38-31: Canopy Fibreglass Fairing - Round 9 - Be Careful what you use on the Canopy Fairing

Heartbreak

Finding a canopy crack on Christmas Eve was the worst thing to happen to me in the whole building process. It was truly heartbreaking. 

The cracks look like they are internal to the canopy glass, and eminate from the surface of the countersink. I can't feel them on the surface of the canopy at all. they are very short (that is a #6 screw for reference). 

Seeking Assistance

As usual, the good folks of Van's Airforce gave me a much needed chill pill, and quickly worked out what the likely cause was. 

Yep.

The Cuplrit

Here is a nice photo showing how i applied some blade putty in the corner of the fairing on the left hand side, in order to fill a low spot (as it was easier than mixing up micro and resin). 

I have used this product on a few fibreglass parts before and it works great - fills pinholes very well, dries fast and sands easily. However, if i had checked the MSDS i would have realised it contained Toulene! What a stupid thing to do. 

Testing that this was the cause

On the forum chat about this issue, one of the possible causes could have been tightening the screw too hard in that corner. So i decided to do some testing to see. 

I had a piece of spare canopy left over, with a countersunk hole already in the corner. So i tightened a screw and nut in that hole and applied some blade putty adjacent to the hole, at a similar distance to the location on the canopy. These were the results:

This was how it looked once the blade putty was applied. No initial reaction.

However, leaving it for a few hours, it looked like this.

This is on the screw head (countersink) side

This is on the inside.

These cracks seem very similar to what i am seeing on the corner of the canopy, so i think the conclusions of Scott McDaniels are correct - this is chemically induced crazing!! 

I am going to sit on this for a bit, and continue to work on the fairing to completion. I will then, once i've calmed down a bit, see if i can wick some Weld On 3 into the cracks...