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Author Topic: The Wonder of Drywall Tape  (Read 114 times)

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Online Deerslayer

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The Wonder of Drywall Tape
« on: November 19, 2017, 08:33:40 AM »
Great stuff - cheap, light, easy to work with, right up there with hot glue for usefulness in the foamology department!

I often use it to make hinges or to repair hinged or damaged areas. If you have to layer up foam or foamboard or such, this is the stuff to use. Having learned about it almost 30 years ago from Gord, I have built several large foam wings with balsa sheeting for small and large glow planes, without setting any spar material in place. Just place some strategically placed strips of drywall tape between the foam and the sheeting to distribute spar and other loading. As well, it can repair a major break in a structure. It has just enough stickum to stay in place.

The following photos show a simple way to create a multi-purpose repair tape:

1. Fasten a strip of the drywall tape to some parchment paper used for baking. That stuff is impregnated with silicone and neither melts, burns or sticks to anything.

2. Apply a light coating or some streams of hot glue to the tape.Don't overdo it, you will be spreading it out into a thin layer and if you run short, you can apply more as needed. My glue gun is an ancient, heavy duty Bostich fellow that has high heat capacity and a nicely formed tip that stays hot enough to re-melt glue.

3. Using the side of the glue gun tip, gradually spread and smooth out the glue. You want to just fill the open weave and leave a film coating across the whole thing on. If you get too aggressive, or if the glue is not hot enough, you will shift the fibreglass threads around and mess up your structure. Drywall tape is not actually woven, the threads are merely criss-crossed and lay in place due to the trace amount of stickum in them

4. Pick up your tape from its parchment paper backing. The underneath side should be shiny smooth. Cut it as desired - either knife or scissors work well.

 To apply a patch or to create a hinge, just lay the section onto the foam,  foamboard, balsa or whatever and apply heat with the side of your glue gun or, as I simetimes do, with a hotknife. (Aside: My hotknife is what looks like a  woodburning or soldering iron with a #11 Exacto blade installed. It has hundreds of hours of great use and I could not build or repair without it!) No need to add any additional glue, what is now in your tape will be sufficient to bond with the surface.

 My experience with drywall tape is that, if you make a hinge and do not have hot glue across the hinge line and/or is you have overdone the heating at the hinge line, it may break if it gets a good shock. If you have done as I suggest and have a completely coated piece, the glue film will add some strength and help to resist a shock loading.

 The final picture in this series shows a reinforcement at the elevon inner junction on a flying wing. Even on full scale aircraft, this junction is a stress riser and the designer has to ensure that it is well reinforced, typically with gussets on top and bottom or other structural features. with a flying wing, if you have an over-stress to the wing or  a hard impact to the nose, there is a high probability that a fracture would initiate at that location and the wing will fail. Been there (model aircraft only, not a real one!)

I hope this gives you some ideas for a rainy or snowy day.
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Offline ganguy

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Re: The Wonder of Drywall Tape
« Reply #1 on: November 19, 2017, 10:57:18 AM »
Very interesting idea about using parchment paper.
 I'm still thinking there's a better hinge idea to come. I do like a mechanical hinge because sooner or later my DW tape hinges shear off, even with the hotglue line.
Because we use foam to build, pin hinges only work for me if you reinforce them top and bottom. The flat mini hinges eventually pop off.
I'm working on it, maybe we can patent it .
GG
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Online Deerslayer

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Re: The Wonder of Drywall Tape
« Reply #2 on: November 19, 2017, 12:13:36 PM »
Very interesting idea about using parchment paper.
 I'm still thinking there's a better hinge idea to come. I do like a mechanical hinge because sooner or later my DW tape hinges shear off, even with the hotglue line.
Because we use foam to build, pin hinges only work for me if you reinforce them top and bottom. The flat mini hinges eventually pop off.
I'm working on it, maybe we can patent it .
GG
On my recent builds, 2 flying wings using Elmers (Dollarama) foamboard and 2 made from the black foamboard (Dollarama), I use paper hinges. In other words, the paper that was already on the foamboard.

The black foamboard's paper is extremely well bonded to the foam, more so than the Elmers white. I use my break-off blade knife to carefully, during multiple passes, cut down MOST of the way into the foam. Then, I break the resultant line at the edge of the table. After that, I cut the bevel on the fixed surface, not the control surface, again being careful not to cut the paper joint. If you do happen to nick it, or cut a short length, it won't matter, as the whole thing will be stronger than needed. Then, I use a long sanding tool and sand the excess or wobbly foam so that there is a decent straight bevel and the surface can move freely.

 The final step is to seal these cut edges. Quickly run a trail of hot glue, using a high heat capacity gun, along the hing area and immediately scrape it with a scrap of foamboard or a plastic card. You will leave a nice thin film of glue across the hinge itself and will have secured the paper to the foam. Or, you could just paint the whole cut area with Mod Podge, etc., or with the polycryllic I use to waterproof and finish the whole aircraft.

 As this is all done on the underneath side of the hinge, the top will be perfect, with no evidence of the hinge, apart from its bend line! Very low resistance and completely sealed hinges make for a highly responsive control requiring minimum servo power. Refer to the attached picture, bottom view of hinge.
« Last Edit: November 19, 2017, 12:15:49 PM by Deerslayer »
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Online Deerslayer

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Re: The Wonder of Drywall Tape
« Reply #3 on: November 22, 2017, 10:03:44 AM »
 Still on the topic of drywall tape:
 
I found a great way to prepare patches or hinges and to keep them on hand.

1. Lay down a strip of drywall tape on parchment.
2. Dribble some hot glue liberally onto it, crosswise, in several strips.
3. Lay down another strip of parchment on top.
4. Using a covering iron, smooth out this sandwich as much as you can. Don't worry,
    you will not damage either the parchment, the hot glue or the drywall tape.
5. Let it cool down for 5 minutes or so, then peel back one side of the parchment.
   Check to see if it looks like the entire section has been covered. If spots are missed,
   apply more hot glue in that general area.
6. Replace the parchment you removed, perhaps with fresh, and set it down again.
7. Repeat Step 4 and 5 until you are satisfied that there is a smooth, filled tape.
8. Flip the sandwich over and iron the other side.

 What you now have is a composite material (fibreglass strands and glue) that is thin, rubbery
and ready to apply to something.

 When you are finished, you can either leave your sandwich as is, or, pull off the parchments,
replace with fresh pieces and trim the resulting new sandwich. Now, you have a nice piece
of material, ready for use, easy to store. It cuts easily with scissors. Just lay it onto the target surface, no additional
glue required, then use a hot knife or spatula or iron to seal it down. Wipe away any excess glue
and you have a really neat repair, or a killer hinge!
My purpose in Life is to serve as a Warning to others