With all due respect to spaklers, microballoners, gluers, etc, there’s got to be a better way to seal an eps blank. To the point, the last board I made I mixed up tempera, elmer’s glue, and enough water to loosen the mixture enough for the airbrush…wouldn’t the glue seal the blank sufficiently if it were a solid spray all over the blank? Alternatively, what about mixing up elmer’s and water and spraying a light coat over the blank prior to other artwork? That would preserve a white background for other than solid color work, but still seal the foam.
What’s “better”?
Handspackling makes no boundry mess, no overspray, very little drippings, takes about 3 minutes. Proven to work.
I know this one, I read it somewhere, but I forgot where (could have been archives but I don’t know) that glue used to be used at first, but it got milky and stuff and got soggy when it contacted waterand had formed delam problems after that.
Or don’t do it at all. Its not a requirement. So you save a little weight - maybe - and about $5 of resin. Skip it. Even Greg L says the boards are strongest & whitest when he doesn’t seal them.
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Or don’t do it at all. Its not a requirement. So you save a little weight - maybe - and about $5 of resin. Skip it. Even Greg L says the boards are strongest & whitest when he doesn’t seal them.
Simplicity is good. Spackling…damn, I’ve done enough drywall for two lifetimes, can’t stand the idea of having to do it when making a surfboard.
As far as water intrusion and subsequent gumming and delam…funny, I never thought about it that way, but I guess that might be a problem.
Okay, no sealing it is.
I thought that people sealed eps because they were using poly and that poly would melt eps but if you’re not going to use poly, then why would you seal? Can someone clarify this if I’m wrong. Thanks.
Rio
Most styro is opencelled, meaning it bleeds.
Imagine lam 'ing the board, then having the resin suck into the core before the lam cures.
Pinbubble paradise, eh?
When sealed, the resin sits in the sealed pools, won’t prolly happen!
I like the way hot wire cutting leaves a tough skin on eps but I haven't figured out a way to melt a skin on shaped foam. From crude tests with a mapp gas torch I do know that was pretty uncontrollable.
Using a wetout table then applying the cloth or skin to the foam after the resin has become thicker but still tacky is another way I would like to try.
Joe
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Most styro is opencelled, meaning it bleeds.
Actualy EPS is a “closed-cell” foam. What happens is while shaping the cells are cut open and pulled out leaving pimples. These cut open cells and the dimples left behind soak up epoxy during laminating, thus adding weight. Sealing the blank fills these cavities with a lighter material than the epoxy thus saving on a small amount of wieght.
The sealing is not needed when using epoxy on EPS but according to many gives the best results. MrJ seals with microballoons/epoxy and GregL seals with spackle. Don’t remember Bert saying if he seals or not.
Negative- EPS is an open-cell foam. Urathanes used in conventional surfboard construction are closed cell. EPS is a bunch of little balls stuck together with an interconnected airspace between, and polyurathane is a bunch of tiny little bubbles in a hard matrix. -Carl
If you seal with spackle and then it gets wet…how easy is it to repair???
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Negative- EPS is an open-cell foam. Urathanes used in conventional surfboard construction are closed cell. EPS is a bunch of little balls stuck together with an interconnected airspace between, and polyurathane is a bunch of tiny little bubbles in a hard matrix. -Carl
Nearly all the EPS manufacture and distribution cites state EPS is closed cell. None that I can find state that it is open cell. The closed cell refers to the individual cells of the EPS, which are closed cell foam. True there is space between the cells that does allow water to penatrate the structure . Here is one cites explanation of what EPS is:
http://www.epsmolders.org/1-history.html
"Expanded polystyrene begins as a polystyrene bead or pellet. The pentane-loaded bead is then exposed to pressurized steam that causes the polystyrene to expand and mold into the desired shape and density needed. Manufacturing EPS does not involve the use of ozone depleting CFCs or HCFCs. The final product is a moisture resistant closed-cell structure that is comprised of 90 percent air. "
http://www.foamconcepts.com/faqs2.html
"2. WHAT makes EPS better than other materials?
