A couple of weeks ago I used some leftover pieces of foam to make two small tables. I put a thin glass laminate on both sides of the foam and the resulting panels were stiff enough to be used as tables.
I am not sure yet what I will do with these tables (garden, boat?). I just wanted to use the leftover foam.
Ofcourse, this isn’t a very efficient way to make a table. I could have used a piece of 18 mm plywood instead. That would have saved me a lot of time. But, so the sandwich theory goes, at least I saved a lot of weight. But did I really?
The tables weighed 3,3 and 3,8 kg respectively. The edge of the heavier table was filled with glass/epoxy. The edge of the lighter table was left untreated (at least for now).
How does this compare to a solid plywood table of similar thickness (18 mm)? The tables were 82 x 57 cm. Assuming a density of 500 kg/m3 (average Google result for okoume plywood) a plywood table would weigh around: 0,82 x 0,57 x 0,018 x 500 = 4,2 kg, The plywood table would still need to be faired and painted. Let’s say the finished product would weigh around 4,5 kg. So the difference is 1,2 and 0,7 kg.
Personally I think that’s quite a big difference (in relative terms). For weight critical applications (e.g. boat interior) I would certainly consider swapping plywood for foam sandwich. I would, however, reconsider the edge treatment. Filling the edge with glass/epoxy added an enormous amount of weight. That was a bit stupid.