I laid these up earlier in the week using IPA to thin the epoxy. Thinning makes resin saturation into the CF cloth easier. They cured just fine but I did them in the house as opposed to the shop. I also use a gram scale to weigh out the resin while mixing.

Yup, heat works.

Since acetone is great for wiping CA runs off ultracote and the label on the can says it was "designed for thinning" epoxy, I keep a can in the shop on the glue shelf. It takes a lot less acetone to get 30 minute brushable than alcohol and it appears to retain it's strength. And it's fairly cheap.

I mold parts fairly often so have some surfacing resin epoxy (Z-poxy) on the shelf. Turns out it's much easier to use it for fuel proofing engine compartments. In fact, the last couple of ARFs that were being put together as electrics had such poorly assembled firewall/motor frontends, they got painted too.

Funny how the quality of the laser cutting, wood, and assembly of ARFs seems to have dropped off now. The RTFs seem to be really bad nowadays. Sadly, most modelers buying those things don't notice and are agast at the suggestion you make about needed fixes. They don't usually have tools, skills or glue. And of course, don't have time.

+1 on the acetone and laminating resin. Acetone is a much better solvent for epoxy than alcohol and also flashes off.

Yes it is but you have to be careful, some mold release films like PVA and some of the dry spray releases don't mix well with acetone. It possible to chemically damage the release and then be stuck with ruined tooling.

I've used as much as 50% denatured alcohol and NEVER had the first problem getting a nice hard cure , ready for sanding with no issues .
Im pretty sure the manufacturers may not want you to make their products go a bit further by reducing it . I also thin out automotive paints and clear coats well beyond specs with zero issues .

You don't have to add the micro balloons! Invariably, when using 30 minute epoxy on a wing it sets up faster than you want it to. The last go around I had with a P-47 wing - - -
The epoxy started seriously setting up as I was cleaning off the excess, at about 25 minutes! And, this was in a slightly cooler area than normal room temperature!

I've been thinning epoxy this way for years without a problem. When this happens, just put a heat lamp on it for a couple of hours and it will complete the curing. You don't want high heat, just enough so that it's warm to the touch (probably 90 to 100 deg F.).

For future reference, after applying thinned epoxy use the heat lamp right away. This will evaporate out the solvents before it kicks off and it will cure normally.