PU with epoxy - shrinking problems

General Discussion
1

Aloha, Help! I have been making PU boards with RR epoxy skins for some time now - about 50 of them. Well they are starting to come back after about 6 months of use with huge sunken areas along the cut laps, fin boxs and tail areas. Some people have said bad blanks - soft spots from over shaping - to thin of glass. Well after glassing some very heavy boards it still happened. All US Blanks red formula - not overshaped. The last one that did it was planed once on the deck and two passes on the bottom. Still collapsing. This doesn't happen with EPS US Blanks or others ever. Is it specefic to using epoxy over PU? Is the epoxy to flexy for the foam type? EPS may be more stiff????

Shoots, it's just so nice to shape PU. Wish it worked. Any thoughts???? Mahalo's,

Chris Upp

www.diaboliksurfboards.com

2

Thanks for the info DMP. The “heat in the stringer” is an interesting thought. The back of a truck bed does get very hot especially with a bed liner or Rhino sprayed.

3

Using KK, CE or 2000?

4

Heat MY GARAGE WENT TO ABOUT 120 one weekend and a new board shriveled up pretty bad in spots along the pour lines.!

It was a US blank.

I would heat up ANY US blank before I wasted time shaping it or use another blank manufacturer till this problem quits.

Curious what did you do for your customers after six months?

Make them a new one for a small fee?

Tell them to pound sand?

Offer them a repair for free/lower cost?

5

[quote=“$1”]

Using KK, CE or 2000?

[/quote

 

haaa’’ greg   it aint the resin fault

    cheers huie

6

You think it’s the foam? I haven’t seen any of the SB’s do it and I’ve seen lots.  You agree?

7

 

at the risk of  causing a storm of protest    i totaly agree

                                                                cheers huie

8

I’ve had the same problem myself and it only started when I began using PU blanks from a different manufacturer. Once I went back to my original manufacturer of PU blanks the problem went away.

9

I’ve posted this pic before, but in case you missed it… here goes. Ice9 PU with RR CE. Heat alone caused this. NOT a resin problem.

[img_assist|nid=1052910|title=ICE 9 meltdown?|desc=|link=none|align=left|width=305|height=404]

[img_assist|nid=1052911|title=Ruined.|desc=|link=none|align=left|width=276|height=208]

10

Bummer.  I just laminated a US Blanks with epoxy.  Not RR, though.  The stuff got pretty hot while doing the bottom last night.  Hot enough for me to have some concerns.  Mike

11

I have seen one with shrunken foam, but it had more to do with the guy leaving the boards in the backyard-sun.

12

So after this, What PU blank works with RR, CE or 2000?? Is the US Blue a prob too?

13

Chrissup,

I started with epoxy, so that was all I knew.  Zero experience with poly, except when I was a kid doing backyard ding repair on my own boards.  I wanted to give my customers a better alternative to polyester but have come to the conclusion that unless they ask for eps or know the difference between epoxy and polyester resin it is not worth the time or expense to use epoxy on pu.  If they ask for it and know the advantages of S cloth and epoxy on pu then they get a warning about the downside of possible foam shrinkage, dark board bags, leaving the board in a car on a hot day, etc. 

I've had almost all pu blanks have issues with epoxy.  US reds, blues, Ice9 mowses, cane was the worst, southcoast aussie foam, etc.  Either high heat, over 120 F or time usually 8 months to a year every single one of them showed signs of foam shrinkage.  Some were very minor and some were super bad.  Problems ranged from minor foam swelling near the nose to full blown elepant skin along the entire board.  The denser the foam was to begin with the more it resisted the shrinkage.  So the Ice9 mowses was the worst, the US blue is a little better than the red.  The Southcoast was a surprise, very dense hard foam but the entire board shrank over an 1/8".  I'm in Hawaii and have heard that in cooler climates there are no to little problems but for me out of 60-80 pu boards all have shown problems.  The eps ones not a single problem. 

A common problem I was having was that people would complain that the stringer was shrinking.  What I found out was that putting a board deck down in the back of a pickup truck, even in a board bag would subject the tip of the stringer to the hot bed.  The wood would absorb the heat and transfer it along it's length.  This would cause the foam to expand next to the stringer giving the impression that the stringer was shrinking.  A simple test with a thermometer showed that in 1 hour a black bedliner could reach 140 degrees at noon in Hawaii.  My personnal solution to the problem is to put my eps boards on the bottom of the bed and the pu's on top.  That and not leave the pu's in the back of the truck ever.

