XPS/Glassing/delamination

Damned I wish I were near you guys to score good cheap foam.

This will be my first XPS (Corning, pink, from Home Depot) board and I have read this thread about delamination problems. Some say current construction XPS has less gassing-leading-to-easy-delamination problems. That will be great if true. I have read that if I just sand no finer than 60 grit, let the roughened board degas a day, wait a day after glassing the first side before glassing the other side, and do not let the finished board get hot, I will have done all that is worth doing and will have a board unlikely to delaminate easily. But some have suggested that it is helpful to go beyond the 60 grit sanding by coarser roughening or by poking shallow holes somehow.

It was convenient to do a little test. My wife's sewing kit had what is called a ponce or pounce wheel for making perforations/indentations along a line. You can Google its various appearances and uses. A local second hand store had a Woodpecker (brand name) for cheap which can make a lot more perforations faster. Model airplane hobbiests apparently like that one. I 60 grit sanded a scrap of the foam and went over a part of that with the ponce wheel and over another part with the Woodpecker. The Woodpecker's perforations looked almost too fine to let resin in. I waited a day to allow possible degassing from the roughened surfaces, and laminated a strip of glass over the three differently roughened surfaces. Next day I pulled the strip off. The glass adhered to the Woodpeckered and ponce wheeled surfaces about equally, and better than on the 60 grit only surface.

How much better? Hard to say. 20% better?

All I can say is I guess I will go beyond 60 grit sanding and Woodpecker my board before glassing......???

Bonding is related to available surface area.  I suspect 40 grit would work better than 60.  EPS and PU foam have many "small pores" making lots of surface area for resin to bond with.

Delam is also related to minimum compressive strength and sheer strength.  Standard Dow and Corning XPS insulation is usually the lowest density/compressive strength.  Low min. comp. strength means it is easier to crush the underlying foam -- which releases gas from the closed cell foam.  Lower density foam is likely to sheer more easily also.  HIgher density XPS should work better than low density XPS.

This post might help some regarding foam density:

http://www.swaylocks.com/comment/1456745/Re-sharkcountry-2-Sheet-XPS-Blanks

I have XPS boards in my quiver for 9 years now.

I noticed that it is easy to protect your board against delams from heat. But it is nearly impossible to protect your board from delams cause by pressure dents.

My XPS boards all delammed from pressure dents. But I don't care, you can still surf it. I drill small holes in my delams to let it breathe, the foam is waterproof anyway.

Make sure to wet your blank with resin before applying the glass. This will dramatically improve delam resistance. But best is to vacuum on a high density top skin.

BgSurfer - Thank you! Your link saved me searching and I now know my 2"x2'x8' $19 Formular 250 plank was rated 25psi, maybe next to the lowest density XPS Corning makes.

hans - I expect my build to reveal shortcomings in choice of materials and techniques. I wanted to start as local, cheap and simple as possible.

surfding - You probably recognize your advice to others in my first post. After this board is built and used I will probably seriously reconsider different materials and techniques.

So far all I have learned myself for sure is that I can shape foam (XPS, anyway) pretty well and easily with ghetto tools, and making the surface rougher than with 60 grit improves XPS-glass adhesion, at least initially. Maybe I will learn more.

John L

Are you planning to cut the rocker from flat sheets glued up to make it thick enough, or by cutting out 2" thick slices of the rocker you want?

I've done both. Been doing more of the later, cutting the rocker slices then gluing them together to get the width I need. Also bent the rocker into flat sheets with Vac bags. I'm alomst done with the block foam I bought a while ago. I think I have enough slices to make one more board, but I bought thicker blocks. Some of the foam was 4" thick, some 3" thick, and I also had 6" thick EPS which I mixed up with XPS. I make them with a stringer, and without.

I've added spackle to XPS on boards that were EPS/XPS mix. I don't think I kept them at 60 grit either some were down to 120 or 220 after spackle. The one place I've had issues was where the slices are glued together. If there's a slight gap, then chances are you will see pin holes. It may be that I pull the lam too dry, but I don't think that's it. I don't worry about pin holes on my XPS boards.

Just make sure the foam is sanded past the slick skin if you are going to use the flat slabs. One thing you can do is glass the board then take that woodpecker and run it up and down the lamination after the lam is setting up. Then maybe even do it again after the seal coat. The old XTR boards used a similar process to let the blanks out gas. Glass the board while the temps are dropping. I can't say how well they hold up because I don't use the same board day after day, I might use one 2 days in a row, but most times I change up between a bunch that I have.   

The green board was carved out of a 4" thick x 24" wide slab of blue dow XPS I got for $20, the blue and white board is a mix of blue dow and EPS, both are stringerless. The blue and white board is also channeled, so it's pretty light.

Hey John L

Xps is great when you treat it well

I keep it very rough (40 grit then roughen it up evan more.) so what you are trying with your tools should be fine

I bend sheets in a rocker jig and glue with PU foaming glue (use good quality) and then shape away.

Do all the advice that you hear (your first post is good advice, thanks surfding). Glass one side leave to gas and then do the other side.