Historic HomeWorks Forum

[johnleeke]

Air Panels(update: 9/20/14 with tips on lumber, painting and sash pulls; 1/31/13 with more tape product names and test results)

Have you heard about the clear film you tape over your windows to keep the cold winter drafts out?

You can get the shrink wrap film kits down at the hardware store with everything you need. Here at my house I tried out a couple of the kits, but didn't like ripping them out and throwing them away at the end of the heating season. At ten bucks per window per year it looked more like a way for the manufactures to fill their corporate coffers than a way for me to save on energy costs. Plus the tape damaged the finish on the window casings. I resolved to make a simple air panel system that would reused the plastic film, that any handy DIY person could make, that would last for years, not damage the window in any way (good for the museum houses), would cost less than $10 in materials, take less than an hour to make, and take less than a minute to remove and install each season.



So I made simple wood frames and taped the plastic film to the frame. Then I applied a gasket around the edge. The whole frame is sized to fit snugly into the reveal of the window, just to the inside and up against the sash. The seal is so good that when the wind blows the panel pops right out, so I hold them in place with screws. I decided the kits from Warp and 3M were too costly at about $10. (I've got 26 windows and that would be hundreds of dollars each year, so forget it!), I bought a whole roll of graphics-grade shrink wrap film for $60. at the art-supply house. I'm not sure how much is in the roll, but it looks like a 50-year supply for my entire neighborhood. Those big corporations are making a killing on their $10. kits. I figure there can't be more than about sixty cent's worth of plastic film in each kit) If you want to stop by my place here in Portland I'll give you some. I have made three rounds of these "air-panels" over the years with minor improvements each time.

My wife says "they make the front parlor much more comfortable in the winter, and cut down on the exterior street noise too." My friends say, "Neat! Can you make 38 of them for my house?" I say, "No. Make your own, here's how..."

Materials

Wood Strips
Clear, straight grained wood cuttings, may be sawn out of wider boards with some defects. I usually rip the frame stock from wider boards on a table saw, avoiding knots and cross-grain.
3/4" to 7/8" thick by 1" to 2" wide by lengths as needed
pine, poplar, or any wood to match interior trim
If you are buying 1"x2" lumber (actual size 3/4" x 1 1/2") and are not ripping your own stiles, sort through the lumber pile to find pieces that are truly straight by holding one end up to your eye and sighting down along the edge to see if it curves. (Be sure to leave the lumber pile neatly stacked to remain friends with your lumber dealer.)


Wood Screws
wallboard-style screws, #6 diameter x 1 5/8" to 2 1/2" long, length as needed for fastening frame butt joints

Weatherstripping

Backer Rod
5/8" diameter foam backer rod
Sof-Rod brand product proven life is 11 years, expected life 20+, no other brands or products tested or in use.
Sources:
Demand Products:
http://www.demandproducts.com/EIFS-items/item.php?l2=3,44,49&sku=GROUPSR
Gordon Glass Co.:
http://www.gordonglassusa.com/group/2987/CRL-Sof-Rod.htm

Pile & Fin with Arrow Anchor
Durable, expected long life (decades),the plastic fin will cause some abrasion on the window trim surface, perhaps not suitable for delicate important paint and fragile aged patinated wood surfaces. Source: John Stahl at ART www.advancedrepair.com

V-Type, ~$.20 to ~$.40/lin.ft.
Frost King V-Seal Weatherstrip, pre-scored polypropylene roll with an adhesive backing on one-half. To install, clean the surface where it is to be installed. Cut the weatherstripping to the desired length with scissors. Fold the weatherstripping piece into a "V" shape. Peel off the adhesive backing, and press into place with fingertips. One roll is 17 feet long, and is 7/16th of a inch wide when folded. The color is brown. $3.86 for 17lin.ft. ($.23/lin.ft.)

Foam with sticky side
foamtapes.net
#191-- Item 33114-00062. Ethertape PSA-1, black foam weatherstripping, .5 x .5 x 70'. This is the last item applied to panel.

Rolled Poly-Sheeting, less than ~$.01/lin.ft.
For making your own rolled weatherstripping you will need 6-mil thickness polyurethane sheeting, one 1/4" or 3/8" dia. wood dowel rod and 1/2" staples

Shrink Film
Should you buy film kits or bulk stock? It depends on your specific situation, how many windows, window sizes, etc.. If you will be making panels for more than ten windows it will be worth doing a comparative estimate to figure the costs both ways. If you will be making 20 or more panels it will probably cost less to buy film, tape and weatherstripping in larger bulk amounts.

