Question regarding stabilizing and crack filling:

[SleepLessThan3]

Hi guys. My goal is to stabilize a couple pieces of 1" thick burl and then fill all cracks/voids/inclusions with a resin mixed with pigment powder. I own a bottle of cactus juice, as well as a bottle of MAS brand deep pour epoxy (I do not currently own penetrating epoxy). The pigment powder I am intending to use is the Meyspring brand powder, in Indigo Obelisk. In addition, I own a vacuum chamber but not a pressure pot. What is the correct procedure here?

1. My first thought is that I just pigment a cup of the deep pour epoxy and then use the vacuum chamber to draw the epoxy in and let it cure, but I am worried that there will not be enough penetration and I will not have properly stabilized and strengthened the burl.

2. Alternatively, I thought that I could stabilize as normal using cactus juice and oven, and then draw the pigmented deep pour epoxy into the cracks with the vacuum chamber again, but in this case I am worried that the cactus juice will have cured and blocked off the cracks that I want the pigmented epoxy to get into.

Is the solution here to just get a penetrating epoxy and use that for the first method?

 

[TimR]

Typically I would stabilize first then cast, being carefull when setting in oven in a way to allow CJ to not settle in cracks/voids that you later want to cast.
Important to not have a step that has heat curing after casting. Pretty sure the epoxies don’t hold up well to stabilize temps.
If you will have cracks that you can’t avoid CJ getting in, use CJ dyes to avoid voids with clearish tones unless that works for you

 

[SleepLessThan3]

Typically I would stabilize first then cast, being carefull when setting in oven in a way to allow CJ to not settle in cracks/voids that you later want to cast.
Important to not have a step that has heat curing after casting. Pretty sure the epoxies don’t hold up well to stabilize temps.
If you will have cracks that you can’t avoid CJ getting in, use CJ dyes to avoid voids with clearish tones unless that works for you

So do I just use the vacuum chamber on the second go with the pigmented epoxy as well?

 

[trc65]

I don't do any casting or stabilizing but have read quite a bit.

When casting with epoxy, you typically apply pressure, not vacuum. Pressure doesn't release the bubbles, rather it shrinks them to a very small (invisible) size. The pressure must be kept on the epoxy until cured.

There are some people who will use a vacuum on the epoxy itself before pouring to remove bubbles from mixing. When doing this care must be taken as the resin will increase in volume in proportion to the amount of vacuum drawn. You can create a mess very quickly if you aren't careful. Pulling a vacuum may also cause some of the solvents to evaporate which may affect the open time of the epoxy. An additional concern is evaporating solvents may damage the pump if it isn't designed specifically for that.

As I said, these are just comments from things I've read. Hopefully some with experience will chime in here, but at minimum, this should give you some things to research further.

 

[TimR]

Good point Tim(trc65) makes regarding the solvents. I think most rely on pressure pot to shrink bubbles, and if you’re working with large pieces, nothing at all. I have used vacuum chamber to remove bubbles from the part or parts of the epoxy that tends to pour like molasses, an issue when they’ve gone beyond their normal shelf life.

 

[SleepLessThan3]

Good point Tim(trc65) makes regarding the solvents. I think most rely on pressure pot to shrink bubbles, and if you’re working with large pieces, nothing at all. I have used vacuum chamber to remove bubbles from the part or parts of the epoxy that tends to pour like molasses, an issue when they’ve gone beyond their normal shelf life.

idk what is considered large, but my pieces are all about 1" thick by somewhere in the neighborhood of 5x8"

 

[TimR]

I would say large in the context of the piece too large for casting with pressure pot.

 

[BangleGuy]

I have done my share of pressure casting and most of my work used CJ ( Methyl methacrylate - MMA) after the resin pour. You are correct in being wary of the MMA blocking off passageways for the epoxy. There’s a major difference in viscosities and the MMA will migrate into the wood via capillary action.

I also agree that trying to cast under vacuum sounds like a huge mess waiting to happen. The wood will evolve gas for a day under vacuum (depending on the species) which means the epoxy will cure like expanding foam. If you try it, best to pull a quick vacuum where you can see what’s happening (clear chamber) and vent as needed. Then, after much of the excitement has passed and perhaps 15 minutes, just vent the chamber and let ambient air pressure do its work. It’s not as good as 80 psi but at sea level you’ll be at 14 ish.

It is true that stabilizing / curing MMA after casting can be risky due to cracking, but I’ve had a lot of success (hundreds of blanks cast) using Alumilite Clear first cured under pressure and then MMA cured at the lowest recommended temperature.

For fine work like filling cracks and then machining afterwards, you’d be best served getting a used pressure pot on Facebook Marketplace or Harbor Freight.

Here’s a few examples of blocks I cast with the above method 10 years ago. Just dug them out of the shed yesterday.

I didn’t stabilize the Red Gum as there’s no need with wood species this dense.

I love to talking about casting, so feel free to ask anything.

 

[BangleGuy]

Oh, and here’s the largest item I have ever pressure cast. It was designed to max out my Binks pressure pot and was about 3” thick. It’s my wife’s favorite jewelry box