Gassing "the G Word"

I imagine just about all of us that have been in the industry for any length of time has had the wonderful (and as yet unavoidable) experience of shaping a beautiful stick, sending it out to glass (or laying it up ourself), only to have some bubbles show up out of nowhere!

We aren’t talking about ‘pin air’…you know the zillions of little bubbles that reveal themselves when you squeegeed out too much resin in a quest to make the lightest board…this is something else.

Gassing seems to always show up along the stringer, although we may also call to mind major delam bubbles that came up through other areas: particularly in the context of extruded foam. To be honest, I haven’t kept up on extruded foams since we dabbled with them (and got our asses kicked) in the 80’s. What is everyone calling them now? XTR’s? Is the solution of drilling tiny holes into the rail really fail safe? As I recall, the foam simply didn’t have the R factor to handle hot days, dark colors, sitting in a car, etc.

But let’s go back to gassing in general. Any solutions out there for eliminating it?

It seems as though when you get a ‘blower’, that even opening up the layup and applying styrene and then some resin, that the thing will want to continue to resist saturating and filling. How many of you have tried presealing with a microsphere, cabosil or milled fibre slurry previous to (or after) layup? Resin baste along every stringer before glassing? Obviously having to do this for a “it might gas” scenario is extra work (and expense) for a maybe.

So who does what when it happens.

Who has had success in correcting the problem?

What is your method or approach?

…or is gassing inevitable, like us old farts that just keep on producing gas no matter what we do?

We have recently had to address this exact issue with our blanks. After glassing some of our test blanks and samples some problems surfaced along the stringer. These consisted of delamination along the stringer, yellowing along the stringer and in some cases puffing of the foam along the stringer. What we discovered is that all these issues were directly related to out-gassing of sulfur from the urethane glue we were using.

As it turns out, most urethane glues out-gas sulfur, especially in the presence of elevated temperatures. Some out-gas worse then others, but it is a by-product of the glue. As we looked into the issue we found that almost all the urethane glue companies advertised that their formula had “low sulfur out-gassing” but few of them actually do.

As the glue heats up it releases the sulfur gas. This gas is trapped between the glass and the foam and creates the delamination. As the glass and resin separates from the foam it allows the gas to spread a little bit outward from the stringer. As the gas cools it deposits yellow sulfur residue along the stringer.

As we studied the problem we visited many glass shops to measure the exotherm temperature of the resin and catalyst mix they were using. The temperatures varied greatly from shop to shop depending on the resins and catalysts used, the quantity of resin mixed at one time, ambient temperature, etc. The maximum temperatures we recorded ranged from just over 100 degrees F to over 200 degrees F. The hotter the resin mix the worse the problem was.

After a board was cured the same problem could occur if the board is exposed to excessive heat. This could include being in a closed car (we recorded temperatures of over 140 degrees F) or being left out in the hot sun. If there is dark paint or laminates directly over the stringer then this tended to magnify the problem. We left a white blank and a blank painted black in the sun and the one painted black reached temperatures that averaged over 40 degrees higher then the white blank.

The solution for us was to switch back to a polyester resin based glue, at least for the time being. We would like to find a suitable replacement that has lower VOCs but until we complete a thorough testing program we will not make the change. Our blanks are polyurethane so this option is open to us as opposed to the PS blanks.

This is not to say this is the complete answer to all stringer out-gassing issues but in our case this solved the issues we were having with out-gassing along the stringer.

Thank you LT for your in depth insight to this complex problem!!!

Often in the past, even very experienced shapers have been left wondering if this was a problem related to improper wood curing of the stringer(s) or poor glue ups causing expanding air to blow for the surface and a ‘lighter’ atmosphere. The sulfur insight is something that many of us had no idea of. In light of what you have been so generous in disclosing, it is apparent that superficial boundary layers aren’t a viable solution.

It would seem to me that there should be a good water based or acrylic bonding agent that could do the job without the current result. What are the drawbacks of using a fast setting wood glue or Elmer’s? Not feasible? Still too slow? What other adhesives devoid of VOC’s are out there that are PE/wood compatible? I should think that the potential volume of business for an environmentally friendly, cost efficient, quick setting glue would warrant some attention.

And finally, I find it hard to believe that there isn’t an existing bonding agent that is perfect for PU foam and wood…undoubtedly you have looked around…or perhaps you haven’t because of time and workload constraints. Perhaps epoxy glues lacking the voc’s aren’t cost efficient?

