Plug finishing

Hi All,

We are halfway through making a 35' plug. Pretty standard construction, MDF cnc cut frames & 1" square battens.

We should be finished the sheeting next week and ready for the GRP, after that the surface prep.

I normally use Duratec for finishing small plugs and moulds, it is very sandable and polishes well.

Only problem is its price. Ive heard of 2 pack paint being used , has anyone experience of this, or indeed normal gelcoat being sprayed on ?

I would prefer to run with duratec but on a project of this size its going to cost thousands of dollars to get a decent thickness on.

Any recomendations ? Whilst Ive build a few plugs and moulds in the past, this is by far the largest and i dont want to mess it up !

Thanks in advance for any help.

Neville. Scotland

 

Two pack paint works very well,but it will not be particularly cheap.It also pays to leave it for a while before moulding,but with a 35 foot long surface to prepare,this will occur anyway.Gel will give a surface that is amenable to releasing but breaking through from one coat to the next may leave marks in the mould surface.Another possibility is Durabuild and it has been a few years since I used it so do some investigating into both the polyester and vinylester versions and the prices compared to the alternatives.

 

Neville, the Duratec is dear, but you at least KNOW that the result will be pleaseing, it will not stick to the mould when you get that far and the working of the material is very good....just do it.

 

Another option can be Polyfill P96 from ATC in Canada. Basicly the same material as Duratec.

Using 2K PU paint is an option as well. It sprays on nicely, or can be rolled, and can be sanded and buffed. There is 1 small hickup though: You need to let cure the 2K PU paint for at least 1 week, before putting on gelcoat. There is no alternative to that. Keep that in mind when doing your planning.

This is actually the most common method in NL for plug finishing.

 

I've used white tooling (no wax) gelcoat on small plugs for years-my plugs were always glassed with polyester. I get the plug smooth after glassing by filling with resin + cabosil and always put two coats of laminating resin on the plug before spraying or brushing gelcoat. Do that so that if you go thru the gel coat you'll have an "indicator" before you hit laminate. But put the gel on thick enough that you don't go through!
If I'm forced to brush the gelcoat I mix a putty of gel coat and cabosil(very liquidy) and fill the brush strokes. If brushing I'll use at least four coats of gelcoat before sanding- filling the brush strokes each time. If spraying three coats works-filling any orange peel between coats. Again,the idea of the thickness is so that you don't sand thru the gel coat. One thing essential for a good plug finish is consistent material all the way thru the sanding process.
Before you start sanding the plug has to be washed with acetone or else the paper will just clog up. I've always used blue dykum dye mixed 50% with acetone as a sanding guide. Apply it after washing the plug before sanding. For each grit, you know when to stop sanding when all the blue dye is removed. I usually go 36-8--220-320-400-600-compound.

 

Thanks guys for your help, now I have even more choices !

Probably not going to go down the 2k paint route as we dont have the time for the cure, so now its a choice between a duratec type product or spray gelcoat.

I like the idea of gelcoat as its about a quarter of the price, but ive only ever used duratec before.

Doug : Can you tell me why you would use tooling gel instead of normal gel for the plug ? i thought that something slightly soft and sandable would be better on a throw away plug.

Cheers

Neville

 

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Actually, Neville it doesn't have to be tooling gel-it just has to be the exterior gel used in laying up a hull- w/o wax. If you use an interior gel containing wax then you won't be able to fill the brush strokes/orange peel-it won't bond and neither would a second or third coat. I used tooling gel because its a better quality of material. The stuff sands well after it is washed with acetone.....

 

MDF for a plug is ok but all sides including the edges need to be sealed with a coat of resin to keep the sheets from moving with high and low humidity !!Even the wood frame its made over should be sealed completely to !!. And be carefull of the fillers you use as the filled areas will eventually show through when you sand and polish .
The face side needs a good penetrating coat or two of resin with no wax and a layer of light glass woven glass then you apply your gel coat !! this will become like a egg shell and hopefully not allow the wood movement to show through to the surface .
Use a pressure pot to spray with and thin the gel coat a little to get the spray pattern to a minimum , because its gel coat you should be able to get a good thickness on in one shot and not have to do multi coats .

Dura tech is better but needs more coats , I always spray with q cells mixed with it so you get a good build up for long board sanding . Last project we sprayed 7 coats before the final surface coat and long boarded and fine sanded between each coat . Each coat was a differant color so the hi and lows showed and did not get completely sanded off to the bare glass underneith !. The last coat of dura tech just the hardener and a little acetone as a thinner to get a nice fine smooth spray with no orange peel . I use acetone because it evaporates almost instantly when you are spraying . Duratech may be more exspensive but its less work and almost guarenteed to get a good finish and a good release .
Time is money , so do your home work to make the decission Gel coat or dura tech ??Gell maybe cheaper but 2 or 3 times the work to get the finish you could be looking for . Duratech is more exspensive but easyer to work with and less hours involved ,so your choice !! Me i'd use duratech everytime !!.

 

Gents, Thanks for the input. Im probably going to go down the route of duratec. Its what i know and have achieved good results with it, and you are right, its quicker to sand.

The designer has said not to bother with tooling gel for the mould, as its too hard and cracks. Anybody care to comment on this ? ive used tooling gel and normal gel in the past for moulds , both with equal success.Again we have a cost implication here !

Finally, can anyone advise on orbital power sanders ? we use the 3m range disc da sanders which are magic but probably no good where the long boarding will be required. Is anyone aware of longish air sanders that can take over from the manual long boarding ?

