Pouring Blanks at home

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Handiy's picture
Joined: 10/04/2022

Hello everyone, 

I live in a place where surf blanks need to be imported, making this hobby very expensive. So i made my own blank mold, and use 3lbs two parts urethane foam inside.

I know this subject has been covered here before but I couldn't find photos or videos showing the actual mold setup and results. So here my constribution to this subject: 

https://www.youtube.com/watch?v=7nwrXkKzdrc

Disregard the intergrated fin box system, it did not work well and i cut the tabs off.

The weight of the foam is acceptable but it feels a tiny bit softer then a factory blank and 4lb density would be too heavy i believe. 

So far i havn't put any stringer into the blanks, instead i add carbon strips top and bottom. I'm mostly making kitesurf boards since my mold is small.

Now trying to figure out the optimal foam mixture to put inside, if anyone has any good suggestions, i'll gladly absorb the info! 

The online information on PU is so spread out that it is hard to figure it all out.

I'm still experimenting with foam colorants, lately i've been adding Titanium dioxide to the foam mix with pretty good results making the foam whiter and hopefully more UV stable.

Cheers

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tenderloin tom's picture
Joined: 12/12/2012

rad

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Scrub it kook

stoneburner's picture
Joined: 12/30/2007

Impressive.

I suspect precise mixing volume and internal mold pressure are ingredients in the secret sauce -- closely guarded.

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McDing's picture
Joined: 05/22/2004

I'm impressed.   And I wouldn't say that if I didn't mean it.  The chemicals used by blank manufacturers is a closely guarded secret.  Standard "two part" foam like you can buy in a supply house isn't even close.  You're gonna have to be involved in espionage to find out what they are and what formulas are used.  I have seen drums of chemicals, but was never interested enough to write down scientific names.  You've certainly done better than anyone who claimed they could do it previously.

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That which can be assorted without evidence was read in an illegal magazine.

gdaddy's picture
Joined: 10/31/2008

+1 = very impressive.  

As for coloring the foam i think you'll want to stick with white.  They were doing colored foams a few years back and we were getting stories about the colored dust getting everywhere.   All your tools, all your work spaces and everywhere adjacent to those work spaces.    You definitely wouldn't want to shape a red foam blank and a white blank on the same day.    

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McDing's picture
Joined: 05/22/2004

There were a couple of guys on here a few years back claiming they could do it.  One guy started a thread that went on and on.  I think he was trying to glean what ever info he could from members here.  Truth is most of us know little about the chemicals and their measurements.   Two things though;  You can buy release paper which is peeled off the blank and discarded.  I don't have a source for that.  And some how or another water is injected.  You have the basic mold down.  Concrete molds are how it was done until other molds were manufactured.

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That which can be assorted without evidence was read in an illegal magazine.

mako224's picture
Joined: 12/26/2005

Great video.  You are certainly on the right track.  I've never attempted it but I've used pour foam for a variety of boat projects over the years.  The supplier I buy foam from offers foam in 2, 3, 4, 8 and 16 pound densities.  I've got experience with the 3, 4 and 8 pound densities.   I believe that surfboard blanks are made using 4 pound density.  I do not believe that the chemicals the blank manufacturers are using are anything special in and of themselves.  I'm fairly certain that it comes down to the mold being very strong to handle high pressure and then adding precisely the right amount of foam mix measured by weight in a controlled temperature environment.  More foam mix in the mold and they get a more dense blank due to the internal pressure in the mold.

Temperature along with the amount of mix in the sealed mold would be the key.  The foam expands and the amount of expansion has a lot to do with the air temperature.  Working on boats there is a noticable difference in how much the foam expands when its 90 degrees vs when its 70.    I'm pretty sure the molds themselves at the big blank manufacturers have temperature control provisions built in.

By the way, the 8 pound density foam I've used is actually just slightly more dense than a surfboard blank with no mold involved.  I've not used the 16 pound density but here is how they describe the product on their website.  "This 16LB density foam is essentially as hard as a rock, you would need a hammer in order to make any dents in this product. Can be used for sculpting or the casting of objects that require superior toughness and strength."

For your next mold make the cavity oversized so there is room to shape the blank and you can cut the blank in two to add a stringer for rigidity.

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stoneburner's picture
Joined: 12/30/2007

Handiy may not have enough points to respond to our comments...

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Swaylocks Surfboard Design Forum: thoughts & theories ... practical & theoretical

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newschoolblue's picture
Joined: 06/30/2004

Wow.  I have nothing to add.  Just want to say how impressed I am.

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Handiy's picture
Joined: 10/04/2022

Hey everyone, 

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 

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newschoolblue's picture
Joined: 06/30/2004

Awesome.

What kind of glass schedule do you use for a kitesurf board?  I've never seen one in person.

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Handiy's picture
Joined: 10/04/2022

I'm using 2x4oz + 6oz tail patch + 3inch unidirectional carbon for the bottom and  2x4oz + 6oz footpatch (back 2/3rds of the board) + 3inch unidirectional carbon for the top.

Using Epoxy Resin. The boards hold up very well, however i'm still getting a small dent under the front foot heel after landing big jumps.

I was afraid the lack of wooden stringer would be a problem, but the carbon strips seem to be a good replacement, at least for kiting.

The weight of the board comes out the same as the average factory kitesurf board.

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McDing's picture
Joined: 05/22/2004

Thank you for this.  As I said;  You've done something many have expressed an interest in doing.  The difference is that you documented the process and had a reasonable success compared to others.

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That which can be assorted without evidence was read in an illegal magazine.