bonding pour in foam to epoxy

In most cases, epoxy resin is applied over cured foam. The bond strength is determined by the usual factors in the prepping of the substrate and mixing and applying the resin.

What if one wanted a good bond, but it was necessary to use a pour in foam over an existing epoxy surface that had already cured? Would it be better to prep and re- wet out the epoxy surface with resin and apply the pour in foam to an uncured surface? or is the bonding strength of the pour in foam sufficient?

I am building daggerboards here

Thanks

 

As long as you de-wax the surface, you shouldn't have an adhesion problem with the foam.

 

I've done it both ways, but haven't had the pleasure of busting open something that's been previously done yet. I would suspect pouring the foam into a space with fresh or still green epoxy will form a better bond (this was my thought), but I don't know if the foam will react with the epoxy cure (it shouldn't) or if the epoxy will have an affect on the foam cure (again, it shouldn't).

By de-wax, I'll assume blush. There wouldn't be a blush on still chemically active goo, so the pour on wet method solves this.

 

In my case, for the first two runs, I formed up the mold interior with the balsa core, protected by plastic sheet, then poured the foam, removed the balsa and popped out the foam, then went back and laid in the triax and replaced the foam pieces and balsa on top, and bagged it all down.

The downside was that it was hard to get the foam out without buggering it up, and it all had to be prepped before it went back in on top of the wet triax.

For this last run, I had run out of foam, so I went ahead and bagged the balsa to the wet triax, and will have to go back now and prep the triax before adding the expanding foam at the leading and trailing edges, and at the board tip. If all else is equal, I guess it all boils down to which way is the quickest. I am thinking the second way might be quicker.

In either case they both have to be trimmed flat and prepped before mating the two halves.

Thanks