Glass fibre Moulding

[Lee_Shaw]

Hello

I’m going to have to mould myself a kind of oblong, trough shaped thing with an integral lid. And either include during construction or retro fit inspection hatches to this lid for access.

I’m gonna do it in grp.

I plan to :-

i) Make a mould out of plywood in a trough shape about 3’ 6” x 1’ 6”.
ii) Wet it out with raw epoxy resin.
iii) Apply the layers of glass fibre into the trough shaped mould/plug, using an additive to the epoxy. I’m gonna oversize the glass fibre so it overhangs the external sides of the trough.
iv) Then plonk an appropriately sized piece of marine ply on top of the trough and flip the overhanging glass onto it.
v) Apply wetted glass fibres to the top of the marine ply lid so the whole things sealed in.
vi) Apply a final layer of epoxy resin with additive.
vii) Sprinkle on some none-slip gunk as this will eventually be my cockpit floor.
viii) At some point after the epoxy has set paint the lot in a 2 pack paint.

I want to have access hatches into the void - see question c).

My questions are:-

a) Will I need to use a release agent to get my fabrication out of the mould? – if so what?
b) What additive should I be using?
c) Am I better fitting the hatches during fabrication or afterwards?
d) Will I have any heat issues?
e) Should I include a fall and small drain hole in the bottom of the trough – or leave it totally watertight?
f) Anything wrong with the above plan?
g) Any other improvements or advice?

Much obliged for any help

Steve


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[Talbot]

You could always make the sides of the mould from very thin marine ply and use this to strengthen the box, and also obviate the need to release it from the mould.

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[Althorne]

When I made some grp bits I used hardboard and planed wood to give a ready made good finish rather than ply etc. I also filled all the edgesso that they were rounded and meant it came out of the mould easy. polyfilla on a finger and sanded finely worked well for me.
Release agent comes in liquid or wax form, I used the wax and did it several times just to be sure of a release. If doing anything on the finished surface afterwards wash it plenty of the wax will spoil it.
Why an 'additive' and what where you thinking of using?
To stiffen mine I moulded in a piece of thin ply.

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[Talbot]

You could also get a mould with a great smooth surface by using mdf, with a gloss paint finish over it to stop any possibility of absorbtion into the material.

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[Guest]

If its first time doing it ...

My honest advise is to go and see a GRP supplies shop .... such as Strand Glass etc. They will give you all the advise you neeed ... along with Release agents, resin, mat / ribbon and finishing cloth etc. etc.

Often they hold classes to show people how to use the materials - even to renting out moulds etc.

Personally I would not use ply ..... as its difficult to seal against locking the mould and grp together with soaked in resin. Best to use such as MDF with release agent etc.

One rick is to make sure that you can break open the mould along a crucial line - as the GRP item often refuses to budge woing to suction between itself and the mould - believe me this is extremely striong and I have had to literally smash the mould to get the item out ....

? Why not fashion the cockpit floor in ply anyway and stain / varnish to get a real cosmetic look ?? and of course no hassle with GRP ????


<hr width=100% size=1>Cheers Nigel http://groups.yahoo.com/group/gps-navigator/ http://groups.yahoo.com/group/searider/

 

[William_H]

You would find the whole project a lot cheaper in polyester resin. It is less likely to cause dermatitus and is easier to manage cure times by increasing or decreasing the amount of hardener.
If you want a good finish on the inside of the (I presume) locker) then you need to make a male mold.
That is a box with the glass laid up on the outside. You could then mold the glass over the top to make a rim onto which the lid can be screwed or hinged. This however would require that you design the box mold to be dismantled (destroyed) from the inside outwards. The other alternative is the box shaped mold where you lay up the glass and resin on the inside of the box. Again a lip can be formed at the top and you can lay the glass on the inside of the lip by being prepared to roll the mold over to glass on the inside (downwards). It is hard to lay up overhead. Again be prepared to destroy the mold to release the product.
In making the mold plaster or polyfilla is good to give curved corners. Glass does not like sharp bends unless these are essential. Use lots of wax (old fashioned floor polish wax works well. If you are using polyester put a layer of resin with pignment if you want colour and allow to go nearly hard then follow with the glass (Chopped strand mat or woven rovings are cheapest and bulkiest). I guess you would need to end up with it about 3mm thick.
Before you build it you should think about the water tight seal you will need around the lid. Flat surfaces with thin rubber may work and is simplest however a goove for rubber may be better.
The need for a slope and drain is a matter of whether you think you can make it water tight. I imagine rain is your biggest concern and you may find there will be enough slope when the boat is on the mooring with no people onboard or again you may need a lot of slope under these conditions.
I hope you enjoy this project. Be prepared to do it all over agqain after you learn more about it all and try to build it in a warm environment. my appologies if what I am picturing is not correct. regards will

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[oldsaltoz]

G'day Steve,

I offer the following and hope it helps:

In answer to i) Make a mould out of plywood in a trough shape about 3’ 6” x 1’ 6”.
A mould this length will need a lot of bracing to prevent movement and make it easy to remove the finished product, at no small cost in time and cash.

