I have been using pva in rc boat moulds for several years now. I apply slightly differeently to Doug (but I will try his pouring method). I brush on with a good quality soft brush. The amount of pva is critical - not enough and brush marks will stay - too much and you get runs in the pva.

A good quality pva will always give you a great gloss - even when your plug/mould is only sanded to 800+ grit.

what i am getting is . the amount of pva, should be a lite coat. on top of 7 or 8 coats of wax? i think i like the idea of brush on. this will give the new person and myself more control of the pva. and if there are runs. can they not be sanded out?.
this is a good topic
good exchange of ideas

Tranth, the stuff tries to an exceptionally high gloss; even when I spray it it dries to a hull gloss but with some spray pattern imperfctions.Since you’re in Australia there might be some difference in what you use as opposed to what I’m using but polyvinyl alcohol should be the same…
When you pour it is important that you do it as I described or you can get streaks, puddles etc. Done right it is equal to wax in gloss.And you have the major benefit of no wax residue on the part. And you can spray paint in the mold instead of gel coat-as long as you test its compatibility first; Imron works and so does regular Krylon-but only with epoxy laminating resin.

Doug Lord
–High Technology Sailing/Racing

PVA sets like a thin skin. You cant sand it. If it gets runs or crap in it the only thing to do is wash out the mould and try applying it again.

FWIW, I have been producing hulls for 20+ years as well as other fiberglass and composite material parts. I don’t use PVA, although I see it used on larger projects where the coverage would be needed due to the size (i.e. full size boats) I can just give you a few thoughts from my point of view.

I know of no window for use of gelcoat. I bought molds that were shot with gelcoat as much as 2 years (YEARS) previously, and I laid up the molds and drew out perfect parts. If it went in right, it comes out right.

I use MOLD RELEASE made by T.R. industries out of Lynwood, CA and the last price I saw on it was about $16.00 US. for the little red can. I have used it for the last 20 years as well, and I swear by it. There are many other brands out there that work just as good I am sure, but when you have something that works for you… hehehe stay with it. Follow the instructions, apply it liberally and as many times as you can manage. MOLD PREP IS EVERYTHING. If your mold is shiny, your part will be also. If your mold is dull, so will your part. I always spend more time working on the mold before and after than I do on the part.

There are many many different weights and weaves and types of glass… from mat to cloth and what you use determines weight and strength of the part, along with finish inside and out.
There are almost as many kind of gelcoat, and resins which vary from different manufacturers and seasons of the year since “Winter” resins have a little help in their construction to kick off a little easier. (to help our Yankee friends that live where it gets cold) Since I am in South Texas we turn on the heater any time it gets below 80 degrees.

I saw no mentioning of “bagging” your parts which draws the air out of your mold, forces the glass more tightly to your mold giving a more even finish, a stronger product, and more control over the finished part. The more vacuum you draw, the thinner your part comes out.(to a point)You can pick up a decent vacuum pump routinely on EBAY for $100.00 *and sell it there afterwards for about the same price : )

Also there are glass sandwiches with foam cores that can be 10 times stronger than normal wet layups but are more expensive and usually require using a pre-preg cloth and an oven to cook the bagged part. These give the greatest control over the finished part since you are not forced to apply the resin yourself… but unless you have access to a professional shop you won’t have the needed hardware.

The variables are almost endless, but the most important thing is that you try it, have fun with it and of course AT ALL TIMES be SAFE with it. Endotherms caused by excessive catalyst, or excessive mixing (*yes… stirring too much can cause some excitement) and you will be treated to a “Mr Wizard” science lesson on chemcial reacions. Toxic fumes and materials… are everywhere. Proper ventilation and work space away from other combustables (and IGNITION SOURCES) is mandatory.

Bottom line… is FRP parts are the most forgiving materials in the world to work with.
While matching gelcoat is incredibly difficult in the case of a repair… the rest is easy.(that is why we PAINT!)

I have seen amazing things happen to full sized sailboats, whose repairs began with a liberal application of a chain saw. 3 days later and you could not tell there was ever a scratch. Get in there and give it a go, and you will discover that working with the stuff is great fun, and not nearly as hard to do as you might think.

