Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: colin-stevens on October 22, 2007, 03:30:05 pm

Title: GRP mould
Post by: colin-stevens on October 22, 2007, 03:30:05 pm
managed to make a 2 part mould out of Resin and Matting of a reasonably simple shape. The first half released reasonably easably, but the second half was a struggle and took just a small amount of the gel coat from the first half with it. not a problem, can be repaired with more gel or resin.
My question is, do i need to do anything to the mould, apart from release agent, to stop the product from sticking to the mould?
Title: Re: GRP mould
Post by: Circlip on October 22, 2007, 03:40:23 pm

   Was always told to do 3 or 4 layers of wax polish,polishing in between and 1 coat of PVA release agent

Title: Re: GRP mould
Post by: colin-stevens on October 22, 2007, 04:51:44 pm
at the risk of being a numpty, any advice on what kind of wax polish? Furniture or dedicated? i was considering using a clear wax i use on my walking boots.
see i am a bit confused as my plug released from the mould with no real  problem. all i used was Release agent.
i am planning on doing a test on just one bit of the mould to see what happens, but been doing this for weeks now and stil no sign of the end product and am getting fed up!! no patience me.
Title: Re: GRP mould
Post by: gingyer on October 22, 2007, 05:10:11 pm
Good quality bee's wax is the best
Polish it to a very high sheen then use your PVA releasant
the wax acts like a releasant and allows you to get a good Finnish


Title: Re: GRP mould
Post by: John W E on October 22, 2007, 05:30:34 pm
There is only one disadvantage of using bees-wax especially for a new comer to fibre-glassing. 

If the bees-wax is applied to the mould too thickly and if the person who is doing the laminating  happens to lay up too many layers in one go, the heat generated in the mould from the curing resin will melt the bees-wax and this in turn can cause mould sticking problems.   

This phenom'enon, however, does not happen when using pva as a releasant agent.   The trick to using pva is the mould first of all must be of a high standard finish and polished well, like a mirror.
Then the pva release agent applied in several goes, allowing to thoroughly dry out between applications.   Depending on the size of the mould, anything over three to four feet, it may pay you to mould into the actual mould air release injection points.   We used to use old car valves (cut out of inner tubes) inserted into the mould at certain points, where we were aware the mould would be difficult to release from.  The injection points had been smoothed on the inside and plugged with a low temperature release wax (bees wax). 

When the time came to release the part from the mould, hot water was injected through these ports thus melting the wax and breaking the seal between the mould and the pva.

John e
Title: Re: GRP mould
Post by: colin-stevens on October 22, 2007, 08:37:55 pm
just done a trial bit, just one end. see what happens.
but when i come to the proper jog i will do what you advice. thank you
Title: Re: GRP mould
Post by: Circlip on October 22, 2007, 08:48:02 pm
  Only problem with doing 'Sample' mouldings is that they use the same ingredients as bulk ones. Beeswax is
   the best but a good quality 'Hard' wax could surfice, the smallest qty of mould polishing wax I bought was
   hardly touched when I dumped it. To put on the ONE coat of pva I was advised to use a soft 'Doping' type
   brush - model A/C type, worked on my mouldings. The only other misconception I found was Amatuers tend
   to add too much hardener cos it doesn't seem to be thick enough, if you're working in a warm enviroment
   you need LESS hardener. I'm no exspert on mouldings but can only comment on personal experience and a
   few fuselages and power pods.

Title: Re: GRP mould
Post by: colin-stevens on October 22, 2007, 09:03:29 pm
ok, chickened out and removed the small bit i had tried, still tacky and was sticking to mould. but pulled out ok then cleaned the mould with Acetone.
Also found my stick of beeswax, will melt a bit over hot water the rub in with a soft cloth.
Keep the sugetions coming, you have all just cleared up a big grey area i had
Title: Re: GRP mould
Post by: Circlip on October 22, 2007, 09:09:49 pm

      Is this still for the Atlantic? If so I can probably turn up the original article from radio modeler where
       someone made an Avon inflatable from thin sheet rubber.
Title: Re: GRP mould
Post by: colin-stevens on October 22, 2007, 09:13:15 pm
yes it is. not as easy as i thought it was going to be. would be gratefull.
Title: Re: GRP mould
Post by: Circlip on October 27, 2007, 02:05:09 pm

  Colin, sorry for delay, if you send me a PM with a 'safe' postal drop address I will photo copy the article and
    send snail mail. UNFORTUNATLY I only have first part of article so if anyone has a copy of RADIO MODELLER
      MARCH  72 part 2 of AVON sportsboat by CHRIS STROSS it's in  there.

