PU / Epoxy Shrinking Problems (Which Blank Manufacturers?)

Apologies for hijacking Chris’ thread. Maybe people could list which blank manufacturers they’ve had this issue with. Mine was with South Coast. Never had this issue with Bennetts. Sounds like no ones had this issue with Surf Blanks either?

This might not be such a nice thread but in respect to the blank manufactures it has always amazed me how tempremental blowing PU foam can be, from the formula, the mold, the heat of the mold, the post cure and the guy who pours the blank, any one of these elements can f@rk it up.  ALL blank manufacturers have had issues and they all have second piles with blanks that have soft rails, paper stuck to them, holes in them ect…

Did the people who are having a whinge buy a second blank by any chance as these have no guarantees?

No seconds in my case. I’m sure making blanks is not easy, but then again neither is making a board only to have it shrink.

In increasing order of problems.

US blue

US red

Some cheap chinese foam (can't remember the name)

Ice9 mowses

Ice9 cane tie with Southcoast.

The new KK is noticeably harder once cured than the older RR resin.  So the US that I've glassed with the KK has faired better.  Too soon to tell for 2 US reds I did for my self with the KK.

Also I have 2 SB greens that just got finished with KK.  If they handle my personnal abuse in the back of my truck on those long drives and sitting in the sun while I surf I'll give my impression.

But as of 2 weeks ago no more epoxy of any brand on PU for orders.  Starting to love the uv poly, so fast and cheap and the sanding is a treat.

**marshy how ya goin                          dmp   did you get rid of the nastys


**                      cheers huie

Dean I wasn’t having a go at anyone just thought it wasn’t mentioned on the other thread that maybe someone used a 2nd.  A good point made about the hard work going into a board to have it shrink on you and especially when you live in a far off freezing paradise. 


All good down here Huie, been very busy with all sorts of stuff. 


Curing at some elevated temperature probably eliminates lots of this.  We did elevated cures at Firewire with some urethane and never saw a problem.  Even on some MDI foam.  The temperatures were moderate 120F … 50C


hmm i wonder if thats a good enough test on its own?


**         greg on a lighter side  midget has sent me a nice little blank that i want to use for a special little person    so lite so strong

**your resin is now just down the road from me now  so for me it will be a first haaa’’               i am confident there will be no prblms

**will post my thoughts  but still a few weeks off that job.







boards i made in 2004-2005 in N. Florida:

clark foam - first quality - green, blue, and red densities

laminated and hotcoated with clear RR and Additive F. speed spray finish on top of sanded hotcoat. 

they were good at first - they yellowed easily though - but after 6months to a year start shriveling up - stringer, laps, fin boxes, and pour lines protruding.

havent done an epoxy on a PU since then......


I haven't had a chance yet to try your tips with the brush.  I have to break some old habits I have from using epoxy.  Brushes are 75 cents so they get tossed, but it is wastefull and adds up over time.

I copied and saved your post.  Thank you again for sharing your knowledge.  Over the years I've found that the little tricks that the experienced board makers have are truely priceless.  You can stumble around in the dark for years and then someone screws in the light bulb for you and you have one of those "duh!" moments.


Never had problems with Clark except for ultralight as long as UV absorber was added to the resin.  Did lot’s of blues.

Ice 9 … bad results.  Never tried a moses though.

Also bad results with some of the MDI foams which are all now gone.

No problem with Walker who is gone too. Did quite a few and still have a couple that are 3-4 years old.

Bio foam was just bad … not just for shrinking.  I think it would have shrunk under a steel skin.

No problems reported with Surfblanks.

Seems that MDI foams are the worst.  All I tried did shrink even with UV absorber except for some which had elevated temp cures…  But their all gone now so …

TDI based polyester foams are fine but not at very low densities. Clark ultra light.

TDI based polyether or polyether/polyester foams seem to do best although South Coast is supposed to be that so …

EPS is no problem from anyone you buy it from.  Never seen EPS have this issue.

Curing at some elevated temperature probably eliminates lots of this.  We did elevated cures at Firewire with some urethane and never saw a problem.  Even on some MDI foam.  The temperatures were moderate 120F … 50C






Great you are testing SBUSA Green - good luck with them - remember, cut any urethane core deep enough and it will fail with heat!

