Which gelcoat to make a mould?

[nevilleh]

Hi Guys,
Im making a 35' plug at present and should be ready at the end of the week to start laying up the mould.

Just wondering which gelcoat would be best ?

Ive used tooling gel for small moulds, but Ive been advised by the designer to use normal gelcoat on this mould as it wont be as hard and will allow flexing without cracking.

I think he may have a point, and im quite happy to save maybe $2000 on the gel, but I want to get it right.

The maximum number of lifts the mould will get will be 30 - 50.

Can anyone help with this?

Off to order the gel on tuesday !


Regards

Neville
Scotland

[Herman]

Simple: tooling gelcoat. How much flex do you expect from a decent mould? I presume you make the mould thick enough. It is the small, thin moulds that suffer from flexing.

Are you planning on using tooling resin as well? Or do I mess up your plans now?

[nevilleh]

The mould will be approx 15 mm thick with the normal heavy stiffening. We relied on the advice of the designer who has traditionally not used tooling gel and only used standard resins.

Our other moulds are of a similar design and do flex slightly. I have not seen any large moulds that wont flex very slightly.

I have noticed also that moulds that I have made using tooling gel have been slightly more prone to cracking.

I am going to contact the resin manufacturer tomorrow for their advice.

As for tooling resin, forget it !


Neville

[ondarvr]

Building a 35' tool is expensive, but even using the lower 30 parts from the tool figure, the cost difference you claim of $2000.00 is only $66.00 per part and $40.00 at 50 parts.

I can't see cutting corners on building a tool of that size with that many parts possibly being made on it.

If you're worried about cracking go with a VE tooling gel coat, better resin, and more bracing.

[Landlubber]

...tooling gelcoat is DESIGNED to be used for mould making, why are you even considering using cheap gelcoats...the mould NEEDS to be heavily reinforced and is usually done in steel framing, it is at least 3 times the costs of a part it will make, so if you expect the mould to make 20 to 30 parts, then do it properly, there is no shortcuts here mate (or anywhere else for that matter either)

[nevilleh]

The mould is getting adequate reinforcement worked out by a structural engineer in steel and 18 mm ply.

Problem is to stop flexing completely it would be more or less impossible at that size when we use crane to lift etc.

I have looked at some popular 30 - 50 ft yacht moulds and they all have the same slight flex.

Im not wanting to use normal gelcoat to be cheap, i have just been told its really common with the larger boat builders as they have found that the differences are quite insignificant.

Has anyone here built a mould this size?

I certainly most likely wont be using tooling resin for the main layup as the cost for 4000 kg is significant and all of our other moulds which are 10 - 20 years old have been made with nothing special and seem to have lasted quite well.

I have always presumed that the big guys used tooling resin for everything but then after a few calls I found different. Sealine over here use normal gelcoat & resin on 50' etc.

[Landlubber]

...yes, I have made many moulds this size, the tooling gelcoat is a harder and less porous material than gelcoat, it polishes to maximum lustre and is less likely to delaminate. The mould will flex, yes, but as long as they are not abused too much they will serve for the required number of uses easily. make sure the product is removed with water or air before trying to lift out, so that no banging is required to demould...some people actually lift and drop the mould (and job) to release it, not a good idea...

[srimes]

Originally Posted by Landlubber

...yes, I have made many moulds this size, the tooling gelcoat is a harder and less porous material than gelcoat, it polishes to maximum lustre and is less likely to delaminate. The mould will flex, yes, but as long as they are not abused too much they will serve for the required number of uses easily. make sure the product is removed with water or air before trying to lift out, so that no banging is required to demould...some people actually lift and drop the mould (and job) to release it, not a good idea...

I've heard of air, but this is the first I've heard of using water. Makes sense, pump in water and "float" the part loose. What are the pros/cons of water vs. air?

[Landlubber]

...the water cracks the job out simply and very kind to it....yes it basically floats....and is not compressable, so something has to give....yep, the job.

[nevilleh]

Landlubber, I have always found tooling gel gives a nicer lustre, but I have also found it has had more potential for chipping a little, probably due to its hardness. I used optimould last time which cost me a fortune. It was black. Our designer has told us to stay away from dark colours of gel aswell as when we put our moulds outside even the little bit of sunshine we have over here will cause them to warm and post cure even ages down the line, and cause visible shrinkage throughout the mould.

I had a look at som eof his older moulds which were lighter colours and not one had any visible shrinkage. I know proper curing times between layers and post cures is really importand on mould making, but he reckoned the idea of lighter coloured gels to reflect the sun away was a major player in keeping his moulds straight !

[ondarvr]

Just because somebody uses a standard resin doesn't mean its a poor grade of product, because some companies use good resins in production and they may work OK for tooling. Other companies use junk resin to build boats and it doesn't do a good job of even building the products they sell.


There are a few reasons people use to justify using a lighter colored tooling gel and only a couple of them have much truth to them. If you are spraying black, or very a dark gel coat, then use a lighter color, and possibly if you are leaving the tool outside uncovered and don't want it to become as hot in the sun.

Covering a 35' tool isn't that hard though, and after the time and money put into building it, it seems like a waste to leave it uncovered, plus a tarp can be custom made to fit it fairly easily.

If I want to know I built a good straight mold, I use black, if I want you to think I made a straight and true mold, I use some other color.

With black you see every defect the instant you walk into the building, with other colors you need to get the light just right and even then the defects may not be very noticeable.

[nevilleh]

So really a good reason to use a dark grey or black final coat on the plug such as duratec?

Probably more important to get the plug finishing correct and that should get the mould straight !

Its sometimes diificult to know how far to go building this stuff. The cost of the plug / mould venture will be approx $100000 inc designers fees. I have paid for this in cash from my own hard earned money so I do scrutinise every thing I do.

Ive made so many mistakes in the past running out and buying products for little or no gain in the long run and most of the succesful boat builders over here reccomend that I concentrate on keeping my costs down to survive !, staying away from fancy products but it would be painful to me if I didnt use tooling gel and a few months down the line the mould was in poor condition .

The one product that I am really happy with now is wax free resin. I dont worry at night about boats delaminating when I know I have gone as far as I can to use the correct materials and the correct proceures.

I guess a call in the morning to the tooling gel manufacturers should install me with a little confidence.

Thanks guys.

[ondarvr]

I know it can be very difficult to control costs in building boats, this covers all aspects of it from start to finish. One of the big money pits I see is poor tooling, all too often the choice is made to save time and money on the building of it, only to spend far more in the repair department on every part produced, plus repairing the tool every few parts.

[nevilleh]

You are bang on there. Our most popular boat which is 28 ft has come from moulds in very poor condition and as such require substancial finishing on each product. It is my intention to retool or resurface this one soon, but as usual financial constraints apply. In the long run it makes sense to have good tooling, but when you are up against a budget at most small builders are, the short run and expensive route apply.

Although I have to admit that poor & hurried handling have most likely caused alot of our tooling damage. My guys are often to lazy to tape up moulds when we are only using part of the mould and then we have a costly clean up of the hardened resin on the exposed part of the mould. Or people walking with gritty boots on the mould surface. They wouldnt treat their carpet at home like that. Now im starting to moan !

[Landlubber]

...you have just started using wax free resin for lamination.....hard to believe...who is your shippy, sounds like you need a new one.

The plug is far easier to make perfect than any mould is, so make sure the plug is perfect before flopping it off......