[D Springer]

Hey all, been testing multiple different resin epoxies and have really liked the Resin Obsession brand name resin, BUT have a question. I *may* have gotten a little nuts with some cellophane for some resin opals and caused some decent sized voids in some inlay work I was doing. I am to understand that SOME resins are one shots and that another layer does NOT bond to the lower layer chemically, and some this is not true and they do bond. What happens if I attempt to layer more of the Resin Obsession branded resin into already cured and hardened of the same material? What prep do I need to do in between… I presume a scuff up to create a bonding surface to “grab on to”… thanks for your help! D

PS, do we know the by weight mixing values for that brand? I may have to calculate it, but was hoping not to

[Katherine Swift]

Hi David,

You will be fine applying a layer of resin to the same resin. I have even had good luck applying a layer of epoxy to a cured layer of another brand’s epoxy.

You can also mix the Resin Obsession super clear resin 2:1 by weight, but you will end up using more hardener. Results will be the same.

[D Springer]

Hey again, so when applying into specific voids, in a highly clear pour, can you *see* in the interface between the old resin and the new resin? It’s a greater question about how it takes to layering I guess, I’m attempting to figure out if I need to use staging on fine detail inlays to avoid shrink problems that I’ve experienced with Castin’ Craft (evidently I used too much hardener and it shrank towards the big mass on me). I’m using a vacuum pump (which cause their own set of issues) to try and pull air out and am having issues getting everything completely good for the surface (keep ending up with bubbles on the surface that then dry, get sanded and end up as “voids”). Thanks for your help! D

[Katherine Swift]

In general, if you wait until one layer is starting to gel, you can apply the next layer without seeing any lines.

As for vacuum casting, have you considered pressure casting instead? What you describe is what I find as well where you have ‘beer foam’ on top because the bubbles don’t pop all the way.

[D Springer]

Also followup on the mixing comment… so 2 parts resin to one part hardener by weight. I’m unclear why I would use more hardener if I did this vs the volumetric? Sidebar: Since I didn’t know the mixture, I’ve been running the incorrect 50/50 by weight… which has worked but REALLY uses hardener 🙂

[Katherine Swift]

The hardener weighs more by weight than the resin does. Mixing by either weight or volume is fine.

[D Springer]

Hey Katherine, so funny you mention the pressure casting… so the difference between the vacuum and pressure is how the oxygen gets dealt with. In vacuum, I’m getting the beer foam as oxygen is pulled out, but as I get more and more bold it seems that if I let it roll long enough it actually goes away and return back to fluid liquid without the foam. in the pressure casting, I’m trying to compress the liquid so the oxygen is no longer visible, but it has the consequence of trying to drive the epoxy INTO the wood 🙁 I haven’t screwed with it for fear that it’ll break through my sealant layer and just be a modified epoxy impregnation. Thoughts?

Oh and the multi layer thing, i don’t get to know if I have voids until way after it’s set due to sanding. So for example my sequence is as below for one project: I’m trying to create resin opals in an inlay, so i mixed up some the resin obsession brand epoxy, mix in my cellophane and some medium glitter and apply into the inlay. The first one I made wasn’t super sparkly, so I really doubled down on my second and laid it in as best as possible. I overfill it so when i sand i can get a perfectly flat surface with respect to the wood surface, otherwise i’m trying to eat the wood surface to drop it to the epoxy level which gets super risky of eating your inlay AND taking forever AND not being flat 🙁 . In any case, unbeknownst to me, some of the cellophane bridged some features on the top and basically didn’t allow resin to flow underneath, so i ended up with a significant void which I only found when i sanding it all flat… am I going to have lines when I refill them? Can I use chemicals that break down the epoxy (for like cleaning) in those areas to make them tacky so I could get a better rebond? Appreciate your help… the reason this is obscenely detailed and technical is because i’m an engineer 🙂 Thanks, D

[Katherine Swift]

This is a response my friend Charlie who has a lot more experience than I do working with wood and resin:

I haven’t really fixed in my head what he’s going for yet, but a few things come to mind as I read it..

I’m not sure about the cellophane part, so I can’t really comment on that. And when he talks about layering, he’s right to mention a ‘clear pour’ .. if there’s anything in the resin (like glitter) it will probably highlight the line between layers.

I don’t know that I’d ‘scuff up’ the resin before layering .. the resin will either bond or it won’t. Scuffing won’t really help and could show up as a line.

Bubbles .. the bane of our existence!
I know many casters who quote Boyle’s law and think they’re going to compress the air bubbles in the resin till they’re invisible.. but it just won’t happen without some heavy duty commercial equipment.

Most pressure pots available to consumers are rated in the 50-60psi range .. or 3.5 to 4 atmospheres. That means that even if you push the pressure up as high as safely permissible, those are bubbles are about 1/4 their original size. That’s still highly visible.

So rather than look for ways to hide the air bubbles, I’d be looking for ways to stop them from occurring in the first place.

I’m not sure if the air is getting mixed in because of vigorous stirring or perhaps there is a chemical reaction going on because of incomplete curing of the sealer. Just because the sealer is dry doesn’t mean it is ‘cured’ .. often finishes can take a month or more to fully cure, and during that time they can (they will! ) release gasses and be vulnerable to chemical reaction. There could also be incompatible materials under the resin besides the sealer.

Vacuum can only help so much in clearing bubbles. It is better than nothing, but not ideal. It does make the bubbles larger and easier to pop. But thinking that it makes them rise faster because there’s “more air” in them is incorrect, too. (Boyle’s law, again) Under vacuum, those bubbles still contain the same amount of mass, it is simply spread out over more area.

He mentions ‘driving the epoxy into the wood’ when using pressure.. but that should only be a concern if the sealer isn’t cured yet. Once hardened, we’re not talking about so much pressure that it would penetrate a cured finish. (unless he’s using some high pressure equipment)

If I were trying this, I’d use my old stand-by routines.. fully cured finish on the wood (even if it takes 4-6 weeks!) gentle stirring and a gently warmed resin so it flows and the bubbles (if any) are free to rise to the top.
But .. not seeing the project, maybe I’m all wrong, too!

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