Title: Re: GRP mould
Post by: colin-stevens on October 27, 2007, 06:25:29 pm
i will do a hunt and see if i can find the mags. would love to know how it was done. as far as i can see the slightest error would make the tubes deform. would be interesting.
Title: Re: GRP mould
Post by: Subculture on October 28, 2007, 02:23:16 am
I always had real problems with PVA release agent- it tends to seperate if you brush it into the moulds, as it needs to be really thin for it to dry in a consistent coat.

You can try wiping the PVA over with a lint free rag, or use a good sponge.

If you have an airbrush or spray gun, I'd use that for the best results.

i find thinning the PVA is also good.

You may like to follow the advice in this article-

I found it gave good results.

Title: Re: GRP mould
Post by: Subculture on October 28, 2007, 05:30:48 am
Also I find adding a hole in your mould to enable a compressed air line, to push the cured lay-up out works wonders.

It's like thousands of little hands all pushing at once.

Especially useful when moulding deeper objects like cones etc., which are difficult to get wedges under.

Less chance of damaging the laminate too.

Title: Re: GRP mould
Post by: colin-stevens on October 28, 2007, 10:11:22 am
Thans very much for the pointers ona and all. thought i would put down a breif summary of what i did.
had a realy long week, so decided i needed taking my mind of it and decided to do the layup. started abot 18:00, after all how long can it take.
as a release agent i used MackWax release agent. Sprayed on severeal coats.
gave the mould a coat of Epoxy resin and left it for about an hour. Cut up squares of light weight cloth.
Gave the mould another coat of resin then started laying in the squares.dabbed them down vigoursly, then layed down another layer.
Left it for about an hour, then repeated the the room was realy hot the next layer went on about half an hor later.
while this was gelling i cut up strips of plastic card. these were then super glued to the inside protruding proud. then mixed more resin mixed with micro ballons, the two halfs joined together. and went to bed. About 12:30.

Released it in the afternoon, no probs. (i lie, a couple of spots were stubborn). lovely finish, but hadnt put in enough "glue" and a whole lenth has not joined. thank gawd for super glue.Thick.

The one question i never asked was the weight of cloth to use. i used light weight and even though there are at least 5 layers, the product is a bit squeezy. but its still a bit green and may well harden up a bit more.

all in all i am well pleased, thanks for the advice.
Title: Re: GRP mould
Post by: Circlip on October 28, 2007, 11:32:19 am
  Andy, you hit the nail on the head re PVA, thats why I said use Soft dope  type brush and 1 layer cos just like
   painting on top of wet dope, even when dry, PVA will still pull cos it's soluble to itself. Only way to do multiple
   layers is to spray it.
  Colin, It will stiffen up but it takes time, - Repost in about a week and tell us * Finer WOVEN cloths give smoother
   surface finish, only use RANDOM for thickening molding up andTISSUE for mending cars - full size. If you get a good
   coating of PVA in the mold you can always try soaking in HOT water to release the molding. These are only MY OWN
   findings, - There are many roads to Rome!


           PS  ultimately CYANO is water soluble
Title: Re: GRP mould
Post by: John W E on October 28, 2007, 11:48:51 am
hi ya Colin

Curing time, as its known, should take no longer than 48 hours for the hull to 'stiffen up' or come to full cure.  When you have removed the item out of the mould, it is always best to stand it on a soft surface e.g. some soft foam, and try to keep it as upright as possible to minimise distortion.

As far as layup is concerned, we were always taught, and this was by Lloyds Regulations, Gel coat first, followed by tissue matt, and then it depends on what you are actually moulding.   

To give you some idea, we used to do the fire retardent lifeboats for the real ships and also the inflatable lifeboat cannisters.  Their build up was (on the lifeboats) fire retardent gel, tissue matt, one layer of 1oz (1 ounce) chopped strand matt, followed by 2oz chopped strand matt and then followed by fire-retardend core material which was approximately 1/2" thick, followed by 2oz woven roven matt, and on top of that ounce matt, followed by a final coating of tissue matt.  This was all done with fire retarden resin.

So, that may give you some idea of layups.

One of the tricks is, to try and cut your matt as large as possible and dont forget you cant lose matt when you are moulding (in other words - if its too big and you try and fold it over on itself, it will always spring back).

Glad you have been successful, the more you try it the easier it becomes.

Hope this if of some help.

aye john
Title: Re: GRP mould
Post by: Subculture on October 28, 2007, 12:48:03 pm
I leave my moulds a couple of days to cure before popping them, unless it's very hot, or I'm impatient to see the results.

Some laminate experts recommend leaving them for about two weeks (polyester layups), as it does keep moving throughout the life of the laminate. I reckon that's a little excessive, especially in the case of modelmaking applications.