I use epoxy resin and paint in the mold instead of gel coat; there is a window for most paints(the ones that will work: (krylon, imron, certain primers) after which you will not get a good bond-for instance with the primer I use it is about 1-2 hours absolutely max-if you go longer than that when the part is pulled the primer may not stick to the epoxy.
My boats are made in split molds with fairly thin laminates. After spray up with paint or primer the hull is laid up, then the deck and the two are bonded before the epoxy sets creating a primary bond between hull and deck and eliminating most prepatory grinding. While this produces and immensely strong hull/deck joint with all components installed the downside is not being able to use a vacuum and having to fix the flange on some of the boats before painting since it is a horizontal flange. The finished part shows no evidence of a flange at all…A vacuum system would not work with this method since the parts MUST be bonded while both sides are wet and there are other obstructions like trunks and spinnaker troughs that are bonded at the same time.
I worked with polyester a long time as well and much prefer epoxy for most applications but still use polyester to make plugs.
Welcome to the forum-would love to hear about your boats or what boats you are interested in…

Doug Lord
–High Technology Sailing/Racing

Hey Doug… I have never tried that… applying the paint directly to the mold… but I will give it a try. The theory is solid… that you would get the finish from the mold… just as in animation cells being painted on the reverse side. Sadly… I have several EC-12 molds that I can practice with before I destroy them. Atleast if I screw them up it won’t matter
now that we are all being required to re-tool.

I was thinking of starting a thread for the fun of it… as to what I can do with obsolete EC-12 hulls. They can’t be released as EC-12s because someone might get honked later on… sold something that is not correct and find out later the hard way.

I have one that I am going to make into a tremendous light air boat with winged keel and 120% genoa.

I am at present producing hulls or plugs for the following: J Boats Ranger, Endeavor II, Shamrock V, possibly Rainbow. OD Class would be the Santa Barbara, Soling M, Half-meter, and I am #3 on the AMYA list to receive a leased mold for the EC-12. Then I am producing my own design for 10R, M, and 36/600 and AC, and under “A” Class I still offer the 6 M and Kubernettes that were produced by John Reynolds of REYNOLDS MANUFACTURING. They are both heavy displacement hulls that would not be competitive with the new composite “A” class hulls, but are beautiful in the water. The 6 M is quite similar in performance to the Newport 12M and the Kubernettes is the same size and displacement as a “J” boat, but sadly is not a “J” so she is out on her own as well.

I have my own winch design for genoas that should be ready to go in a couple of months, along with our own aluminum spars and mast fittings. Pekabe fittings are being used on all the standing/running rigging, and I am researching an airfoil style graphite mast as well. Sails will be offered from the standard known brand names, and hopefully my own sails will be offered within a year as a less expensive option for those that are just interested in getting out on the water. I don’t pretend to be able to produce competition sails comparable to the guys that have been doing so for 50 years, but I can get you out sailing.

I have not given any thought to the ODOM, US 1 meter, IOM, Soling 1 M… because the competition appears so thick at the moment. They are clearly the hottest ticket at the moment. I would love to see the old classics such as the S/B come back into fashion because they were just such good solid boats that sailed well.

Model sailing has to be the most harmless and un-offensive hobby in the world. It does nothing but silently bring color and beauty to the local ponds and lakes around the world and offers only pleasant thoughts and emotions without polluting or contributing anything negative to the landscape or its inhabitants… unless it would be messy people that leave trash behind, and I have yet to experience any group that acted that way. All the ponds and clubs I have visited were always extremely cautious about their conduct, language and overall image as seen by the public. It is something I have been eager to pursue for a long time and I am thankful that I am at the point in my life that I can give it a shot.

Hey, the future’s so bright… I gotta wear shades…

Larry, see the PM I just sent you.
If you try my paint technique be sure to remove all trces of the TR wax from the mold; it has small amounts of silicone in itthat causes fish eyes. Re wax with Partall #2 paste wax, then POUR PVA into thmold leaving it mostly vertical butupside down to dry.
Then spray off the shelf krylon(original formula) or imron wait 30 minutes and layup with epoxy-works and produces a brilliant gloss at about half the weight or less than gel coat.On most of my boats I use high pressure and spray the PVA since I spray primer in the mold and it gets lightly sanded(after the hull is pulled); pouring is the best solution for a finished paint surface.
Sounds like you have quite a fleet!
Look under New Classes for the topic by Tranth about EC 12 hulls called “please take a look here”-- weird name for a topic but thats what it is about…

Doug Lord
–High Technology Sailing/Racing

Howdy folks,
If anyone has experience with this I’d be eternally gratefull.

I’m building an IOM Triple Crown Plug, but I’ve run into a problem.

Background: I made my plug out of solid MDF. I cut vertical sections and glued them together (I drilled a hole through each piece and used a threaded rod as a “clamp”). I used 3mm MDF for my templates. To fill in the spaces I used a combination of 16mm MDF, and every 10th piece or so - 12mm MDF sections. Problem is, the MDF turned out to be different densities, the 12mm MDF is more dense so when I sanded the hull plug I ended up with slight ridges.

