Surface finish issues

[Hanaldo]

Yeh that’s definitely the issue then. 1000 grit is faaaaaar too fine, that won’t give any adhesion at all. With epoxy, you want to be using 80 grit to scuff it for mechanical adhesion. BUT, with a gelcoat you don’t want to be sanding it at all. First of all you still won’t get the same level of adhesion as you would with a chemical bond, and secondly if you scuffed it with 80 grit to get a sufficient bond then the gelcoat would no longer be clear and defeats the purpose. It NEEDS to be done while the resin is in a tacky state.

As for your parts, I don’t think the look TOO bad for wet-layed parts. If you’re drawing resin out of the part while it’s under vacuum, why not clamp off the hose?

Wildcard, apologies, I hadn’t seen that photo. You’re possibly correct about that, though with the cost of Frekote’s sealer I personally prefer to just get the mould to a better finish haha! Having an inadequate bond to the gelcoat layer is also likely to have caused some issues there.

[Gilbert]

I have been practicing a lot and I am having better results. Here is my issue now: when I go to clear coat my part to make it shinier the clear bleeds into the part. I am using a 2 part automotive clear. It seems like the clear soaks through at the weave and creates a wavy surface or more of a pinhole surface. After the clear has dried I have flipped over the part and you can see clear on the backside. I have even used sealer on the backside prior to clearing which helps a little but still have bleed through. I still feel like too much resin is pulled out of the fabric, any suggestions?

[Gilbert]

Any advice at all guys? It’s getting frustrating pulling out parts that have pinholes and then clearing them to only have the clear bleed through the part right at the pinholes no matter what I try

[fasta]

Sounds like your parts must be just one layer of carbon/material that it would bleed right through like that. Maybe the problem is the part and you should try more layers or a different finish on the backside with peel ply or release film to try and make a non porous part.

I fear though that if this is the problem then you may solve the problem of paint running through but if the surface still has porosity then you will still have paint problems like many do with parts from moulds.

[Gilbert]

I have done 2 layers up to 4 layers with the same results. It almost looks like fish eyeing on the clear from a car but at a closer look you can see where the pinholes were is where the clear bleed through the panel. What kind of clear would you recommend to use for a finished glossy look that fills voids well?

[fasta]

I can’t imagine how the paint can bleed through 3-4 layers of material! I’m stumped.

Porosity and voids are always a problem for many. Search this forum and you find some methods for painting.

It’s not usually as easy as just spraying a paint since often it will not fill into the voids.

[EKOMPOSIT]

If you ruined a mould I would say you need to get a better release agent. What do you use? If you want a good finish you can use Marbocote fastcote or their 227ce release. Both are a wipe on and leave release so you do not need to buff them up and both will give a good cosmetic finish.

Here is a cover for some diving bottle system and it releases wonderfully…

Now for the voids and pinholes. I have done quite a lot of wet lay vacuum bagged parts but all of them have been in polyester resins. I found I could get a good part but it was variable and failure rates were too high for me making cosmetic parts. I swapped over to pre-preg because of it… But I would use a preforated release film with the least number of holes possible as it would restrict the loss of resin from the part but still allow some trapped air off the part. I also found putting some peel ply round the perimeter helped too… I would put the peel ply over the last layer on the flange area and that would help too… I always used to run a full vacuum.
I swapped to pre-preg just to save money to
be honest… OK the materials do cost more but if you do wet lay vacuum bagging you only need to have an oven and controller… The money I saved with the lower percentage of scrap parts (single digit I would say) it just made sense.

The oven can be quite simple and made using a fan heater and MDF.

Even getting the controller from ebay is cheap and accurate. I was testing mine here to see and used an old meat thermometer to check and I get it to 1 degree maximum deviation when I check it on the opposite side to the controller thermocouple and at a lower level. With parts in there the turbulance should make the oven even more accurate.

Nice and simple oven. What controller are you using? Can it do a controlled ramped up?

Best regards
Mads

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