Reddit mentions of Meguiar's M8 Maximum Mold Release Wax - 11 oz.

If you have absolutely no access to a CNC milling machine (such as a Shopbot) of appropriate size, disregard my comment. If you do, please do not follow the hobby tutorials about making a female mold from a male plug.


The female fiberglass molds made in this way suffer from systemic lack of stiffness simply due to being too thin and flexible. It is vastly preferable to have a "brick-like" mold with a carved-out layup surface than a "shell like" mold, both for workability reasons as well as quality issues that arise from doing essentially 3 layups by hand and the imprecise processes that accumulate into dimensional errors along the way.




Here is how I have done it.

https://www.ericpillai.space/blog/2018/11/11/compositepart1

The end result looks like this:

https://www.instagram.com/p/BwpraXIhN4Z/?hl=en

I have exclusively used MDF as a mold making material. It's not exactly the "best" material for molds for a variety of reasons, but it is more than sufficient for one-off parts. It is also very accessible, cost effective, and easy to machine/work with.

Prepping the mold for use is done in 3 steps:

1. Spray painting the mold surface with sandable fiberglass primer paint like this: https://www.amazon.com/dp/B006ZLQ4HQ/ref=cm_sw_r_cp_apa_i_1INmDbCTS0H2R
   
   
2. Sanding the inside to as smooth of a texture as is reasonably achievable
   
   
3. Coating the mold in mold release wax using a microfiber towel in 2 layers (let the first layer dry before putting on the 2nd): https://www.amazon.com/dp/B002J854E8/ref=cm_sw_r_cp_apa_i_TKNmDbR2EDJKX
   
   We have had very good results with this method, with a few caveats:
   
   
4. Your mold will be "hairy" once you pull out the part (MDF fibers lifted from the surface). At this point, it is basically unusable unless you wanted sand it down again to make a part that was 2% bigger in every dimension than the original.
   
   
5. If you don't do a good job letting the filler dry, sanding it, and applying wax, your finished part will transfer large paint flakes on the outside. Not terrible, but a pain to remove.
   
   Don't feel duty bound to any of the specific products I linked, these were just the ones we had on hand. Other equivalent brands are probably about as good or better.
   
   Also, getting a good surface finish will require post processing, there's no getting around it without a very very expensive mold. Just set aside an afternoon with you, a fresh box of sandpaper, and a nice spotify playlist if you want a mirror finish on the composite.