Fiberglass vs Rondo

GL 2814

New Member
I have been reading up on how to finish pep work. From what I have read you resin the outside but my question has to do with the inside of pieces. My first question is what is the better choice on the inside, rondo or fiberglass? Is it easier to work with rondo? Is fiberglass that much stronger to make a difference? After resin coating the outside of your pep can you use the rondo on the outside also or just go with straight bondo?
I haven't used rondo, as far as I know there are certain products just not available here in NZ.

That said step one: resin the outside then the inside and leave to cure both times then FG the inside and use those putty like products on the outside. The resin used in FG will run and drip to a greater or lesser degree and it is easier to clean up from the inside than the outside where you may change the features.
the putty like products are much easier to manipulate to where you want them to be and they don't slump or self level ;) They are not as strong as FG especially FG using matting. It has to do with the ability to make chemical bonds resulting in a weblike structure right through FG vs shorter chains in the putties etc. It is also why you are supposed to lay all the matting in one go rather than laminate in layers: the bonds go through all layers in the former and only short chains between layers.

Yay chemistry and physics ;)

Also the putties are much easier to sand and cut back than FG.
if you dont want to use fiberglass resin you can you a product called fiberglass jelly.. that you can find at walmart and most automotive supply stores.. it does require alot more sanding cuz getting it smooth while putting it on is very hard unless you work in very small patches.. it was my first time using the jelly on pep but i built a rocketeer helmet and it stiffened it to rock hardness . after sanding it you can apply more of the jelly then sand it and bondo it.. thats the steps im taking
You do not want to use rondo for a wearable piece. Rondo's only real use is for mother molds and even that can be done with fiberglass. For pepakura you want to resin the outside, then resin the inside, and apply cloth and or mat to the inside. You will use bondo to detail the outside. the result will be a strong, lightweight piece.
the advantage of fibreglass over rondo that its statics are better. so it can be pulled or pushed a little bit, and go back in shape. rondo is not that flexible, and could break
I always thought it was a resin/bondo mix lol. but yeh fibreglass allows the piece to have a little more 'give' as opposed to rondo, that could crack.
I heard rondo stays tacky and has that uncured sent of resin.. If you want to do it right just use fiberglass cloth and resin.. There is no short cuts in making a finished prop or costume..

Ask any bodyshop specialist.. They can point you to the right direction..
Rondo is equal parts bondo and resin, with bondo cream hardener. I have used it many times and it always cures hard, never tacky, but if you don't put enough hardener in then it wouldn't cure....
You can use any ratio of resin/polyester filler aka Bondo in your "Rondo" mixture.
the truth is, Bondo is just talc and polyester resin. You can actually buy a pound of talc and a gallon of resin, and manipulate your viscosity. For this I would recommend using a red 30% MEK-P aka hardener, and use 12 drops (approx. .5cc of MEK-P) per 2 oz. of resin.

You can also use this combination as your primer if you add some acetone in it. You just have to do your math and make sure you use 1cc of MEK-P per 4 oz. resin.

However, I don't recommend using Rondo alone for reinforcement. I'd recommend using 3/4 oz. chopped strand fiberglass mat. if weight is your concern.
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