So I was mind shaping today. You know that time where you’re just thinking about your next project and how to pull it off.
working each step of your workflow trying to see with your mind if there are any hitches. Anyways…
I was thinking about how people have said that the drawback to using eps is that it sucks in water pretty good. But aren’t those coffee cups (styrofoam) made out of eps? And they hold water (coffee in this case). So how do they get the cup to be water tight? Am I off? I believe eps is styrofoam. So do they do it with a really dense eps? Do they coat it with anything? -anyways its been bugging me for a couple days now. Thanks in advance to all your replies.
1# EPS is the crap that water-logs. 2# isnt bad about that… the denser you go, the more watertight it gets… also, if you sand well and SEAL the blank, it wont take on water if you get a ding.
they are little foam beads mashed together…
unsealed blank (2#):
O O O O O O O
O O O O O O O
Sealed blank (2#):
OoOoOoOoOoO
oOoOoOoOoOo
styrofoam cups:
oooooooooooo
oooooooooooo
edit: seal it with microballoons or Q-cell… or if your cheap, spackle. (spackle yellow’s over time though)
p.s. I have bought Pu/Pe boards and made my first out of epoxy… never gone back to Poly… I’m exclusively an epoxy man. easy to handle… hardly toxic… hardens slowly over time (no gelling)… and soaks into the glass (doesnt need to be forced in w/ a squeegee)…
1 drawback… its like 3x more expensive… but worth the cost… good EPS blanks from www.sfoam.com
Today’s EPS takes on less water per density than urethane. 2# EPS is lighter than an Ultralight urethane (2.35# density) and leaks less. 1# EPS doesn’t have a urethane equivilant therefore it is seen as inferior but in reality it simply has no equal. 1# density urethane would leak like crazy too if there were such a thing.
I’m not in agreement with the statement that spackle yellows over time. SOME does. Just depends on the brand. Dap F&F is generally considered the right stuff and I’ve never experienced yellowing with that product.
IMHO, the price drawback isn’t reality either. Epoxy goes twice as far at twice the price. Shortboards take three pints of epoxy or three quarts of polyester. I would call it a wash accept the quality of epoxy makes the finished product more valuable.
Wait till people start seeing boards built with 3# or 2.5# density EPS. The stuff is incredible. It’s going to change some views. Through the roof strength gains.
yeah, some spackles yellow… i use the stuff from the hardware store, so I add pigment to fight the yellow.
as far as my statement on epoxy costing more… its an initial cost increase… which goes down with volume… my first board cost me as follows…
$75 blank
$110 epoxy
$40 fiberglass
$150 other expenses (includes fins)
so total: $375
but the next board cost less because I used the leftover resin from board 1
edit: I did not factor in shipping charges… i bought everything but the blank from foamez.com and had it shipped to texas. I blew alot in shipping charges, but most live in CA so I dont factor them in.
I had a question regarding tinting/pigmenting epoxy (since you are the resident expert). how do you get a uniform color across the board? do you mix in the tint/pigment in the entire gallon of resin before mixing w/ hardener? also, can you just tint the hotcoat or would that caused bonding problems? usually when i glass, I mix up small amounts at a time to make sure I dont waste any. so would adding pigment to the jig bottle then mixing thoroughly work better? also, if I pre-mix in the pigment, how does that affect the epoxy/hardener ratio?
I say its the pressed surface beads straight out of the mold which means a styro coffee cup won’t take water.
Also they’re way denser than the foam we shape out of…
I suppose the molding process involves some sort of wax release agent also…therefore the outer foam is coated.
Have you ever seen an uncut EPS block? ( Styrofoam is just Dow Corning original trade name for it…)The outermost texture is exactly like a coffee cup. And it won’t laminate very well unless roughed up.
Cutting the beads in a EPS blank ( I.e shaping it!) would expose the unsealed surface.
Its interesting to read Greg speak of the comparative absorbsion of PU - It is a fact that all boards will absorb water, PU through dings (…and micro cracks in the molecular structure of fatigued PE resin…? Greg?)
But the clincher is that water can be drawn back OUT of EPS with no permanant damage, whereas water in PU is there to stay, exacerbating the breakdown and browning.
