Pin holes (again)

On Tuesday, April 4, 2017 at 11:56:12 AM UTC-4, wrote:
On Tuesday, April 4, 2017 at 10:53:46 AM UTC-4, wrote:
Go with Hanks advice. He guided me in the refinish of CF and it turned out great. I was constantly advised by spectators as to how I "should do it". One guy grabbed a gear foot and promptly sanded through to the foam core.. From then on I didn't mind being rude to the next neighbor with the "better idea". In short, don't make it complicated.

Simtec also has a filler if you are using their products.

Lane

Simtec 2081 does not sand anywhere as well as Polyprimer. JJ put me on to Polyprimer.
UH

2081 sands fine if you add a little gelcoat. i'd be interested to try polyprimer sometime.

...start by mixing up a small batch of filler, and squeegee it onto the wing (or whatever) with a plastic bondo spreader...

The problem I and others have had with that approach is that the filler does not wet out the surface of the pinhole very well. Even though it fills the pinhole, it does not establish a bond with the surface. Often, the pneumatic pressure of the air in the pinhole forces the thick filler back out, so you get only a very shallow fill over the top of the pinhole.

As it ages and the wing (or whatever) flexes, the filler is likely to break free from the interior surface of each pinhole. Then the pinholes start mirroring through the finish paint, and eventually might start cracking in a checkerboard pattern.

Squeegeeing on a couple quick skims of runny epoxy helps wet the interior surface of each pinhole, and forms a rounded meniscus over its sharp irregular internal contour. Filler sprayed or squeegeed over the epoxy skim has a better surface to bond to, and there is less internal volume in each pinhole for air that repels the filler and impedes the bond.

--Bob K.

I'm with you, Bob! That's why I think I'd brush on an epoxy coat (maybe squeegee'd) and then peal-ply everything, so she's ready to accept prime without any sanding needed. OBTW........please shoot me if I ever take on another re-finish job! My son and I bid a set of LS-6 wings at $40/hr................we got $25/hr
NEVER AGAIN
JJ

On Thursday, April 6, 2017 at 5:49:39 PM UTC-4, Bob Kuykendall wrote:
...start by mixing up a small batch of filler, and squeegee it onto the wing (or whatever) with a plastic bondo spreader...

The problem I and others have had with that approach is that the filler does not wet out the surface of the pinhole very well. Even though it fills the pinhole, it does not establish a bond with the surface. Often, the pneumatic pressure of the air in the pinhole forces the thick filler back out, so you get only a very shallow fill over the top of the pinhole.

As it ages and the wing (or whatever) flexes, the filler is likely to break free from the interior surface of each pinhole. Then the pinholes start mirroring through the finish paint, and eventually might start cracking in a checkerboard pattern.

Squeegeeing on a couple quick skims of runny epoxy helps wet the interior surface of each pinhole, and forms a rounded meniscus over its sharp irregular internal contour. Filler sprayed or squeegeed over the epoxy skim has a better surface to bond to, and there is less internal volume in each pinhole for air that repels the filler and impedes the bond.

--Bob K.

that has not been my experience. it's worked pretty well for me for the last several years, during which time i've done a few dozen refinishes. also, filler seems to be less viscous than runny epoxy. and you can spray right over, immediately afterwards without any sanding. i also believe that it does create a good bond, especially since there is a mechanical bond in there. i have not had any problems with filler pushing back out of the pinholes. in fact, there is a soft of capillary action, and it seems to soak in like a sponge. i remember doing a wingtip that was heavily crazed, by squeegeeing some resin. it was messy, and not so nice to sand afterwards. no question, your method works well, but i think mine does too. there advantages to both.

Let me pass on a good trick to deal with Kevlar fuzz. If you accidentally sand into a Kevlar layer, you find it won't sand, it just fuzzes up! We soaked the exposed Kevlar with CA (cyanoacrylate) from the local hobby shop, then hit it with Fix. This left it stiff as a board and simply scrapped most of it off with a sharp razor blade.
Also had raw Kevlar exposed at the trailing edge of flaps and ailerons. These areas must be sealed up or the Kevlar will "wick" in moisture! We got some 1 oz fiberglass tape (1" wide) and 1" peal-ply. Wet it out and wrapped it around the trailing edges, held in place with masking tape orientated for/aft.
JJ

On Friday, April 7, 2017 at 8:49:33 AM UTC-4, ND wrote:
On Thursday, April 6, 2017 at 5:49:39 PM UTC-4, Bob Kuykendall wrote:
...start by mixing up a small batch of filler, and squeegee it onto the wing (or whatever) with a plastic bondo spreader...

The problem I and others have had with that approach is that the filler does not wet out the surface of the pinhole very well. Even though it fills the pinhole, it does not establish a bond with the surface. Often, the pneumatic pressure of the air in the pinhole forces the thick filler back out, so you get only a very shallow fill over the top of the pinhole.

As it ages and the wing (or whatever) flexes, the filler is likely to break free from the interior surface of each pinhole. Then the pinholes start mirroring through the finish paint, and eventually might start cracking in a checkerboard pattern.

Squeegeeing on a couple quick skims of runny epoxy helps wet the interior surface of each pinhole, and forms a rounded meniscus over its sharp irregular internal contour. Filler sprayed or squeegeed over the epoxy skim has a better surface to bond to, and there is less internal volume in each pinhole for air that repels the filler and impedes the bond.

--Bob K.

that has not been my experience. it's worked pretty well for me for the last several years, during which time i've done a few dozen refinishes. also, filler seems to be less viscous than runny epoxy. and you can spray right over, immediately afterwards without any sanding. i also believe that it does create a good bond, especially since there is a mechanical bond in there. i have not had any problems with filler pushing back out of the pinholes.. in fact, there is a soft of capillary action, and it seems to soak in like a sponge. i remember doing a wingtip that was heavily crazed, by squeegeeing some resin. it was messy, and not so nice to sand afterwards. no question, your method works well, but i think mine does too. there advantages to both.

I've seen some times when trapped air pushes the filler back out of the pinhole to some degree. The reason I went to the roller method is that each individual area gets multiple passes from at least 2 different directions which I have found minimizes this. I also have found that I can get a more uniform surface with the roller than I can with a squeegee. I've done it both ways and still occasionally find that the squeegee helps.
Sanding this filler back flat does no new damage to the surface where sanding epoxy is harder and, I have found, more prone to adding more damage.
I have not seen any pinhole repairs come back to the surface with this technique.
It's worth noting that there are several ways to skin this cat.
UH`

JJ and Uncle Hank, do you shot PPG Concept right over the polyprimer or do you use a PPG primer also?
Thank you

On Saturday, April 8, 2017 at 8:09:09 PM UTC-4, wrote:
JJ and Uncle Hank, do you shot PPG Concept right over the polyprimer or do you use a PPG primer also?
Thank you

I seal with epoxy primer. I think JJ goes direct based on his prior comments.

I have done it both ways, but prefer polyprimer because it is white!
Another tid-bit I have tried is to wet sand with 800 grit after 12 to 24 hours cure, then buff out right away. Shines like no tomorrow, believe the paint is moving under buffer, just enough to eliminate the 800 sand marks.
JJ

The difference in heat between "flowing the paint" and burning it is a close one. When I do final polish wax, I like to get it warm on the surface with polishing load. It gets a nice shine.