hey folks
this is a post for all the expert out ther to help with the new people and old. to show use how to make molds? make a cheap fibreglass hull
does this sound like a good idea?

Yes, please tell me how this process works.
At some time I would like to build my very own US1M.

Seawind #80

A simple way that produces intense gloss with no optical waves is to first decide if it is the hull and deck you’ll be making and what kind of flange you’ll use. Then plank the hull with 1/4" thick balsa strips-coat with resin(iso polyester); sand with 36 grit, fill with bondo and sand lightly again.Then glass with two layers of 6 oz cloth using isothalic laminating resin. If you don’t have a spray gun coat the plug with 10 coats of isothalic polyester gelcoat; filling with gel coat putty between coats(make putty out of aerosil or equivalent-do not use microballons). Put only two coats of gel on perday so the polester shrinkage does not warp the plug.When built up wash mold with acetone before adding blue dye. Use liberal amounts VERY CAREFULLY! Then coat the plug with blue dye and sand with 36 grit.Don’t leave any blue spots. Continue to go to 80,220,320 400 and 600 using the dye between each sanding. Then compound with fine and course compound.
This takes longer than some other methods but the point is to build enough thickness that when you sand you won’t go thru to the glass below. When you’re done the plug will have a bright gloss and be ready for wax. Doing it this way provides a hard consistent surface to sand and by using a six inch by 1.5" sanding board made of 1/8" balsa and sanding double diagonally you can produce a professional plug with virtually no waves or imperfections.
You can use other materials as long as the surface you’re sanding is not porous and is consistently the same material thruout the whole sanding process it should be a hard material like iso gel coat which has fewer voids and air bubbles when used in this application than does epoxy gelcoat.
edit-add info /fix spelling
Doug Lord
–High Technology Sailing/Racing

doug what type of mold release wax do you use? i am using part all. and brushing on pva. it is not that good . but so far i have made only one hull. and destroyed 4 plugs. so this might help some people . you need to use some type of barrier between the mold and the hull you are laying. i am going to try and use a tooling gell. for my mold. i hope that will work too… build up maybe 1/2 inch of firbeglass in the mold. then i can use the mold for other hulls. club memebers and freinds. simple a case of beer. and the cost of materials

Wax,let dry at least an hour,polish. Do this 7 or 8 times. Then use PVA.

Vancouver Island

Use a sponge or soft cloth for pva, almost as good as spraying it on minus the hassel.

Luff 'em & leave 'em.

i still get spot where the hull sticks. then sometime the glass will not leave the mold. out on the web people are playing around with rtv. i dont want to do this. just keep it simple. use fibreglass and maybe a differnt wax?

Cougar, what I described was how to make a PLUG which is identical in shape to the finished boat. IF you do it the way I suggested you will achieve professional results. After compounding you give it 5 coats of “Hi Temp” wax. After the last coat dries a couple of hours you can build the MOLD. I always build plugs out of polyester and MOLDS out of epoxy. Epoxy gel Coat(from Freeman supply) can be sprayed or CAREFULLY brushed on. NEVER let the brush touch the mold surface and NEVER touch it with your hand or finger! Apply the epoxy gel coat so that it is 20-30 mills thick. Allow it to dry to the point your finger does not pick up gel coat if you lightly touch it. Epoxy gelcoat has a laminating “window”; don’t screw up here(follow the manufactures recommendation exactly). DO NOT USE POLYESTER GEL COAT if you’re mold is to be epoxy-it will work technically but the shrinkage will distort the mold finish.Epoxy gelcoat allows parts to be made with tighter radiuses and sharper corners than does polyester.
When the gel coat is ready to lay up add 9 layers(Fiberglass Supply 4/1 epoxy laminating resin) of 6 oz cloth at the same time-keep room temperature 68?. You can lay this up all at once because with 9 layers the heat build up is minimal and there is no shrinkage. Allow the ninth layer to start getting tacky and then add “core putty” (Freeman supply) this allows you to build up a 3/8" to 1/2" core easily and cost effectively stiffen the mold. As soon as you’ve added the mold putty you can add an additional 9 layers or two layers of 6 oz. cloth plus 2 layers of 18oz. woven roving.
When that tacks off (staying within the window) you can glue on legs for the mold. Allow to sit 48 hrs-to 72 hours then you can pull the mold off the plug and you’re ready to layup a hull.
There are some an advantages to using PVA in laying up hulls: 1) no wax transfers to the part so it can be painted immediately,2) You can use some paints like big boat builders use gelcoat and spray in the mold then layup and when you pull the hull it is painted .PVA isolates the paint from wax preventing fish eyes; an extremely LIGHT way to achieve an excellent finish.Krylon and Imron work for this but only with PVA. Pva for model mold applications works best when POURED not sprayed or applied by other means. You have to set up a recovery basin and a way to hold the mold(vertical but so no puddles collect)-and the mold must be VERY CLEAN. If using PVA you SHOULD use Part All #2 paste wax-not Hi Temp or any other wax. Failure to use this wax can be disastrous. PVA is water soluble so if you’re laying up a polyester part(you cannot use the above paints with polyester!!!) on a high humidity day you better be sure that the wax is under the PVA because polyester absorbs moisture and can remove PVA.Better to build parts with epoxy anyway…

Doug Lord
–High Technology Sailing/Racing

The instructions for the PVA I’ve been using say to spray it on, its also an alcohol based solution rather than water based. Only once had somthing stick and that was because I was in a hurry and only used 2 layers of wax under the PVA. BTW most of the products I have access to are made/supplied by SP, more than likely a bit different to what you guys use on the other side of the pond…

Luff 'em & leave 'em.

