of epoxy unreduced, and then wet sand 600. Not for adhesion but to get a perfectly smooth substrate for the paint with no nibs or peel. Unreduced epoxy is more robust than reduced epoxy as well. It's still always sanded within the 7 day window. Generally I will spray the final coat of epoxy in the morning, wet sand it that evening, and then the following day clean with WGR, do any seam sealing if required, then paint. It's always a good idea to activate your base coat to prevent serious headaches later.

All that being said, I am getting lazier and want to do things faster so I've been starting to reduce my epoxy 10% and not sanding, just doing any nib correction.
 
I have always used SPI epoxy reduced as a sealer and never had any problems whatsoever. Sometimes 1:1:1 or sometimes reduced 25% . I've laid tape on painted panels to put on the smaller rolls of paper cause my paper machine has 18" paper on it. Never one time had paint lifted on me. If it were to cause a problem it may be because they sprayed outside the adhesion window. Temperature plays a lot into it also.
 
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