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epoxy to firewall bond

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bill mcclellan

Joined: 28 Jan 2010
Posts: 43

Posted: Sun Apr 25, 2010 1:14 pm Post subject: epoxy to firewall bond

I have run into an alarming situation.  I find epoxy BID applied to the firewall material does not have great bonding characteristics.  I have not seen this brought up before.  I discovered this, as to attach the instrument panel, I epoxied a 4 ply BID flange onto the lower firewall inside face.  After cure, I was shaping the flange and found that it peeled away without much difficulty.  This brings into question the bond of all the many places that fiberglass BID is used to reinforce the reduxed joints on the firewall.  I have attached a picture showing the scuff sanding preparation I did to the firewall surface.  Hopefully the photo remains attached.  I am using new epoxy and no unusual temperatures were prevalent.  The epoxy cured as expected so the epoxy mixing proportions shouldn't be in question.  It seems that the phenolic firewall material just does not allow a good epoxy bond?  Is this something that is known and expected or is this not as it should be?

Thanks,

Bill McClellan

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Sun Apr 25, 2010 2:46 pm Post subject: Re: epoxy to firewall bond

Hi Bill,



Can you tell us how you prepped the firewall for bonding?



It needs to be chemically clean and well scuff sanded to provide

a good key.

_________________
Ira N224XS

fklein(at)orcasonline.com
Guest

Posted: Sun Apr 25, 2010 6:46 pm Post subject: epoxy to firewall bond

On Apr 25, 2010, at 2:04 PM, William McClellan wrote:



 	  Quote: 	
		    I have attached a picture showing the scuff sanding preparation I  

 did to the firewall surface.


	


Bill,



Your scuffing looks about like mine...as a rule, in addition to  

scuffing, I fire up my compressor to blast away loose particles before  

wiping surface down w/ acetone...then brush on a tack coat of  

resin...and, only then apply BID. Near as I can tell, my BID tapes on  

the firewall are not suspect.



your mileage may vary,



Fred

bill mcclellan

Joined: 28 Jan 2010
Posts: 43

Posted: Sun Apr 25, 2010 7:35 pm Post subject: epoxy to firewall bond

Thanks for the replys, I am at a bit of a loss as I followed my usual routine, scuff sanding (80 grit)cleaning with alcohol then allowing to fully evaporate (clean paper towel), laying up the 4 ply on cellophane to insure proper wetting of the layers of glass, and I had done the surface prep just prior to layup so not likely and air borne contaminates got on the surface.  In this case I left the cellophane on top as I used the instrument panel against it to establish the mating of the flange and the panel.  No peel ply used.  I would guess that if any mold release was used in the original creation of the fire wall, it was on the other side, in any case as usual, I took the surface down to newly exposed material.  I have tried to separate or pry off an epoxy to epoxy surfaces before and it is undoable, but has to be sanded or ground off.  I have also had to remove a reduxed phenolic pad and it also can only be ground off.  Maybe it only leaves to do another test lay up as again see if I can pry it off.

Thanks,

Bill McClellan

frans(at)privatepilots.nl
Guest

Posted: Mon Apr 26, 2010 12:52 am Post subject: epoxy to firewall bond

On 04/25/2010 11:04 PM, William McClellan wrote:

 	  Quote: 	
		   I have run into an alarming situation.  I find epoxy BID applied to

 the firewall material does not have great bonding characteristics.


	


Well, the description and picture are identical to what I experienced

with the strenghtening and flap drive bonding of one of my wings. In

that whole area all epoxy work just snapped loose if I pried with a

screwdriver.

Disturbing was, that after a second attempt (even more sanding,

cleaning, double checking proper mixture, temperatures, etc.) I got into

the same situation again. For some reason it was impossible to get a

proper bond in that area.

General consensus was that there must have been some release agent

residu from the factory left behind, or silicone contamination from

whatever source (maybe a factory employee wiped off some spoiled coffee

with a contaminated rag?)

So, in the thirt attempt, I not only used acetone, but also soap, gas,

alcohol, vinegar, and a dozen other solvents, to get this invisible and

unknown "release agent" off.

One of these solvents must have worked, because after that the bond was

finally OK.



I just keep wondering how many others must be flying around with a

similar local contamination and never found out about it because

everything just looked right.