If we don’t ask, we don’t get.

             "They called me a genius, but actually I didn't know what the hell I was doing"

No worries regarding sharing information and ideas. It seems a shame to stamp it confidential and stick it in a drawer. The more we all know the better our products get, the more choices there are, the more innovation there is, the easier it is to fend off overseas competition. Just our opinion. Now I’ll get off that soap box.

The biggest constraint for us is in the speed that the glue sets. (We have developed semi-automated glue jigs and target is to get 4-5 boards per hour per jig. That means a 10-12 minute set time.) There were other glues that had the adhesive strength but they wouldn’t work in a high production environment.

We experimented with many different epoxies and regardless of the promise of “5 minute set times” by the salesman they always took considerably longer. Many would work fine for shapers only needing to glue up a few boards a day. You are quite right that there are numerous bonding agents that would be perfectly suited for a PU/wood interface.

We are continuing to search for a glue that will be lower in VOCs and hope to have a replacement glue in 2008. As a start-up we have plenty of other priorities that need addressing before we’ll have a chance to get back to this issue.

As for your comment regarding wood, it is quite possible that issues related to wood could have an effect on stringer delamination. If the wood has too high a water content that can pose problems. If the wood is too young that can pose problems. Some types of wood, like cedar, have oils that come out that can also cause issues. Etc. Very critical issues.

Not a production guy here but a homeshaper with boat and surf experience…

Your wood type is imho really critical. Humidity and oils will prevent adhesives from working properly. Marine ply is really well suited as it has none of these particular problems and will allow a real “five minute” epoxy to work. Of course using ply for stringers may not be an option for you production guys, if it is, then you may want to experiment with the epoxies again.

adhesive technologies in NZ make just about the best 5 min epoxy ive ever seen

ive got dings i fixed with it 2 years ago

makes a great stringer glue

and really does set in 5 minutes

To LT & Surfer Dave,

Yup, improper curing for the wood could pose significant problems. I’m hip to the marine ply approach (no voids in MP)…glue lam strength, and readily available over optional wood sources.

I was surprised to see a (white) “structural” pine offered from Midget Farrelly (Surfblanks Austrailia), believing that the sap (oil?) would be prohibitive. SA offers a wide variety of stringers in t-band sizes per individual need. Approximately 4 stock & 7 custom stringer choices appear on their price list. Ice Nine & Homeblown also have distinctive offerings of ply stringers, as does US Blanks and others. Ply is pretty widely available at this point in time.

…because there are varying grains in ply layups, they are stronger than a single piece of wood in the same dimension…but care in shaping these stringers is required. Blunting is something that is not currently being considered or at least stated to the shaper. Ply has its attributes, but can also be a bummer. I recall the plys used in Peru in the late 70’s requiring the stringers being sealed with resin because voids went all the way though to the other side(!) Color work on one side could show drips thru to the other side. Of course, these were the ‘early days’ where we also used melted wax instead of surfacing agent.

Although basswood and cedar appear to have become an industry norm, there are other woods that have good structural and shaping qualities. Butternut was used for a time at Clark Foam. As I recall this was in the late 70’s …I found it appealing and user friendly. Redwood (at least the good “old growth” redwood)became expensive and less available, and Clark was looking for options.

Bamboo is yet another avenue for stringers that is viable to expand upon. Growth can be very rapid and is certainly sustainable. Bamboo has admirable linear strength. I am not up on the blunting aspect, but I have a feeling it will quickly dull tools . Of course this may depend upon the genus used.

Divinycell or a high density foam is another avenue worth exploring. I am not currently using a PVC approach, but I can certainly envison doing so.

None of this directly relates to the challenge that sulfur presents in laminating a delamination free surfboard, but is worthy peripheral dialogue for consideration.

Koa? Redwood? Balsa? Polyurethane? EPS? Soft? Carbon? Kevlar? S2? Bamboo? Hollow? Inflatable? Aluminum?

When did it ever get so complicated to just go surfing?

Some of our customers prefer the unidirectional poplar plywood that is aircraft grade. We have found during testing that the bass wood we are supplied is more consitent in it’s properties then the plywoods we have tried . Do you use unidrectional ply or standard cross grain plywood? I believe that Australia does not have a national standard for “aircraft grade” plywood other then the out-dated ANO108-23 (Specification: marine plywood for aircraft use). Does the marine plywood you use meet the national standard AS/NZS 2272?

