White spots showing through base material.

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SSSGAV
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White spots showing through base material.

Post by SSSGAV »

I'm working on a project laminating white UHMW to maple veneer and I have pressed many successful ones in past years however this year I have had several come out of the press with white spots visible through the base. I can't seem to determine what the issue is. I have tried more epoxy, less epoxy. We are roughing up the surface and flame treating the base. Could these be air pockets? Any other ideas?
20221125_170606-01.jpg
20221125_170606-01.jpg (397.21 KiB) Viewed 1658 times
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chrismp
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Re: White spots showing through base material.

Post by chrismp »

Looks a bit like air pockets - especially since they clearly occur around the knots you can see in the picture. What type of press are you using?
SSSGAV
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Re: White spots showing through base material.

Post by SSSGAV »

Hydraulic cold press.
Jonrezz
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Re: White spots showing through base material.

Post by Jonrezz »

yeah I agree with chrismp - in addition to his question - are you providing a way to "bleed" excess epoxy? think of how a typical ski squeezes excess expoxy out the sides when pressed - these could also be epoxy pockets from excess having nowhere to go.
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vinman
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Re: White spots showing through base material.

Post by vinman »

Agree, looks like air. Increase your pressure and make sure it’s fairly even.
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sammer
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Re: White spots showing through base material.

Post by sammer »

Looking at your pic, I think the answer is shown just above the p-tex.
Looks like bubbly cured epoxy.
Could be cavitation from your spreading technique?

Wet out your maple and your base. Try not to whip up any bubbles.
If you're using heat the air will expand and those bubbles have no where to go.

Just my $0.69

sam
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chrismp
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Re: White spots showing through base material.

Post by chrismp »

SSSGAV wrote: Mon Nov 28, 2022 2:17 pm Hydraulic cold press.
Could be a couple of things then. Your pressure might not be even enough (it's hard to get mold surfaces even and matching perfectly) - to mitigate this, you could use a thin layer of soft material (silicone foam sheets work well as epoxy doesn't stick to them) in the press on top of the base material to get a more even pressure distribution.

Another reason might be your epoxy already kicking before it gets into the press. Check the working time of your epoxy and compare that to how long it takes you to get everything into the press after mixing the epoxy. However, this is not an exact science as working time is usually stated for a mix of 100 grams in a cup - so if you mix significantly more than this and leave it in the cup, it will go off quicker and on the other hand spreading the epoxy on the workpiece will prolong working time if it hasn't already started kicking (i.e. getting too warm).
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vinman
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Re: White spots showing through base material.

Post by vinman »

How much resin did you use and how much pressure ? Since there is no fiberglass between your wood and your base, could it be possible you squeezed out too much?

Likely problems

Pressure: Too much, too little, or not even

Resin too little or kicked too fast, did you wet both surfaces?

Poor mold conformity maybe
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SSSGAV
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Re: White spots showing through base material.

Post by SSSGAV »

Jonrezz wrote: Tue Nov 29, 2022 5:58 am yeah I agree with chrismp - in addition to his question - are you providing a way to "bleed" excess epoxy? think of how a typical ski squeezes excess expoxy out the sides when pressed - these could also be epoxy pockets from excess having nowhere to go.
Lots of epoxy squeezes out the sides and ends. It is not trapped by any means.
SSSGAV
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Re: White spots showing through base material.

Post by SSSGAV »

chrismp wrote: Wed Nov 30, 2022 3:18 am
SSSGAV wrote: Mon Nov 28, 2022 2:17 pm Hydraulic cold press.
Could be a couple of things then. Your pressure might not be even enough (it's hard to get mold surfaces even and matching perfectly) - to mitigate this, you could use a thin layer of soft material (silicone foam sheets work well as epoxy doesn't stick to them) in the press on top of the base material to get a more even pressure distribution.

Another reason might be your epoxy already kicking before it gets into the press. Check the working time of your epoxy and compare that to how long it takes you to get everything into the press after mixing the epoxy. However, this is not an exact science as working time is usually stated for a mix of 100 grams in a cup - so if you mix significantly more than this and leave it in the cup, it will go off quicker and on the other hand spreading the epoxy on the workpiece will prolong working time if it hasn't already started kicking (i.e. getting too warm).
We have tried many of these things and did manage to get rid of the white pockets. We ended up using less pressure, more resin, and silicone sheets. The result looks great, unfortunately we are still ending up with some delamination! Again, we're flame treating, cleaning with alcohol, abraiding, etc.
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vinman
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Re: White spots showing through base material.

Post by vinman »

Maybe add some fiberglass veil between you layers to hold resin??
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chrismp
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Re: White spots showing through base material.

Post by chrismp »

There are some things you could try (or a combination). Many epoxies are quite brittle, so adding a bit of flexibilizer can help with delaminations. Make sure to test if the flexibilizer works with your epoxy on a sample!

And as already suggested adding some sort of filler to hold the epoxy, such as fiberglass veil or cotton flocks, should help too.
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