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Fiberglass crack

#1
I have a motorcycle saddlebag I'm painting and the top hatch door has a crack underneath on the side,
doesn't appear on the outside gelcoat. Should I vee grove this out and add resin or is there something
better to use? I'm concerned it may crack again from opening and closing the door then come through
my paint. Thanks
 

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#2
jim, you will need to "V" that out and patch that with some glass...unfortunately. dont use just resin. if you dont use glass it will probably crack again. you might get by with mixing up some epoxy resin and adding a thickener to make filler out of it BUT glassing it it will be best.
 
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#3
So, add some fiberglass matt strands to the resin? Is that what you're saying?
Should the surrounding surface have a layer of cloth added?
And do you think I should go ahead and vee out the other side too?
 

Chris_Hamilton

Trying to be the best me, I can be
#4
Check out this video by SEM. Should answer all your questions.

Although they are talking about SMC (sheet molded compound) the principles still apply. And you can use the SMC repair compound on fiberglass as well.
 

jlcustomz

evil painter
#6
If you can't see anything on the good side, probably best leave it alone. Any repair will shrink some now & a tiny bit later throughout time, so I wouldn't create another issue if I'm sure I didn't need to. When you grind into the backside , you may see the crack stops....
Cloth is not something you'd want .
I've generally done similar repairs the traditional v- groove & a little matt with resin. Polyester can work, but epoxy is best.
I haven't looked into the new repair stuff like in the link Chris posted, but I have cut & glued back together thick fiberglass(butt joint) on the end of my personal custom car hood with Smart's 3-m 8115 type panel adhesive 3 years ago & it won't budge when beat on, so some of these new to me repair options may be easier for you.
Hood in picture was cut to change from 2010 camaro profile to more angular 2016 profile. small part upfront was leftover cutout part used to extend now longer front profile. Point is yes the new adhesives are strong, BUT before paint on the upper side that will show the most it will get a traditional v-groove repair job to avoid a possible bad shadowing issue from all adhesive joint with no glass fibers.
Strength , shadowing, & shrinkage are the main factors to consider in a fiberglass repair.
20160724_111505.jpg 20160724_111505.jpg
 
#10
Making a VEE should not describe what it looks like, per se...

My typical repair for something that cracks all the way through: I would use a roloc sander on a stress crack like that and sand down just over halfway through the thickness, with the width about 2 to 3 inches wide, or more. (Not the 1/8” or so that you show). The strength is going to come from spanning across the crack. Let the first layer set, sand down, add another, repeat until you are about flush with the surface. (Let cure between layers). Now flip it over, and do the same thing again from the back side, making sure you sand just over half way through (you should see your repair from the front) and add your mat to the back side, adding layers as needed, sanding down and repeating until that side is flush.


If the damage is not visible from the outside, I’d use the same procedure as laid out above on just the one side, but sand down more than halfway until you can almost see through the layer. Then make the repair adding layers as above. I fear with the minimal amount you VEE’d out the crack, the repair has limited strength, and the crack will reappear in short order. Those saddle bag covers take quite a bit of abuse in opening and closing. Needs a bit more thorough job in adding strength back in that area than what you’ve done, IMO. I’d hate to see you waste paint to a soon returning crack because the repair isn’t yet up to par.....
 
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#11
Agree with Robert. The heat from the sun could cause issues too. Ghosting is one of the things that drive me nuts and always error on the side of caution especially when doing glass work.
 
#12
Making a VEE should not describe what it looks like, per se...

My typical repair for something that cracks all the way through: I would use a roloc sander on a stress crack like that and sand down just over halfway through the thickness, with the width about 2 to 3 inches wide, or more. (Not the 1/8” or so that you show). The strength is going to come from spanning across the crack. Let the first layer set, sand down, add another, repeat until you are about flush with the surface. (Let cure between layers). Now flip it over, and do the same thing again from the back side, making sure you sand just over half way through (you should see your repair from the front) and add your mat to the back side, adding layers as needed, sanding down and repeating until that side is flush.


If the damage is not visible from the outside, I’d use the same procedure as laid out above on just the one side, but sand down more than halfway until you can almost see through the layer. Then make the repair adding layers as above. I fear with the minimal amount you VEE’d out the crack, the repair has limited strength, and the crack will reappear in short order. Those saddle bag covers take quite a bit of abuse in opening and closing. Needs a bit more thorough job in adding strength back in that area than what you’ve done, IMO. I’d hate to see you waste paint to a soon returning crack because the repair isn’t yet up to par.....
That makes sense to me, thanks!
 

jlcustomz

evil painter
#13
What may have been a little confusing here is that the traditional v-repair, that some of us learned long time ago does generally include a large amount of feathering back or beveling back so that the whole area has a new layer of interlocking fibers with the new resin.
But at least as I showed where I butt joint glued ends of a hood back together, these modern epoxies are pretty strong. Being that the upper surface wasn't showing, hopefully this won't show through. Could take several years to find out, which would be out of warranty.
 
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