Reduce weight with hollow xps board?

[stoneburner]

Open cavities fill with water quick and drain poorly/slowly — a lot more than enters a ding in a glassed, solid EPS core. XPS won’t absorb water and the cavities can be drained when it is convenient.
Yes the problem with EPS is water absorption. But for some builds I have no other option.

XPS and EPS are made from the same material (polystyrene) with same surface energy. The bonding issue is related to closed cell foam vs. foam with interconnecting passages. The most common error building with XPS is using low density XPS. XPS requires special surface prep and the right density. Search past threads — I have discussed this many times now.

A few short, quick threads. I have done several other more detailed discussions over the years.

XPS gassing - or is it?

  XPS is “closed cell” foam.  It absorbs very little water (virtually no water).  The gas bubbles in the foam are very small and closed (no interconnecting air passages like EPS has).  The only way gas can be released is if the cells are ruptured.  Even after sanding, the surface is not porous, just a thin surface layer of very small ruptured cells. As result the epoxy has very little surface area to bond with and virtually no foam penetration (no soaking in like in EPS).  This is why those who…

Shed Technology: XPS & Other Tests

Ive used two types of Dow XPS in the past…white and blue…as far as I was told by Dow , the only difference is the colour. There is another one = Dow pink . I was told that the “pink” had memory…ie it would robound from a heel dent without creating a small delam. I built an 8’ 6" log using both white Dow and blue dow. The board was primed with straight epoxy , no thickener to keep the viscosity low , and penetrate the foam as much as possible.It did penetrate…not as much as EPS does , but it did …

EPS or XPS blocks source?

This is what Wartenberg pinwheel roller perforations look like: The 7-row Wartenberg rollers (22 pins/wheel) I have make 44 perforations per square inch. Pinwheel diameter, pin-tip to pin-tip, is 1.125" (28.6 mm). Roller width is 1" (25.4 mm), pin-tip to pin-tip. Pin length is approx. 5-6 mm. Perforation hole diameter at the foam surface is approx. 1 mm. Space between perforation holes is approx. 4-5 mm. [Pin_Roller_600a] [XPS_Perf_6]

Perforated XPS requires an epoxy pre-seal before laminating.

Cork & XPS

My next experimental build tech project for this summer is a cork deck skin over an XPS foam core, then cover with FG. I feel confident that cork skins over XPS cores, under glass, are the path to a durable XPS surfcraft. IMO Cork Skin advantages are: Impact absorbing Compressive strength greater than foam Low thermal conductivity Does not soak up water Increases surfcraft skin thickness without adding a lot of weight Lighter than composite cloth saturated with epoxy. So I…

Cork skin between FG Layers will be the toughest.

Accept. Reject. It does not affect me.