Plank Stiffening

[tasar]

Guys......best method to stiffen a soft plank......I've got 2 1/8th" inch drop when loaded center ??

[Ken Smith]

I had good luck using unidirectional glass roving from Wicks Aircraft.

http://www.wicksaircraft.com/catalog/product_cat.php/subid=8477/index.html

This 3 inch wide product, two lengths, were applied to the bottom surface of the plank. 

I know that the glass is more effective in tension then compression, and the bottom surface of the plank is in tension.  The analysis of a wood-glass composite shows that glass on the bottom lowers the centroid of the plank, making the compression surface (top) in a lower stress state for the same weight on the plank.  That plank was discussed in an earlier string, use the search in the upper right for a look, if it is still there.

Wet the bottom of the plank, and lay on the roving starting at one edge.  The two layers may overlap slightly along the centerline of the plank.  I used peel-ply over the roving which helps get the excess off.  Once set, just peel off the peel ply (if used)

[Bob Gray]

  Another source of unidirectional glass is www.fiberglasssupply.com.  They have some 13 oz. 16.5 inch wide for about $2.50 a yard. Check under "knitted fabrics".  I got some recently and it's pretty nice stuff.  BOB

[tasar]

it so happens I have plenty of a 3" woven bi or triaxial glass......would this prove to be too stiff ?

[Ken Smith]

All the fibers not running the long direction on the plank are not doing any good for stiffness, just adding weight.

The glass added will make the plank thicker, which is stiffer.  The fibers running the right direction will add more stiffnessThe bi and tri directional glass can help, just not as efficiently as unidirectional materials.

Ken

[tasar]

thanks fellas.....that uni glass stuff looks like a blanket.....will epoxy ooze thru or will you have to wet-out first and then again over the top of the glass ?

[Geoff Sobering]

thanks fellas.....that uni glass stuff looks like a blanket.....will epoxy ooze thru or will you have to wet-out first and then again over the top of the glass ?

Most uni wets out pretty well.  I've had good luck painting on a thick coat of epoxy, then laying the glass onto it, and working the resin through the glass with a brush and roller (usually adding some additional epoxy as/where needed).  It's really the same process you would go through to wet it out beforehand, you're just using the plank as a work-surface.

Cheers,

Geoff S.

[tasar]

thanks Geoff......will give it a try.....hey it's bottom side, who'll see it ! ?

[John Davenport]

Tasar,
If you are going to continue the "Joy of Building" like most of us, you should learn how to use vacuum bagging for your lay-ups.  There are many sources available to understand the process, but my favorite is explained by the Gougeon Brothers either in their book, “The Gougeon Brothers on Boat Construction” or in their brochures found in marine hardware stores that sell West System resins.  The benefits are high fiber to resin ratios, (removes excess resin), flat finish surface, fewer bubbles/voids and it removes the “blush” from the surface.  Blush is the waxy film on the surface after the epoxy has cured.  Blush retards curing of urethane, varnish & paint.  Start here.  http://www.gougeon.com/

Enjoy,

John Davenport US-4961

[tasar]

thanks John.....hey, you still have an A class cat ?

[Geoff Sobering]

Short of full-on vacuum bagging, I would suggest getting some "peel-ply" fabric.  You place it over the layup and squeegee the excess resin through it, then peel it off after the resin has cured.  This gives a better resin/glass ratio than a simple wet-layup, creates a surface ready for further bonding or finishing (without sanding), and removes the amine-blush. 

[tasar]

what's a cheap reliable source for peel ply ?

[Geoff Sobering]

what's a cheap reliable source for peel ply ?

Fiberglast.com sells polyester fabric at ~$12/yd: http://www.fibreglast.com/showproducts-category-Vacuum+Bagging+Supplies-106.html
US-Composites sells it for $5.50/yd    http://uscomposites.com/vacuum.html

I know folks who have had good luck just buying medium weight polyester fabric at the fabric-store.  I haven't gone that route yet (but I'm thinking about it for my next layup).  The bottom of a plank would be a good place to try it; worst case (if the fabric wouldn't peel off) you would just have to sand it off.

[John Davenport]

What Geoff has said does work to a certain degree, but it's the pressure that really makes it work.  I have used polyester from a fabric store and it works just fine.  Just use white if you can.  I got a great deal on some camo colored fabric one time and the color printed through to the lay-up.  I wasn't making a duck boat, so I had to sand more than I wanted...

John

[Geoff Sobering]

... but it's the pressure that really makes it work. ...

John: for a simple layup like this, do you think a shop-vac would provide enough suction?

It would be noisy...