PVA is polyvinyl alcohol and is water soluble making it easy t remove from a part. You’re exactly right about the instructions ,Matt , however I found by experimenting that you can get consistently excellent surface finish results by pouring it rather than spraying(models and small parts only). One of the biggest compaints I’ve ever heard about PVA is the difficulty in spraying it so that the finish is mirror perfect-may be Fl. humidity. But in models and small parts if your work area is really clean pouring can give as good a finish as the best wax(like Hi Temp). Just be sure to use Partall #2 under it because other waxes may contain traces of silicones and cause fish eyes in the partall and come thru in the subsequent finish.

Doug Lord
–High Technology Sailing/Racing

For the cheap and less chemically adept out there… a guy in our club showed up last month with a beautiful home built US1M. He made a standard balsa over shadows plug, built a box around it and then made a female mold by pouring on plaster of paris. He says it took about $14 of plaster, but he ended up with a very servicable mold (and, one that can be repaired or modified using spackling or other plaster-like compounds). He used it to pull a fiberglass hull that came out quite nice. Just thought I’d throw that in for any other shoestring budget modellers out there.

I have always built a female plug first. These plugs are always solid and made out of pine or partical board or something similar. Fairing, building this way can take sometime but the finished job is worth it. I find that if you use full length boards that are "fixed together with 19mm dowels it’s quite easily done.(the reason for this i will explain later).
After you have the shape you want spray sand, spray sand,spray sand with gelcoat and 120-240 wet and dry paper. This will eventually give a smooth clean finish.
Remember the dowels mentioned earlier? the idea for this is so that the “deck board” can be removed from the dowel and a piece of ply cut larger than the hull (previously gelcoated etc) can be placed over the dowels. Return the deck board and you have a complete hull and deck mould with flange.

I use a two part liquid wax. Applying with a cheesecloth, use part A in a circular motion. As the moulds are quite small, and the weather is not to hot apply in this fashion to the entire mould surface. Wipe this off lightly with another clean cloth. Repeat this step 3-4 times allowing 15-20 minutes between coats.

Now apply part B with clean cloths in the same manner. Wipe on wipe off. Repeat this 4-5 times allowing 15-20 minutes between coats. Allow the mould to sit for 24 hours.

The lay up for the male mould should be minimum 5 times thicker than the hull being built in it. i.e if you are planning to use 1oz cloth to build the hull, use 5 layers of 1oz cloth on the mould. This lay up should be done in one session. Do the bottom section of the hull first up to and including the flange. Glass on at this point the previously made to fit wooden stands. Leave this to dry for 24 hours. Repeat on the deck side including wooden stands, and leave now for 72 hours minimum. Remove the moulds from the plug and repeat the part A part B waxing on the inside of the two moulds. (provided that there are no points that stuck and need repairing first)

Building plugs and moulds in this fashion don’t need painting and if done properly will allow several boats to be built in them.

Hope this helps.

has anybody tried using pam cooking spray . as a mold release agent? i was just on a web site and this guy used pam? i want to used the pva. but i dont have a spray gun. i have been brushing it on… could i used a cheap air brush?

If you’re making a part out of a mold pouring the PVA is an excellent solution and produces BETTER results than spraying.Be sure to use Partall #2 under the PVA.

Doug Lord
–High Technology Sailing/Racing

Just a thought
PVA is generally only used the first few times a mould is used to produce a part. When a mould is used for the first time, heat generated by the curing gelcoat melts the wax at a microscopic level causing some patches to stick where the wax is a bit thin. The PVA provides a barrier to prevent mould and part becoming one! With repeated use and waxing however the mould itself becomes a “non-stick” surface and there is no need for PVA. The amount of times it takes to achieve this depends on the thoroughness of the waxing but ultimately there should be no need for any PVA.
Just my two cents…

Tranth is right regarding a mold that will have gel coat sprayed into it asthe first step in layup.But in building model hulls Paint-such as imron or even Krylon can be used in place of gel coat but only if you use PVA or a 100% silicone free wax. A further advantage of PVA -poured on- is that it leaves no wax residue on the part so regardless whether you use paint or not the PVA applied as discussed previously has significant advantages.

Doug Lord
–High Technology Sailing/Racing

I agree that PVA can make life a bit easier, but the quality of the product from a mould which is PVA coated (especially “poured” and not sprayed on) wont be as good as one from a mould which used no PVA


In an extremely clean environment if the PVA is poured then dried with the mold just slightly off vertical and upside down the finish quality can be indistinguishable from an excellent wax finish. But pouring can’t be done on all molds and the correct technique has to be learned. On full size parts and boats for a professional finish wax is the best. But on models PVA has a number of benefits if poured ,not sprayed, but the technique must be correct and the environment very clean.

Doug Lord
–High Technology Sailing/Racing

Checked with a number of r/c boat builders, they are in agreement with Troy. They all use wax, not pva. Particularly, the “poured” pva method appears unique to Doug Lord. Are there any others out there who have successfully used this technique?

When you pour the PVA and it dries doesn’t it have a matte finish? If you look at polished mould it should be high gloss which should result in better final quality.