Hey now that's MY trick!
Good stuff SS2...welcome to the forum...looking forward to more of your posts.
With regards to "seasoning" the EPS blank as you call it- does that mean if I took my EPS blank before I shape it and leave it in a black van parked in Death Valley in August with the windows rolled up.....and say the temp goes to 130 degrees, after that if Ileave it in my car in So Cal on a 90 degree day I shouldn't have problems with expanding gases?
In other words, whatever temp I bring the blank up to, then up to that temp I'm pretty safe as far as expanding gases? If so, why don't blank manufacturers just cook their blanks in a room for awhile before shipping?
Why ask why? Unfortunately, in the surfboard manufacturing business that seems to be much too often status quo. Some foam suppliers (mainstream industrial such as Platiscor, Divynicell,...) do season their foam, but not all types, not all manufacturers. PU blanks for example go through a "post cure" process, unfortunately this is done prior to bonding the stringer in (potential for outgassing on bondline depending on the stringer adhesive used). There is also no industry standard for PU blanks so each will vary. I do not know of any EPS blanks that are seasoned and doubt there are any. The out gassing problem is not universal and from what I can ascertain, specific to only a few EPS types.
If you wanted to prevent outgassing, then yes, exposing the foam to a temperature that is above the max temp it will see due to the exotherm would eleviate the problem. You need to define for how long at temperature. Additionally, it would help in assisting the evacuation of the residual gases if the seasoning was done post blank shaping.
Try Marko Foam molded EPS. Very clean net shape blanks with good rocker and deck dooming already molded into the blank and no outgassing that I am aware of. The best looking EPS blank i've wirnessed by a long shot. If they could only switch from ply to PVC stringers....
Newbie to epoxy here. I've worked with lots of other materials though. A couple questions and comments.
After "the fill coat" (SS2 is right), isn't the whole board sanded to smooth things out?
If so, sanding is best accomplished on a uniform material. Hard and soft spots make for high and low spots when sanding. Not good.
That said the ideal filler would have a good bond and sand exactly the same as the foam. Considering the excellent adhesion of epoxy and the fact that it also gets very hard, it would seem that you want to try and get the epoxy as highly filled with soft material as you can to make it as sandable as possible, yet still have a consistency that trowels or fills well.
In most materials, viscocity reducers usually allow the use of higher levels of fill while still maintaining similar working proprties. In other words, wouldn't using additive F with your epoxy allow you to use more fill, making it more sandable while maintaining workability? So you could thin with F and add more filler.
Maybe I don't understand the nature of Additive F.
The downside of visocity reducers is that they often have a threshold at which they cause segregation and you can't maintain a homogeneous, cohesive mix. You wouldn't want your epoxy to run out of your fill now would you?
Just some thoughts.
Wow. A lot of science for a simple problem. Both sealing methods work with good success -- have for a long time. I would consider another cause. As suggested, it may simply be rapidly increasing heat in the work space, sunlight, etc.
I've done over 10,000 boards with spackling compound, never a problem. For all those who prefer microballoons, I've done thousands that way as well. They both work. Spackling compound has advantages, both sides can be done at once, it paints better.
As for your issue, it's the foam that's causing the blow through. Some do it worse than others. What brand you using?
You are right, many real good epoxy composits trick in this post.
Interesting that this debate still comes up. The problem with Spackle these days is finding a good one. I’ve been using Sherwin Williams Liteweight Spackle of late. A lot of the liteweight brands have been reformulated. Too much acrylic and the color has changed to a gray. Acrylic tends to ball up when screened. These balls can scratch your blank. Brands that I have used in the past but won’t use now are; Fast n Final and Ace.