I am restoring a 1969 Columbia C-22, hull #923. In order to make a forward hatch cover I built a mold to lay up the fiberglass in. I built it out of pine 2x4s, filled the corners with plaster, filled the low spots with soft body filler, painted it black, gave it about 10 coats of wax, applied one coats of mold release, waxed it again, and finally added 2 more coats of mold release. Some areas released very well, others didn’t separate at all. Some areas pulled the paint off and other areas pulled the plaster and filler right out of the mold. I am happy with the hatch cover since it can be cleaned up, but the mold is shot. What did I do wrong? Gerald
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Did you get it very smooth? Did you over-work the
first layer of resin/glass and disturb the release coat? Did you chant the proper incantation? Since this was a one time use mold does it matter except for next time when perhaps you want to makeseveral pieces? Look at the places where it stuck. From the look of your picture it stuck all over. Would it have released better if the mold sides could have been removed separately? Seemed like very straight sides. A little more taper may have helped. Did you plan an unmolding proceedure when you made the mold? There are so many ways to get it wrong and so few clues when you get it right. I think that the plaster may not be strong enough. The molds that I have seen for production work are made of fiberglass on a model of the part to be produced. The model is made with great care and polished to provide the mold with a nearly perfect finish. I have made some quick and dirty molds for one shot pieces and then repaired the defects in the final part.
first layer of resin/glass and disturb the release coat? Did you chant the proper incantation? Since this was a one time use mold does it matter except for next time when perhaps you want to makeseveral pieces? Look at the places where it stuck. From the look of your picture it stuck all over. Would it have released better if the mold sides could have been removed separately? Seemed like very straight sides. A little more taper may have helped. Did you plan an unmolding proceedure when you made the mold? There are so many ways to get it wrong and so few clues when you get it right. I think that the plaster may not be strong enough. The molds that I have seen for production work are made of fiberglass on a model of the part to be produced. The model is made with great care and polished to provide the mold with a nearly perfect finish. I have made some quick and dirty molds for one shot pieces and then repaired the defects in the final part.
You did the what?
I've never heard of laying "paint" inside a mold, much less of using both mold release AND wax. Now you've got three materials, three solvents, and who knows what interactions among them--to create a mess and fight each other. I'm not suprised things stuck. You'd normally build the mold, then use *either* mold release *or* wax, in multiple coats. Lay up your fiberglass and then after you remove it--clean the fiberglass and paint it. Some of the resins give off a waxy coating (amine blush) as they cure, and that would literally push any paint off the fiberglass! It has to be solvent cleaned before painting. In professional boatbuilding, they lay up colored gel coat in the mold before laying up the FRP. But paint and gel coat are two very different creatures.
I've never heard of laying "paint" inside a mold, much less of using both mold release AND wax. Now you've got three materials, three solvents, and who knows what interactions among them--to create a mess and fight each other. I'm not suprised things stuck. You'd normally build the mold, then use *either* mold release *or* wax, in multiple coats. Lay up your fiberglass and then after you remove it--clean the fiberglass and paint it. Some of the resins give off a waxy coating (amine blush) as they cure, and that would literally push any paint off the fiberglass! It has to be solvent cleaned before painting. In professional boatbuilding, they lay up colored gel coat in the mold before laying up the FRP. But paint and gel coat are two very different creatures.
wax only
Yes, I agree, there must have been a chemical rxn. that made it go awry. Mold release is generally used over gelcoat to make it cure completely. Many coats of wax only should have worked fine. It's like mixing prescription meds, you never know what's gonna happen when interactions occur.
Yes, I agree, there must have been a chemical rxn. that made it go awry. Mold release is generally used over gelcoat to make it cure completely. Many coats of wax only should have worked fine. It's like mixing prescription meds, you never know what's gonna happen when interactions occur.
Thanks for the comments
I did get the surface very smooth, much better than my car finish. It released in most of the flat areas in the middle. The sides all had a few degrees of angle to match the opening on the boat. I think more angel would have helped, but I had no problem pushing wooden wedges in the sides to break the part from the mold. The sides and corners were stuck the worst. The plaster seems to have been the weakest link. I have read since that if you use plaster, it should be baked in an oven to harden. The part is cleaning up very well and all the junk is separating where it should have. I agree, I should have used gel-coat on the mold. It would have been much stronger than plaster and paint. I also think there was some chemical reactions with the paint, wax, and release. I had found on a web site from a major fiberglass supplier about using both wax and release film. At this point I have no faith in the release product I used anyway. I think I may just use wax on the next project. I don't care too much that the mold is trash, but I was thinking of making some more hatches for other C-22 owners. I mainly want to learn the correct process for future projects. I am planning on making a main hatch cover also. Thanks to all of you for your comments and suggestions, they were very helpful. Gerald
I did get the surface very smooth, much better than my car finish. It released in most of the flat areas in the middle. The sides all had a few degrees of angle to match the opening on the boat. I think more angel would have helped, but I had no problem pushing wooden wedges in the sides to break the part from the mold. The sides and corners were stuck the worst. The plaster seems to have been the weakest link. I have read since that if you use plaster, it should be baked in an oven to harden. The part is cleaning up very well and all the junk is separating where it should have. I agree, I should have used gel-coat on the mold. It would have been much stronger than plaster and paint. I also think there was some chemical reactions with the paint, wax, and release. I had found on a web site from a major fiberglass supplier about using both wax and release film. At this point I have no faith in the release product I used anyway. I think I may just use wax on the next project. I don't care too much that the mold is trash, but I was thinking of making some more hatches for other C-22 owners. I mainly want to learn the correct process for future projects. I am planning on making a main hatch cover also. Thanks to all of you for your comments and suggestions, they were very helpful. Gerald
Gerald, If you are very pleased with the
finished product you can wax that and use it as a plug to make a new mold, avoiding the mistakes made on the first. It is all a part of the learning curve. There is a very good text called "One Off In Fiberglass" by Allen Vaitses. I recommend it to anyone who would work with glass and resin.
finished product you can wax that and use it as a plug to make a new mold, avoiding the mistakes made on the first. It is all a part of the learning curve. There is a very good text called "One Off In Fiberglass" by Allen Vaitses. I recommend it to anyone who would work with glass and resin.
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