Dollar Tree Foam Board Paper Replacement Options

I am always looking for ways to improve the strength and water resistance of Dollar Tree Foam Board.  I was very impressed with Hilldaflyer's articles on the subject.  I used those techniques along with a few ideas of my own and did further testing.  The notes below include a description of each technique, their pros and cons, and what I feel would be the best use.  Instructions for making each type is at the end of the article.

               For reference, here are links to Hilldaflyer's excellent articles.

                              Super Strong Waterproof Foam Core

                              Forever Sharp Hobby Blade

                              Glassed FT-22

                              Adams vs Ross

The best techniques, in my opinion, involve removing the paper from the DTFB.  Because paper is more difficult to remove from Ross Foam Board, I prefer DTFB.  I did not use Ross Foam Board in any of my tests.

Below are a few pictures of my testing process.

Best Results

Polycrylic Fiberglass Board

Description:  Foam board, paper removed, covered with fiberglass and coated with polycrylic.

Pros:  Easy and quick to make.  Results are very similar to using epoxy; however, this method allows you to make a and B folds just like DTFB with paper.

Cons:  Cost.  1 sheet of this costs $10.02 + tax ($1.00 for the DTFB, $9.02 for one sheet of 1.5oz/sq yd fiberglass)

Best use:  This is great for everything, especially wings.  I would not use this unless you certain on your design, are done making prototypes, and are ready for a finished model due to the cost.

5 minute Epoxy and Flox – paper removed (this does not work with thin epoxy)

Description:  Foam board, paper removed, coated with thin epoxy mixed with flox

Pros:  Very easy to make, very hard, nearly as strong as a glassed sheet. 

Cons:  Does not add the strength that the addition of fiberglass would give.  I would not use this on wings or tails.  5 minute epoxy is expensive.

Best Use:  This is only for small areas that need to be very hard and where other methods won't work.  This is a good option for small wingtip floats that are very curvy.

Epoxy and Flox – with paper (this will work with thin epoxy)

Description:  Foam board coated with thin epoxy mixed with flox

Pros:  Very easy to make, somewhat harder and more waterproof than polycrylic alone, nearly as strong as a glassed sheet (if you are using 5 minute epoxy). 

Cons:  Does not add the strength that the addition of fiberglass would give.  I would not use this on wings or tails.  This is only for small areas that need to be very hard and where other methods won't work.

Best use:  Engine pods, wing tip fins, fuselages, other areas that have some other means of structure to provide strength.  This may be a good option for control surfaces.

Red Rosin Board

Description:Foam board, paper replaced with red rosin paper using polycrylic

Pros:  This makes a very strong material, much stronger than Adam’s Foam Board.  It is water resistant and fairly easy to make.  If you put three coats of polycrylic (the initial coat to put the RR paper on plus two more coats), you will have a very smooth, gloss surface that is quite strong.  If completely submerged in water it maintains adhesion to the foam.  It is weak when totally soaked with water, but dries to original condition.  Testing from Hildaflyer indicates that this is one of the strongest methods of paper replacement outside of fiberglass.

Cons:  The paper will still crease if bent too far.  It is water resistant, especially with three coats of poly, but it is not waterproof.  Will wrinkle on inside (concave) curves.

Best use:  Great for curved surfaces that would be difficult to build with fiberglass coated foam.  Applications where you would like a flange on both sides like the cockpit of the FT-22 are examples.  Engine pods or things that are unlikely to be damaged in a crash, or the interior surfaces of a plane.

Glassed Red Rosin Sandwich

Description:  Two pieces of foam board with a layer of red rosin sandwiched in between and coated with fiberglass.

Pros:  Very strong, yet still flexible.  Does not wrinkle except under extreme stress.  Allows for streamlined edges.

Cons:  Requires a multistep process to make.  You need to use CA hinges, tape hinges, or methods other than Flitetest paper hinges.

Best use:  Vertical and horizontal stabilizers.  Anywhere that you would use one sheet of foam to create a flat surface.  You can sand down the foam so the whole thing is about as thick as a single sheet of foam board.

Glassed Single Board

Description:  Foam board with paper removed, coated with fiberglass and epoxy mixed with flox.

Pros:  Strong.  One step to make.  If you have taped areas, you can just coat the fiberglass right over the tape (as long as you scuff it up first).  It bonds right to the tape.

