I feel like I need to address a potential downside to owning a Marstrom boat. If the damage involves the nomex, what do you do to restore the core and provide a surface for the cloth to bond to? I'm well experienced in glass/carbon/foam core repairs, but this kevlar-paper honecomb stuff has me puzzled.

Fred Smith told me repairs are easy, but I'm not seeing it unless you replace the damaged nomex w/ styrene. I was imagining the cells were 6-12mm in diameter from the photo,.
but they could be much smaller, there is nothing I can identify to reference. Knowledgeable people, Thanks in advance. Steve

The normal practice is to fill the damaged core with a mixture of micro ballons (or EPS pellets, extra lite filler, 3M light weight epoxy filler, etc) and epoxy. You want as little epoxy in the mixture as possible.

This is ok for a couple of cells but if the damage is big you probably want to look at replacing the damaged core with a quality marine core (not styrne).

With care you may also be able to use epoxy foam. But if you do, make sure you have a suitable vent route so the expanding foam does not do more damage.

I think that the " the cells were 6-12mm in diameter from the photo" is a little off. I think that the normal cell size is between 3-5 mm. For a quick how to go to.
http://www.fibreglast.com/contentpages-Fibreglass+Repair+Composite+Repair-123.html

In the past I have routed out the bad core section and then vac. bag in a new core, then bag on the skin. If the inner skin is fractured this must be repaired first!

Carl, I was thinking of using the extruded polystyrene (usually pink or blue) that we use in construction to insulate below grade (buried against cement structure) very high resistance to water absorption, 25 psi (available 40psi). This is not as good as corecell or baltek for small boat building but for a small repair it seems very good.

I sent you a pm recently about old Lindahl hulls. Disregard. I have taken another route. Steve

I would not use any type of core that is not specified for laminate worj with polyester or epoxy resins. Otherwise, you might find blistering, de-laminations down the road.

Epoxy, or polyester melts in a small degree the usual styrene type foams. Especially polyester resin. Epoxy only a very small degree. I think PU foam resists epoxy or polyester.
Not 100% sure, but you might want to check or test the foam you want to use first to see how it reacts to the resin. But polyester melts styrene based foams for sure.

If you want a good patch up job you should use specific foams for boatbuilding.

That's true about the solvation of styrene.

My concern was based on the "friablity" of the core bonding surface...certain types break down over time and any adhesion to the glass layer will be lost.

My landsailing buddies use extruded styrene to build their land yachts when using epoxy resins and polyiso when using polyester. So, while styrene may be a workable short term fix, I would certainly prefer a proper repair. With foam core construction one can approximate the building process, but that is not going to be possible for anyone outside of Sweden on a Marstrom. It's highly unlikely that even Marstrom re-autolaves his own repairs. Mike, what is your suggestion? Are corecell and/or baltek better?

It was Mike's post about his repair ordeal that got me thinking (and now inquiring) about the difficulties of dealing with nomex. As I stated above Fred Smith assured me that is no big deal but now I'm becoming more concerned. Steve

I wouldnt buy/build a nomex boat. Foam cores are just as light and much less prone to print through and water absorbsion.

Take a look at Lars Guck's new A3, the inside of the starboard bow looks like a waffle, the pattern of the nomex printed through to the gel coat.

I've also seen nomex cored boats weep water.

Foam doesnt absorb water, and you dont get print through and during bonding or repair you dont have to be as precise.

The downside to foam is it doesnt lay in the mold as nicely as nomex.

Bill

Bill, I really appreciated your input. You have confirmed a growing gnawing gut feeling. Steve