Will fiberglass easily crack with body flex?

I'm thinking about making some custom wide body fenders, as stated in a previous post, and thinking about bondo cracking, i know fiber glass has to be stronger because people use it for sub boxes.

Also is it easy to lay and manipulate? I'm very detailed oriented so i thought that might be a plus...

 

fiberglass will crack under flex just like bondo... but the stress it takes to crack it is greater... to get the most life out of your wide body fenders there are a few ways to do it... first off get some high density foam than can be shaped...i have used surfboard foam here but finding that where ever you are might be hard to do... apply lots of 3m bouble sidede tape to the foam to keep it on the fender and form the shape you want your fenders to be...the foam can be shaped with an electric knife and a grinder for the rough shape then finish sanded by hand with a cheese grader and sand paper until it is smooth... then overlay your fiberglass sheets on the fender and the foam... use lots of mold release to make sure that the glass will come off...pay close attention to keeping the glass as smoothe as possible... this will help in the finishing of the panel when you are all done with the molding... once the glass has dried remove it from the car and you have one fender panel made...and extra fiberglass reinforcement should be put on the underside of the panel to make it stronger... you will have voids where the foam was so as long as you do not build up too think there should be no problems with it fitting... make sure to check it between each step for fitment on the car...you can never check it too many times...finish the panel as you would in prepping for paint... sand bondo sand bondo sand some more...until there are no imperfections in the panel itself... then attach it to the car as you had planned... repeat untill you have all the panels done the way you want them... this method is hard to get exactly right if you are using extreme shapes and curves from side to side... but it can be done...then you can mold in the panel using products like kitty hair or tiger hair and bondo so as not to show any seams...
you can catch me on aim screen name wikd24d if you want detailed instructions on how to work with fiberglass or any of the panel construction... i would be glad to help you out in any way i can...

 

Sounds like you know what you are doing, do you mind if I aim you when I start my project?

 

not at all.. im here to help where ever i can... i used to build custom imports when i lived in cali and this is nothing new to me... its all fun and helping others learn is worth it to me...knowing i did it all myself or helped someone do it all themself... better than payin for it to get done... no one will do as good of work as the person who loves the car being worked on...

 

Well, this was a great read up, ya man, sounds like a nic project, i want to do everything myslf, so this is a definite help. Where might i get the foam to shape? Do you shape itunder heat or is there a different method? Can i get this at a Lowe's or hardware store or is this tye offom hard to find? Thanks a ton, this has helped a boatload