Question: How do I fill in these low spots. I tried Bondo, but it seems too soft - and messy. Also, I’m having a hard time sanding a curved surface in a “straight” line - if you know what I mean.

I’m thinking I should sand off the Bondo, and cover the whole thing with something hard and sandable. Sugestions ??..

  • I’d post a picture if I knew how. -


To get rid of your ridges, you will need to make a “long board”.

Start with a piece of 3 mm or so thick plywood. You want something stiff, yet will bend symmetricaly along entire length. Make about 12- 14 inces long.

Buy some belt sander belts and cut and use spray glue to fasten to the plywood. Before gluing, add two small blocks of wood on opposite side to use as handle. When done you should have a piece of plyood that is 14 inches long x 3 inces wide. Two small blocks of wood on one side for handles and sanding belt on opposite side.

You can use Bondo for filler, or epoxy with microballoons. I have even used wall board joint compound as it sands easily.

Smear on enough so it is too thick, and start sanding. Hold board parallel with the length of the hull and for rough fairing moved it fore/aft along hull. You can bend board to allow it to stay in contact with as much of hull as possible to eliminate hollows.

As you get close to the MDF boards, use them as templates and sand up TO them - NOT into them.

Keep adding filler for fairing until you get a nice faired hull. Change out the paper to finer grit, and add a thin “skim” coat and keeping the board in the same direction. Sand diagonally across the hull and also up/down from gunwales to keel. Try to keep board in contact with the hull for the full 14 inches (or board length)

If you used epoxy, you can finish sanding and polish and then lay up the glass to make your “female” mold. If you used joint compound or bondo, I would give two coats of varnish to seal surface and proceed from there.

Be sure to really do a good smooth, polish job on the "plug, because it will be reflected in the exterior of your hull after layup and removal from female mold.

If you are just using the hull for a “male” plug, you don’t have to worry as much about finish, as you will cover with glass and imperfections will be on the inside of hull. Leave the glass on the plug until you finish the outside surface (filling and fairing) BEFORE you remove the glass (or carbon) hull from the plug. Keeping it on the plug will insure it doesn’t bend out of shape as you finish the exterior. Be sure to be ready to add some internal bracing when you pull hull from either “female” mold or “male” plug. Don;t remove hull until you are ready to do the bracing - or it might warp on you as epoxy or resin will still be a bit soft!

i have great news. i have made my first mold. i want to thank all of you. for your help and input. i used partall #2 and pva. 5 coats of wax. and 2 coats of brushed on pva. then i used just a brushed on fibreglass. then when the resin got tacky. i put on the cloth. and working with a very good friend. we put on 5 layers of cloth. and resin. at the end of 3 layers we stopped using brushes. and just poured the resin onto the mold. we usde our golved hand to spead and smooth the mold.after waiting 4 hours. we turned the mold over and tried to pry it out. by using so much cloth and resin . we had laid down too much wieght for the flange. and the flange bent up. so we had to cut some of the flange , to get the master out. but the mold survived. and is in working condition. i now longer need ben cooke help. and i know he keeps secrets. i still have to pull a hull. and fix the flange.

does anybody have any helpfull hints to help me pull a hull?
could use it. this thread has no personal attack. and everybody gives good information
long live the cup

Thanks for the advice Dick.

I made “long boards” using some old 3mm veneered wood panelling (the stuff everyone used to have in their basements in the 70’s), it works very well. I got a 25’ role of 3 1/2" sandpaper down at my local Canadian Tire for $4.69 - good price.

<u>Question:</u> I’m wondering what the consensus of opinion is on male vs. female molds?

i.e. which is easier, problems, weight issues etc…

I’m hoping to have my hull plug faired this Saturday.
Looking forward to any opinions out there…

P.S. My inspiration is Michael Sharmer of Germany. Check out his latest boat. Everything is homemade!!


