Repairing chip in mold gelcoat

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#1

What do you guys use to repair small chips or scratches in the gel coat of your composites mold?

I just pulled the plug from a particularly challenging mold and it came out great… mostly… but there is one or two small sections where I chipped the gel coat with the tool I used to crowbar the plug from the mold.

Part of me thinks I should use more gelcoat but, I’ve never had an easy time sanding down gelcoat additions to the point where they don’t show up in the finished cf part.

I could use Bondo and I know it will be quick and easy to sand smooth but then it won’t be as strong.

Are there any other products I should consider?

Any help would be greatly appreciated because I really don’t want to start this mold from scratch…

#2

Additional gelcoat in the damaged area would work, but it will not be a permanent repair. I have repaired multiple molds using both tooling gel coat or body filler, it will only last a few cycles. If you drill or create a deeper void for the repair to bond to, you will get a stronger repair.

#3

Mix some of the original tooling gel with chopped strands of fiberglass to thicken or carbosil. Always worked for me much better than bondo.

#4

Depends on the repair. If surface quality is important and if gelcoat will fill the void, that is what I would use. As an alternative, I’ve also used P17 from Adtec. It is a vinylester based resin paste with very fine filler so the surface isn’t porous like regular body fillers are. It also stands up to heat better and doesn’t shrink as much. I would never use regular body filler.

I believe Duratec has a mold surface filler as well but I’ve never used it.

#5

Thanks for the info guys.

Sorry for the delay in responding. I’ve been trying out your suggestions. I see what you mean about bodyfiller only lasting a few cycles. It’s not a permanent fix.

For some reason, I don’t seem to have the skills to apply new gel coat over the scratches and then sand it down to the point where it is usable. The shape of my mold cavity is awkward and I seem to make more of a mess than I had before when I try to sand it add uncomfortable angles.

I even bought a proxxon detail sander which was the biggest waste of money yet. It’s really a horrible tool!

I ended up using body filler as a temporary fix so I could use the mold to cast a new plug to recreate it without the damage. I was more careful removing the plug the second time… I used epoxy putty to add a handle on the plug to make it easier to remove with jamming something sharp in the gap around the edges.

I later repaired the original mold by forcing the plug into the cavity under pressure with a fresh gel coat layer. That came out as good as new and seems to be the fastest method of mold repair for me.

#6

the Duratec filler is a vinyl ester. I have used it with good results

#7

Are you talking about the Duratec surfacing primer? I have some of that stuff. I used it once (unsuccessfully) to coat a mold surface and I had written it off as being unusable without a compressor and decent spray equipment. I hadn’t thought of using it for repair of small scratches.

If this is the product you are talking about, what advantages do you find over just applying more gel coat?

#8

You can definitely use the Duratec surface primer if the scratches are fairly minor, though I believe Tom and Roger were referring to the actual vinyl ester mould repair putty that Duratec have, which is more like a body filler in consistency and the fact that it uses a benzoyl peroxide paste catalyst rather than MEKP.

The repair putty would be the better stuff to use if you have chips or biggish sections of damage that won’t fill up with primer. It also polishes up quite nicely, better than the primer.

If you just have some scratches though, the Surface Primer will do it. It’s main benefit over applying more gelcoat is that it sands easier, so it is quicker and easier to correct imperfections. It won’t however polish up quite as nicely though, and so you may be left with a slightly differently textured finish on your final product. It would polish out easily enough, but depends on your needs.

The other alternative is to use the Duratec high gloss top coat if you are just filling scratches, as this also sands easier than gelcoat but will polish up to a full gloss.

#9

No it is a VE mold repair paste. kind of creamy used with bondo hardener. there is a company out here called revchem. I get some of my supplies from them the owner of revchem also owned and patented duratec and ran it as another company. He passed away a few years ago and there was a good article written about him.
I found it http://www.compositesworld.com/news/revchem-dura-hawkeye-founder-douglas-dennis-dies
Revchem carries all the duratec that many others do not.

both companys are in Bloomington CA. and they have a branch store near me, a walk in with a lot of materials in stock

http://revchem.com/
http://www.duratec1.com/Hawkeye/

#10

Thanks guys. I’ll check it out. A paste / body filler type product is much better for my needs than the surfacing primer because I have a lot of vertical surfaces.