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Ask an Expert About Epoxy for Building Skis/Snowboards
February 25, 2007
To build durable and high-quality ski/snowboards, you have to
use the right epoxy and use it in the correct manner. Who do you ask for sound and meaningful
information about epoxies -- an epoxy expert, of course?! We invited
members of the SkiBuilders.com forum to probe Roy Wheeldon, Technical Director
of QCM Adhesives and Coatings, for answers to their wildest questions. The
company QCM specializes in developing epoxies for the ski
and snowboard industry, and Roy has many years of experience under his belt.
Below, he kindly shares his thoughts with the ski/snowboard-building community:
Questions by SkiBuilders.com forum members
Answers by Roy Wheeldon,
Technical Director,
QCM Company,
930 Central Avenue South,
Kent, WA 98032 |
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Disclaimer: Contributed articles express the views of the author,
not necessarily the views of SkiBuilders.com. SkiBuilders.com accepts no
liability for the content of this document, or for the consequences of any
actions taken on the basis of the information provided. If you don't like what
you read, then stop reading it.
CONTENTS
GENERAL EPOXY QUESTIONS (Q1 - Q9)
Q1: Why are heat-cured epoxies generally
stronger than room temp epoxies?
The cross-linking of the epoxy is always stronger at elevated temperatures
– in any system. You can easily triple the flexural and tensile strengths of
epoxy systems by curing at 170 to 200 deg F. Also adhesive properties are
greatly improved – particularly important when trying to bond to Nylon, ABS or
UHMW or other Polyethylene tops /bottoms. I know of no room temp cure that will
ever be as good as an elevated temp cure. Don’t believe someone who tells
you the opposite.
But my biggest concern is for people that cure below 70 deg F – now we are
looking at below normal standards and potential ski or board failure on the
slopes – not a good idea. Get a heated shop/ hot blanket/ space heater or
something that resembles heat. Not a cold garage please.
Q2: Can you suggest good epoxies (heat cured and room temp) for skis and
snowboards? What qualities to look for in choosing an epoxy?
Tough question to answer. The epoxies and hardeners on our web pages have
all been used over the years to make boards or skis by high production Ski or
Board companies. You can mix or match any of our hardeners with any of our
resins. ETH-003 was used (and still is used) by many water ski/ wakeboard
companies and is particularly helpful where poor fitting of core to outer mold
causes dry areas. In the hand lay up if you always have “dry areas” in a certain
spot, it can be because the cores you had made are not congruent with the mold
you had made – hence ETH-003 to the rescue.
Put extra mixed epoxy in the dry area that is causing problems. When you
“press the epoxy” by Compression mold or Air-Bag Press, this time more epoxy
will stay in the “dry area” because we have increased the hydraulic pressure of
the epoxy , so it is harder to squeeze out of the press. It tends to squeeze
into the glass and core more and is squeezed out of the press less.
The only disadvantage to this is that it makes a slightly heavier
board/ski. But I would rather have this than a ski/board with a weak toe or rear
end ( or center for that matter) – it seems that most “dry spots” appear in the
toe end of the ski or rear end of the ski.
But if you have good fitting (engineered) cores that fit the molds
perfectly, then go for a typical lower viscosity epoxy like EMV-0049 - this was
used for many years by Morrow and it got them out of several poor quality years
(they had a different Supplier prior to QCM) into a long season of quality
boards where they were able to sell out to K-2 for a very healthy price.
The hardener is a personal choice based on how quickly you can lay up and
how complex your design is. ECA –408 is the slowest, longest potlife and ECA-312
is only for Superman guys who have lightening fast hands. If you are making a
100 skis a day (Pros do this), then you get pretty good at fast lay-upping. But
if you are a normal person making a normal lay-up –not too many layers- in a 70
degree shop, then most people like ECA-032 or slightly faster people like to use
the ECA-315.
Q3: What solvents will work to loosen unwanted cured epoxy from ski press
parts?
None really. Epoxy when cured properly is very solvent resistant. Remove
mechanically (abrasion or file). But if you cure your skis in a 45 degree garage
with a 45 degree Sand-Bag press, then MEK or Acetone will soften your already
soft epoxy. A well cured epoxy would take many days of soaking in MEK to soften,
although I have heard there are Cured epoxy removers , I have never found one
that worked well.