Thanks again. Neville

 

Longboards are to get things fair and flat , Takeing off the high points and get it Fair !!
Tooling gel ! Yes it is harder and thats what its for !!,to make moulds from !!
Its hard so it will take more wear and tear .:idea:
Cracking !. think about it ,how do moulds get cracks ?? in all the years i have worked with glass the only way anything gets cracks is from someone hitting it with something !! Why would you want to hit you very exspensive mould with a hammer . If its waxed and has pva it will simply float out without even thinking about hitting or even tapping with anything .
Even decks can be released with water . Not in favor of high pressure air !, unless its something small and the person really understands what they are doing . If you hit either the mould or the artical you are asking for trouble . Star cracks in the artical or the mould are bad news . In the mould they are there forever and it gradually gets worse over time untill it is repaired and even then theres a mark that sometimes shows !!

Orbital sanding dri or wet is a good way to go !I prefer wet but dri is ok . I use a little dish washing liquid with the water to act as a lubrcant and keeps any finger print marks off the mould surface . I use a big sponge soaked in water rather than a hose . Theres always a fine trickle of water comes out of the sponge whith is enought to keep the paper wet and carry the sanding dust away . If you use a deep bucket all the dust and any grit will settle in the bottom as you are working . On big jobs its possible for one person to use two sanders together one in each hand to get the job done quicker .

 

Tunnels : Ive never used two sanders at once, maybe my arms are not up to it!
Ive seen some longish (15") orbitla sanders on the market which may be good between the long boarding process and the DA sanding. Just wondering if anyone has used these .

As far as cracks in the gel go, i employ laminators who sometimes get a bit heavy handed with releasing moulds, who can blame them, they are in a crappy job and want to get things done. Most of our production moulds are damaged through poor release methods, thumping, dropping and general lack of IQ !

Normally its the deck moulds that have poor release angles due to comples shapes and lack of thought at the design stage. This contributes to frustration by the lads when releasing and probably also being a little heavy handed when driving in the plastic wedges .

Hopefully with our new 35' mould things should go smoother...

 

Ok i know what you have to put up with but simply put its only hard to get out because the waxing hasnt been done properly !!If i found any one hitting with anything the person was told to piss off and the hitting things be it a hammer or what ever went in the bin !
I learned a long time ago about pva and like we all thought it was a waste of time and looked terrible when the artical came out of the mould . I was shown by a English guy working in Brisbane how to use it properly .
Please take carefyl note of what i am going to tell you ! Its majic and works a treat .
Get a spray gun and 1/4 fill with pva straight from the bottle , the other 1/4 use just plain tap water . You end up mixing 50/50 !!Give it a good shake on the gun . Screw the air supply to max pressure and wind the needle in so nothing is coming out when you pull the trigger , Hold the gun so you can see when the mix starts to come out as you slowly wind the needle out so its starts to come out , its a very fine spray you need !! dont be temped to keep winding the needle out about 1/2 a turn maybe no more . You need a very fine spray with lots of air flow . now spray the mould !! Simply put if you can see the pva spray on the surface of the mould theres to much on !! The gun has a stage where when you pull back the trigger just air comes out without any spray blow just air across the surface of the mould to completely dry the pva/water mix so when you wipe it gently and quickly with you hand its dry and nothing happens .
Practice with a flat panel first that you can see in the light , Its also possible to wipe off dust that gets on the pva after you have sprayed it , keep the air fow going and dry you hand in the air flow and gently wipe the flat of you hand across the area that has dust and it will come off. .
Practice this untill you are comfortable with what i have just discribed . i have done this for a long time and shown lots a people how and what to do .THe place in Brisbane never used wax at all always pva only ,There was one gun preminantly set up specialy for that purpose . Its also a good way of getting clean monskid pattern out of a older mould as well when its got a lot of unremovable gunk stuck in the tread pattern . I always pve new plugs , i always pva new parts out of new and old moulds doing this , there is no need to be rough with you moulds or the parts reguardless how small or how big they are . One litre of PVA will make 2 litres and that will last you a goo year or longer in any glass shop . Use only WATER nothing else to mix with the pva . Let me know how you get on !! Fine spray with high air pressure !! dont forget !! . Heres my email address . stuartwrcom@gmail.com anytime !

 

And demould with water. I once made cradles for trailers, for a trailer company. As my mould was very slippery, and very simple, I could pop the trailer mould right of the mould, without using water. The PVA stayed on the product. I never care to wash them down.

At one time I noticed one of the owners of the company grinding with an angle grinder on my nice new trailer moulds. I asked him why, perhaps he needed a course surface for his glue (they glue carpet or artificial grass on the moulds). No, he said, the glue is fine, but there is a layer of material on it, which sometimes can be peeled off, but I tried to dissolve it in all kinds of solvents, never had any luck.

I told him to try water. He looked at me with his face, white from the polyester/glass dust, looking a bit hopeless. He never realised that water also was an option...

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Another good story, about hitting moulds with a hammer. I have a "polyester handbook" which describes about anything polyester. The book is from 1969. In it it is described how to demould a part. It also says:
"Do not hit mould or part with a hammer. This will create star cracks. Do not hit anything with a wooden shoe either!"

I guess you can expect that from a Dutch book...

 

Oh, a hint for spraying PVA: add some ink or any other watery colorant to the PVA, this will allow you to see what you are doing.

And tooling gelcoat is for tools. We did not invent it for not using it.