Using cellophane as a molding aid

I was doing a little work over the weekend - specifically making a new deck (the cockpit part) for my IOM and also experimenting with a fin built over a shaped core material. The deck is glassed over a male mold, built on a building board - very conventional.

Anyway - I draped the male deck mold with a sheet of cellophane. Unlike a convex mold (such as a female hull mold) all the angles are in one direction and so no creasing or folding of the cellophane occurs.

This worked well, so I felt brave enough to expend some of my precious carbon on an experiment with a keel fin.

For the fin, after wetting out the unidirectional carbon on one side of the core, I layed the wet side on cellophane, applied the carbon to the other side, completed the cellophane wrap so the the fin was encased (open at top and bottom) and applied pressure by way of a roller to squeeze out excess resin. After this the fin was placed in its jig, under moderate pressure, in the normal was to ensure it cured straight and true.

This is all very conventional and standard stuff - except that in the past I haven’t used cellophane as the film between the part being epoxied and the mold or whatever. Mylar is the “standard” for this purpose - see the other thread running at present about the wing mast.

The cellophane releases easily, is readily available and is very low cost. The results were great. The only downside I can see compared to mylar is that, because the cellophane is so thin, it can crease if the roller (or whatever) catches it the wrong way, and the shape of the crease will be apparent in the end result. The same would apply with a light mylar, but a heavier mylar (say 4 mil) will be less of a problem. I had no problems with tearing at all.

The cellophane was used straight off the roll - and so was completely free of creases when applied.

Has anyone else tried using cellophane as a substitute for mylar in this way? Are there any other downsides or problems in its use that others have experienced?

After using the so-called German rubber method, with latex rubber rolled out to spread the epoxy and eliminate excess, I also tried the technique with waxed paper. Both work on parts such as fins and rudders. I remember reading that epoxy should not be mixed in waxed paper cups because the epoxy tends to dissolve some of the wax, and that affects the epoxy. Maybe so, but so far I’ve seen no ill effects on using waxed paper as a rollable layer over epoxy and carbon fiber or fiberglass. I imagine “cellophane” (polyethylene film, right? - don’t know that actual cellophane is all that available) would be very similar.

Mike Biggs

I’ve used ‘Clingfilm’ - very thin transparent film used to protect food. The results are not satisfactory: because the film is so thin and has a (deliberate) tendency to stick to itself it is very difficult to apply smoothly. Also, its stretchiness means that there is zero tolerance for any variations in pressure (local excesses of resin): bulges stay bulges.

Not recommended.


This is the type of stuff…

Much easier to work with than cling film, and quite unlike waxed paper.

So far so good.

Right - off for more retail therapy!


I see used the work “convex” above, when of course I meant “concave”.

Nobody pulled me up on it - so you obviously knew what I meant. :slight_smile:

I have been using plastic packaging tape for years (1997) as a relase film over foam. Works fine, releases easily, leaves the thickness of the tape as an edge of surface but that is so thin it is easy to fair out.

Ah yes Dick - I remember seeing that in some photos of yours. Thanks.

By the way (completely off topic) - if you haven’t visited Alan’s site today, check out the new 800mm trimarans that the North Sails guys in Auckland are playing around with.

Been there, done that - even registered!

Alan did a nice job on the site development and covers quite an array of classes. As noted on a different thread - scary to think one of those 800 mm multihulls could upstage a bigger boat - just by staying on their feet.

Hope Alan will post some still photos to get an idea of what they are doing.

Nice to see encouragement and an invitation to ya’all to come to the “dark side” !