West Clear over MAS?

Submitted bydaviddewitt onFri, 07/10/2020 - 10:39

I am in the process of building a CNC Vember and used MAS LV epoxy for the layup and initial fill coat.  This is the second boat I have built using MAS recently.  While I love the ease of wet out, the bubbles are driving me crazy. On this particular boat I applied an initial seal coat and let the boat cure overnight.   The layup was performed at a constant 75 degrees (as measured by a digital thermometer sitting adjacent to the boat).   The first fill coat was applied by brush (using Nick’s suggested technique) according to the cotton swap test.  While I tipped off the fill coat with a light horizontal pass from dry to wet and went over the boat with a heat gun, I still ended up with a zillion tiny bubbles.  Yes, they can be sanded out without that much work but ...

For the second fill coat I am thinking about switching back to West 105 with 207 special clear hardener.   I used this epoxy on a cedar canoe many years ago and did not have any problems with bubbles.

Does anyone know why this combination (West over MAS) would be a problem?


Fri, 07/10/2020 - 11:53

Once epoxy hardens it's inert. No reaction or compatibility problems will occur. Just wash the surface of any blush that might be on it with a little soap and water and wipe dry with paper towels. I use those kitchen abrasive pads. I have used many different brands of epoxy on top of other brands with no problems unless there was blush on the surface.

Bubbles are usually caused by a rising temperature squeezing the wood fibers releasing air. Not only constant temp is needed but you need to bring that kayak up to temperature many hours before you start coating. Since yours is coated, you will not have to worry about that but I am still cautious with pre-heating the boat never-the-less. That heat gun technique you describe would make me a bit nervous. I always raised the temp in the shop fairly warm for several hours and actually back it down a bit when I started.



Fri, 07/10/2020 - 19:32

Thanks.  Will go ahead with West Clear 

As for the heat gun.  Have you not seen the video of Nick Schade taking his propane torch to his freshly applied epoxy?  That is scary.  I use a heat gun frequently as a tool when bending wood (not just on strip kayaks).

I remain skeptical about the source of all the bubbles.  With the boat well sealed they did not emerge from the the wood itself. This boat has literally almost no gaps between strips.  The boat and the epoxy were all at a constant 75 degrees both before and during throughout the process.  Our shop does not have AC so it is not possible to lower the temperature.

That said, as a scientist, I intend to run out a set of controlled experiments in my house where we do have AC as well as heat.   My working hypothesis is that they are a by product of the curing process of the MAS epoxy itself.  Stay tuned.