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

Hi,

Thanks again to all for the help. I plan on going to the local
university library to learn a bit more about fiberglass before making
my decision. Do you have any personal favorite books on the subject?
The Vaitses book has already been mentioned, it is on my list.

I'd like something fairly basic, nothing that gets too in-depth about
the chemistry, or about industrial-type methods. I'd like to learn
about covering plywood with glass, making a 1-use mold, and also
free-forming (doesn't have to all be the same book). Also I'd like to
learn about the different properties of mats/cloths, different types of
resins, gel coats, foams, etc. Thanks.

I don't think a university library will be much use . The sorts of things
you need to know are exactly what Universities are NOT about.

I'd spend a bit more time on the web, looking at manufacturer's sites. I'd
also do some careful cost estimates based on what you might end up paying
for appropriate materials. Then double it for the inevitable learning curve
and wastage costs for the first time one- off, add another 100% for fixing
it sometime in the future ... and compare this with what a commercial
product is worth. You might decide it's not something you want to do.
Perhaps talk to a small commercial manufacturer, see if you can make a mould
and have them produce from it ...
David
wrote in message
oups.com...
Hi,

Thanks again to all for the help. I plan on going to the local
university library to learn a bit more about fiberglass before making
my decision. Do you have any personal favorite books on the subject?
The Vaitses book has already been mentioned, it is on my list.

I'd like something fairly basic, nothing that gets too in-depth about
the chemistry, or about industrial-type methods. I'd like to learn
about covering plywood with glass, making a 1-use mold, and also
free-forming (doesn't have to all be the same book). Also I'd like to
learn about the different properties of mats/cloths, different types of
resins, gel coats, foams, etc. Thanks.

Try to find "The Gougeon Brothers on Boatbuilding." These are the guys that
developed and marketed West System epoxies and their newsletter has
described uses including lots of applications in swimming pools,
architectural stuff, etc. As you might suspect, the book describes the many
boats they've built using all sorts of techniques. Well written with lots
of pictures. Their techniques work well with System Three products, but
don't tell them. http://www.westsystem.com/

System Three gives away "The Epoxy Book" on their web site.
http://www.systemthree.com/index_2.asp
Free if you register and download and print it yourself. It covers much of
the same material in a lot fewer pages, but do read both. (Skip the first
few paragraphs of The Epoxy Book if you really don't want to hear about the
chemistry.)

Roger (I think S3 might have less blush than West, but then maybe I've
just been lucky.)

http://home.earthlink.net/~derbyrm

wrote in message
oups.com...
Hi,

Thanks again to all for the help. I plan on going to the local
university library to learn a bit more about fiberglass before making
my decision. Do you have any personal favorite books on the subject?
The Vaitses book has already been mentioned, it is on my list.

I'd like something fairly basic, nothing that gets too in-depth about
the chemistry, or about industrial-type methods. I'd like to learn
about covering plywood with glass, making a 1-use mold, and also
free-forming (doesn't have to all be the same book). Also I'd like to
learn about the different properties of mats/cloths, different types of
resins, gel coats, foams, etc. Thanks.

Hi,

Having read some of the references you folks directed me to, I think
I've eliminated some options. I'm going to either use:

- exterior grade (ie CDX) or high density overlay (HDO) plywood, with a
coat or two of quality epoxy, and make a 5'x7'x3' box.

I don't think I'd even glass it, just caulk the seams and put a liner
in. One problem with this method is that if I used 4x8 sheets of
plywood, the 5'x7' bottom would have to have a horizontal seam. I'm
guessing I'd spend $150-250, plus the liner.

- cold-mold a tub with more comfortable contours and curves, using 3-5
layers of approx 1/8" fir (because I have an enormous free supply)

I've read in an article (not sure of the date) that cold-molding cost
about $3.30 per pound, at 1 pound per square foot, including the cost
of the wood. My tub would be about 107 sq ft. So by that person's
calculation, it would cost just over $350 for the raw materials. I'm
wondering how much of that cost was due to the wood, and how much for
the epoxy. I have a good amount of free time, and would love an excuse
to learn this method, so labor isn't an issue.

- I've heard that there was an article in Home Mechanix (somewhere
around 1990, I haven't found it yet) that described plans for building
a tub by fiberglassing over masonite (hardboard). Sounds interesting,
but I'd like to find the article first. Masonite is very cheap, and
that "supply of fir" I have includes 2x4's, which could be used for
additional framing.

Thanks for the continuing help.

I wouldn't worry about the seam (5x7 vs 4x8). Scarfing isn't hard, but this
would probably be the place to use the technique of just putting fiberglass
tape on each side of the plywood along the joint. Your structure makes up
for any lack of strength and you can fair in the lump easily.

I'd think CDX was the way to go. HDO is much nicer with fewer voids and
more plies, but you don't need it and it's pricier. For boats, it takes
bends with fewer lumps.

Too bad you didn't buy the lumber before Katrina hit.

Roger

http://home.earthlink.net/~derbyrm

wrote in message
oups.com...
I've eliminated some options. I'm going to either use:

- exterior grade (ie CDX) or high density overlay (HDO) plywood, with a
coat or two of quality epoxy, and make a 5'x7'x3' box.

I don't think I'd even glass it, just caulk the seams and put a liner
in. One problem with this method is that if I used 4x8 sheets of
plywood, the 5'x7' bottom would have to have a horizontal seam. I'm
guessing I'd spend $150-250, plus the liner.

- cold-mold a tub with more comfortable contours and curves, using 3-5
layers of approx 1/8" fir (because I have an enormous free supply)

I've read in an article (not sure of the date) that cold-molding cost
about $3.30 per pound, at 1 pound per square foot, including the cost
of the wood. My tub would be about 107 sq ft. So by that person's
calculation, it would cost just over $350 for the raw materials. I'm
wondering how much of that cost was due to the wood, and how much for
the epoxy. I have a good amount of free time, and would love an excuse
to learn this method, so labor isn't an issue.

- I've heard that there was an article in Home Mechanix (somewhere
around 1990, I haven't found it yet) that described plans for building
a tub by fiberglassing over masonite (hardboard). Sounds interesting,
but I'd like to find the article first. Masonite is very cheap, and
that "supply of fir" I have includes 2x4's, which could be used for
additional framing.

Thanks for the continuing help.