Expanded Polystyrene (EPS) is a rigid, closed cell, cellular plastic with density dependent properties. What makes EPS attractive for many applications is evident in its physical properties, its frequency of reuse and recycling, its competitive cost, and lastly, its availability. "
and many others…
i think many of us are sealing for different reasons therefore the choice of sealer will differ.
i have a very specific reason for choosing to seal in the first place, my choice of sealer is a bit more vague - makes sense and works for me.
the reason i seal is not to save weight. I wet out on a table so I’ve overcome the problem of having weight gaining resin dissappear into the inter-bead voids of #1. In fact my result will be heavier by the weight of the sealer. What I’m trying to achieve is a good bond between the inner lam and the corecel sandwich skin. Getting a good bond between the inner lam and the eps is not a problem and that stuff is so weak that the bond generally exceeds the strength of the eps. However I have found that unless some resin is forced into the corecel a poor bond will occur. I once had a very poor bond so structural strength concerns me.
What i have found is that if I seal the eps AND wet out on table, then the result is light and economical with resin (but not as light as simply wetting on table and rolling out on bare eps). However the wetted out glass will hold more of its resin when placed on the sealed eps. Then when the corecel is placed on wet glass and given good compression in the vac bag the soggier glass will expell more resin into the corecel, thus achieving a better bond.
An alternative way to get a good bond is to follow the corecel manufacturers installation recommendations. They recommend priming the corecel with resin - the consumption per/sq ft of primer they publish was too much for a lightweight surfboard. corecel has quite a course cell structure. I have tried a modified version of this - prime with micro-balloon sludge. Even this produced an undesirably heavy result for me.
so considering that all i’m after is a good bond. Smoothness and ease of painting are not a concern (my sealer gets covered by corecel skin) an epoxy based sealer makes sense. Maybe i could get similar results with spackle but never tried it.
Sealing the eps prevents the resin from being absorbed into the core. This is good for flex, as any stiffness in the core would restrict shear movement. DanB had a pretty good guess at Bert’s process (http://swaylocks.com/forum/gforum.cgi?post=197430#197872) – seal where flex is important, and leave specific areas of the core unsealed to improve strength (such as directly under your back foot). As far as I remember, both Bert and Greg recommend sealing eps.
If you choose to seal however you need to set up some kind of venting system. If you don’t, the air trapped inside the core will expand and cause all kinds of problems when it A) gets hot – or B) is moved to an area of lower pressure (such as on an airplane). That alone may be reason enough for many to just let the resin soak in and take up the voids. Less work for the end user.
???
whether you choose to seal or not, your blank is SEALED when the lam coat is added.
Stands to reason you should use some kind of vent regardless of sealing or not!
Or just say it’s such low volume it won’t matter!
Eps is light and crushable, snaps easily but has good shear properties. fiberglass is dimensionally stable when resin is applied (laminated). Epoxy is not a good sealer of eps. Flexible white glue is a good sealer, bonds well and and can move with the eps. Epoxy is a good match for fiberglass cloth but a poor match to eps foam. How about rolling some “tacky” white craft glue onto the eps to “seal” the eps AND bond a 2 oz fiberglass cloth layer to the eps (no epoxy at this stage) When the “tacky” craft glue is all dry, treat this as your starting “blank” either lay-up fiberglass and epoxy layers, or do the pvc or corecell trick, the veneer or timber layer and just use epoxy as glue between the dimensionally stable layers?
4est- I stand corrected! Thank you -Carl
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Epoxy is not a good sealer of eps. Flexible white glue is a good sealer, bonds well and and can move with the eps.
Why not use a flexible epoxy to seal the EPS if flex is what you’re after? I would guess that epoxy bonds better to epoxy then to white glue. Personally I don’t know what all the fuss is about. Unless you’ve got really crappy EPS it won’t soak the lam dry. You will stiffen up the structure without spackling, but so does a stringer. If you have one vertical stringer in you blank you don’t know enough about flex as a design element to even think about tuning it right with epoxy anyway. Secondly, EPS impregnated with epoxy is no longer all that crushable. Try stripping of some glass and test. regards, Håvard
y
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ou don’t know enough about flex as a design element to even think about tuning it right with epoxy anyway
Thats why we need to try and figure out what flex means. If somebody more knowledgeable than me could explain it then the backyard builder would never need to build the same board twice. The trial and error method (take one shape and on one board use kevlar on the tail, the other use 6 oz on the tail, the next … and see how the boards characterists change) just isn’t realistic for me. I’ll never make a thousand boards. But if you had an idea of what characteristic was desirable or not for particular surf conditions you could play with different materials with some hope for success.
hey guys,
would 3m 5200 or Sikaflex 221 work good to seal a EPS blank? I can get these products, but I´m not 100% shure if they are good enough.