Some say methylene chloride will work, but nobody uses it any more (except
big Commercial companies like Boeing Co) because of hazardous chemical issues.
Q4: What other substances or environments will degrade epoxy
(post-cure) over time, thereby weakening the lay-up? Acetone? Citrus Degreaser?
As stated above, epoxy when cured properly is very solvent resistant. Over
time, acetone and MEK (methyl ethyl ketone) will soften epoxy to a weakened
state, (but we are talking total immersion in MEK for at least one week). I
don’t know of any ski slope Companies that clean up with MEK or acetone. Hmm,
maybe avoid yellow snow areas.
Q5: When a ski loses camber, is it the epoxy bonds breaking down or the
fiberglass reinforcements breaking that causes this?
My belief is that the epoxy in the board has still not fully cured for
camber to go South. Take Morrow for example they cured for 18 minutes at 180 deg
F. The epoxy is 95% cured at this stage. Partly because warm epoxy can move
somewhat freely, they then put their boards into a Post-Camber press for an
additional 24 hours. Mr. Camber was saved. Even with a full cure at elevated
temp, like above, the epoxy is still curing for the next 7 days. 95% to 96% to
97%, etc. All Epoxy companies do their data sheets based on a 7 day 70 degree F
cure – to optimize results.
Q6: Can a room temperature curing epoxy be mixed with a higher temperature
epoxy on prepreg fibers and still work?
This is a strange question. All epoxies are ultimately high temp cure
epoxies. Cure at room temp at your own risk. Never put a Prepreg epoxy into the
mix without a high temp cure (normally 200 to 220 deg F.) By Prepreg fibers, I
take it you mean Prepreg epoxy soaked cloth? The raw epoxy has to see the raw
glass and then see the heat. No exceptions.
Q7: What happens to the epoxy bonds if the ski is heated too much with a
waxing iron? Does a heat-cured epoxy have a higher service temperature than a
room temp epoxy?
You guys are cracking me up. It’s a good job it’s Friday afternoon and I
am vegged out after another loony-tunes week. Well-cured epoxy is heat resistant
– up to 150 degrees F normally. A few minutes at excess temperatures will not
hurt. Yes, a heat cured epoxy will have a much higher service temp than a room
temp cured epoxy, by at least a factor of 2. All properties improve with heat,
including heat distortion temp.
Q8: When repairing skis a slow cure epoxy is almost always preferable to a
quick set epoxy because it's more ductile. Does the speed with which heated
epoxy cures limit its ability to absorb flex? In other words is heat set really
stronger or just a stronger initial bond.
You are confusing Adhesion with Flexural strength. A heated epoxy cure
(repair) (quick-set) will have superior Flexural strength than a room temp cure
(slow-set) epoxy (repair). The quick set epoxy does not bond well to the cured
ski if it is done at room temp. A slow cure epoxy (probably a Polyamide
hardener) has good grab (sorry, I mean adhesion) at room temp to cured epoxy
(better than a fast-set hardener done at room temp). Our hardeners are mostly
Polyamine type that give superb adhesion and flexural strength at elevated temp.
NOTE: If you made a ski out of Polyamide hardener it would be too
rubbery/flexible. And it does not harden enough even with elevated temps.
If you are going to do a room temp repair , then OK use slow Polyamide
hardeners like our EAS-1 or EAS-20 – also on the web pages under ADHESIVES.
Q9: During layup when all the materials are pressed together, what affect
does pressure have on the strength of the epoxy and bonding of the layers?
Pressure helps tremendously (which is why Boeing uses it to make 777
airplanes). (Please don’t make any airplanes cured at 50 degrees or below with a
sand bag press in your garage). With a wet lay up epoxy the pressure helps to
push the epoxy into the fibers, into the core and into all the plastic parts
(tops, bottoms, inserts, edge strips, etc). It helps maintain intimate
contact with all of the above during cure. This also saves weight because more
surplus epoxy will be squeezed out. Low pressure will not allow epoxy to
get to all areas. You can calculate the optimum glass to epoxy ratio, but
don’t ask me please – consult your local University Composites Research
Professor (you may have to buy him a Starbucks or two).
ENVIRONMENTAL ISSUES (Q10 - Q14)
Q10: Have you worked with Soy based resins? Do you supply soy-based
resins?