Also don't get me wrong.  I'm still a die hard fan of epoxy.  The RR kwick kick is amazing.  A US red with a KK 4 oz.. s cloth glass job makes for a strong light responsive board and not having to seal the clear eps blanks is a major time saver.  Up until the SB blanks became available here all my personnal board were this combo.  Also what has become a revelation for myself is how my 3 year old EPS boards still ride the same.  They have yellowed and the decks have crushed down but they float like no other and ride like they were new.  A full season on a epoxy/pu and it starts to wrinkle and die.       

 I still use s cloth and epoxy/pu on my personnal boards but have stopped on regular pu orders.  The wrinkling and swelling/shrinking is usually cosmetic, but for some people they flip out.  If the new SB foam resists the shrinkage I may start to offer it again but for now it is for eps and special request only.

I'm trying some SB greens but no exposure to enough time or heat to tell yet. 

14

Your welcome.

This came after going back and forth on the phone with one of the owners of Ice9.  Everyone kept swearing that the stringers were shrinking.  But there is no way a kiln dried sliver of bass let alone ply is going to shrink at 140 degrees.  He did tell me that his foam at the time would continue to blow at 140 degrees.  The temperature here stays a pretty even 85 degrees.  I figured on the hottest days a bed liner might get 100 -120 at the most over a long period of time.  Used a meat thermometer and watched the thing shoot to 140 in 60 minutes.

If you look at the pictures that njsurfer posted you can see the puffing next to the stringer.  I'm not sure what happened to that particular board but it will look exactly like that picture.  Sometimes just near the nose sometimes along the entire length.

Seems that it always starts at the stringer and then over time it spreads to random areas and almost always on the bottom.  The theory that I have is that the more flexible epoxy allows the foam to swell causing the glass to stretch.  The sometimes lighter glass on the bottom is more prone to stretching.  Then when the foam shrinks the glass doesn't follow causing wrinkles.  Why the foam can swell with heat and then shrink I don't understand.  Also why not eps?  It swells and contracts.  Never not once did this problem come up, not even a delam.   

I have 2 SB greens that I just glassed with KK that are my own.  I'm hoping that they do the trick but then again it really is just cosmetic.  It looks bad but unless it gets super wrinkled you can't tell.

The first US red I glassed with KK seemed to handle until one day I forgot it in the back of my truck for 2 hours and it puffed along the stringer near the nose.

Also all of my boards go into the dakine day bags.  The ones with the reflective material on one side and white on the other.  They really are only good as long as what they are touching isn't hot.   On top of a black bed liner it acts like tin foil.

15

CE and 2000 but not sure whats what now. I have switched to the KK and have been loving it. I don't think it's the resin though?????

16

I had to give him one of my personel boards that was in way better shape than his. At first I told him he had melted it. He said no way - got stinky and huffy in my shop. I hadn't seen this before - so I hooked him up. He's happy - I'm not. But I have to stand behind my boards. This one and two others are really bad while a few more have spots. Back to eps I guess, shit sucks.

What if we put one of PeteC's goretex vents? It was my understanding that eps gassed out and pu was pretty stable. And why doesn't it happen with polyester resin?

I have some boards that have been ravaged in the sun by myself and freinds that are eps with RR CE and nothing happens. I have seen some bubble delams from boards with dark pigment that maybe I put to much pigment. But the white pigment or clear board lasts a long time in direct sunlight sitting on black sand/rocks that get pretty hot themselves. I can leave those for 2-3 hours on the beach. try that with one of my pu/epoxy's (they ride very nice dammit) and it will shrink melt collapse whatever you want to call this blight.

I found a post that says US Blanks is having $ trouble and knows about this. Bad batches/mixes soft spots, uncured parts of the blank that keep gassing out for ever. Anybody know about this? Cause if this is the case I'm gonna want some free blanks you hear?!!!

 

17

maybe check your thermal stability of your resins. quite a lot of epoxys start at about 60degrees celcious before they become elastic. this is 140 degress farenhite. easily acheivable in a car in tropics

#quick google

 

Using a Labcraft 227-876 thermometer, we measured
the increase in interior temperature of two cars exposed to the sun.
Serial readings were taken every 10 minutes from 2:30 PM to 4:00 PM in
downtown New Orleans on July 27, 1995. The outside ambient temperature
was 93°F at the beginning and end of the testing process. The sky was
partly cloudy and the relative humidity was reported by the US Weather
Service as 53%. Car #1 was a dark-blue sedan with the windows closed.
Car #2 was a light-gray minivan with both of the front windows open
approximately 1.5 inches. The thermometer was in direct sunlight in Car
#1 but was shaded from direct sunlight in Car #2. The thermometer was
placed upon the front car seat to match the likely position of an
occupant. The seats in both vehicles were cloth.