Window Film Kits, ~$.20/sq.ft.
Typical cost is $10 to $16 for one 62" x 210" sheet of film, includes double-stick tape (~$.15 to $.20/sq.ft.)
Brand names are Warps, 3M, Frost King, etc.
Available at many hardware stores and building material suppliers

Clearmount Ultrafilm, ~$.043/sq.ft.
Manufacturer & Supplier:
Clearmount Corporation
630 Silver Street
Agawam, MA 01001
508-543-0155
800-541-5472
info@clearmountcorp.com
http://www.clearmountcorp.com/ultra.htm

GRAPHICS GRADE, polyolefin, Acid Free, 100 Gauge (1 mil) thick; on rolls of 500 linear feet; Widths - 24" - 28" - 30" - 36" - 41" centerfolded so folds out twice as wide
100 gauge thickness, (also known as 1mil or .001")
minimum order is 1 roll, 36" roll is about ~$128 + shipping (~$.043/sq.ft.) direct from the manufacturer. Partial rolls may be available.
My local artists' supply house had 500' by 36" rolls for ~$70, and it may also be available at art framing suppliers.
Additional source for shrink film, including a heavy duty 2mil film:
http://www.uline.com/Grp_49/Shrink-Film-Rolls
(~$.03/sq.ft.for 1mil, ~$.03/sq.ft. for 2mil)


Double Stick Tape, with backing strip
I find that the adhesive in the double-stick tape lasts 1-2 years if the film is taped to the face of the frame and if the panel is left in place year-round on the sunny side, and 3-4 years if removed seasonally and is on the shady side. The same double-stick tape lasts 5-8+ years if it is applied to the edge of the frame where it is under under the gasket, where it is protected from the deteriorating effect of light. 3M tape lasts longer than Warp's tape. Ordinary office-supply double stick tape is no good.
I have been testing various double stick tape products to learn which lasts the longest. Specific tape product testing results, Dec.2012:
(All the following tape products have multi-year durability when used on film and tape. See other failures as noted.)
Ace, Double-Stick Tape, "for mounting shrink film or poly sheeting", 1/2in x 52ft., $8.00, $.16/ft, 12-2011
3M Scotch, Window Insulator Tape, "for indoor use", 1/2in x 13.8yd, $8.00, $.20/ft, 12-2011
3M Scotch, Outdoor Mounting Tape, "for 3M Window Insulator Kits", 1/2in x 13.8yd, $8.00, $.20/ft, 12-2011 (failure of adhesion to Sof-rod backer rod gasket, 10% failure after 4 months with panel in window, 80% failure after additional 8 months with panel in storage)
Now beginning to test:
TAP Plastics, 8 mil Clear Double Sided Tape (aka Double-Sided Permanent Bond Tape) 1/2" x 36yds, $9.45+ship
http://www.tapplastics.com/product/repair_products/adhesive_tapes/double_sided_tape/411
(if you try out this tape, post a message here to let us know your results)
Another double-stick tape to consider:
foamtapes.net
#314-- Item 33E00-00002. White mounting tape, double-faced tape .03 x .5 x 216' per roll. Minimum order of 12 rolls.


Clear Tape 2" Wide
Don't use the cheap packing tape, it will not last long enough.

Duck® HP260 High-Performance Packaging Tape
polypropylene film, acrylic adhesive
1.8" wide, 3.1 mil thickness
35-lbs.-per-inch tensile strength
Ultra-violet light resistant
Long-term resistance to aging
Specially formulated for wide temperature range applications (-10° to 150° F)
Manufacturer: Duck, http://duckbrand.com/Products/packaging-tapes/hp260-packaging-tape.aspx
Source: Amazon.com, http://www.amazon.com/Performance-Packaging-1-88-22-Crystal-1067839/dp/B000XJOBUS/ref=pd_sbs_op_2



3M Spray Mount Artist's Adhesive
for use with fin & pile weatherstripping when you are using this weatherstripping to secure the edge of the film in the weatherstripping slot, to keep the film from slipping out of the groove
Cat. No. 6065, 3M I.D. No. 62-6065-4826-1
one-surface re-positionable adhesive for short-term bonding with acetate, foils, fabrics, light tissue and newsprint; long-aging
$8.77 for 13.5oz aerosol can

Tools

Tape measure
Power drill with twist bit and Philips screwdriver bit, or hand screw driver
Screwdriver, Philips (two power drills are handy for higher production rate)
Handsaw, crosscut, fine toothed
Miter Box, for cutting square joints
Table saw, if you are cutting your wood strips to width
Hair dryer, for shrinking plastic film

Procedure

I make simple wood frames of straight grained pine stock 3/4" x 1", with wallboard screws fastening the butt joints and a horizontal rail at the same height as the window sash meeting rails. I use double stick tape to fasten shrink wrap plastic film on one face of the frame. It would be possible to put another piece of plastic on the other side of the frame, but I don't bother. Around the 3/4" edge of the frame I apply a gasket or weatherstripping. The whole frame is sized to fit snugly into the reveal of the window, just to the inside and up against the sash, with the gasketed edges fitting against the interior stops, the stool at the bottom and the header stop at the top. I shrink the plastic after the frame is installed for the first time.

