blisters appeared on epoxy mould gelcoat surface

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#1

Hello Everyone,

I have made my epoxy wet lay-up moulds with Momentive Hexion F300 epoxy gelcoat and L326 tolling epoxy resin,I did hold the moulds while a day at room temp.And I put them into the oven onto plug firstly at 60 degrees for 8 hours then postcure at 80,100,120 degrees for 2 hour without plug.When I took them out,I saw blisters on the gelcoat surface.:confused:Also gelcoat was not bond the epoxy resin.I have been applying 2 layers of gelcoat.I did wait 45 min between layers.And 4 hours later I started to wet lay-up.I have asked to Momentive Hexion but unfortunately nobody did back to me.I could not understand where I made mistake.Do you guys have any advice to me?

Thanks.

#2

Can be a bonding problem between gelcoat and back layers. 4 hours can be to long. Most epoxy build up a skin so that you will have that problems.
What does the datasheet say? Most there is a time for next layup. Alternativ you have to let the gelcoat cure and grind it.

#3

Thanks DDCompaund for answer,I am agree with you.Right, 4 hours seems long,TDS is not so clear actually,it does not say a specific time to wait before layup.The seller has told me.I need to wait for 4 hours,I think he was wrong about it.When you said grind it,you mean sanding?

#4

Yes, I mean sanding to make sure you get a mechanical good bond. You can also wait until the gelcoat is just tacky and than disturb cotton flocks on the gelcoat. When it is cured take down cotton flocks that did not stick to the gelcoat and go on with layup. Than you don’t have to sand.

#5

Hmm. That’s an interesting one. If it was to long after it had gone off you would just get release over large area’s I’ve had similar before in hot conditions just leaving it to long ( got called away)
On the other hand I have had a similar effect as you have and it was trapped humidity between surface tooling coat and lay up.
Most epoxy tooling coat’s shouldn’t be used in anything over 70% , as the surface can build up a layer of moisture as it exotherms and cures.
Thus , when continuing this get trapped between it and the mould , once heated it expands a lot causing surface bubble beneath the tooling coat.
Just something to think about as it can be Cool and moist this time on year for you.

I just got back from a euro holiday… Turkey will be next christmas :slight_smile:
You live I a great place :slight_smile:

Tim

#6

The explanation of your process is not clear to me so I will just throw some questions at you that may or may not be relevant. DD has covered the obvious question. Did you post cure the moulds on the plug? Was the surface of the plug fully out-gassed and cured. Was the plug made of material unaffected by heat (thermal degradation and pyrolysis)? Did the plug have a similar thermal coefficient of expansion as the mould?

#7

Sorry ASB if I could not explain well, I did not post cure the moulds on the plug.Because the plugs are able to heat up to max 75 °C.But I need to post cure them till 120 °C.The moulds also need to pre-curing at 60 °C.And I have pre-cured the moulds on the plug at 60 °C for 8 hours.And there was no problem on the gelcoat surface till I heat the moulds at 120 °C(For Post cure).Yes you are right about plug.The plug is made of Polyurethane(Raku-tool MB-0670).If I heat the plug more than 75 °C,The plug out-gassed.As I said my first post,the blisters appeared after I did post cure till 120 °C.

Step by step what I have done
1-)I applied first layer of gelcoat.
2-)45 mins later I applied second layer of gelcoat.
3-)4 hours later I started to wet lay-up.(1 layer 49 gr/m2-1 layer 163 gr/m2 glass fabric)
4-)And then 4 layers 300 gr/m2 biaxial and 4 layers 300 gr/m2 UD glass fabric.
5-)I let the moulds at room temp for a day.
6-)I put the moulds on the plug into the oven at 60 °C for 8 hours for pre-curing.
7-)I removed the moulds from plug.(No problem on the gelcoat surface)
8-)I did post cure the moulds 2 hours@80 °C /2 hours@100 °C/2 hours@120 °C as ramp.

#8

Are you sure that these bubbles are just the gel coat?

I have had similar problem with a polyester mould where air bubbles in the laminate (due to inexperienced help) then expanded the first time I heated the mould in my oven for pre preg use. Just a few bubbles but they push the gel coat/skin layers up??

#9

Hey fasta,I checked it after your post.And yes these bubbles are on the gelcoat.

#10

Time ago I did toolings with epoxy to utilize in PU RIM process, I always sand the polymerized epoxy gel coat before apply the back layers and never had this problem.