Instead of plug/mold for roof?

Greetings to all,

Instead of using a mold/plug to create a hard-top roof for my boat, why can't I just use foam material and design the roof the way I want, cover it with aluminum foil and then plaster on top of it all?
Possible or not?
Downsides doing this method?

 

Are you talking about cement plaster as used on exterior walls of buildings?
It is often applied over styrofoam, but that foam is always securely fastened to a solid substrate, where your hardtop is usually fastened to a skeleton of tubing. How will it be fastened?
What is the function of coating it with aluminum foil?

 

Dodger build for a sailboat, foam and fiberglass.

 

Is there some reason why you can't use simple foam sandwich?Just hold the foam to shape,glass the easiest side,flip it and glass the other side.

 

Will use XPS foam in sandwitch and then sand and cut to get the design I want.

 

Will use XPS foam in sandwich and design it with curves and indents. Aluminium foil will be used as barrier in case the foam cant handle the polyester resin. Have not thought of what to use as release agent though.
When the roof is done and fiberglassed and dried I will then turn it upside down and do some more plaster on the inside to prepare it for aluminium tubing and reinforce areas.

 

Thanks! Never heard word dodger before in boating terms =) Nice video! But what a pain to do it with those thin foam sheets.

 

Really? Where on EARTH have you been?!

 

Somewhere where using XPS for a boat is a good idea? A good quality thin foam sandwich build would be ideal.

 

The bond between the skin and core is hugely important for the integrity of the end product, so using anything that breaks that bond is is a mistake. Find foam and resin that are compatible!

 

The easiest way to build the hardtop is to make a frame of the shape and strip plank with marine foam or use scrim or fasten it to formers.

XPS is not suitable for a hardtop. The shear rating is too low and so is compressability. Marine foams are much better, but a hardtop usually also gets coosa or plywood inserts where hardware attaches.

 

If I understand correctly, OP is thinking of using XPS+foil+PE resin for a tool/plug/mold instead of a core.
One would need to do a whole tooling prep 'wax on/wax off 'procedure before molding to get the part's PE gelcoat or resin to release cleanly from the tooling's PE resin. Lots of coats of Partall #2 wax and maybe some PVA...the pro's can explain this better than I can.

 

All true. You missed out what happens when polyester resin meets polystyrene though.

 

I found this post to be confusing, did I miss something, perhaps on an entirely different thread?
“Instead of using a mold”, and “plaster” indicates something entirely different.
Aluminum foil? You must be joking!

 

I like the aluminum foil.
Imagine the radar reflection the search helicopter would get back from it.
Multi layer of course.