Some months from now SBUSA Superstrong will be available ex Waipahu.

Andrew should be blowing some SBUSA Superstrong Pinks (approx 8% lighter than Yellow) in the next week or so.

Superstrong has amazing dimensional stability.


Thanks Midget!

I'm floored you saw this post.  Now I feel I have a bit of responsibility to follow up. 

I'm really hoping your foam will be the answer to my problems.  If anything just for myself as I use epoxy on my pu's. 

Once that 2nd board is sanded I'll take a few pictures and see how they fair on a hot day.  I've found that if there are going to be serious problems it only takes 2-3 hours in the back of my black bed lined truck and that is inside of a dakine day bag with reflective foil.  I have a feeling that a few people are interested in seeing what will happen.

Your foam is making an impact here locally on Kauai.  Derek is doing a great job at getting people set up with blanks.  The non epoxy guys are loving the yellows with the heavier glassing schedules in poly.   Very similar to eps/epoxy in weight but with that poly flex that most people are used to.

Sounds like the pinks might be right at the 2lb eps weight.

Midget I was hoping you would chime in. Would you have any suggestions on what might be causing this problem? My guess is some parts of the blank are not curing properly and are reacting to something in the epoxy. Can you assist?


Blank making is said to be a black art - we (blank makers) all do something different in formulation.

‘Off the shelf’ urethane technology barely applies to what the long time makers practice.

Dimensional stability is what it is all about - how do you achieve it - at light densities too?

There are multi national (chem cos) that would like to know this - we keep the industry in our hands by not telling them.

Process of elimination is what the board maker is destined to use until the right foam is selected.

It was always said ‘good urethane foam is impervious to solvents’ - it is still true!


Thanks Midget. If a urethane is not imperveous to solvent will it shrink or just dissolve?

    Howzit DMP, If you are using the wood handlehog bristle brushes it takes a while to stor shedding bristls but when they do they never do again. As for your 4" brushes order the white plastic handle Aussie brushes from Fiberglass Hi. If they don't know them as aussie brushes then tell them the white plastic handle ones. They cost about $7 but well worth it since they only shed a couple of bristles the first couple if times you use them plus keep them in clean acetone. I would do a + cut in the lid of a 2 lb margerine bucket to keep them in with the acetone. Hope all is well on Kaui and I miss it but will survive. Aloha,Kokua

Mahalo Kokua!

I'm hoping that if I can be busy enough to start shaping more I'll start using John and or Dave for the glassing. 

I know what you mean about the cheap brushes though.  I have a little routine of fluffing the new brushes before I use them for the sand coats.  It knocks out those strays before I have to chase them on the board.

I'm really intrigued with Huie's no acetone brush cleaning techinique.  If I get a quality brush I'm going to have to give his tip a try before I get into the benzene juice, argh!


Observations over time…

When you look at the white mass that is urethane - it is very hard to tell what will happen to it once exposed to various fluids and heat.

Acrylic lacquer will shrink soft rails - hot plug or box installations likewise.

I have never seen urethane dissolve like EPS doused with acetone.

Huie has been encouraging epoxy over urethane for a while now - most reports indicate success.

Chris Russell (APS San Diego) and Darren (Entity) have used epoxy on my blanks for some time.

I don’t think RR Epoxy needs any UV additions to make it work on urethane - while UV may delay yellowing in resins - yellowing in isocyanate foams is normal.

If you have urethane choices - exercise them until you feel safe with a brand.

After Grubby closed - everyman and his dog tried to make urethane - most did not survive critical analysis by board makers.

In Australia newcomer cheap blanks were everywhere - eventually the foamers lost their shirts - took some time but the board makers woke up.

If the makers didn’t wake up - their customers did - I had a friend bring me a new board (major Brookvale brand) that you could put your fingers straight through the rails - wasn’t sand through either!

Believe it or not that same foammaker is now on the Gold Coast supplying the same kind of penny pinching board makers with the same kind of foam.

Imagine the joy those blanks will bring to the end user!!!

Bottom line is still - ‘suck it and see’!


Have I made shrinking blanks over the many years?

Yes I have!

Did I learn anything from the experience?

Bloody well hope so!!!



Thanks Midget.