We prefer to use the bass wood as we can insure quality much more easily as opposed to the plywood which has certain issues that concern us. For instance, depending on which of the gluebonds used (Type A phenol-formaldehyde, Type B melamine forified urea-formaldehyde, Type C and D urea-formaldhyde resin UF) there are issues of out-gassing of formaldehyde which is released out of the glue especially in the presence of elevated tempeatures.

Another issue with the plywoods we find is that there is variation in the glue ups that results in variability of the flex properties. Also, since we are unable to personally inspect the core or crossbands so we can’t insure knot free condition, etc.

Our bass wood has been very carefully specified to try and provide consistent flex profiles. Our purchasing specification delineates which of four key worlwide forests we select our bass from, which lattitudes the trees must be located in, the months that it is harvested and cut, how it is culled, the age of the trees used (80-120 years old), knot free culling and water content among a host of other items. By specifying this we find that the stringers exhibit very repeatable properties from one lot to another.

What wood(s) is the plywood you use made from? We are very concerned that any woods used in our standard stringers are a product of sustainably managed hardwood forests and try to avoid using rainforest woods such as coachwood, mahogany, etc.

I certainly don’t disagree that wood choice is critical and has far reaching ramifications. There were many more parameters to lock down in our purchasing spec then we would have at first imagined.

a high quality 5 minute epoxy will work well if applied lightly and carefully

and will have a bond stronger then the foam in 5 minutes

not all glues are equal

most 5 minute epoxies are shitty and take too long to cure

do you guys have to bend the foam at all

or is it at the correct rocker

that would make a big difference

heres an idea

you could set up a large jointer to surface the blanks for a perfect joint

and a holding rack the would hold ten or twenty blanks on there sides

then glue the stringer on to the one side of all the blanks with a light clamping system or weights

after they were set

then glue up the other sides one or two at time with the blanks still on there side in the rack

maybe the base of the rack would have some hooks so you could hook a rubber band down there

and pull it over the top and hook it back down the other side

3 bands lightly clamping should do it if the joint is good

should be able to knock out 6 or 7 an hour

The ply I have used is “Meranti” marine grade ply approved by the Forest Stewardship Council ( I am unsure of the glue or standards but I will have a looksee tomorrow and let you know as I have not had any problems with it.

Thanks. I look forward to reading the info.

The meranti we were able to easily get a hold of during testing unfortunately was not certified by the FSC. The core was of Indonesian origin and without certification we were afraid it might be the product of irresponsible forestry.

Also, the meranti we looked at was certified to BS-1088 and although that was great from the standpoint of knots and pinholes it allows for small splits in the core veneer and could potentially compromise the integrity of the stringer and make a weak spot where the stringer is intact only on the outside veneers. The spec also allows for water content from 6 to 14% which is a bit wider tolerance then we are looking to hold.

yeah meranti is rainforest

no such thing as sustainable rainforest logging imo

There are two types we used

BS6566 Meranti the simple stuff

BS1088 Oukume this is actually the better stuff and my supplier tells me this is heavy duty boatbuilding rated. Glue is phenolic they say.

Both have FSC stickers so I assume it is sustainable. Then again nowadays you never know but here it is pretty much impossible to get anything that isn’t at least on paper “sustainable”, that’s why we have no balsa in significant quantities.

Furthermore of note is that the Netherlands has no idea what Paulownia is, except as a garden plant. I spoke with three major importers about it and they had no inkling nor interest.

As I work with EPS only I have since moved to stringerless blanks and compsand methods.

LT…I’m curious how the poplar stands up against basswood. Poplar is widely used for stair treads and ballusters and accepts paint well. Seems cost efficient too. Is basswood stronger overall?

Interesting to hear more in depth about the ply being used in the Netherlands…

I will be shaping up the two Ice Nine blanks this week and starting to collect data on them as I put them through glassing. The 10’3" is slated to become a 9’8" noserider for a team rider that surfs Point Arena (he lives in Guaylala). This is the guy that rides stingers (just made him 2 more 12 lb. EPS 9 footers). We have decided the Ice Nine will also be a single/double concave stinger. I’ve been making him stings for a dozen years. This approach developed because he rides very far forward for longboards…made sense and we’ve never needed to go backward.

The Ice Nine blanks are really inviting…love the texture and weights available. So more info coming this week!

Gee, if you guys make it big, maybe you can advertise on that new show Jimmy Smits is starring in “CANE”. (LOL).

