The problem is with the mould surface after demoulding from the master. Polishing the surface does not help to improve the parts of the surface that is affected. I have made moulds for 15 years now, and most of my moulds get affected by this problem. The first parts that comes out of new moulds gets the same surface imperfections and needs polishing. When the moulds get used and covered with wax the problem shows less on the parts... The imperfections on the mould surface shows up like a more dull, less shiny area. I have experienced the problem with the following gelcoat/wax combinations:
-SW18 and Norpol W70
-R&G P and TR wax
-F200 and PAT921
-F200 and HM racing Dolphine wax.
Backing epoxy have been L385/H386 or R&G epoxy L with hardener L.
Modus operandi:
All moulding operations are done in a composite lab at work that is temperature and humidity controlled.
Wax:
Before waxing the master gets cleaned with silicone remover or alcohol. (Only silicone free soap and water if it is a plexi-master)The master get waxed 5-8 times. Wax is applied and wiped with new piece of clean cotton cloth after a few minutes. The wax get polished later to shine. The waiting time in between wax layers are at least 6 hours. After last wax layer I wait at least 12 hours before moulding.
Gelcoat:
The gelcoat get mixed by hand in small 100g batches in a disposal cup with a stiring stick only rotated in one direction. After thorough mixing I pour the gelcoat from the cup over on a disposable paper plate without scraping the edges.
Before applying the gelcoat I check that the waxed surface is perfectly shiney and clean. The gelcoat gets applied with an R&G epoxy brush. I start at one end of the positive and only apply the gelcoat in one direction only. When applying the gelcoat I always start the brush stroke on top of already applied gelcoat to make an even coat. I let the gelcoat gel until not sticky to the touch anymore and always apply a second layer of gelcoat after this.
Backing layers
I use a very thin coat of epoxy mixed with cotton flocks, this is just to make sure that the edges don`t have bubbles. The layers are always two layers of 105g aero twill glass. Then I use a heavyer layer of glass and continue with multiaxial carbon and Poraver. The moulds get to harden for at least 15hours before adding backing layer on the Poraver.
After around 48 hours of hardening at around 25 degrees I put the moulds and master in the oven and ramp up 5C/hour up to around 45C and keep for at least 12 hours.
The moulds get demoulded after around a week of hardening. The surface get cleaned with soap and water or alcohol and if needed gets polished with 3M Perfect-it.
What am I doing wrong? I`m in the prosess of making new moulds and need to get to the bottom of this problem.
Currently I`m using SW18 and Norpol W70. The positives are made from plexiglass. Anyone had the same problem, and how did you solve it? Gideon, Arne, Sven care to comment?