One good way to make a professional plug is to cover the initial shape with glass using isothalic polyester resin and then put ten coats of iso laminating(exterior-remains sticky) white gel coat. The brush strokes are filled using gel +cabosil/aerosil.This assures enough of a buildup so that you won’t sand thru the gelcoat. Use “blue dykum” dye after washing the plug with acetone following the final coat.The dykum is a dye that allows you to know just exactly how far to sand.MAKE SURE YOUR BUILDING BOARD IS COATED WITH RESIN as well as any exposed wood that might get wet when you wet sand! Start with 36 grit(dry) and go to 100(dry),all wet-220,320,400 and 600 ;use course and then fine compound to polish the plug. You will have a mirror perfect mold finish. I suggest sanding using at least a 6" piece of 1/8" balsa (stiff in the f & a direction) with paper wrapped around it and sand ONLY in a double diagonal direction removing the blue dye at the same rate on the whole plug rather than removing it in one area first. Double diagonal sanding is critical to produce a fair plug; the dye gives you a precise measure of how much to sand.
The lightest hull with the best finish results from a female mold built on a male plug; you have to give serious consideration to how your flange will work. Production molds should be built fairly thick mine are from .5 to .75" thick using epoxy, glass and core putty(Freeman)."Quickie non -production molds cn be thinner. Epoxy molds can be laid up all at the same time; polyester molds (thick) should be stretched out over days.

If you have an excellent finish on your mold you can use Partall #2 wax(2 coats) plus POUR in the PVA leaving the boat almost vertical but upside down to dry. This allows you to spray in PAINT instead of gel coat: two paints that work with my resin (Fiberglass Coatings 4/1) are Krylon and Imron; you should test your paint and resin compatibility first-will not work with vinlester or polyester resins. The technique produces a high gloss hull already painted when it comes out of the mold-very light.

Doug Lord
–High Technology Sailing/Racing

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by KANDU

<u>Question:</u> I’m wondering what the consensus of opinion is on male vs. female molds?

i.e. which is easier, problems, weight issues etc…

<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>

The rule of thumb that I have followed (a personal decision) is that “Male Plugs” vs. “Female Molds” was one of quantity of boats to be built?

Consider that either one requires a lot of sanding a fairing before the hull is done. Here are my thoughts:

MALE PLUG METHOD: Used for one-off boats. Work to finish hull will be done on exterior of the hull while it is still on the male plug. The male plug doesn’t have to finished as well as a female, as that surface will be “inside” your hull. It still has to be fair and still needs a parting agent though.

FEMALE MOLD: More work up front. Requires an excellent finish to a male plug - from which you make a female mold. All work is still done on the male plug. You then make a multilayer mold (over the top of the male plug) and when removed this becomes your female mold. The inside of the female mold will be reflected on the outside of your finished hull. It has to be smooth, polished and free of any dust, dirt, etc. This mold can then be used to make more than 1 hull, saving you finishing time. This means that (usually) when you pull the hull from inside a female mold, the hull exterior should need very little finishing. The problem I have found is getting the cloth to sit down and stay in the tight and usually very thin bow portion of the hull mold. If you are laying up a hull with a flat stem at the bow (for eventual bumper) it is a little easier. But the process is definitely more for multiple hulls from same mold.

Again, from personal view, if I do a hull off a male mold, and like performance, style, look, etc. I can always use the prototype to make a female mold later. If you are doing prototype work with possible hull modifications, you waste a lot of time building a female mold for only 1 use. In fact, I prefer the foam core/plug method, where foam is shaped, then glassed and the design tested. If no good, you have invested in very little time and very few materials. If it works - use if to build a mold to make hulls for friends or profit. If it doesn’t work, dump it and start over. Or, hack off the stern add some new foam, shape and glass and try again. Very easy, very inexpensive, no way near the time expending gluing up and fairing individual strips of wood.

Simply look at the big boat world and take cues from them. One-off boats can/are strip built with wood, cold molded using veneer, (time consuming) while boats that will have a lot of hulls made will go through the expense of making a mold, and recover cost in volume of sales.

For little boat of the r/c variety, the same is true… if you make a mold and only a few boats are sold, costs will be high in order to recoup the cost of the mold. As volumes go up, costs come down. It is a mfg. gamble whether they will sell - so initial boats may also be more expensive - or they can be really cheap if costs are low initially to get buyers.

Microsail doesn’t sell a lot of F3 foilers, but has the same tooling costs (on average per hull) as does Peter at Climate Boat Works with his Epoch tooling. I’m not going to debate the subject here - but if you only sell 4 boats, it has to impact the overall cost and profit of your sales, compared to the sale of 50- 100 or more.

Now, if we all had access to CNC milling and could turn computer designs into milled plugs, certainly it might make a difference.

I guess in the end - if a personal design/prototype, I would use male plug method. If a proven design, and you think you will make more than one hull, use the female mold.

I’m sure others will comment and have their opinions that may differ. These are mine.

