Building a mold

In the compsand building I've done, I've been frustrated with creating the rails over and over exactly the same. Also, in the composite construction, I have wanted to include a concave in the bottom. So I am going to build a mold of the bottom of a "magic board" so that I can reproduce the bottom contour and lower part of the rails.

It's Play Dough! Modeling clay:

The first step is to build a dam around the perimeter of the board at the high spot on the rails. Hopefully I can accomplish this in two days. It will need some touch up, so maybe a total of three days layout.

Is there anything you won't try?

cool jeff- but you should inlay some of the santa fabric into the next design!

Hey Ed,

No...I am not risk averse...I tend to be of the "bring the failures on FAST so that I can learn" genre. I'm a little concerned about the part line in this mold...in looking at an Inland Surfer, I DROOL over the incredible finish those boards have out of the mold. I want a different rail though. Most of the boards that I know are molded, I THINK have a part line on the bottom of the board. Maybe I'll just end up with a decent BOTTOM

Hey Matt - that table cover is funny isn't it? The kitchen table is this gorgeous butcher block wood. Judy won't let me within 10 feet of it unless it's covered up. I CA glued some balsa to that covering So that is now my "work bench" cover. Judy is so good to me

The resin dam applied. The board is acting as a "plug". The mold will be made over the plug. The first part of the mold will be two layers of gel coat. To keep that from sticking to the plug we cover the plug with wax. To insure that we have a good sepration I will apply 4 layers of wax, buffing after each application.

The dam applied:

I use a product from Fiberglass Supply. It's a mold sealer/wax suitable for porous surfaces. This plug has never had anything applied so I want a good waxy surface.

First layer:

Layer two!

You'll want to buff before the was is truly setup, still soft. Also, make sure the clay has a good covering of wax and that you are careful polishing it, so that you don't disturb the dam.

The last two things that I did that I didn't civer. The fin boxes are taped over and waxed. Also, I moved the partline to the bottom of the board and will pursue a three part mold.

In typical Fiberglass mold making, after the wax is applied three misting coats of PVA are sprayed over the wax. I don't have the ability to spray the PVA and brushing it on can leave an unequal mold surface. In lieu of the PVA, I have found that unscented old fashioned hairspray is similar in chemical makeup and comes with a built in sprayer The only disadvantage is that PVA is green so it's easy to see when you have good coverage - not the case with hairspray.

Gelcoat is polyester which requires a catalyst to kick. I mixed the gelcoat a little hot to make up for the cooler temperatures.

We'll want to apply at least 2 layers of gelcoat to get a good surface. The gelcoat will be the mold surface that I'll apply epoxy and glass in. My expectation is that I'll have some slight imperfetions, and the extra thickness of gelcoat will allow me to sand and smooth those imperfections out.

I used a standard gelcoat as opposed to a tooling gelcoat. Typically in a mold the gelcoat will be black so that when you apply wax or spray on a coat of paint, you can see the coverage easily against the black. Tooling gelcoat is mostly orange and is a slight different makeup to allowing the mold to be used repaetedly. I don't have that expectation of usage, so I just bought the cheapest gelcoat that I could find.

The first coat of gelcoat will invariably leave some thin spots. We'll want to make sure that the second coat covers those.

It's hard to see but in this picture the dark spot is the shadow being thrown from the low spot in the gelcoat.

As I mix the second batch of gelcoat I sight verify those low spots and use the mixing stick to apply a generous amount of gelcoat. Then after all of them are filled, I pour the rest of the batch in a circular pattern across the surface and spread it as evenly as possible with a bristle brush.

Second coat spread.

Gelcoat doesn't surface cure so it does NOT require any sanding in between coats. One of the joys of polyester is that this coat will be cured by the time I finish breakfast

The next stage of the mold making process will be to add some structural integrity. I will layup several layers of chop strand mat (CSM). It is a non-woven fiberglass that conforms to the shape easily and adds strength. I will cut that to shape, then roll on and squeege polyester laminating resin to bond the CSM to the gelcoat. I am planning on only a few layers. Then I will bond a layer of bulkier, in my case 4 mm coremat. The coremat contains microballons that will fill up a considerable amount of space, without the added weight of 10 layers of CSM and resin. I will also, vacuum this to a wood form that will hold the rocker in place as the resin cures. It will also add rigidity after the mold has cured for a few days. The wood form will become a permanent part of the mold. You can NEVER get a mold TOO stiff.

As I mentioned above, CSM is non-woven. This is 1.5 oz CSM. It takes considerable amount of resin to wet it out. I used 21 oz to wet it out fully. One thing you DON'T want to do with Polyester is run out of resin, so go heavy rather than light when mixing up a batch. With epoxy, it doesn't matter...if you run short, just mix up some more...with polyester, one it starts to gel you can't easily add more.

The mold is just a tool, so I don't need water white ultra filtered resin for the construction. The cheapest polyester laminating resin is more than adequate.

Polyester resin is SERIOUSLY toxic. Organic respirator type masks are a MUST HAVE.

Tools of the trade. Green spreader and a roller. The roller is a permanent tool, we'll clean it in acetone after use. The spreader...I typically toss them away, but they can be cleaned up and used for quite some time.

Ever seen the back side of a fiberglass shower stall? The CSM wetted out and laminated to the gel coat. The process is fairly easy. Pout the resin out on to the mat which is laid out on the plug. Reserve about 1/4 to followup on dr spots. Next use the spreader to move the resin around quickly and get it spread evenly. Then use the roller to work the resin into the CSM and spread it out to the edges.

The first layer wetted out.

Plug out of the mold. The clay needs to be cleaned off the surface of the mold, then I'll trim and clean up the edges, finally laminate some wood structure to the bottom.

Jeff, I'm trying to picture the look on the cahier’s face when you showed up with a can of hair spray

Keep the posts coming

I don't understand. Why would you say that Ed?

I think the above picture needs to be your profile picture.

Such a great idea!!!!!!!! Done!

I don't know who that masked man is supposed to be. This is the Jeff Walker that I know.

The next shot needs him covered in foam dust holding a planer or something. He also needs the obligatory flip flops all the while standing in his shaping room with pictures of hot girls on the walls and templates in the background.