patching exterior wall

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patching exterior wall

Postby sxjames » Sun Apr 01, 2018 5:48 pm

Quick Question - I'm ready to start patching the countersink holes (and fill in a seam between two sheets of plywood) on the exterior of my tiny trailer before applying the exterior coat (CPES followed by exterior paint). What do folks recommend I use for patching? Is inexpensive wood filler good enough, or do I need something more exotic like a plastic Bondo type material? I guess my real question is what is compatible with the CPES...or, alternatly, what should I avoid.

Stephen
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Re: patching exterior wall

Postby les45 » Mon Apr 02, 2018 2:41 am

Do not use Bondo as it is not compatible with epoxy systems. I used Smith's Fill-it epoxy filler for all my patching including all screw head holes and blemishes in my plywood skin. However, I applied my CPES first so that it would penetrate deep into all the holes and blemishes. The CPES goes a long way and I think I ended up giving it four coats with special emphasis on all the plywood edges. I used fiberglass tape and an epoxy system on all corners and butt joints and then topped it with two coats of Zinsser oil based primer and three coats of Rustoleum.

You can see the details of my epoxy and paint work starting at about Page 4 of my journal: http://tnttt.com/viewtopic.php?f=50&t=49333

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Re: patching exterior wall

Postby sxjames » Mon Apr 02, 2018 10:03 am

Thanks for the reply. So, if I understand correctly you put on the CPES before patching...yeah, that makes sense. And thanks for the link to your build - It looks great!

Stephen
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Re: patching exterior wall

Postby tony.latham » Mon Apr 02, 2018 10:19 am

Do not use Bondo as it is not compatible with epoxy systems.


I'm surprised to read this. I've had no problem epoxying over polyester based kayak layups. (And of course, Bondo is a thickened polyester resin). There's an adage that I've heard for thirty years: You can fiberglass over polyester but you can't polyester over epoxy.

I'm talking epoxy, not CPES. Which ––if I understand it–– is epoxy thinned with something, perhaps acetone or toluene. Which isn't healthy on polyester. I know someone had problems with CPES delaminating luan plywood.

Thoughts? :thinking:

Tony
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Re: patching exterior wall

Postby les45 » Mon Apr 02, 2018 11:06 am

tony.latham wrote:
I'm surprised to read this. I've had no problem epoxying over polyester based kayak layups. (And of course, Bondo is a thickened polyester resin). There's an adage that I've heard for thirty years: You can fiberglass over polyester but you can't polyester over epoxy.

I'm talking epoxy, not CPES. Which ––if I understand it–– is epoxy thinned with something, perhaps acetone or toluene. Which isn't healthy on polyester. I know someone had problems with CPES delaminating luan plywood.

Thoughts? :thinking:

Tony


You are right in that it technically will work if the Bondo is fully cured and properly prepared (roughed up). The problem I had when I did my work was that no one could tell me what "fully cured" meant and I didn't want to wait to find out. Most of the comments I read said that you can glass over Bondo but "it wasn't the greatest thing to do". That's why I went to a different filler that I knew would be compatible with my fiberglass system.
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Re: patching exterior wall

Postby tony.latham » Mon Apr 02, 2018 1:00 pm

les45 wrote:
tony.latham wrote:
I'm surprised to read this. I've had no problem epoxying over polyester based kayak layups. (And of course, Bondo is a thickened polyester resin). There's an adage that I've heard for thirty years: You can fiberglass over polyester but you can't polyester over epoxy.

I'm talking epoxy, not CPES. Which ––if I understand it–– is epoxy thinned with something, perhaps acetone or toluene. Which isn't healthy on polyester. I know someone had problems with CPES delaminating luan plywood.

Thoughts? :thinking:

Tony


You are right in that it technically will work if the Bondo is fully cured and properly prepared (roughed up). The problem I had when I did my work was that no one could tell me what "fully cured" meant and I didn't want to wait to find out. Most of the comments I read said that you can glass over Bondo but "it wasn't the greatest thing to do". That's why I went to a different filler that I knew would be compatible with my fiberglass system.


No doubt thickened epoxy is thee way. We’re just talking screw holes though. Any sandable wood filler would work fine.



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