Wooden Mold Prep for Release

General Composites Discussions Composites Talk
#1

Hi Guys,

I’m doing a little bit of research on preparing four wooden molds (square shaped upside down bowl approx 10" (254mm) on all sides at the bottom - smaller on top)

The molds will be used only once for an epoxy based vacuum bagging operation.

I was planning on:
Sanding/Priming/Sanding/Painting/Sanding/Painting/Sanding
Then follow up with Frekote B15 Primer/Final Sanding and then four coats of 700 or 770 NC release.

For the initial paint layers, I am planning on using some “engine” spray paint that can be picked up locally which is OK up to 500F.

Any ideas if this plan will work? Should I look at some other type paint? I called Frekote and they are still talking to the engineers, so I’ll call them back later this week if I don’t hear from them first.

Thanks in advance,
Dallas

#2

Don’t forget polishing after color sanding.

Are you planning on using an envelope vac bag or are you building flanges on the molds?

#3

Flanges on the mold, yes.
When you say “polishing after the color sanding”, what exactly do you mean?

Some sort of buffing compound I assume? If so, what do you recommend?
(Tools and Products)

Thanks!
:slight_smile:

#4

What kind of timber are you coating you will need to make sure it is stable and I would recommend taking up your wood mould up to what ever temperature you intend to cure your epoxy at prior to coating it all up. Also I would think about elevated curing of your paint to ensure it as fully cured after its all painted up prior to applying your release. When I do use high build paint for plugs I have clear coated them then polished and waxed.

Duratec is the product normally used for this purpose. It is quick tried and tested method. Again as with the paint make sure it is properly cured prior to doing any layups or you risk it sticking up.

#5

I should have mentioned that I’ll be using 3/4" MDF for the form. The spray paint I am looking at recommends a 200F cure temperature, so that won’t be a problem with cure temperatures. The Duratec product you mention looks to be what I really need, but a gallon size is way too much. Maybe I’ll be able to find someone local that can sell a pint or so when the time comes. Thanks for the replies, I do appreciate it!

Dallas

#6

This product http://www.tools4grp.com/Catalog/Product/493 comes in smaller amounts and works well on mdf for final finishing flat pannels it does not have any high build properties but I have used a automotive highbuild then once finished down to a 320grit finish have shot it over with this and have had no problems with release I think its quiet a good product and you are right about the Duratec its a real pain when you only need a small amount. If you cant find these two products go for a automotive clear coat overa automotive highbuild primer they will be much easier for you to to get hold of in small amounts . Make sure you do a small test panel to make sure you can get a good release with your epoxy.

http://www.tools4grp.com/Catalog/Product/493

#7

Hi Dallas

Once you have your plug (smooth) , easier if MDF has been resin soaked and wet sanded.
I’d just v-bag some of this over it. Lay up your part and v-bag again. Very simple quick way , and the result is shinny plastic Finnish :slight_smile:

Tim

Check out this video on YouTube:

[ame=“http://www.youtube.com/watch?v=EIJS8PSxqJU&feature=youtube_gdata_player”]Stretchlon 200 - YouTube[/ame]

#8

What temperature do you plan on (post)curing? MDF isn’t the most stable material. When built from several pieces it will crack too.
I usually coat with epoxy one or 2 times,sand, coat with a high build coating,sand, and apply a 2K pu paint,(polish).

But those moulds are production quality to use 5-15 times. For 1 time use, bagging some high stretch film around the mould is much easier.

#9

Awesome! YOU GUYS ROCK!! :smiley:

#10

Depending on the needs for finish quality of the inside (part touching the plug) you can sand then cover with packing tape and wax. If you take your time with the tape you can get pretty good results. Saves a ton of time over paint/sand cycles. Also the Duratec products are great but only come in a gallon which is fairly pricey and have a short shelf life.

#11

I’ve used MDF just blank with wax as a mould, but that surface does need some work. On the surface which is quite smooth you can polish the wax out, and on the edges ou can just apply it without rubbing it out, but apply generously. It has a slightly better surface than with tape, as you don’t have any ridges. For a simple box it works great, srew some MFD togheter, apply some wax, round the corners with clay, and there’s you mould. But for more complex shapes pulling a vacbag over it is easier.

#12

The brown packing tape and wax mentioned works well, you will need to do a bit of sanding after de-moulding to remove the tapelines that’s all.

You could also use a release tape product designed for composites know as flash tape it comes in various widths I use this a lot for making small one off parts. Its readily available across the US

Google “flash tape composites”

#13

Flash tape is a much nicer product to use but quite a bit more expensive then packing tape. That said it has a number of nice qualities, among them; it is quite a bit stronger than packing tape making removal easier and it has a high temperature adhesive that can withstand oven temps and vacuum cycles. HBM Supply is a great source for it in the states though they don’t have it listed as such. You’ll need to ask for 0.001" or 0.002" Mylar tape with high temperature adhesive. It’s considerably cheaper than Airtech.