Cons:  This is a very nice material, however, it will wrinkle if bent too far.  You need to use CA hinges, tape hinges, or methods other than Flitetest paper hinges.  It can tend to delaminate on a freshly cut edge.  In those cases, use hot glue or epoxy to seal the edges.

Best use:  Fuselages or other areas that have some other means of structural support.

Instructions

Polycrylic Fiberglass Board

Supplies:

Dollar Tree Foam Board with paper removed.

Minwax Clear Gloss Water Based Polycrylic

How to make:

Remove paper from foam board.  Lay a sheet of fiberglass over the top.  Mix up some flox in your polycrylic and coat the fiberglass with a brush.  No need for a squeegee.  For a smooth finish, sand and coat with polycrylic.  You may need multiple rounds of sanding and coating to get a very smooth finish.

Use a bead of thick CA to protect any exposed edges.  Use a scrap piece of foam to spread it out.

Note:  The most efficient way to make Polycrylic Fiberglass Board is to make a full sheet of DTFB at a time.  Getting the paper off an entire sheet is tricky, but doable if you have patience.

Results are very similar to using epoxy

Epoxy and Flox

Supplies:

Dollar Tree Foam Board with paper removed.

5 minute Epoxy (do not use thin epoxy)

Flox

How to make:

Remove paper and apply epoxy mixed with flox.  The paper can be left on, but does not add much strength in a small area.  If you are going to use this on a wing, I would leave the paper on.  For a smooth finish, sand and coat with polycrylic.  You may need multiple rounds of sanding and coating to get a very smooth finish.

Epoxy and Flox - with Paper

Supplies:

Dollar Tree Foam Board – with paper on

Epoxy – 5 minute for a very hard surface, thin for a lighter, but still waterproof surface.

How to make:

Same as Epoxy and Flox except you don't remove the paper from the foam board.

Red Rosin Board

Supplies:

Red Rosin Paper

Adam’s Foam Board

Minwax Clear Gloss Water Based Polycrylic

How to make:

Remove paper from both sides of Adam’s Foam board

Coat one side of the foam board and red rosin paper with polycrylic

Put the two together and coat the dry side of the red rosin paper

Use a squeegee to squeeze out all extra polycrylic.  Do one side at a time.  When it is dry, put a well distributed weight on it overnight to take out any kind of curling.

Recoat 1-2 times to increase the strength and water resistance.

Glassed Red Rosin Sandwich

Supplies:

Red rosin paper

Super 77 adhesive

Two pieces of foam board, paper removed

1.5 oz/sq. yd fiberglass

Minwax Clear Gloss Water Based Polycrylic

How to make:

Layer two sheets of foam board, paper removed on the sides that will be in the sandwich, with one sheet of red rosin paper in between.  Adhere them together with Super 77.   Once dry, remove paper from the outside and sand bevels into the edges if you want a streamlined piece.  Coat with fiberglass and polycrylic.  Sand all the edges when epoxy dries.  For a smooth finish, sand and coat with polycrylic.  You may need multiple rounds of sanding and coating to get a very smooth finish.

Glassed Single Board

Supplies:

Foamboard, paper removed

Fiberglass

Thin/Finishing epoxy

Flox

How to make a wing with this method:

Remove paper from foam board.  Tape the fiberglass in the middle of the wing. Lift up the fiberglass and fold over to the other side.  Use a roller to apply thin epoxy to the foam, then pull the fiberglass out to the tip.  Apply a bit more epoxy with a credit card squeegee while stretching it out.  Sand the edges once dry.  For a smooth finish, sand and coat with polycrylic.  You may need multiple rounds of sanding and coating to get a very smooth finish.

See this example: https://youtu.be/rRoFMDj7mz8

Other Methods Tested

Paper off, 5 min epoxy, no flox

- Too soft

Paper on, 5 min epoxy, no flox

- Too soft

Red Rosin Sandwich using polycrylic as an adhesive

- Polycrylic can't dry when sandwiched between foam.

Red Rosin Board – single coat of polycrylic

- Nice, but is much better with 2-3 coats

Polycrylic Only – Unaltered Adam’s foam board coated with polycrylic

- Delaminates in some areas when submerged in water for 20 minutes.  Adds little additional strength.