Some time has passed but here is the update.
I have made the mold boards out of laminated hardboard; I have reinforced it by means of a longitudinal piece of the same hardboard.
Moldboard with contours in pencil
The masters were prepared, polishing with automotive polish several times until one could use them as an mirror. Next I have applied the release wax, 5 coats in total, polishing the masters between the coats. Finally I have applied the release liquid with a soft cloth. The masters were ready to receive the gel coat.
The master were presented to the mold board and the contours were copied to the mold board by pencil. I was pondering about how to attach the master to the board. In first wanted the use screws but let the idea go. Finally I have opted to use some special modeling clay, when it is heated (microwave) the stuff becomes really soft almost in a liquid state. My intention was to heat the modeling clay, make a string, apply the string on the molding board following the contours in pencil, then to press the masters onto the molding board squeezing the modeling clay. I had to make another approach because the moment the modeling clay made contact with de cold board the clay hardened and could not be squeezed anymore. So finally I made thin strings of modeling clay, laid it on the molding board on the contours and heated the stuff up with a paint stripper until it became really soft then pressed the master on the molding boards. The modeling clay squeezed out nicely and the after it was cured the masters were perfectly attached to the board. The excess of the clay was cut away leaving an nice seem between the board and the masters.
Seem between master and board
To make the molds I have purchased two 2 m² of 150gr glassfibre cloth, 1 kg of gel coat, 2kg of polyester resin, release wax and release liquid.
I had also purchased an good quality half face reusable respirator with adequate filter elements to protect myself against the nice vapor of the polyester resins.
Now everything was ready to apply the gel coat…..it was really strange to cover the nice and shiny master with the gel coat logically one expect this will turn out really bad
I laid down two coats of gel coat with the necessary curing time in-between, then applied the polyester resin with the cloth. After the last coat was applied on the 2nd master I started to clean up everything. It has been a long day, started at 8h00 and finished at 22h00. When I picked up the measurement can for the hardener my hart jumped over a few times I noted the hardener of the last coat was still in the can…..After some nice vocabulary that lasted several minutes I took the decision to apply pure hardener with a brush on the last coat of resin and hoped for the best.
The next day (very early in the morning) I rushed to the garage to see if my attempt to rectify my stupid mistake worked. I was surprised to see that it had worked quite well, only some miner spots on the 2nd master mold were not cured.
Gel coat applied
I left the everything cure further fore Five days, then I tried to extract the masters out of the molds. At first I thought that everything was clued to each other I could not remove the masters, but with some gently applied force (read: red face, pumping veins) I managed to removed them. I was a little disappointed to see that pieces of the master remained in the mold, what went wrong?
I place the whole in my boot and drove to the Polyester store for advice. First of all he told me that for a first mold it was a very good result, I told him I did everything by the book. He suspected that de automotive paint did not cope with the resin of the polyester as it is an one component paint.
After the molds were cleaned and the pieces of the master removed (gently sanded), I was pleased with the result. But the clueing of the master to the mold kept crossing my mind. The paint is protected by the wax and I had applied 5 layers? I applied a layer of wax on a undamaged part of the master and polished it as I did before. I inspected the surface of the master and found it was shining but could not find any trace of the wax, I had polished so hard that I had removed the wax! Now I had found what I have done wrong. This lesson I will remember when waxing the molds.
What I also noted on my molds is traces (brush marks) of the release liquid, even though I used a cloth to apply the liquid. So for making the actual hulls I will spray the release liquid to the molds. But I did not have an air compressor (it was still on my which list).
Damage to the masters
Molds after cleaning
As my workshop is in the basement of the house an regular compressor was not an option due to the noise it would create keeping the children awake. I now have an silent air compressor that has also the possibility to hook up a vacuum pot.
I’m waiting for the paintbrush I ordered through the internet and then I will start to make the actual hulls. Meanwhile I can make the vacuum pot to place on top the compressor and connect it to one of the two available suction lines of the compressor.
That’s it for now…… see you next update.
Practical wisdom is only to be learned in the school of experience.