Laminating ? - UV vs normal Catalyst

Hi guys,

I’ve heard it mentioned quite a few times that if you shoot your MEKP catalysed resin too slow, that more resin is absorbed and the result is a heavy board.

Although, people are now using UV catalysed resin and I’ve read about numerous people taking 20-45 minutes to do their laminate. Why are these boards not ending up heavy? Is it just a relative thing, that the boards are heavier, but not excessively so?

Kind Regards,

Matt.

Having worked with both for many years; here is my guess why the UV soaks less into the blank. The UV resin is kicking more homogeneously when you are laminating for 25 minutes. This slight reaction starts instantly and is due to the ambient lighting. I found that regular flourescent lights will kick the UV resin just enough so that your squeegee feels “draggy” after a few minutes. Unless you are glassing in TOTAL darkness, you can expect some reaction to occur. Anyway, as the UV resin molecules start to cross-link I am guessing that the viscosity is changing JUST ENOUGH throughout the layer to keep most of the resin put. MEKP resin just does not cross-link quickly/evenly as the UV resin when running a slow batch. There are ways around this but it would be a subject for another thread. In support of this hypothesis, I noticed that Greg Loehr’s epoxy has a viscosity that allows you to laminate quite easily yet the molecule’s size is such that it does not soak much into polyurethane blanks. Hope this helps…

Please explain why UV cures more evenly. Do you propose that the catalyst in even a well mixed catalyzed batch is unevenly dispersed?

As an aside, I don’t think resin soaking into the blank is a bad thing, here’s why…

One, when you consider that the microscopic foam damage during shaping can only extend a few thousandths of an inch below the surface, there can’t/won’t be much soaking.

Two, the normal failure mode of a snapped board starts with delamination of the compression side glass from the foam. If there’s any resing soaking/penetrating the blank, this would deepen and improve the foam/glass bond and retard the delamination, resulting in a stronger board.

Okay Honolulu, here goes my attempt at creating more confusion (Sorry in advance)… …“more evenly” refers to the fact that UV resin (when used in transparent layers as with laminating) is activated everywhere light exposure occurs. In contrast, MEKP will have a quicker catalisis in areas of increased volume concentration such as thicker patch work or even resin droplets. When the resin “soaks” down into the pores of the blank, the thinning resin is much less likely to go to completion. This resin that is deeper into the foam gets so thinned-out and decreased in volume, that basically it will never fully, properly harden. So in some respects this uncured under-soaking acts as a parting agent rather than the reinforcment that we would all want. Back in my early university days we did tests on this very subject, we called this effect “panel stiffness” and found more failures occured with more resin content (per set amount of glass). Resin, when fully cured, is about 1/8th to 1/20th as resistant to elongation than glass filiaments. Findings suggested that this disparity in material elongation meant that filament stability should be achieved with a minimum of resin. In simplified terms, the resin’s elongation was not super even, thus micro-cracks soon propagated in high-stress areas where resin de-bonding from the glass filaments resulted in failure. In compressive skin buckling modes, bulk resin helped to a degree. Compressive buckling is just one mode of failure for a broken surfboard as tensile failures are also quite common. For the best possible resistance to skin buckles in compression, the defense would be maximizing the stability of the skin. Granted, if we could be sure that the resin that soaked into the blank was fully cured, then we’d be onto something good. Unfortunately, one of the parameters of this thread was the “slow batch” scenario, which testing has shown to be problematic. If we could have assumed a good cure then we could exploit the binding/stability scenario. You’ve probably seen shapers use a wax comb to make grooves in the finished shape in high stress areas like along the bottom/rail area and stringer, and even the fins; and as you alluded to, this works. One last interesting note, we also found that the stiffest skins resulted from vacuum bagging, where “less is more”; that is, less resin gave us more strength. I know, it didn’t make intuitive sense at the time until i saw it. Smashing the weave up against the blank super hard until cured made INSANELY strong panels. I wonder if anyone has made a board with UV polyester resin and somehow activated it while the board is in the vacuum bag??? hope this helps more than aggravates… Mahalo.