We use some soy-based raw materials in our PVC molding and coating systems
and PVC textile inks. Unfortunately there are no Organic or biofuels being
used yet to provide the strength properties required for ski manufacture. With
the advent of Biofuels taking off, there is hope that production levels will
reach much higher levels and that the fuel will be available for “cracking” just
like they “crack” petroleum OIL to make many raw materials for plastics
manufacture.
Right now none are available. Soy based products are very weak fatty acid
derivatives that would give a ski a strength rating of >1 on a scale of 1 to 10
- where 10 is the heat cured epoxy resin ski, I am talking about above.
Q11: How does the strength/flexibility of soy based resin compare to
traditional resins?
See above: but basically one tenth the strength of heat cured epoxy, if
that. Only sell these skis to your mother-in-law.
But watch out over the next 10 years for more “Organic” plastics to appear
in our daily lives. We will certainly be moving in that direction , where we
can. Our textile inks for T-shirt printing are moving strongly in that
direction, but the strength property requirements are significantly lower for a
T-shirt ink..
Q12: Regular epoxy resins suffer from UV light changing their colour. Is
there also degradation in mechanical properties?
There is a minimal degradation of physical properties with UV exposure. If
you leave skis in Miami or San Diego sunlight every day for 5 years, then expect
a small percentage reduction in physical strength. But I would expect this to be
in the 5% range. A good water ski that sees strong UV light every summer in
Florida is good for 25 years plus, and is more dependant on the skier’s skills
or lack thereof. But this ski was made in a compression molded ski press
and cured at 180 deg F. I would not say the same for a room temperature cured
epoxy ski.
Q13: Are those special resins with UV protection able to resist the
amount of light a ski gets for about (100days / 6h a day - assumption for a skis
life) in high altitude or is there an additional Topcoat needed?
Yes, we can make ski epoxy with a UV resistant epoxy and yes the UV
protection would be significantly better. But this has mainly a cosmetic
benefit. The drawbacks to using UV resistant epoxy is it is even harder to cure
well at room temperature; it requires much longer to cure even at elevated
temperatures and; it is about 3 times the price of “normal” epoxy. Again the
only real advantage is cosmetic, and a Urethane topcoat will provide significant
cosmetic protection and additional scratch resistance. But make sure you get a
Urethane that has UV resistant properties. There are many, many Urethanes
around, with and without good UV protection.
Q14: Does the addition of colour paste improve the UV resistance?
Yes. In the old days, water skis were mainly black and nobody ever
complained about discoloration. White skis have good Uv protection , but do fade
a little and the only pigment I would never recommend is a fluorescent pigment
where the Uv resistance really sucks. But in the “old days” we sold a lot of
fluorescent epoxy to ski manufactures, because it was trendy.
Don’t your skis have HDPE, PBT, P-tex, ABS and/or nylon tops and bottoms
anyway???? This is where your UV resistance is required. In most snow skis, the
epoxy sees virtually no UV. But maybe you have a bare-bones ski. I’ve heard of
“naked” motorcycles, but never “naked” skis. I guess I’m too old for
“naked” skiing.
MATERIAL ISSUES (Q15 - Q22)
Q15: How do you deal with different thermal expansions in materials in a
heated press?
Very carefully. Fortunately, most of your ski is going to be a
plastic of some sort. With similar Coefficients.
Small metal inserts are rarely a problem, but see below.
Take Volant for example. Anybody remember Volant? Am I showing my age
again. Well, they had a Stainless Steel bottom (VERY lethal if you ever got hit
by that puppy). Now here is a different thermal expansion problem. But it was
solved by a clever engineer who put a thin rubber sheet in between the SS and
the epoxy ski. Hey Presto, problem solved. Now many ski manufacturers copy this
technique where there are significantly different Coefficient of thermal
expansions in their material choices. (you should be able to get this from your
plastics supplier). As I said most plastics are in the same range of
Coefficient/Expansion/numbers.
Q16: What is the best way of cleaning materials prior to bonding?
Wipe with acetone or MEK. You need a solvent that will flash of and not
remain on the part. Low volatile solvents like D-limonene cleaners and alcohols
can stay on the plastic for a long time after wiping. If it’s a very smooth
plastic sheet, mechanical abrasion with a coarse grit will improve bonding,
mainly needed for HDPE and Nylon sheets. The HDPE should be bought in as
“flame-treated” or “corona-discharge” treated form. Or do it yourself.