**
RESULTS

**

Within 20 minutes, readings in both
cars exceeded 125°F and reached a maximum stabilized temperature in 40
minutes (Figure). The temperature rise in the first 10-minute interval
was more severe for the dark-colored enclosed sedan than for the
light-colored minivan. The maximum stabilized temperature was also
higher for the dark enclosed sedan (140°F compared to 138°F), which was a
temperature rise of over 45°F in less than 1 hour.

 

 

i think the average range of average epoxy is in the 140 to 180 degree farenhieght. i think polyester have  generaly higher ratings on average utilility type resins.

so resin is elasticating, wood outgasses and foam expands and outgasses with heat . the problem i assume is involved in the relationship of these 3 variables.

This would happen in varying degrees with all surfboards with differing results.

i guess that the higher thermal stability of the polyester stops the skin from elasticating, or at least has a slightly higher temperature stability ( lets assume that the car would need to hit say 180 degrees before problems may occur). so perhaps even tho the foam is expanding ( in places) the stiffness of the skin keeps it in its pants. perhaps the reason eps has fewer problems is because it maybe outgassing through a hole to release pressure, or because the nature of the foam is a more UNIFORM  and stable structure wrt to density and blowing agents/properties

the combos that seem to work while other dont ?.  maybe look at socio economics and ambient summer temperature. does the surfer drive and leave 2 or 3 boards in the car or do they walk or cylce in boardies with their only board, under arm. This maybe the only difference yet the overall result could vary greatly., another shaper in a cooler climate like NZ would have no problems.

how dry the  stringer material and is the wood used prone to outgassing

thermal stabilty of foam

type of glue used on stringer

 

possible solutions may be to check the thermal stabilty of the foam and use the one that is highest if you make boards in hot climates where people leave boards in the car.  a low temerature post cure can raise the stability of the epoxy a fair bit. i have  been using a resin that is good for 180 degrees faranhite with a 8 hour post cure . slow ramped to a mere 115 degree faranhite.Put a warranty void for heats exceeding the thermal rating of your shooters. label your product with a thermal rating

or perhaps completely ignore me and disregard what i think

18

one more question for chris . why do you leave your board in the sun? i try and look after my stuff. i rinse my wetsuit and hang it up in the shade, is why it lasts 2 or 3 seasons and still in good nick. and i keep my board in a reflective cover. i change the oil in my car every 5,000 kms and keep my edges on my snowboard sharp. if people cant look after there stuff thats is their problem ey!

two types of kids. bike on lawn or bike in garage

19

whilst it looks good to post up a long list of blame everything.

 

               this is a characteristic sign of 2nd teir foam

 

 

 

20

I work with epoxy over poly.  Ive never had a problem but I live within walking distance of most of the places I surf so I rarely subject my boards to heat.

Here are my thoughts on the issue though:

Variable #1.  When heated then cooled everything expands and contracts.  Some things expand and contract more than others but it is still going on regardless.

Variable #2.  The foam and stringer will expand and contract at different rates of one another.

Variable #3   Resins soften and re-harden when heated and cooled.

The problems are likely occurring when the resin softening and re-hardening are out of tune with the expansion and contraction of the foam and stringer. 

For example:  Board is left in the car and the blank begins to expand.  Given that the resin is hard the foam initially has nowhere to go so pressure just builds up. 

Now ratchet up the temperature a bit more and increase the length of time and the pressure within the board grows and grows.  Meanwhile the resin begins to soften.  The glass job actually begins to stretch under the intense internal pressure of the blank expanding.

Now cool the blank.  Depending on the rate of cooling and the timing of when the resin hardens back up in relation to the contracting of the blank you would get rippling or the perception of shrinkage.

Given that all blanks are going to expand and contract I believe the answer is with the resin being made to not soften until higher temperatures are reached.  Beyond that I would say venting everything.  Advise customers to go with a poliester board if they are going to leave them in a car.  Or better yet......Never leave any board exposed to heat cause its not good for any of them regardless of what they are made of.