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  #1  
Old 06-07-2021, 03:46 PM
RVFan671 RVFan671 is offline
 
Join Date: May 2020
Location: Seattle
Posts: 75
Default Epoxy is chipping or delaminating on my cowl

Would like to hear some opinions on what I should do here. I have an RV-4 that was built in 1991 and it appears time when they installed the piano hinge on the top and bottom cowl they put a 2 to 3 inch wide piece of glass under it and used the same epoxy to do a final coat on the inside of the cowl.

Now 30 years later (it's only flown 280 hours) it seems like there was never a bond or that bond is no longer there. Near the strip of glass it is completely delaminated from the layers below. In the middle of the cowl it looks like little air pockets where the top most layer of epoxy has lifted.

What I've done so far is take a plastic scraper and ran it over things to flake off what is easy to flake off. On the top cowl I went ahead and broke the glass strip near the piano hinge.

Should I just leave it as is for now and keep scraping it off over time or is there a need to sand it all off and put a thin coat of epoxy down? I am not sure if he was using polyester resin or just skipped the step of scuffing before applying epoxy so it would stick.
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  #2  
Old 06-07-2021, 07:48 PM
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BlackhawkSP BlackhawkSP is offline
 
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It looks like the builder did not prep the cowl by rough sanding the cured part, before adding the additional layer of glass and and epoxy to the cowl. If the glass keeps delaminating, I would just peel it back and break it off to the hinge line, where the hinge and rivets will mechanically hold it on. As far as the rest, you can clean the cowl inside, sand prep the inside properly (to provide "tooth" for the resin to stick to), and reseal with a fresh coat of epoxy. You might also ask Van's if the resin is a Vinyl ester, or epoxy on the original cowl.
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  #3  
Old 06-07-2021, 09:48 PM
RVFan671 RVFan671 is offline
 
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Do I even need to put that layer of epoxy on to reseal, or did the original cowl have what it needed for strength and sealing? I'll have a dig through the original instructions to see if it asks you to put a layer of epoxy over the cowl too.
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  #4  
Old 06-07-2021, 11:29 PM
arffguy arffguy is offline
 
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Default Early cowl material

Quote:
Originally Posted by BlackhawkSP View Post
You might also ask Van's if the resin is a Vinyl ester, or epoxy on the original cowl.
If you truly have a 1991 or earlier cowl, I'm 100 percent sure it is polyester with a layer of white gel-coat on the outside.
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  #5  
Old 06-08-2021, 06:26 AM
Southern Pete Southern Pete is offline
 
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A layer of epoxy on its own will do nothing, a layer (or 2 or 3) of glass must be added if strength is required.
If the epoxy/polyester resin is peeling off then its because the preparation was inadequate - that is clear as the layup underneath is shiny. Laying more on top isn't really going to help.
From the pictures I'm not sure anything is required. Removing the flaking stuff runs the risk of making it all peel off! If you decide it needs a layer of glass rough up the old layup with a 60 grit disk, vacuum well and apply the resin & glass. Epoxy can be used over polyester but not the other way around.
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  #6  
Old 06-08-2021, 10:08 AM
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BlackhawkSP BlackhawkSP is offline
 
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Quote:
Originally Posted by RVFan671 View Post
Do I even need to put that layer of epoxy on to reseal, or did the original cowl have what it needed for strength and sealing? I'll have a dig through the original instructions to see if it asks you to put a layer of epoxy over the cowl too.
No need really to re-coat, unless there's a pin hole somewhere that is letting engine oil through the cowl to the top. I'm assuming the layer of glass was added to line up the hinges better (just guessing here).
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RV-Super 8 N88XT SOLD
RV-10 QB N38LA Flying
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At IU Health Retired :-)
Although Exempt,
Donated for 2021
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