Sunday, May 9, 2010

1. Materials used for making the Cab-Over Molding (6/2/10)

The last post was basically,  how to make a mock up of the motor home's front edges [drivers and passenger] side Cab-Over section.  With this done, I can now go off to my garage/shop, and make moldings that I can later install on the motor home's front corners.

OK, that part is done and I coated them with 2 coats of resin to seal the wood.  Next I add a layer of cloth tape, sand and re-resin to build a nice smooth plug.  From this Plug, I will make the 2 moldings needed.


 I want a molding a bit larger than what is traditionally used on these older rigs (which was 7/16 x 7/8").  The manufacturers of class C motor homes finally got wise and started to pay attention to their build quality, or prior lack of it, and have in the past decade or so, used moldings that cover more surface area on either side of the horizontal and vertical seam joint.


Below:  Mold is Ready!


This grants the installer some extra room for sealants to do their job.  No reason to skimp on this. They have learned to do it better, and I am only following suit.  Before I started this project, I looked at many rigs in lots, on the road and in every campground I shared with them.  I'm adapting and making my own moldings, probably 1.25 or 1.50" wide on either side of the seam.  The goal is to keep water out, forever!

Now that the mold is ready, I thought I would explain the materials I'm going to use to actually make the molding.  In the past, I normally would use Epoxy Resins as that's what I have used for years on boat repairs, but found the material takes way too long to dry for this application.  I don't want to spend a month on this!

My supplier:  FIBERGLASS COATINGS, INC.  Look them up online   (

  They will ship to you; answer your questions via their online web site's clear instructions or thru a phone call if necessary.  They also can ship you a catalog.  Good guys and gals there and products are equal to any I've used from other manufacturers.  I have no affiliation with them but do recommend them and their fabulous supply.

At one of their locations, one of it's top guru's suggested on my cab-over clearance light project, that I use Surfboard Resin.  I tried it and am happy with the choice.  It 'kicks' off fast (dry time is quick), so you can get on to the next coat.

Along with this, I seem to buy 2" brushes by the dozen or box.  Not the cheapo's, but the thicker ones if I can get them (3/8" rather than1/4").  They are natural Chinese bristle and work as good in my applications, as expensive natural bristle brushes.  During stages, I clean them with Lacquer thinner and get a many uses out of them before they hit the trash bin.  On the left is a small jar of white pigment.  I might add a little to pre-tint the molding so I don't have to paint it more than 2 or 3 coats for coverage. , but its not a necessity.  (white paint does not cover dark resin well)  On the right is a bottle of PVA-- Poly Vinyl Alcohol.  Consider it a liquid plastic that is alcohol based for quick drying, sprayable and brushable and water soluble.  Use if for a mold release between the mold and the piece you want to remove from it after manufacture.  You can wet it and the PVA will dissolve, making separation of the 2 pieces easier when necessary.

Fiberglass Cloth, is my favorite for little projects like this.


 I't not the strongest and only comes in thin material thicknesses.   Advantage is it's quite flexible so great for working around corners, bends or changing angles while you are applying it.  Layer it up  with 3  or more layers and you can get all the strength you need for these small components. CLOTH, comes in sheet's of large rolls of 30-60", but also 1,2,3,4 and 6" rolls.  you can buy this smaller or larger stuff by the foot or yard.


 I just bought a small roll of 4" Cloth Tape for this project and will have plenty left over for my next brainstorm.  The cloth is woven in 2 directions perpendicular to each other.  You can see it here.

Also showing it here from behind sort of, looking out from my garage towards the daylight on the street, so you can see that it probably has 90% fill.  (less than 10% is daylight-90% or more, is fiberglass)  That gives plenty of strength, can still be easily bent around corners and can be layered up(I will use 4 layers) for thickness and superb strength.  With all this though, the molding will probably be about 3/32" thick when completed and certainly, no more than 1/8".

Why do I keep repeating "strength"?  Well, I don't want this molding to ever crack and in so doing, open up the likelyhood of water intrusion and future rot.  So I'm trying to build it as well as I can.

Just for the sake of explanation, Fiberglass Mat, is the material consisting of short threads

of fiberglass held together in a binder/comes in sheets or rolls too and is only good for helping to build thickness or hide the printout of heavier materials. It is NOT used for structural tasks normally.  It could, but I'm not going to.

Also shown here from both sides, so you can see how much light there is between threads..  Light means the only strength you have later on is the resin between the threads.  (Not too strong-the strength comes from the fiberglass material, basically not the resin..which is the binding material)

Just for the heck of it too, I'm showing you a close up of Woven Roven.
 It's thick material used for building up multiple layers for strength, as when building the hull of a boat.  Doesn't bend well so no application here for my needs.  Also, going to show what is called Fab-mat.  It's fabulous, for certain projects requiring real strength with minimal material and quick build time.  It is 2 layers of fiberglass, NOT woven together but straight parallel strands layed over one another, and STITCHED TOGETHER.  This leaves the strands straight and strong---you see you loose strength when the fibers are bent in the weaving process.  Straight is stronger.  Fabmat also has a layer of Mat sewn into it on the underside.
Cloth Tape shown in upper right and Fab-Mat in lower left.

Note on this Fab-Mat the rows of stitching (top to bottom)about a 1/8" apart.  Strands of fiberglass are not woven together, but stitched together.  A layer of Mat is bonded underneath the double layer of parallel strands.

One other product I have used, is good in the making of molds, if you want to add a backing over a seam or gap for the cloth....a support during mold making, is a small tape used in Drywall construction.  It comes with a sticky adhesive on it for quickly taping joints to hold Joint Compound or Spackle.  I used a bit of it on this project in the nose area, to support the gap, resisting a depression of the cloth tape I will apply next, rather than take time to fill those gaps with bondo or other fairing compounds.  It has minimal material and lots of airspace.  Good for holding other materials like joint compound or Bondo fiberglass repair material used in Auto Body work, as it allows the material to be forced between the open weave.
Spackle tape used for early support over gap for Cloth Tape.

OK, now that the Mold is glassed, resined, sanded and well, ready!  .... I'm cutting the Cloth tape in various lengths to make handling easier during application with resins.  I try to stagger all joints. With multiple layers I could use Butt joints, but it's just as easy to stagger them now too.  When dried, I can sand out any imperfections.

This afternoon, the Mold itself, was sanded with a Disc Orbital Sander (DA) and 220 grit paper to take out the brushing and dust marks in the resin.  Then, it received 3 coast of the PVA liquid Mold Release agent/half hour dry time between coats.

Ready for tomorrow to make a "Molding"!  Yea!!

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