Q17: What is the best way to bond steel edges on base and fiber? Do you
have to treat them to get better bonding?
Steel edges are mostly post bonded using a cyanoacrylate adhesive. They
can be molded “in-press” too using the epoxy as the adhesive. Heat cure is
strongly recommended. Mostly, just abrade with coarse grit paper and than
solvent wipe with a ketone. Adhesion of any substrate is always improved by
abrasion and solvent wipe. And heat.
Q18: How does epoxy adhere to ABS vs. PA plastic, if there are any
differences? Are there any preferred treatments of plastic before glued with
epoxy to other materials like steel and wood?
What is PA plastic?
Epoxy will bond OK to ABS if it’s the right epoxy, but acrylic adhesives work
much better. Heat cure will help considerably. We make an ABS epoxy for bonding
down ABS road buttons to the highway. It’s called EAS-60.
PA is polyacrylate, polyacetate or what? Polyacetate should bond well with
epoxy. Check with the manufacturer for their recommended types of adhesives on
this one please. PA could mean many things.
Polyolefins like HDPE, LDPE and UHMW should be pre-treated with “ Corona
Discharge or Flame Treatment”. There are primers (we even sell one) , but
the standard in the industry is “Corona Discharge or Flame Treatment” Bonding to
steel and wood is a perfect application for epoxy resins. Just abrade and
solvent wipe the steel/wood.
Q19: What kind of rubber makes the best bond with epoxy?
Black rubbers like EPDM and Buna are I believe the best for epoxy bonding.
Neoprenes are more difficult to bond. We have an excellent primer for rubber
pre-treatment called Chemlok 7701.
Q20: Would it be useful to glue the core and everything else together with
epoxy that contains (added) cotton flakes? The cotton flakes are often used as
far as I know when building aircrafts to enhance the flexibility and ductility
of epoxy and the materials that are glued together. The epoxy works as the
matrix between the material, the cotton flakes enhance flexibility and
ductility. So ... my guess is, it would be a stronger bond and a more durable
ski. Am I wrong or could this be correct?
My take on this is: that the strongest ski will be that which glass cloth
is bonded to a wooden core. Although cotton has fibers, they will be nowhere
near as strong as glass fibers or aramid fibers (stronger) or carbon fibers (the
strongest).
Strength = Carbon>Aramid>Glass> >>>>>cotton.
Cotton fiber in aircraft manufacture? Was this when they were trying to make
lightweight airplanes or cheaper airplanes? Please don’t tell Boeing or Airbus
about this one or I may never fly again.
Cotton fiber graphic sheets were used in water ski manufacture about 10 years
ago in place of a top sheet (top sheet manufactured skis are now called Cap skis
by water ski companies). Anyway in the old days, the fancy graphics were printed
on 100% preshrunk cotton fabric and laid up in the final top layer before
pressing. The cotton graphic was fully wet out before pressing. The skis looked
beautiful. Anyone remember this ? They simulated everything form natural wood
grain to wild ass graphics for about 5 years, before Cap skis came out. It was
used for strictly cosmetic reasons, and did not add any strength, flexibility or
ductility.
Q21: The epoxy resin I use during the layup cannot adhere to the ABS
topsheet. I was recently told that this is because the layup resin is too rigid.
Is this true? Why? Finally, what epoxy will work that is affordable by the
gallon? Will this adhere better than simply making the surface of the ABS sheet
an adhesive with MEK?
Are you bonding at room temp or elevated? If at room temp., then the
epoxy/polyamide systems like our EAS-1 and EAS-20 will work better for ABS. But
you do not want to make the whole ski out of epoxy/polyamide system.
If the layup resin is heat cured at 160 to 180 deg F you will get much
better adhesion with the “rigid” resin. Most skis are made with “rigid resins”,
and our rigid resins still have 5 to 10 percent elongation , which is just
enough to flex the ski. 30 to 60% elongation such as the Polyamides will
give you a rubber ski with too much flex. Flexural strengths of “ rigid epoxies”
are phenomenally high. This is why we can fly around in a Boeing Composite
aircraft or Airbus for that matter. Have you ever seen the wings flex in heavy
wind? They flex pretty well. Aluminium or Composite. The point is that the ski
flexes and recovers immediately, thousands of times on every slope.