Epoxy resin has a much lower shrinkage rate than polyester, which is why a lot of people like it- the hulls once cured overnight will not move any more, plus it's a much tougher product. Problem is, it's about 4-6 times the price of polyester resin. Plus it's totally unforgiving of any contamination and poor mixing ratios.

When it comes to laminate thickness, I use a layer of glass tissue, and two layers of 300 gram chopped strand matt, with maybe a little extra reinforcement in high stress areas. I find that is good enough for boats up to about three feet in length. I have got good results with this combination, but everyone seems to have their own personal favourite way of moulding.

The tissue isn't essential, but is a very worthwhile addition, as it conforms/floats nicely over the lumpy gelcoat. This helps prevent annoying voids in the laminate between the gelcoat and the glass/resin mix.

You can float/top coat the finished laminate, which looks nice, but doesn't really add much, if any extra strength, just weight.

Title: Re: GRP mould
Post by: Circlip on October 28, 2007, 12:49:42 pm
    Bluebird, TOTAL respect to someone from the trade re fullsize F/G process, used to supply mech. bits for what
     ultimately became one of sons' first command - a tupperware minesweeper - Hunt class - and was amazed at its
     hull construction, to specs like you say, trouble is reducing to our toy sizes it has taken many years to develop
     successful HALF A CUP techniques, the same materials apply but we have to modify the rules.

Title: Re: GRP mould
Post by: John W E on October 28, 2007, 06:46:00 pm
thanks and no thanks Circlip  {-) 

the thanks really goes to the Companies who tried to educate me in the use of fibre glass resin and what I have learned I do try to pass on.  Although, when I have done a bit of research this afternoon some of the techniques and materials have drastically changed, since when I first was involved with commercial products.

Just a few more pointers, to help people which I notice hasnt changed, when working with fibre glass resin there are several hard and fast rules which must be adhered to whilst working with fibre glass or even epoxies and they are well documented in other topics on this forum.   One of the main pitfalls, which I have seen are people who are new to the fibre glass scene, as you have already stated, tend to add too much hardener.  The other one is, that people think the more laminations you add to a hull, the stronger it becomes.   I have seen models of some 4-6 feet in length, with hull thicknesses varying from 3/8 inch thick up to 1/2 inch and around the stern section, and, the rudder supports being laminated up to near enough an inch thick.   When laminating to this thickness around sub structures this will only bring on problems later on in the life of the hull.  As has already been stated, fibre glass moves and shrinks, causing problems. 

Its trying to educate people that a hull of 5 feet in length need not be 3/8 inch thick to have strength, merely only 1/4 inch or even less.  But, to add strength to the hull by adding longitudinal stiffening down the centre of the keel by means of say, laminating in 1/2 inch square softwood with two layers of matting over the top, and the same around the sides of the vessel - maybe 3/4 inch down from the deck line, when these had been laminated in, one would be surprised how rigid and  light the hull would be.

The other thing I have seen in some hulls is what they call 'resin rich' which is where too much resin has been mixed and what they have done is just worked it into the hull.

A good rule of thumb, as we were taught, the ratio should be 2.5 to 1 of matting, a good experienced laminator should be able to work in 2lbs (two pounds) in weight of resin for every pound weight of matting.  An average laminator between 2 and 2.5 lbs weight of resin to every pound of matting.   If you are just a beginner 3 to every pound of matting, but then you are starting to over-saturate the matting.  With a good roller, and a good rolling technique one should soon be able to work at the 2.5's.

The other thing to mention is, if at all possible, and you are new at the game, try and work with clear resin with no pigments in.   The reason for this - airpockets and airbubbles - are easily detected and can be worked out before the laminate goes off (bit like wallpapering - yikes  :)  ).

The last thing I would mention for beginners is to try not to lay too many layers of matting in one go, try and plan so you work alternatively i.e. from corner to corner on large hulls, therefore avoiding heat generation.

Hope this is of some help. 

John E
Title: Re: GRP mould
Post by: kayem on October 28, 2007, 07:01:29 pm

All good sound advice there Bluebird, just a minor problem with the spelling....
Title: Re: GRP mould
Post by: John W E on October 28, 2007, 07:05:53 pm
Woops just been corrected by the Grand Master of all

Blue Gee - Glass Chopped strand matt 300grm 1M x 1M
Title: Re: GRP mould
Post by: kayem on October 29, 2007, 10:37:02 am
Hmmm... A tricky hand to play, what's the best move?

