Hi Guys,

A little off topic but i am sure that this is where the experts will
be and will help me out !! (A little Flattery always helps !!)

I am building a Cover for a Spa (in USA - Jacuzzi)

The external dimensions are 2.4 x 2.4 metres. This is a heated spa
that runs at about 40 degress Celsius.

The design requirements are as follows:-

1) Covers must be able to hold a 150KG weight across their longest
span (we have two rottweilers who love to sleep on the spa in the Day
to stay warm !!!) Also as this is in a recessed position in a deck
there is a very real chance people will walk on this.

2) The covers will be exposed to the heat rising from the water as
well as UV from external SunLight

3) The covers must provide thermal insulation to retain the heat in
the spa.

4) Light Weight (20KGs or less per cover) so they can be easily lifted
by my wife

My Design therefore was as follows:-

1) Polystrene Foam Core 50 mm thick.
2) 5mm Polyurethan covering bonded to this all over
3) Create the covers in two pieces = 2 x 1.2m x 2.4m

Fibreglass Top and Bottom and sides - insert a central Fibreglassed
Balsa Beam across the 2.4 metre length and glass in place for
additional strength

I have been told that the resin i intend to use reacts with
Polystyrene and hence covering with Polyurethane will stop this
occuring - anyone have any experience on this. ??

The covers will not need a fancy finish - i intend to paint them later
(is it possible to paint Fibreglass ??)

My basic plan was to contrusct the Styrene and Polyurethane sheets and
to then pain the fibreglass matting on wet on wet on the bottom, once
dry then do the tops. Finally do each edge with strips of matting that
overlap on the tops and bottoms to lock it all together and seal it
off.

Does this sound feasible ?? Am i missing anything ???

regards

Craig Curtin

Some answers/comments:

#2) If you're worried about UV exposure then probably the best
thing to do is paint the pieces. There are plenty of paints that
adhere to fiberglass, and most of the time the only surface prep
required is a light sanding.
#3) Foam core will help retain the heat, the thicker the better.
One thing to keep in mind is that some foams don't like heat very
much - the boatbuilding foams are rated for certain temps, and the
higher the temp typically the more expensive the foam. For
non-structural applications the temp rating isn't all that important,
but if the foam is structural then it should be a higher quality. Also,
since the foam is structural I'd avoid the typical beaded foam
you find at home improvement centers. If you really expect
people and dogs to spend time on it, then you should consider
a more expensive boatbuilding, heat rated foam.
#4) weight should be achievable.

As far as the design goes, I don't see how the PU covering does
anything for you. You'd be better off buying epoxy instead of the
cheaper polyester resin - the cost will be higher for the resin but then
you save on the PU. Also, there's no way of knowing if the
resin will bond well to the PU without doing an experiment.
The Balsa beam probably won't help with the stiffness too much,
but it may give you something to attach hinges to or grab onto.
What's really driving the strength of the panels is whatever is
attached to the foam - this will be the most dominant structural
part. Fiberglass or even some door skins might do the trick for
you. If you do use epoxy resin, then don't use matting - use
cloth or roving. Finally, overlapping the glass over the
edges will be the hardest part. Make sure you overlap from both
top and bottom so you have something to grind off when you're done.
You'll want to invest in some bog or fairing compound to clean
up those edges.

Matt


"Craig Curtin" wrote in message
om...
Hi Guys,

A little off topic but i am sure that this is where the experts will
be and will help me out !! (A little Flattery always helps !!)

I am building a Cover for a Spa (in USA - Jacuzzi)

The external dimensions are 2.4 x 2.4 metres. This is a heated spa
that runs at about 40 degress Celsius.

The design requirements are as follows:-

1) Covers must be able to hold a 150KG weight across their longest
span (we have two rottweilers who love to sleep on the spa in the Day
to stay warm !!!) Also as this is in a recessed position in a deck
there is a very real chance people will walk on this.