If you are heat pressing a sanded/ MEK wiped ABS sheet with our epoxy, you
should be getting good bonds. If not pleased call me and we can discuss why not.
Maybe a fresh MEK wipe of a sanded ABS sheet will be better. But don’t flood the
ABS with MEK. It will soften it too much.
Q22: After a ski has been pressed, the excess material is trimmed by using
either a jigsaw or band saw. I’ve experienced increased wear and damage on the
saw blades, and noticed significant heating of the blade. Does the cured epoxy
have anything to do with this? In other words, can you suggest ways to extend
the life of the cutting tool? Should I consider using a lubricant or coolant?
Yes, consider using a cutting oil of some sort. Remember everybody is
whining about the skis being as strong a possible. Certainly, nobody wants to
ski the slopes on a compromised floppy ski. Therefore the epoxy is tough
and hard to cut.
HEALTH ISSUES (Q23)
Q23: Any health-related issues that I should know about when working with
epoxy, for example, how harmful is the resin and hardener?
There are health issues with every chemical we use, from bleach in the
kitchen, to weed-killer, ant-killer and paints in your garage; the list goes on
and will do for many, many more years until we have an “organic Earth”.
Hmm, that might be a while if Exxon continues to have its way. So we
separate chemicals into Hazardous, Toxic, Extremely Hazardous and Carcinogenic –
these are just the main categories. Epoxy falls under Hazardous as do most
plastics like polyethylene, polyester, acrylic, polystyrene, PVC, Urethane.
There are dangers with all of them if you are involved in their manufacture or
processing. Even soybean manufacture has its hazards and waste disposal
problems.
And soybean oil does not work for many applications in the real world. Or
your ski will dissolve on the slopes. Organic plastics are just being born. And
they have not come very far. Our best bet may be biofuels from Soybeans,
Linseed, Rapeseed, Corn, other vegetables and seeds. And then to crack the oils
that we make from the organic fuel into similar plastics and resins that Exxon
and Dow and Shell, etc, make now.
Once cured, most plastics are completely inert and non-toxic and
non-hazardous, including our PVC’s which Greenpeace regularly “slams” with a
biased non-technical barrage of data that is unsubstantiated by any actual
plastics-manufacturing Chemists. They will not reply to my e-mails on this. That
is another story that you do not need to worry about.
Ok this is the future and it is coming soon. For now, wear gloves and
sleeve protectors to avoid skin contact. One in a hundred people are sensitized
to epoxy, probably because they allowed it to be on their clothes, shoes or skin
for too many hours/days/ weeks. Change contaminated clothing/shoes. Don’t
continue to wear the same epoxy soaked clothes. Other words, don’t keep constant
skin contact with epoxy/hardener. Everyone of is different. Everybody has
different chemical resistance genes, as you know. I still have a business friend
who has been around chemicals his whole life and smokes and drinks everyday. He
is 80 plus years old and plays golf and softball. It’s not fair is it?
Wear eye goggles or glasses to prevent eye contact and have a positive
ventilation away from your lay-up area, venting any fumes to the outside. (This
technology is commonly called a fan with the window open.).
I have worked around epoxy and people who work with epoxy for nearly 30
years now. In my younger days we cleaned the epoxy off our hands and fingers
with MEK. Now we wear all the above protective equipment to make sure we are not
one of the ones who become “sensitized” to epoxy. Good hygiene measures should
be detailed on the MSDS.
Follow them. If you don’t have a Material Safety Data Sheet – get from your
supplier immediately. And read it please. Having the paper in your room will not
protect you.
The hardener is going to have more fumes and they will be quite alkaline
(ammonia-smelling) if breathed in. So be more careful to avoid contact with the
hardeners. Never sniff a just-opened can of hardener. There is a build up of
fumes in a freshly opened can. Give it time to vent. (20 minutes).
Once mixed with the epoxy a lot of the fumes go away (are locked in the
mix). If you get epoxy mix on your skin wash it off fairly soon with soap and
water (not MEK or acetone, which will drive the chemicals into your body).
Your friendly advisor, Roy, signing off. Happy Ski-making
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