Because of this experience I have subjected all my bonds to the

"screwdriver" test. You should pry until you get some fibers off as a

proof that the bond is ok. If you instead hear a "snapping sound" and

the whole layup changes color, you have the dreaded "contamination error".



And yes, my firewall bonds survived the "screwdriver" test. There were

no other problem area's, only this specific area of one of my wings had

this "impossible to bond" problem.



Frans

loboloda(at)execulink.com
Guest

Posted: Mon Apr 26, 2010 11:05 am Post subject: epoxy to firewall bond

A quick spray of water will indicate if there is contamination.

If the water beads there is a problem.

Having had a similar experience, I tried many things, water based  

prep washes from auto body shops work well

as do Comet/Ajax type kitchen cleaners, these foam and scrub and do a  

great job .



Dave C-FBZI

On 26-Apr-10, at 4:48 AM, Frans Veldman wrote:



 	  Quote: 	
		   

 <frans(at)privatepilots.nl>



 On 04/25/2010 11:04 PM, William McClellan wrote:

> I have run into an alarming situation.  I find epoxy BID applied to

> the firewall material does not have great bonding characteristics.

rparigoris

Joined: 24 Nov 2009
Posts: 797

Posted: Mon Apr 26, 2010 5:18 pm Post subject: Re: epoxy to firewall bond

Hi Frans

"the strenghtening and flap drive bonding of one of my wings." 



Where exactly is flap drive bonding? On root of flap where you drill into aluminium for drive pin?



Ron Parigoris

frans(at)privatepilots.nl
Guest

Posted: Mon Apr 26, 2010 9:40 pm Post subject: epoxy to firewall bond

On 04/27/2010 03:18 AM, rparigoris wrote:

 	  Quote: 	
		   

 

 Hi Frans

 "the strenghtening and flap drive bonding of one of my wings." 

 

 Where exactly is flap drive bonding? On root of flap where you drill into aluminium for drive pin?


	


I meant the flap attachment plates. The middle one and the inner one of

the outer pair. That area was contaminated, and also the aileron

closeouts of that wing wouldn't bond.



Frans

jglazener

Joined: 14 Apr 2010
Posts: 76
Location: Schoonhoven, Netherlands

Posted: Tue Apr 27, 2010 11:40 am Post subject: Re: epoxy to firewall bond

I am pretty sure contamination is an important factor. The acetone cleaning ritual certainly helps for me. However, don't forget another factor and that is the curing of the epoxy. Sure, after a few hours it gets hard but it is by no means cured. The full process can take weeks, even months in which longer and longer polymer chains are formed. In fact without a post cure it never really finishes- which is why we do it of course.



I would not be surprised if this also plays an important role in bonding to the substrate. Part of the bid tapes on my firewall came off practically by looking at them. I redid those parts, but all tapes are now solid as a rock.



Message: don't panic if the bid can be easily taken off the next day. Give it a week or more and only then decide if you really need to rip it all out.



Jeroen

bill mcclellan

Joined: 28 Jan 2010
Posts: 43

Posted: Thu Apr 29, 2010 12:09 pm Post subject: epoxy to firewall bond

After having done some additional tests, bonding epoxy to the phenolic firewall material as well as testing of my previous firewall bonds, I have satisfied myself with a conclusion.  It is that epoxy does not form even a somewhat adequate bond to any unabraded glossy phenolic firewall material.   The bond is almost non existant compared to that of an otherwise epoxy to unabraded epoxy bond.  So leaving any glossy phenolic surface unabraded is well more detrimental to the overall bond than leaving some unabraded area under a epoxy to epoxy lay up.  



I still consider that on the areas where only one ply of glass/epoxy is over the foam sandwich, one has to be careful not to sand off too much of that single ply to get down to a complete abraded surface, not so on the phenolic firewall material.



The front (engine side) of the firewall, requires less sanding and material removal to get below the glossy surface, as it is smooth having been against the mould in the original lay up, compared to the less smooth firewall backside with its depressions from the embedded woven material.  So you just have to remove more material on the firewall backside to get below all the gloss for an adequate bond.



Contamination on surface was not the culprit in my case.  Though removal of real or potential surface contamination is alway a necessary step in bonding preparation.



Bill McClellan

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