Take a look at this picture.  Does this look familiar?  Are you getting large open gaps on the surface of your part?  If so, read on to learn what is causing them and how to easily avoid them in the future. 

This is a very cool RC car body one of our customers made.  As you can see the surface looks terrible due to the large gaps.  Bubbles are a common problem for carbon fiber makers but the most troublesome bubbles are the small 1-2mm sized.  These large gaps are not really bubbles but just gaps in the resin but these huge gaps are easier to fix. 

The problem revolves around the mold wax and PVA that is applied to the mold.  This stuff does a great job at keeping the resin from sticking to the mold but it also keeps the wet resin from flowing over the surface of the mold.  Think about water that is spilled on a concrete floor.  The water stays where it’s spilled and gets soaked into the concrete.  If you were to use a brush or broom to push the water around on the concrete you could get the water to spread very evenly all over the floor.  

Now think about water spilled on a non-absorptive surface like a kitchen counter top.  The water forms into ‘globs’ because of surface tension and because the counter top doesn't absorb the water.  If you tried to smooth the water over the counter it would just form into more 'globs' of water and would never evenly distribute.  This is what can happen to your part.  The first coat of resin in the mold is repelled by the wax and PVA and forms globs.  Just like a counter top, some of the surfaces of your mold can remain completely dry.  

The fix is easy.  Just brush on the first layer of resin in a well lit area and keep an eagle eye on the mold surface.  Continue to move the resin around and make sure that the entire mold surface is wetted.  This might take some time as well so you must be patient.  You may have to continue to brush until the resin starts to setup enough so that it cannot snap back, or do a second coat so long as the first coat has not gotten tacky yet.  The process would be you brushing the first layer on, watching it, and then every now and then touching up the dry areas until the resin no longer snaps back.  You can try the heat gun too if you want but to address these gaps, it’s really not necessary.