And I hear that tech is being figured out in which the EPS absorbsion factor will be reduced further. I think Greg has posted on the subject.
I think the EPS sucking water thing is more to do with pressure differentials. When you go surfing, most of the time, the air temperature is higher than the water temperature. So when you screw in your vent plug, the air inside is trapped at a certain temperature/volume. When you put your board in the water the air inside cools but becuase the board is sealed, a vacuum is created. If you get a hole the air pressure equalises - sucking in water. With the coffee cup the eps can breath so no pressure differentials are created.
I think the EPS sucking water thing is more to do with pressure differentials. When you go surfing, most of the time, the air temperature is higher than the water temperature. So when you screw in your vent plug, the air inside is trapped at a certain temperature/volume. When you put your board in the water the air inside cools but becuase the board is sealed, a vacuum is created. If you get a hole the air pressure equalises - sucking in water. With the coffee cup the eps can breath so no pressure differentials are created.
This kinda makes sense to me because I’ve seen floatation devices that are made from styrofoam with regular cloth covering. If they got wet the styrofoam would be exposed to water but they don’t take in water. I don’t know if its the density or what but seems pretty water tight to me.
So is there a way to glass the deck of a board strong and forget about the bottom and keep it water tight? suppose we put perimeter stringers and put a sandwich on the deck but leave the bottom just plain eps (except for the fins of course). would that work? seems quite a stretch of the imagination but it would make a really light board, no?
I posted pics and results of a minor experiment awhile back that demonstrated (to me anyway) that the higher density EPS has little if any air space between beads. The 1 lb density EPS I used in the experiment transmitted vacuum all the way through my test sample. The 2 lb density EPS did not.
Today, after reading this thread, I tried holding samples of two different densities EPS underwater and squeezing them… The 1 lb density sample emitted quite a few bubbles from between the beads. I was able to squish water out of the sample afterwards. The 2 lb density sample emitted only a couple of bubbles - these appeared to originate more from the surface - maybe from fractured surface beads rather than air space between beads? I couldn’t really get anything out of it when I squished it. I would imagine that 2 lb, 2.5 lb or 3 lb density EPS foams are nearly impervious to water intrusion.
I would also agree that pressure differentials with temperature changes would be a factor with water intrusion into a damaged board.
I would encourage anybody to snag some samples and try it out. A single experiment without confirmation is meaningless.
Sorry if this is off topic - I guess I never addressed the coffee cup thing.
I think that pretty much answers the coffee cup thing. They probably use higher density eps. And since you say that a small change in density (1lb to 2lb) of eps makes a great change in its property to absorb water then thats probably what coffee cup manufacturers use. I was also thinking of those swimming paddle boards and cheap body boards that are made of styrofoam as being impervious to H2O. Hmm. I guess this gives us more reason to use EPS.
Hey Guys, this is my first reply so don’t rag on my spelling! Anyway, I was in the EPS business for 13 years back in the day, and we made a lot of these little boards in various styles. We used the largest bead available, which was designated as an “A” bead. All polystyrene beads are classified by screen size, starting with “A”. The cups the original poster asked about was made with a “T” bead, the smallest size made. Most modern blanks that I’ve seen up close use either a B or a C bead. The density of the little belly boards was around .5. (.5 lbs per cubic foot) Most large blocks (5’ x 8’) are molded from 1 pound or lighter bead. The blanks that Greg is talking about are relatively heavy (for the EPS industry) at 2.5 lb/cu.ft. but are incredibly strong at that density.
To reply to the original post, the reason that cups are waterproof is that the beads are totally fused (melted) on the surface from the heat of the mold. There is no coating used. Each cup takes just seconds to make and the mold is so hot is can cause serious burns if you accidently touch it!
I think maybe Ben Shipman’s fine example of a Senior Surfer pop out also has a semi-sealed or fused surface as a result of the molding process. As I recall, once the surface is scuffed up a bit, they start to absorb water. In the photo the unmarred surface shows flattened/fused beads - in the gouges, the exposed beads appear to have more air space between.
As kids we used to run and jump on them in the pool nearly always breaking them in short order. The few that stayed in one piece gradually became waterlogged.
