Avoiding Mask Blow Outs 

Compiled by: Sally Elliot

Revised: August 03, 2005

This article has been compiled from responses to a related question on the sandcarving Forum.  Contributors to these responses are: Christopher, Rob, Rick Wilton, Phyllis and Peter Sitell.

Mask blow outs are a common problem amongst newcomers to the sandcarving industry.  It’s going to happen sometime and you’re always going to wonder why and what you can do to prevent this from happening.  Below are some tips to follow which will hopefully keep those blow outs under control.

1. Spraying technique is of the utmost importance. A good test or drill is to take a clear piece of 6" X 8" (or so) scrap glass and do an opaque or (frost) blast on it. When you think you are done, clean and dry the piece and hold it up to a light. If you see light and dark spots and what appear to be lines then you are not being consistent with your spray strokes. You need to practice some more.  Straight, smooth, even strokes, will give you a much better blast and help prevent blow outs.

2. Make sure that your sand to air ratio is not too lean. Too much air in the mixture, even at only 15psi, will lift the resist. You might consider using a little more abrasive in the mixture. 

3. Clean glass is very important. Everyone has a different method for cleaning their glass but whatever you find is best for you make sure you don’t miss this step. A good test is to clean pieces of glass using different methods. Take a common grease pencil and draw a line on the clean glass. If the grease pencil skips or is smooth in some areas
   you will most likely have a blow out (the glass is not clean).

4. A roller is an important burnishing tool and a good investment.  If you are using a squeegee this will only work while the cover sheet is in place. When you remove the cover sheet, there is lift on the little pieces, your finger has oil on it, things stick to it, you press down fine but as you lift, so does the center of a letter

5.  Make sure you are blasting at a 90 degree angle to the glass.  A good way to do this, especially when working with fine letters on small curved pieces, is to hold the nozzle still and turn the glass slowly with the other hand. This will insure that you are blasting straight against the glass and not at an angle. 

6. It is best to start your blast further away from the glass and slowly sweep in to the area you wish to blast.  Remember that the longer the session, the closer you will get to the glass. However good you are, moving closer and closer to the glass tends to be a reflex action. The best thing to do on small letters is to blast away the membrane from about 10 inches and when it's gone you can move in a little closer. 

7. Overwashing film can cause loss of adhesion strength.  Try washing the film for a lesser amount of time and see if you notice that it is stickier when you do so. 

8. Warming glass with a heat lamp can increase adhesion, especially if it is cold, or even if you are not quite sure if you have and adhesion problem.  An infrared heat lamp bulb is an inexpensive (hardware store) and worthwhile addition to the sandcarver’s toolbox.

9. Preparing the glass with glue, before putting the stencil on, can be especially helpful to those who want to blast at different angles for special effects.  Peter recommends using Sandblast Filler #2 manufactured by 3M and using Anchor Stencil #128.

 

If you have a tip for preventing blow outs that could be added to this article, please e-mail selliot@infozoid.com