Fibreglass & Plywood help

[helliconia]

Despite the fact I'm not remotely handy I've been encouraged by some of the projects I've seen on here to start planning my (first ever!) attempt at fibreglassing an underfloor killtank/esky.

I have a loosely drawn plan having measured up the space available, but I wanted to grab some info before I go all gung-ho and start buying bits.

My plan is to make a plywood frame for the base, line it with foam insulation and encase it all in a fibreglass shell. The lid will be the floor panel that covers the space and will have a fibreglass encased foam insulation sandwich attached to the underside that should fit "fairly" snugly into the base.

The reason for going with a home made one is the size and shape of the space. It isn't very deep (about 180mm) and has a V shaped bottom so I was going to make a similiar shaped base that would sit on the stringers. The stringers already have space beneath them for water to move past and I won't be moving any flotation to use the space (it was designed for an internal fuel tank).

So, the questions begin here.

Firstly, considering the frame will be completely encased in fibreglass does it HAVE to be marine ply? If not, is it worth using it anyway? I was looking at some 6.5mm structural ply with low grade (CD or DD) facings as an alternative since they are significantly cheaper.

How thick should I be making the fibreglass? Is it better to do several thin layers using finer matting or would a couple of layers of thicker matting be better?

Whats a good thickness and material for the insulation? I'd like to be able to keep the contents cool for 12-18 hours using ice or an ice slurry. I thought about using that expanding foam then shaping it inside the ply frame for fibreglassing.

Any other things I should be aware of considering i'm a rank amateur at this stuff?

EDIT: Additional details.

The space I am working with has a carpeted ply cover and the underfloor area measures:

1100mm long

570mm wide

180mm deep at the centre

130mm deep at the sides.

I measured from the top of the frame the cover sits on and not the floor height.

Whats the best way to handle the space where the lid meets the base? Should I attach some kind of rubber or silicone seal or is fibreglass on fibreglass sufficient?

Edited February 14, 2011 by EmptyHooks

[davebrewer]

Bunnings has cheap marine at the moment so I'd suggest using that,in 12 mm.I'd use something like 300gsm woven cloth,but similar mat would do,it's just a bit messier to work with.Epoxy resin is the stuff to use,polyester doesn't adhere to ply anywhere near as well.This link has everything you need to know about using it:

http://www.westsystem.com.au/west_system/basic_techniques

Don't forget to fillet your joins with thickened epoxy before glassing,fibreglass doesn't bend around 90 degrees very well.It's all in the link.

Cheers,

Dave.

[tuffy]

Empty Hooks, I did exactly that for a mate's boat and in fact I think the sizes were almost identical. 12mm CD ply is all you need but make sure you treat the ply with Everdure first to seal it from water, then do as Dave B suggested with epoxy resin with corner fillets.2 layers of glass mat will suffice and we finished ours off with a layer of Flowcoat to give a smooth finish. Don't forget about drainage as well.

Any help needed just give me a call on 0402 110 666.

Cheers, Russ.

[helliconia]

Thanks for the replies guys

With the filleting, how big does it need to be and whats an easy method to achieve it? I was thinking of a run of epoxy through the join then round it out with a piece of dowel? Would that do the job?

I warned you I'm not handy. I failed woodwork in year 7

Just thought of something else.

I'm thinking I will need to build the shell in 2 stages, glassing one side then turning it all over the glass the other. How do I handle the join between the top and bottom sides? Should I just leave a border of glass mat dry around the edge of one side and epoxy it in when I do the other side with an overlap?

Edited February 14, 2011 by EmptyHooks

[austral]

i agree with the 12mm ply, you dont need the marine stuff..

[tuffy]

Thanks for the replies guys

With the filleting, how big does it need to be and whats an easy method to achieve it? I was thinking of a run of epoxy through the join then round it out with a piece of dowel? Would that do the job?

I warned you I'm not handy. I failed woodwork in year 7

Just thought of something else.

I'm thinking I will need to build the shell in 2 stages, glassing one side then turning it all over the glass the other. How do I handle the join between the top and bottom sides? Should I just leave a border of glass mat dry around the edge of one side and epoxy it in when I do the other side with an overlap?

Fillets need to be 15 to 20mm radius.

"Build a shell in 2 stages". What do you mean, the box which will go into your recess?

[helliconia]

Yes but I was going to fully enclose it in fibreglass so there would be 2 "sides".

The outside will face down into the recess, the inside will face up and it will be all one piece. Then the lid will be separate.

How thick will/should the fibreglass be so I can allow for it in outside dimensions?

Edited February 15, 2011 by EmptyHooks

[Bruce the Postie]

G'day mate,

I did a similar thing in my boat a while ago and i am very happy with the results.Although my boat is fibreglass the process will be very similar,do a search on underfloor esky and you can see mine from start to finish.

If i were going to do this in an ally boat i would'nt se any timber at all,but would use some melamine sheet to form the contour of the bottom of the area and sides,and using this setup as a mould,glass over this and then separate the two,now you have a fibreglass shell that can be insulated then glased over and flowcoated etc.With this method you have no timber at all to wory about,no rot, ever.

Give it a go and good luck.

Cheers,

Bruce

[PPSGT]

Dont use marine ply - the treatment and glue to make it water resistant stops

the resin soaking in properly. If its easier you could use MDF.

If you are going to coat it in fibreglass matt you dont need any strength from the wood or

ply, a couple of layers of mat will be more than enough. The resin will soak right into

the MDF just paint a think coat of catalysed resin into it to seal it and make in completly waterproof. If you then flowcoat it afterwards it will

work great.

