Thanks for all the cool replies,
Indeed the optimal foam mix recipe seems secretive. From what i can find, blank manufacturers are using a high pressure mixing gun to pour the foam into the mold for the best possible mixing, but also for practicality. These high pressure mixing gun machines are way out of my budget and only make sense for large productions.
So I’ll probably never be able to acheive the same results as an industrial blank.
However the blanks im making are plenty for my needs. The foam density is evenly spread out throughout the enitre blank without bubbles (by using cooking wax realease paper instead of saran wrap, seems to let the air out). The blanks sands as good as a normal blank. Once i sand the crust off the blank, the texture of the foam is almost identical to a normal Blank. Adding a white pigment to the mix makes the blank almost white.
The mold weighs around 350 kilos, took 3 days to make, and cost me around 250$ in materials. Once the mold is made, the process of making the blank is fast, 10 minute prep work, 2 minutes of mixing and pouring, and 10 minutes of curing. I can start shaping it 20 minutes after it is poured. I could technically pop out a blank every 30 minutes. Right now a blank is costing me 40$ instead of $150+ if i import them (I live in a carribean island with high import and tax fees).
As Mako224 mentioned you can select a variety of foam density to your liking. Now, i’m trying to figure out if just by increasing the amount of liquid into the mold, does it increase hardness of the foam? techinically it increases density but does it also change the hardness of the foam? for example if i poured 1 liter of 2lbs density foam into a mold, would i get the same density/ hardness as 1 liter of 4lbs into the same mold? Both blanks would weight the same, at first it seems like the 4lbs density foam would be harder but the 2lbs foam expands twice as much, so that should create more pressure in the mold which should help with density/hardness… ? So thats where im at now. Like stonerburner said “precise mixing volume and internal mold pressure are ingredients in the secret sauce”
The mold i made was to create kitesurf blanks which is why it is so small, I would love to make a bigger one for surfboards, however the mold would be bigger and a lot heavier. Something like that is very hard to move once made so it has to be created where is going to stay, not sure if i want another massive box full of concrete in my basement right now.
Here is a photos one of the boards created using my mold