Vacuum bagging tutorial

Since we are spending most of our boat building time on laminating panels on the vacuum table now, I though it would be useful to describe my process.  This is basically the same process described by other, more professional types of experts.  Note that in this example I am just laminating one side of the panels at a time so I don't have to punch a million tiny holes in these foam sheets.  Laminating both sides simultaneously is quicker (by almost exactly a factor of two), and can use less material.  If I were to do this again, I would buy some perforated foam core to make panels.  Nonetheless, the end product is just as good in either case, and plain foam core is a bit cheaper.  So here we go (take notes as there will be a test at the end!):

1)  Start by preparing all of your materials.  You will need:
- The foam core cut to the desired size and shape, and pre-sanded to remove any residue that would inhibit bonding with the epoxy,
- The glass fabric cut a couple inches oversized,
-  Peel-ply cut a little bigger still,
-  Perforated release film so it doesn't stick to the bag, and
-  Breather fabric cut large so the air can get out.
I also have a rectangle of sealing tape laid out on my table top with the vacuum bag sealed along the back edge.  I also have the vacuum feedthrough installed in my vacuum bag and the pump ready to go.  Note the vacuum bag is really just the top layer that seals to the table top.  The table top forms the bottom half of the "bag."  On my roll cart I have my epoxy (paint) tray and roller set up and waiting.  The more you can do before you mix epoxy, the better.

2) Now that we are ready to laminate, let's mix some epoxy!  I use pre-marked mixing cups to make measuring easy.  These cups from Noah's have marks for various mixing ratios and quantities.  I use an electric drill with a paint mixer attachment to mix the resin and hardener.  I have found I need about 45-mL of mixed epoxy for every square foot of laminating.  Regardless of quantity, I always mix for 2-minutes.  I adjust speed of the drill to compensate for quantity, and try to avoid sucking air into the mix.

Here is a tip I came up with for joining pieces of foam core into a single panel.  I just staple the pieces together on the face NOT being laminated.  This hold the seam together until the first side is laminated.  When I flip the panel, I remove the staples and epoxy fills the holes during the second lamination.  In this case, the panel needs to be about 47-inches long, but the  sheet of foam was only 46" wide.  So I just used a piece of scrap foam to cut a 1-inch strip and joined it to the larger panel.  Once laminated, it is as strong or stronger than a single piece of foam core.




 3)  Now it is time to wet the foam core with a good coating of epoxy.  You could skip this and do a "dry lay up," but I think it is good to work some epoxy into the foam texture before laying on the glass fabric.  Although air entrapment should not be an issue on a vacuum lamination, I figure the less air the pump has to suck out, the less likely there will be an unexpected issue.

4) Once the foam is wet, I carefully lay the glass fabric on the foam, ensuring there is glass over all of the edges.  I then stroke the fabric along the direction of the fibers to get rid of any wrinkles.  Be careful here or you can make it worse.

 5) Now you can roll on more epoxy to saturate the glass.  I find it works best to roll on one stripe of epoxy at a time.  Then move to the next stripe while the previous one soaked in to the glass.  You know it is working because the glass disappears.  In this photo you can see how the glass becomes transparent when saturated (right half).  You don't need to over-saturate the glass, just enough to make it transparent with no white strands remaining.

6) As soon as the glass is saturated with epoxy, lay the peel-ply on top.  Try to lay it out carefully with no wrinkles.  Once it starts to absorb the epoxy It will become more difficult to adjust.  If you move it around too much it will start to drag the glass which can make a mess.  In general, less handling is better with all steps of the lay up.  The peel-ply serves a couple purposes.  First, it absorbed excess epoxy, which result in a lighter, stronger part.  Second, once peeled off, it creates a surface that is ideal for bonding to epoxy during later assembly.  Third, it creates a very smooth and uniform surface.

7) Now roll over the peel-ply to set it into the wet epoxy.  I start by making a cross through the center of the panel.  Roll slowly so the peel-ply sticks to the panel and not your roller.  Don't add any extra epoxy, rather let the peel-ply soak up the excess epoxy from the glass.  This step is another that is not really necessary, but I think it helps avoid problems later.  I think this step helps ensure the peel-ply doesn't get creased when pressed under vacuum.

8) Now you can lay the perforated release film on top of the peel-ply.  This film prevents the breather fabric from sticking to the part being laminated.  The film has small holes punched through to allow air and excess epoxy to escape.

9)  Next on the stack is the breather fabric.  There are various types, but I like the high-loft type that feels like a fluffy blanket.  The breather need to overlap all edges to give air a path to escape when the vacuum starts.  I cut it long and then fold a pleat at one side where the vacuum feedthrough will sit to serve as a manifold for air escaping under the pressure.

 10)  Now the vacuum bag layer is layer on top and sealed to the table via the sealing tape (yellow) around the perimeter.  This takes some practice to get the seal uniform without lots of leaky wrinkles.  Be careful about pulling the bag too tight when sealing because it may pull the sealing tape off the table once the vacuum starts and the bag stretches to conform to the shape of the panel.  Notice the vacuum feed trough nipple at the far end of the table on top of the breather fabric pleats.

 11) On goes the vacuum hose and the pump starts sucking the air out.  I continue to massage the seal to work out leaks.  I found my ears to be the best leak detectors.  I walk along the seam with by ear almost touching the table and listen for leaks.  Once the seal is tight my pump runs until it reaches its set point and then kicks off until the pressure creeps back up.  You can also use a continuous running pump with no reservoir.

As the atmosphere presses down on the evacuated stack of materials, excess epoxy will seep through the holes in the perforated release film and get absorbed in the breather fabric.  This is good for making a strong, lightweight panel.  I am working at almost 7000 feet altitude, so I don't have as much atmosphere to press down with as those of you at sea level, but it is still adequate to make an excellent panel.

 12)  After the epoxy cures for a few hours (6-12 hours, or more, depending on the temperature), you can remove the panel.  If you are careful, the vacuum bag with sealing tape and the release film can be reused.  The breather is best used only once.  The excess glass and peel-ply can now be trimmed with a sharp knife.  If you do this within 24-hours, the knife will cut the excess off very easily and cleanly.  If you let the epoxy fully cure over days, it gets tougher and may require more effort to trim.

And Voila! here is your laminated panel (or half laminated if this was the first side).  To do the other side, just repeat the above steps.  With a little practice, this is very efficient and you will be able to make super-strong lightweight panels.  Initially the process can be frustrating due to excessive mucking with the layers.  Remember, less handling is always better, and the process is generally self-correcting.  So far I have not had any panels come out looking bad, much less unusable.  The same cannot be said for my effort laminating by hand (see discussion about the first float half about a year ago).