Filler for Fiberglass - RCCanada - Canada Radio Controlled Hobby Forum
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Old 05-20-2014, 07:03 PM   #1
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Filler for Fiberglass

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I have replaced the engine on one of my planes and am in the process of repairing a number of holes in the cowl from the old engine. I have almost completed the fiberglass work and will need to do some filling. I am looking for suggestions on what to use as a filler. I was thinking of automotive Bondo but am sure that there are alternatives. Any suggestions would be appreciated.


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Old 05-20-2014, 07:32 PM   #2
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Re: Filler for Fiberglass

For Corvette repair I use a mix of body filler & the resin used for the fiberglass repair at roughly a 50-50 mix & brush it on to be a gel coat. I use a bit of the hardener for both products, It usually sands out easier than filler alone but filler will work too OR this spot putty is nice.

It's available at most auto parts places like NAPA etc.
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Old 05-21-2014, 11:40 AM   #3
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Re: Filler for Fiberglass

Hey Chris,

There is a short strand filler that is perfectly suited for putting over a fibreglass cloth patch. It can be bought at Canadian Tire, etc. The downside is that it's a bugger to sand and it doesn't "finish" well (has voids). The upside is that it's stronger than bondo and fills big dents fast.

If you don't need to fill much (less than 1/8"), I'd just go with good quality filler (not the Motomaster crap at Crappy) you'd get from a body shop supply. I think it used to go by the name "Solid Gold". U might be able to get it at NAPA. It finish sands really nicely and you might not even need glazing putty.
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Old 05-21-2014, 03:53 PM   #4
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Re: Filler for Fiberglass

There is a glass bead filler specifically for epoxy and fiberglass, called cabosil and available at Freeman Supply,and epoxy supply houses.The benefit is that cabosil is totally inert,unlike body filler,which uses clay as a main ingredient.Canadian tire also sells a waterproof marine filler,which for all intents is the easiest to get.
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Old 06-03-2014, 11:36 AM   #5
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Re: Filler for Fiberglass

You can also use micro balloons if you don't need any strength, just need a filler. Works well with either polyester or epoxy resin, as will cabosil. You can get the micro-balloons from your Fiberglass supply or even a hobby shop.

If you are in a pinch though and are using epoxy, you can even use baby powder, it even smells nice when sanding.
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Old 07-09-2014, 10:19 PM   #6
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Re: Filler for Fiberglass

All are good suggestions as mentioned in previous posts, I have been using Auto glazing putty for many years to fill small holes or voids on fibreglass parts, it works great it you apply in light layers and build it up. If applied in thick layer chances are it may shrink a bit.
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