How much to sand for additional layers

[swapmeet]

sorry for the goofy subject I didn't know how to make this a short topic title.

How far do you need to sand in order to bond a new layer to the OUTSIDE of the hull with epoxy resin?

The layers on my ski from the outside going in are (I think) paint, primer, gel coat, carbon, and then carbon/Kevlar, and more carbon/Kevlar.

I want to beef up some areas with carbon that I can't get to from the inside. So do I need to go down to the carbon? Or all the way to the carbon/ Kevlar weave?

I assume just roughing the paint / gel coat isn't enough of a bond?


Thanks

 

[swapmeet]

Bump

 

[jo5hi3]

If it's carbon then it should be all paint. From what I under stand gel does not stick to carbon very well.

 

[Vumad]

sorry for the goofy subject I didn't know how to make this a short topic title.

How far do you need to sand in order to bond a new layer to the OUTSIDE of the hull with epoxy resin?

The layers on my ski from the outside going in are (I think) paint, primer, gel coat, carbon, and then carbon/Kevlar, and more carbon/Kevlar.

I want to beef up some areas with carbon that I can't get to from the inside. So do I need to go down to the carbon? Or all the way to the carbon/ Kevlar weave?

I assume just roughing the paint / gel coat isn't enough of a bond?


Thanks

You sand to the first layer of composite.

The epoxy will bond ot anything mostly. You dont sand the gelcoat off because the epoxy doesnt bond to the gelcoat, it does, very well. You sand the gelcoat off because the gelcoat has a weak bond to the composite. The only reason i know of to sand into the composite is if it was poorly built inthe first place, such as a bad repair you want to replace.

 

[SkiPro]

Swap you aren't going to sand into that beautiful paint job on the chan are you?

 

[swapmeet]

You sand to the first layer of composite.

The epoxy will bond ot anything mostly. You dont sand the gelcoat off because the epoxy doesnt bond to the gelcoat, it does, very well. You sand the gelcoat off because the gelcoat has a weak bond to the composite. The only reason i know of to sand into the composite is if it was poorly built inthe first place, such as a bad repair you want to replace.

Bro... I read this twice and I'm through confused.

 

[swapmeet]

Swap you aren't going to sand into that beautiful paint job on the chan are you?

Yes and no. But given my options it's really the only choice I have.

 

[Yami-Rider]

Vumad post made complete sense to me.

Your need to clean down to the first layer of composite you come to, unless the composite is delaminating, then your need to remove the delaminated composite.

For a real strong repair with carbon, I would recommend vaccum bagging your layup. It's not all that difficult.

 

[Midlake Crisis]

Hope this is related enough not to be thread-jacking;
I have used a coarse wood rasp/file to quickly rough up small areas of SMC for repair,
is there another tool that works well for fast roughing of larger surfaces without kicking up a lot of dust?

 

[hornedogg79]

I feel your pain swap. First few carbon chan's had gel that obviously didn't adhere. We are the forgotten members of the Phantom R&D team.

Sent from my SM-G900V using Tapatalk

 

[Vumad]

Hope this is related enough not to be thread-jacking;
I have used a coarse wood rasp/file to quickly rough up small areas of SMC for repair,
is there another tool that works well for fast roughing of larger surfaces without kicking up a lot of dust?

I use a variety of tools depending on the job, but most create dust.

Angle die grinder with 2 and 3 inch discs
4-1/2 grinder with flap discs
Da
Random orbital sander
Inline sander
Various sanding blocks

The tool I choose rarely has anything to do with dust. If dust is an issue, build a room, wear a respirator, and if applicable, you can incorporate a vacuum or water.

I rarely use rasps or files but I have them and have used them. The only time I prefer a rasp is a rounded one working concaved angles.

It really doesn't matter what you are using when you are going to layup over it. The layup slightly changes the shape of the part anyway.

 

[Vumad]

Bro... I read this twice and I'm through confused.

You said the layers are paint, primer, gelcoat, carbon/Kevlar.

Carbon/Kevlar is a hybrid fabric. Glass, carbon, Kevlar, hybrids of any of them, it's all the same end result. Mix them with a resin and they become a composite.

Paint, primer and gelcoat are no composites. They are used for finishing a part. They provide no structural contribution to the part.

So, going back to your question, and my reply...

Sand down to the first layer of composite. It doesn't matter if the first layer is glass, carbon, a hybrid, whatever. The ski can have whatever layup schedule. As long as the original layup was done correctly, and you have a solid structure, sanding through layers of composite won't do anything positive. It just means more reinforcement. There is no reason to sand into the composite unless it is damaged or was poorly laid up to begin with.

As for my other statements, I was making the point that you can layup your repair over anything. The epoxy repair will stick to the paint, the primer, or the gelcoat. The problem is that the finishers will eventually delaminate from the part. Since the repair is sticking to the finish and not the structure, it will come off. It's not that the repaired failed, but rather the finish the repair was attached to failed.

So, with all that said, if it's still confusing, then ignore everything that provides a critical thinking explanation to the job and just go the following...

Sand down the paint, primer and gelcoat, and bond to the carbon.

 

[simofx-1]

the only areas you cant get to from the inside is the tray, i presume this is the area you want to beef up?