3mm MDF wodul be even better as it will bend to the shape - ieven if the wood gets wet years later

and rots away the fibreglass shell will be strong as the day you finished it

Make sure you buy resin resistant foam - if you use regular foam the resin will eat straight through it

Jason

[helliconia]

I hadn't considered molding because this is my first venture fibreglassing and I didn't want to overly complicate things for myself.

That said, how do you stop the fibreglass from sticking to the MDF mold if I went that route?

[Bruce the Postie]

The poly resin should not stick to the melamine coating,but a little release wax,cooking srpay or the like never hurts.

Cheers,

Bruce

[PPSGT]

You dont need to make it as a mold, you use the mdf to get the shape

then glass it both sides.

You could even use packing cardboard - the strength doesnt come from the wood

it comes from the glass fibres.

Just make the shape out a material that is porous (ie will soak in with resin)

then coat in layers of fibre glass. If you dont use wood, do a couple of extra layers

of matting. Go to a proper fibre glass shop it is very cheap, maybe $15-20 a linear metre

not $20+ a square metre you pay at a boat shop - resin will also be much cheaper

You want to a make a sacraficial mould - that will either become part of the end product

or can be pulled off at the end. The whole reason to you fibreglass is to save weight

as well as being super strong if you make it out of wood its will be heavy than it needs to be.

I woudl make the "box" out of card board, and tape and join it all together on the side that faces

into the boat. Then paint the inside of your carboard mould with catalysed resin.

Wait for it to set hard then coat with several layers of glass mat or a couple of layers of mat, then

resin resistant foam, then a couple of more layers of glass let it dry then flowcoat it.

Once it is all dry, pull it out of the boat, then either remove all the tape from the other side

leave the cardboard on and cover it in resin a thin layer of glass then flowcoat it or remove your cardboard

mould material and glass it with a couple of layers then flowcoat.

If you want to make it smooth and more like a mould, make your cardboard mould, then cover the whole inside

with aluminium foil - the glass wont really stick to it, and you can peel it off though it works better if you wax it. You can then glass it maybe foour times for strength then pull the whole lot out. The carboard thickness

will give you clearance when removed for it to fit easily back into the underfloor space

Jason

[helliconia]

Thanks again guys. I like the cardboard idea, although I'm picturing myself with a saggy mis-shaped esky Wishing I hadn't been so quick to throw out the box that came with the new fridge at xmas!

Someone in another post mentioned a fibreglass shop in Seven Hills. I might try there since I work not far from them.

The weight factor and the strength of the fibreglass was why I thought of the thinner ply/MDF sheets at 6.5mm or less, that and its a cheaper

Now, what tools and equipment will I need? I'm thinking so far I'll need:

plastic scraper to spread the resin - or should I get a resin roller?

heavy scissors to cut the cloth

gloves

goggles (cause I'm bound to have stuff flying around)

breathing mask

sacrificial container to mix the resin in

What do i use to spread the flowcoat?

I just bought a live bait tank I have to fit to the back today so I'll start looking at this one over the weekend

[davebrewer]

They don't treat marine ply to make it waterproof-whoever told you that needs to do some research.The glue and grade of timber used are what make it marine.Boatbuilders,including me, go to a great deal of trouble to encapsulate vessels constructed of marine ply in at least 2 full coats of marine grade epoxy,and usually more if adding fabrics like glass or dynel,to make them waterproof,before applying undercoats,paint or varnish.It's ok to use good exterior ply for non-structural jobs but I wouldn't use it in a hull.

[PPSGT]

They don't treat marine ply to make it waterproof-whoever told you that needs to do some research.The glue and grade of timber used are what make it marine.Boatbuilders,including me, go to a great deal of trouble to encapsulate vessels constructed of marine ply in at least 2 full coats of marine grade epoxy,and usually more if adding fabrics like glass or dynel,to make them waterproof,before applying undercoats,paint or varnish.It's ok to use good exterior ply for non-structural jobs but I wouldn't use it in a hull.

The glue used on CD & Marine ply are exactly the same so it seems we are both wrong there .("Urban Myth" from Mr Plywood site)

Its only the quality (which increases the strength - which you are right) of the veneers that differ AA not CD

When i used CD play i paint it in resin thinned with acetone so it soaks right in before glassing it

If your not using it for a hull use CD ply.

But as suggested make a sacrificial mould from Cardboard or light wood, so you end up with a fibreglas only end product

Look up sites on making an esky or workign with car parts heaps of useful information

Try FGI at Brookvale for your supplies if that is close to you, most of the others are further out of the city in Industrial areas

[Fester]

Fibreglass material service at Sevenhills was the one I mentioned in another post, Bowden road I think, off Powers road.

[helliconia]

Thanks everyone

I'm thinking of going with the cardboard mold idea, cause it sounds cheaper and lighter in the long run than a wooden frame.

Once I get started I'll post pics to show you how it goes.

[Bruce the Postie]

Good onya mate,

Give it a go ,That cardboard idea sounds like a great alternative(must have a crack at that myself,thanks Burley king).

Looking forward to your updates.

Cheers,

Bruce

[dave nagy]

Use a syringe to mix the resin and remember how hot the ambient temp is, it all makes a difference when mixing.

Not enough hardener and it doesn’t go off or to much on a hot day it’ll go off way to fast.

I used a 2 litre milk container with the top/front cut out and left the handle and also mixed it with a cordless drill and a bent coat hanger

[tuffy]

They don't treat marine ply to make it waterproof-whoever told you that needs to do some research.The glue and grade of timber used are what make it marine.Boatbuilders,including me, go to a great deal of trouble to encapsulate vessels constructed of marine ply in at least 2 full coats of marine grade epoxy,and usually more if adding fabrics like glass or dynel,to make them waterproof,before applying undercoats,paint or varnish.It's ok to use good exterior ply for non-structural jobs but I wouldn't use it in a hull.

Correct.