If you want to be creative with the shape of your hot tub I would suggest
you use the foam materials, Diab and Core-Cell are two good options. All
foam must be covered with glass and should tapered off where your jets and
drains are. Anywhere you are going to perforate the tub should have no
exposed foam. The vinyl ester resin subjected is a good option and I think
needed to avoid blisters on the finish surface. However it is a very
expensive product, to keep the cost down do all your laminations with a
general grade poly resin and the two surface layers of mat with the vinyl
product. (I would go three mat here). You should take a look at a few of the
sites that are out there on manufacturing with glass, there are a number of
way to make a break-away mould at a very low cost to produce a top of the
line product.

Good Luck
Doug Christie
wrote in message
ups.com...
Hi,

I know this is a bit off-topic for this group, but I'm not sure where
else to ask it. I'm going to build a hot tub (more like a soaking tub),
and I'd like to use fiberglass. I will first build a 2x4 frame, then
(maybe) attach plywood to the inner part of the frame, then apply
fiberglass cloth. But I'm trying to decide whether the plywood is
needed for structural reasons, or just to give shape to the fiberglass.

Do I need to use something heavy-duty (ie 3/4" ply)? Or can I just use
1/4" ply (or even just a stretched-out bed sheet) and fiberglass over
it? In the DIY car audio world, people sometimes use t-shirts to create
a sort of mold. If the fiberglass can bear the weight of the water, I'd
just assume not use any plywood. I fear that the heat and steam coming
off the hot tub might cause delamination with regular plywood (and
marine grade plywood is just too expensive for this project).

I'm open-minded to completely alternate building materials, but weight
is a concern, so no concrete. Due to the location this is being
installed, most store-bought tubs won't fit, so I can't simply buy a
used tub. Thanks for the help, and sorry if this is a bit off-topic.

Shamus