Fibre glass hull, mould making.

[Barking Mat]

I do fibre glassing, but I've never made a hull from a mould.

This task would involve making a hull from a former.

I understand the principles involved, resin, gel coat, wax, blah, blah, blah.

Anyone any first hand experiences of doing this ?

I'm quite qualified in this department, but never taken on this role, there's alot I don't know.

I know it's not rocket science, and temperature plays a huge role.

Over to you.

 

[angellonewolf]

for a hull would you not need to spray the fibers and resin depending on the size

 

[ajlelectronics]

for a hull would you not need to spray the fibers and resin depending on the size

No. After a full wax and polish, the buck receives two coats of resin to form the gel coat. Then it is laid up in the conventional manner until stiff enough not to warp, with battens inlaid as necessary.

Leave it to fully cure, then separate. Mould is then perfected, waxed and polished ready for its first use.

 

[roofman]

Mould ultra smooth (this is were the work is)...wax..gel coat with colour choice..start laying down the mat and resin

 

[Barking Mat]

for a hull would you not need to spray the fibers and resin depending on the size

So you make a former.

Three coats of wax, minimum.

You typically apply three coats, of gel coat, air fed pistol.

Then fibre glass...

Then pop it out.

 

[8ob]

Had a body shell mold made, a coulple of things cropped up. Firstly was any stiffners/framework for the mold need thinking about or they will pull on/distort the finished mold as they cure. Other thing was getting the thing to release, mine had to have schrader valves dotted about so compressed air could be blasted into it to aide release.Its buried in the corner of the yard, if I can get to it I will take some snaps.

Bob

 

[ajlelectronics]

So you make a former.

Three coats of wax, minimum.

You typically apply three coats, of gel coat, air fed pistol.

Then fibre glass...

Then pop it out.

Nice to spray it but not essential. Just get all the air out.

Batten the mould for strength and watch out for 'wrap arounds'.

 

[Barking Mat]

I did some training course and we used vacuum forming, but it's a distant memory.

Might have to dig through YouTube undoubtedly.

They're offering me a workshop, and all that.

Fibreglass and steel hulls.

 

[roofman]

A lot easier to take a plug mould from an existing hull or as its known "splash moulding" i have done a couple in the distant past but in the boating world its frowned upon for many reasons and the main being copy theft.

 

[Barking Mat]

A lot easier to take a plug mould from an existing hull or as its known "splash moulding" i have done a couple in the distant past but in the boating world its frowned upon for many reasons and the main being copy theft.

Yeah, no, none of those issues.

 

[addjunkie]

A lot easier to take a plug mould from an existing hull or as its known "splash moulding" i have done a couple in the distant past but in the boating world its frowned upon for many reasons and the main being copy theft.

For bigger stuff the moulds are often two part and are split to get the hull out. With boat hulls they use like fibreglass rods in the chines and bilge keels etc to give longitudinal strength. Bulk heads are also often glassed in before the hull leaves the mould, as they are also part of the stiffness that allows force to be used to separate the mould.

If mould isnt waxed properly when you lift out the hull, some of-the gel coat stays behind and needs repaired afterwards.

Symetry is a big issue with boat hull plug making!

 

[Keith 66]

This was my trade for many years. First, what do you want to produce as a finished part & how many of them? This will dictate how far you have to go with the plug & mould.
First thing in any project is to make a plug, this can be an existing article such as car body panel, boat or canoe or whatever, If you dont have this you have to build the plug from scratch, MDF, Gallons of body filler, whatever it takes to get the shape lots of hours. Paint it or spray with Durabuild polyester surfacer filler. Spend many more hours knocking it back with sandpaper & wet & dry until its smooth as a babys bum. Sand through the filler & have to spray more on, More sanding!
Now get compounding with a foam head on a polisher & G3 or 7 , when its proper shiny start waxing. For a new plug or mould you will need Six coats of wax minimum, Each coat must be allowed to dry for a few hours or you will strip the previous layers of wax off if you try & repeat too fast.
DO NOT be tempted to start laying up at this stage, A Stick up where something wont release is a real bummer & makes you sweat!
When its wax polished good & proper its PVA time, (Dont confuse this with PVA glue) Blue PVA release agent is what you use, Best way of applying it i was told by an old GRP boatbuilder nickname of Tunnels, a few years ago, Half fill a spraygun with pva release agent, add some water, shake to mix.
Set the gun air pressure high then turn the delivery screw down until you can barely see the spray fan coming out the gun. Spray your plug or mould. You will be hard pushed to see the release agent going onto the surface. When its dry you are ready to start, Gelcoat first, then layup with Chopped strand mat.
A production mould intended for a long production run will be three times as thick as the part its intended to produce.

It isnt cheap & eats materials, time labour & money, all those have or should be factored into how many parts you need to sell to cover the cost of the plug & mould. Last plug & mould i made was for a 17ft rowing skiff, i have built two boats from it, When i get to 20 it will be paid for!
Styrene tends to send moulders nuts... Thats my excuse.

 

[Milkybars]

All I know is I once visited a shed in Tilbury where a bloke did this kind of work ...I still remember the smell, how he had any sence of smell left i'll never know !

 

[Wedg1e]

I remember seeing some of the bodyshell moulds at TVR... they had scaffold tubes glassed-in, for handling as well as stiffness!

 

[Johnnybravo]

Thoroughly think out where your split lines are going to be. Don’t be stingy on reinforcement and bracing. Plan ahead with this that it can be installed whilst the main layup is still wet to minimise distortion. Bond in penny washers where the bolts go through. If you need additional bracing make sure to use the minimum catalyst required to give you a slow cure that it doesn’t pull.Celotex bonds in nicely if you need to stiffen things up without making it overly heavy. Don’t know if you can still get it but paraffin wax polish is brilliant under a water based release agent. A big syringe filled with water can ease bits that are sticking on demolding, give it a squirt,go for a cuppa and come back to remove it once the desire to bludgeon the whole thing to death passes. Washing powder works better than acetone for cleaning brushes and your arm hairs that invariably get resin on them . Add a bit of water to the powder to make a thick paste and rub it in.

 

[500e]

What's used instead of Miirror Glaze now, when we were making panels and spoilers for the hill climbe cars that's what we used.
The spoilers were hell to get out we ended up with 2 part moulds
Also used it on a boat project but that's another story

 

[Morrisman]

I remember seeing some of the bodyshell moulds at TVR... they had scaffold tubes glassed-in, for handling as well as stiffness!

I've used lengths of garden hose pipe before, to stiffen doors and floors in hot rods. Not because the hose adds anything, but it curves easily and creates a hollow glass tube around itself, which gives the strength with little extra weight.

 

[500e]

Used fg rope as well as pipe, @Morrisman
Expect to see finished products soon Mat

 

[Keith 66]

Release agents are a subject all on their own, Mirror glaze was a commonly used one, Honey wax another, Parafinn wax was good as well. I am on the last bit of a tin of floor wax i have had for years, terrific stuff!
Years ago me & a mate were given a sample bottle of stuff by a supplier to try, milky white colour, he called it mold whizz, You didnt even need to polish anything just wiped it straight on over anything & it gave a perfect release every time. It was very expensive to buy though!
If you ever get a big stick up it can be an absolute disaster, i had one years ago, had to break the plug up to get it off the mould, fortunately the mould wasnt damaged.

 

[500e]

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