Avoiding Mask Blow Outs
Compiled by: Sally Elliot
Revised: August 03, 2005
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.
blow outs are a common problem amongst newcomers to the sandcarving
industry. Itís going to happen sometime and youíre 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.
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
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.
Make sure that your sand to air ratio is not too lean.
much air in the mixture, even at only 15psi, will lift the resist. You
might consider using a little more abrasive in the mixture.
glass is very important.
Everyone has a different method for cleaning their glass but whatever you
find is best for you make sure you donít 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
will most likely have a blow out (the glass is not clean).
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
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
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.
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.
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 sandcarverís toolbox.
Preparing the glass
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.
have a tip for preventing blow outs that could be added to this article,