Ply wet out with an epoxy is ok, but will be heavy and may flex a bit depending on the thickness used, also any holes (even for screws) will have to be treated to prevent water getting in.
Have you considered construction using foam, very light, very strong and easy to shape and work with.

ii) Wet it out with raw epoxy resin. If you go with the ply, coat it and double coat the edges, wash it when cured to remove deposits left on the surface, use clean water and a plastic kitchen scourer till no beads form.

iii) Apply the layers of glass fibre into the trough shaped mould/plug, using an additive to the epoxy. I’m gonna oversize the glass fibre so it overhangs the external sides of the trough.
I see no need for any addative, leaving the glass overhang will not leave a good flat join area for the lid, better to cut any access off when cured and overlay the join, stronger and better finish this way.

iv) Then plonk an appropriately sized piece of marine ply on top of the trough and flip the overhanging glass onto it. Make sure you have sealed the underside of the lid prior to glassing onto the base, a single layer of rovings is about all it needs.

v) Apply wetted glass fibres to the top of the marine ply lid so the whole things sealed in.
Good move.

vi) Apply a final layer of epoxy resin with additive.
Why? addative, you can apply this extra coat of protection as you build, just wait till the glass layer is very tacky and overcoat, remember you must wash the surface after curing and before adding more layers or other coating.

vii) Sprinkle on some none-slip gunk as this will eventually be my cockpit floor.
Sounds fine, practice with some sand in a stocking.

viii) At some point after the epoxy has set paint the lot in a 2 pack paint.
After washing then sanding with a 200 grit just to remove the shine only.

I want to have access hatches into the void - see question c).
Best done before the lid is glassed onto the box, you will need access to the inside to ensure no resin runs and you may want to glass the internal join (I would).


a) Will I need to use a release agent to get my fabrication out of the mould? – if so what?
If you use foam no mould required, if you do mould, I find the wax easy to work with, but do make sure the surface is clean and very smooth.

b) What additive should I be using?
None that I can see, you might like to thin the epoxy if coating the ply, Metho will do this at about 40% maximum.

c) Am I better fitting the hatches during fabrication or afterwards?
See above.

d) Will I have any heat issues?
I would not expect any assuming you are not laying up more than 5 layers at a time.

e) Should I include a fall and small drain hole in the bottom of the trough – or leave it totally watertight?
As this is to be on the cockpit floor, the chances of it remaining watertight are slim, I would give the base a fall, one in 30 should be ok, but check this against any existing fall in the floor first.

if) Anything wrong with the above plan?
A good project.

go) Any other improvements or advice?
Add some stiffeners to the sides and base, a simple 'DO shape 50mm wide and 25mm high will do, 3 each side and 2 in the base, best fitted on the outside.

Fill all internal corners with a mix of epoxy resin and closed cell balloons, use the back of a plastic (not steel) spoon or very small glass jar to form the radius, this will make cleaning very easy later on.

Make sure all external corners are rounded as glass will not lay at 90* too well.

Only lay up between 10-30am and 2-30pm to avoid problems with humidity (Less than 74% is ok)

Latex disposable gloves are good.

If moulding, leave to cure for at least 48 hours.

I would go with the foam to save weight and it would also double as a cool box or fish tank.

Andavagoodweekend...............



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[Lee_Shaw]

Fine body of men.

Thanks for all the replies guys - some excellent advice there.

William & Oldsalt thanks for taking the time to provide such detailed responses. Very much appreciated.

Oldsalt, I feel a bit cheeky asking but would you mind explaining the foam thingy to me please – I intended to use the void area as a dinghy locker but your suggestion of a cool box come fish store sounds very appealing indeed. Makes the idea of a dinghy locker seem like a bit of a wasted opportunity really. No probs if you can’t spare the time though.

Thanks again fellas

Steve


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[JohnL]

Re: Fine body of men.

Check out the Calor Gas Marine site for box cylinder sizes also thickness, fire retardent resin etc. Its regulations and insurance again.

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[snowleopard]

Re: Foam construction

i've built a couple of boats from the stuff and would always use it as a method of choice though it isn't cheap.

the stuff you want is called 'Herex' and is obtainable from larger grp suppliers like scott bader (try google)

don't use REP (polyurethane foram) which is fragile and absorbs water.

to make up a box, lay polyester resin/glass on both sides of the foam pieces and leave to set when it will be rigid, then tack the sides together (i use hot melt glue) before laying more glass to make the structure complete.

the use of a foam core makes for much greater rigidity for a given weight of grp and gives useful insulation.

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[robind]

Re: Draws Foam construction

Make sure you have a "draw" on your mould and no undercuts. this will enable you to get the finished product out easily. ie slope the mould so that the open end is larger than the closed end. fit a tye type schrader valve into the bottom of the mould if possible and then if model "sticks" it may be possible to use a Bike/foot pump to release the mould from the model. I personally, have had some exciting events with pressure air release systems so be very careful. Just a suggestion and not a reccomendation.
Regards

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[snowleopard]

Re: Draws Foam construction

to make an easy-to-release mould, make it from melamine faced board (e.g. contiboard) and use a wax polish release agent. as robind says you can get the moulding out without breaking up the mould as long as the mould is widest at the open end. for releasing large moulds i have used water, push a blunt knife between mould and grp then dribble water into the gap- it floats the whole piece out and applies a great deal of pressure completely safely.

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