Ah yes, I know. I'll see your misprint in a minor retailer's catalogue Bluebird, and I'll raise you a second major manufacturer's printed carton.
Title: Re: GRP mould
Post by: The long Build on October 29, 2007, 11:49:03 am

Re Oxford English Dictionary.  Mat can also be Matte or Matt
and as far as this thread is concerned I thought it was about GRP Moulds, and not perceived spelling errors, why not start a thread about spelling errors  on the general chit chat site , sure you will get a lot of response there.. NOT..

Title: Re: GRP mould
Post by: chingdevil on October 29, 2007, 12:01:27 pm

Calm down everyone, I have spoken to Kayem about their posting.

Title: Re: GRP mould
Post by: Circlip on October 29, 2007, 12:44:41 pm

     I'm glad that when I jumped in I only referred to cloth (or should it be clothe?) I got the thanks ref.
     Bluebird but missed the no thanks?  And can you PLEASE not tell everybody ALL the secrets at one go?
     We've got to have SOME mystique left to show these kids we've done it all before?

      regards   Ian

        P.S.  I've always known it as MATT.
Title: Re: GRP mould
Post by: John W E on October 29, 2007, 04:42:48 pm
Hi there Ian, the no thanks bit....was referring to memories ..... some bad ones.  Can you remember the smell that used to linger around you, doesnt matter how many showers you had, the smell still there, cutting resin off your hair and elsewhere, and, in the summer when the factory was red-hot the itching that you eventually become immune to, not to mention, when things go wrong and you have spent days working on a mould and it all goes wrong.  Then there is some wise guy leaning over your shoulder, pointing out everything, but the right thing....aye.... and all you want to do is take that mould and shove it where the sun don't shine...aye that's the no thanks bit .... cos you know you have to start it all over again.  ;D ;D ;)

john e
Title: Re: GRP mould
Post by: Martin [Admin] on October 29, 2007, 06:31:07 pm
Topic swept and tided up......  :)
Title: Re: GRP mould
Post by: Bryan Young on October 29, 2007, 07:36:42 pm
John E

You really ought to write a book on this subject. Your ideas are far in advance of an old Nexus (?) item I learned from.  As far as stiffening up a long hull (looking at 6' plus) I use 1" angle iron clagged in with "hairy-filler" (bought or home grown). The alignment of the iron has at least 2 benefits.
1. It sure adds rigidity to a long hull.
2. Placed accurately it makes a ready-made home for batteries and such like. (And my bigger ones really need the weight!) Keep going. Obviously feeling a lot better now. Cheers. Bryan.
Title: Re: GRP mould
Post by: Circlip on October 29, 2007, 08:10:09 pm

     Colin-stevens, I just hope that next time you want help on such a contentious subject you remember the skin,hair
      and two moderations that you've caused with this one!

         Luv  Ian
Title: Re: GRP mould
Post by: Colin Bishop on October 29, 2007, 08:24:31 pm
As an example of what looks like bad practice this picture of my 1:1 scale boat may be of interest. Having got her out of the water I'm now trying to track down a minor leak around the forward part of the hull around where the tube for the speed log paddlewheel goes through. Having stripped off the paint I found what appeared to be some cracks in the bottom of the hull near where I think the problem is. I used a scraper blade to dig into them and found I was pulling off chunks of pure resin around 6mm thick. On first impressions it looks as if it may have been poured into the mould to make the "corner" where the flat bottom meets the side. There is no GRP mat in it at all and there is a sort of greyish substrate which I assume is the hull proper. Most of the clear resin seems to be bonded to this but there are some areas, as you can see, where the resin has separated. The original layup would have been in 1983. It looks as if I shall have to clear out the loose stuff and replace it with epoxy filler.

This may not be the actual leak which could in fact be going up the side of the plastic tube through the hull that the paddlewheel unit sits in.

Title: Re: GRP mould
Post by: colin-stevens on October 29, 2007, 08:58:53 pm
Ian, as per usual i seem to have missed the fun. never had a thread moderated before, wish i knew why!!!
never did i think it would be contentios. (?)
dont care, i learnt alot from it, even though the mould i was puling had no detail, and was relativly simple.
keep the hints coming, i am sure i am not the only one interested.
Title: Re: GRP mould
Post by: Circlip on October 29, 2007, 09:04:28 pm

    This one to other Colin (Bishop), can't quite make out hull construction but if its G/F it is probably polyester molding
     so epoxy don't stick to it very well?
Title: Re: GRP mould
Post by: Colin Bishop on October 29, 2007, 09:21:28 pm
Yes, it would be polyester but being so old I reckon you will need to abrade the surface to get a mechanical bond. It may be worth putting on a thin layer of that epoxy paste that is used to seal leaks and will cure underwater - seems to stick to anything.