2) The covers will be exposed to the heat rising from the water as
well as UV from external SunLight

3) The covers must provide thermal insulation to retain the heat in
the spa.

4) Light Weight (20KGs or less per cover) so they can be easily lifted
by my wife

My Design therefore was as follows:-

1) Polystrene Foam Core 50 mm thick.
2) 5mm Polyurethan covering bonded to this all over
3) Create the covers in two pieces = 2 x 1.2m x 2.4m

Fibreglass Top and Bottom and sides - insert a central Fibreglassed
Balsa Beam across the 2.4 metre length and glass in place for
additional strength

I have been told that the resin i intend to use reacts with
Polystyrene and hence covering with Polyurethane will stop this
occuring - anyone have any experience on this. ??

The covers will not need a fancy finish - i intend to paint them later
(is it possible to paint Fibreglass ??)

My basic plan was to contrusct the Styrene and Polyurethane sheets and
to then pain the fibreglass matting on wet on wet on the bottom, once
dry then do the tops. Finally do each edge with strips of matting that
overlap on the tops and bottoms to lock it all together and seal it
off.

Does this sound feasible ?? Am i missing anything ???

regards

Craig Curtin

Put either a polypropylene hinge in the middle so you can fold it in half,
or a "hatch" so you can check the water, add chemicals etc. without having
to move the cover.

Folding it in half really helps to move and store, and gives access without
having to move the entire cover.

--


Keith
__
The journey of a thousand miles begins with a broken fan belt and a leaky
tire.
"Craig Curtin" wrote in message
om...
Hi Guys,

A little off topic but i am sure that this is where the experts will
be and will help me out !! (A little Flattery always helps !!)

I am building a Cover for a Spa (in USA - Jacuzzi)

The external dimensions are 2.4 x 2.4 metres. This is a heated spa
that runs at about 40 degress Celsius.

The design requirements are as follows:-

1) Covers must be able to hold a 150KG weight across their longest
span (we have two rottweilers who love to sleep on the spa in the Day
to stay warm !!!) Also as this is in a recessed position in a deck
there is a very real chance people will walk on this.

2) The covers will be exposed to the heat rising from the water as
well as UV from external SunLight

3) The covers must provide thermal insulation to retain the heat in
the spa.

4) Light Weight (20KGs or less per cover) so they can be easily lifted
by my wife

My Design therefore was as follows:-

1) Polystrene Foam Core 50 mm thick.
2) 5mm Polyurethan covering bonded to this all over
3) Create the covers in two pieces = 2 x 1.2m x 2.4m

Fibreglass Top and Bottom and sides - insert a central Fibreglassed
Balsa Beam across the 2.4 metre length and glass in place for
additional strength

I have been told that the resin i intend to use reacts with
Polystyrene and hence covering with Polyurethane will stop this
occuring - anyone have any experience on this. ??

The covers will not need a fancy finish - i intend to paint them later
(is it possible to paint Fibreglass ??)

My basic plan was to contrusct the Styrene and Polyurethane sheets and
to then pain the fibreglass matting on wet on wet on the bottom, once
dry then do the tops. Finally do each edge with strips of matting that
overlap on the tops and bottoms to lock it all together and seal it
off.

Does this sound feasible ?? Am i missing anything ???

regards

Craig Curtin

Guys,

Thanks for the feedback and answers on this one.

It has given me something to go on now.

I will check out Poly hinges - i had been wracking my brains on what
to do with that and was thinking os some heavy duty rubber bonded to
it.

I will check out the local boat building places and see what i can
find.

Thanks for the tips on the Epoxy over polyester resin (unfortunately i
already have it so am stuck with it)

I will check out the higher quality foam products - although i believe
mine is heat rated to 90 degrees (c)

regards

Craig




"Keith" wrote in message ...
Put either a polypropylene hinge in the middle so you can fold it in half,
or a "hatch" so you can check the water, add chemicals etc. without having
to move the cover.

Folding it in half really helps to move and store, and gives access without
having to move the entire cover.

--