Gee, if you guys make it big, maybe you can advertise on that new show Jimmy Smits is starring in “CANE”. (LOL).

Definitely LOL! We’re still trying to make it “small” before we worry about making it “big”.

The poplar and basswood are actually quite similar woods in many ways but the basswood is not quite as dense as poplar (26 lbs/cu. ft. vs. 30 for poplar), not quite as stiff (1507 psi vs 1580 for poplar) and has a lower bending strength (8700 psi vs. 10100 for poplar). For application in a stringer we think those are positive attributes for the basswood.

For us, however, the choice of basswood has as much to do with consistency as anything else. The poplar seemed to vary quite a bit and we couldn’t be certain that we could source a consistent product. Our goal was to be as certain as possible that a stringer purchased this year will perform the same as the same stringer shape made out of a different batch of wood the following year. This comes down to the quality of our purchasing spec and the ability of the supplier to meet it.

We have toured a variety of forests and mills to find the “right” one. Once we found a forest that met our requirements (consistency of growing season, sustainably managed, availability of trees 80-120 years old, the proper latitudes, grain patterns, etc.) and a mill that performed to satisfaction then we could be certain of the consistency of the wood quality.

We are driven by the concept of the magic board. We are fascinated by the idea that a “magic” board could be painstakingly duplicated but not quite work the same even when great care was taken to match the original dimensions and shape. Our feeling is that the variation in the underlying blank has a lot to do with this. If you start out with a blank that has a slightly different density gradient or a stringer that has wood with different properties (as a result of wide tolerances in the variation allowed by the blank manufacturer) then even if everything else was matchd perfectly you still wouldn’t be able to recapture the feeling of the magic board.

In other words, although poplar might have had properties that would make it an acceptable substitute it was more difficult to purchase it with the rigorous quality specification we were able to implement with the basswood.

I applaud your tenacity and in depth study of the many facets of brnging us the best blanks possible. Just remember there are an insane number of variables that could contribute to one magic board being different from ‘the other’…doesn’t matter if it’s CNC’d, molded, whatever. If we want to labor it, we could take it down to the N’th degree: did the glasser use the same cloth? Did he cut the laps wider? Resin rich lam? Was the board sanded the same? Which rack was it glassed and cured on? On and on. Then we get into the “one man’s magic is another man’s poison”…a Bobby Martinez Model might work great at 6’2" with a guy that swims it in and uses the bubble underneath to lane on…but the scaled up 7’6" BMM is a nightmare for a 35 yr. old guy trying to catch the wave. The computer scaled it up correctly, but something was lost in the process…maybe sell it and get something that works for YOU and be glad you didn’t shave your head.

Don’t get me wrong…you are quite correct in isolating the variables as a ‘medium provider’ to us shapers.

Let’s just agree that we are making square houses on a round planet, so technically nothing is “flush and plumb”. Capiche?

Still, holding yourself to such high aspirations pays dividends in the long run. My experience with Clark was largely very satisfying, but having said that, there were times when I realized it wasn’t me that was off on the shape but the stringer. When Clark introduced the new way to order custom rockers in close tolerace blanks, it was a tremendous feature to access, but even then I had a blank that the rocker specs didn’t begn to resemble what I had ordered. Grant that it was a pretty complex layout I requested but it still wasn’t even close. So much for the Velzy copy job.

I’ll cut this short by just adding this:

There is something beautiful about custom surfboards and the energy that transcends from human mind, spirit, and body onto and into a handshaped blank. There will always be something extra special about a finite product. Nothing can numb the mind more than when a thing is homogenized to the point of sterility. Approximate can be a good thing that once in a great while, equates to magic.

Give us the greatest ‘canvas’ you can for us to create our art…we will return the favor in kind.


I didn’t mean to say that the blank was the key to the magic board. The magic is definitely in the HANDS of the shapers. Our goal is to make sure this isn’t impacted by unmagical variation during blank production.

We often use the same canvas analogy you mentioned. We are not artists nor do we aspire to be. We just want to make the finest, most consistent canvases we’re capable of. If the wood doesn’t perform consistently then the stringer and rocker the shaper specs won’t perform predictably.

We’ll leave the “insane number of variables” to the shapers and instead we’ll just tackle a few of the unplanned for variables we feel shapers shouldn’t have to deal with.

No disrespect intended!


I grok what you say earthling.

Galaxies apart, but on the same wavelength.

Keep up the great work…it is appreciated!