Very fine cracks in a fiberglass cast? Best way to eliminate them?

tubachris85x

tubachris85x

Master Member
Found an older fiberglass helmet in storage. It has very fine cracks in various parts (nothing that affects it's structural integrity). I run my finger over a few of them and I can "feel" it a bit which suggests that it's raised slightly on one side VS the other side. I'd like to throw some filler on them, as I would any other crack, but is there a way to eliminate them completely? I'm afraid that they may still pop through the paint after I do so...thanks!
 
I don't know if there is a solution that is specific for fiberglass, but this is a method that I use:

Knead together a pebble of Milliput. Hold it between thumb and forefinger and put water the other side. Then rub the pebble over the fine cracks, but don't press too hard. Apply more water when necessary. The Milliput that dissolves from the water should gather in the cracks. After a few minutes, wipe off the excess if necessary.
 
I'll throw some pics up tomorrow, was pretty busy today! I think any filler would do, but I've had this before in the past with another item, and I couldn't get it to disappear then...though, I'd like to think it was my less experienced self just unable to do it properly..
 
robn1 said:
When I have trouble getting filler into a fine crack I grind it out a bit, then fill.
Click to expand...

This is exactly what we do in the motor trade when fixing the fine cracks that appear in the gel coat on FG car body's. Make the crack big enough to accommodate a fine filler. Filler wise I'd recommend Upol Top Stop. its a 2 part stopper & its very smooth.

HTH :)
 
If the cracks are super fine - I'm talking hairline stuff, you might be able to drip a little styrene into it to stop it cracking further. That works when repairing tiny cracks in surfboard glass.
 
For super hairline cracks I have used good old super glue and floss. Dip the floss in glue and lay it into the crack, sand gently and repeat as needed. I have used this on a number of fiberglass bow limbs that I still shot with. Certainly not a by the book method at all.

If it can withstand a 50lbs draw bow's pull force it should be okay for a helmet. Just my two cents.
 
Depending on the size and depth of the crack it could be an easy light sanding and repaint or a complete sanding, filler, sanding, primer then repaint...
 
Sorry for taking so long to get these up!

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The idea of grinding it out kinda worries me to be honest...
 
I have success using a water thin cyanoacrylate adhesive & accelerator. That will wick into the crack & stabilize it. If it works for quartz countertops then it will work for the helmet. Also, reinforce those areas inside the helmet, either using more fiberglass & resin or epoxy adhesive & resin. I have used 5 min epoxy & glass cloth with success. That part of the helmet is a weak area & prone to cracking when flexed.
 
bigkidbiggertoys said:
I have success using a water thin cyanoacrylate adhesive & accelerator. That will wick into the crack & stabilize it. If it works for quartz countertops then it will work for the helmet. Also, reinforce those areas inside the helmet, either using more fiberglass & resin or epoxy adhesive & resin. I have used 5 min epoxy & glass cloth with success. That part of the helmet is a weak area & prone to cracking when flexed.
Click to expand...

Yea that's the drawback to this helmet'a design unfortunately. Some of the cracks are over spots that don't flex, like the upper rim, and the side where the ears go. I'll try the CA glue method like you mentioned. Didn't even think of using something like that.

The problem was my helmet took a spill during my last move.
 
Wow, some of those are miniscule. Have you thought about simply using a good quality auto primer, and then wet sanding? You may need to repeat a few times, but the primer will act as a super fine filler.
 
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