The only thing about a male plug made into a finished boat is that normally they end up being extremely heavy. For a weight sensitive class such as M, I would have a very hard time making a single male plug into a boat when compared to a female mold produced hull that I can either sandwich with the male plug,(a two part mold that sandwiches the glass between the two molds and creates an extremely thin part) or using the female mold and bagging it and drawing 3/4 atmousphere on the little devil. The advantage here would be complete control on the amount of material that goes into the hull which allows me to accurately predict the final hull weight.


Larry -

you are correct, and I guess I should have posted something about … “in the absence of vacumm bagging or double mold experience or equipment I would …”

Normally (perhaps ?? [:D]) most beginning builders will not have a setup or experience using bagging or taking the time to make both a male plug and a female mold - with one being slightly smaller/larger than the other.

Imaging a builder that misses one critical step in the mold release process, or who makes a mistake during the bagging process. Disaster, as well as an unhappy camper. Even this should be tempered with the suggestion to learn the process on simple objets or parts before you blow all your hard work on that plug or mold [:-cry]

hmmmmm thank guys
i have made my first succesfull female mold. and i am going to pull a hull this weekend.
i dont have a bagger. i am using a brush to put on pva. and a rag to wax it . i know this is not perfect . but if i can get it to work just once for me. than yes . i will try harded the next time
any helpfull hints my way . like how to wax the bow? would be nice
long live the cup

Cougar,it is really risky to use a brush to apply PVA over a waxed mold! The brush making contact with the mold surface can cause sticking; MUCH better to POUR the PVA or spray it. Pouring gives a better surface finish to the part. If you don’t think you understand how to do it post here or e-mail me and I’ll explain in more detail.
To get wax down in a thin bow put wax on a clean rag and use a wooden tongue depressor to work the rag+ wax into the bow; wipe it/polish it the same way.
Make sure there are a couple thicknesses of cloth between the wood and the mold surface at all times.
One more caution: if you’re using polyester resin with PVA be sure the humidity is LOW: polyester is hydroscopic meaning it will absorp moisture; this in turn can remove the pva and cause a disaster-very serious sticking…
Good Luck!

edt:add caution
Doug Lord
–High Technology Sailing/Racing

thanks doug
i keep the work shop pretty warm, and have a ventolator hook up so that the fumes dont spread., BUT I have never pulled a part before. we had a friend pull and make the hulls. but now I have to do it. i made the plugs. so now i have to make the molds. and the hulls. this is what he told me .first you wax the mold. then you use a brush. soft hair. and brush on the coat. the wax is the important part. there has to be atleast 3 coats to 7 coats before you apply your firbeglass
and yes i need help. i am asking for it
long live the cup

Cougar, Partall #2 wax should be applied in three to four coats each one buffed out before applying PVA according to their instructions for an INITIAL molding cycle. I don’t recommend using a brush for PVA- it can cause sticking but if your mind is made up just don’t press the brush hard against the mold but why not try pouring? Its simple, quicker than brushing and leaves a far better surface. If you pour you would want to make sure the mold is very clean -not the inside which already is but the outside as well.
You will want to have a basin about 18" by 18" by 4". You stand the mold up in the basin and pour the PVA-make sure you have at least a half gallon of PVA so you can pour quickly.When you actually start pouring have the mold right side up and angled so that you can get PVA on the transom or bow- whichever end is up- and then keep the mold mostly vertical as you finish pouring; you may have to go down each side to coat the whole mold. Once poured you stand the mold up mostly vertically but upside down on some rags or paper towels(or another small basin) as it will continue to drain. Make sure that the mold stays in this position until the PVA is dry!-one hour or so since the coating is fairly thick compared to spraying. DO NOT TURN THE MOLD END FOR END AT ANY TIME DURING OR AFTER POURING! Use a fine mesh strainer and pour the PVA collected in the basin back into the PVA container. The mesh filters out any dirt that may fall off the mold and just helps to insure the PVA you don’t use is not contaminated.
You could try pouring BEFORE you wax if you have enough PVA; you won’t lose much PVA and you’ll get an idea how to do it. You can wash off the mold after you do it and proceed any way you want to- or try it again before you wax-whatever. It’s pretty easy and you can’t lose out because even after you pour and after it dries if you look at the mold surface and you don’t like it you can wash it off ,re-wax and try again. But if you make one or two dry runs w/o wax you won’t spend much time and you should get the knack pretty easily…
A long time ago I tried pouring because spraying didn’t produce the excellent finish I wanted; it worked and I’ve used the technique for over 15 years succesfully.
The motivation for using the PVA initially was to be able to use paint in the mold(instead of nothing or gel coat); I had tried painting on High Temp wax and it didn’t work so I experimented with PVA…

edt: add mold pos. for drying.
Doug Lord
–High Technology Sailing/Racing