Here is the step-by-step procedure:

1. Measure Window Openings
The air panel will fit within the window parts on the interior side, typically in between the interior sash stops. The opening to measure is on the interior side, within the window frame. Measure horizontally between the interior sash stops. Measure vertically between the window stool below and the header stop above.
Always make more than one measurement along the stops and stool. Usually the measurements will be the same, but if the window is "out of square" the measurements could be different. More than 1/16î difference could be significant. If this is the case, make a sketch of each opening showing the different measurements.
Measure each opening. Even though all the windows may appear to be the same size, there may be subtle variations that will make a significant difference. Measure to the nearest 1/16". Sometimes a folding carpenter's rule with a sliding extension provides more accurate measurements than an ordinary tape measure.
Also, check each stop and stool to see how straight it is by laying a straight edge on it. If it has a bow or crook that is more than 1/16" out of alignment, the gap between the window and the edge of the air panel may vary greatly which must be noted as you select a weatherstripping system to fill the gap.

2. Select Weatherstripping System
Select a weatherstripping system to fill the gap between the window and the edge of the air panel. If the window openings have significant bows or crooks then you may need to select a weather stripping system that has enough thickness and flexibility to allow for the greater variations in the gap. The following list is ordered from the most effective at stopping air-infiltration at the top of the list to the least effective at the bottom. If you are operating on a very limited budget the Rolled Poly sheeting at the bottom of the list is most cost effective if you already have 6-mil poly on hand or can get some without having to buy a whole roll.

Types of weather stripping:

Split Backer Rod


This weatherstripping system is made of 5/8" diameter foam backer-rod that is split lengthways to a D-shaped profile, then fastened to the edge of the wooden frame with double-stick tape. Use a pair of sharp scissors to split the backer rod down it's length. This was the first weatherstripping system we started out making for the air panels ten years ago. It makes a very tight air seal and causes little or no damage to the window ís surfaces. We custom-fabricate this system for each job.

Fin and Pile


This is a specialty weather stripping material that we also use on the edges of wood window sash. A narrow slot must be cut in the edge of the wood frame, requiring more woodworking skills.

V-Type

A long strip folded back on itself along its length, this type of weather stripping is made of either metal or plastic. It forms a springy strip that bridges the gap to prevent the movement of air. Durable, long-lasting and easy to install, V-strips come with a pressure sensitive adhesive; once you have cut a strip to the proper length, you can stick it in place on the frame without the use of tools. V-type weatherstripping is commonly available at hardware stores and building supply houses.

Rolled Poly-Sheeting


This is the least costly weatherstripping, especially if you already have some 6-mil poly-urethane sheeting on hand. To make some start with a 6" to 8" wide strip of the sheeting, and roll it lengthways around a 1/4" or 3/8" wood dowel rod. Slide out the dowel rod and staple the rolled sheeting to the edge of the wood frame. The poly sheeting might last just a few years, but a thick fuzzy wool or cotton fabric might work well with this method and last for decades.

3. Plan the size of the frames
The frame should be somewhat smaller than the window opening to allow for the weather stripping around the edge of the frame. Typically the frame is 1/4" to 3/8" less in height and width than the window opening. Exactly how much smaller depends on which specific weather stripping product you are using. The weather stripping product documentation may state how much to allow. You will be wise to make up a sample frame to test the gap allowance and weatherstripping before buying all the weatherstripping or cutting the all the wood strips. Install the sample frame to test for the proper gap allowance that will work best with the weatherstripping, taking out and putting it in a few times, making any necessary adjustment in the size of the frame to vary the width of the gap. If you have sash pulls on the bottom sash rail that stick out, check to see how the bottom rail of your frame fits underneath the pulls.

4. Make up wood frame
I usually rip the frame stock from wider boards on a table saw, avoiding knots and cross-grain. If you are buying 1"x2" lumber (actual size 3/4" x 1 1/2") and are not cutting/ripping our own stiles, sort through the lumber pile to find pieces that are straight and true.

Cut the horizontal rails and vertical stiles to length. Make the ends very square and even. Use a miter box if necessary.

If you are going to stain or paint the frame, this is the time to do it.


Assemble the frames by screwing the corners together. Pre-drill 3/16" shank holes in the vertical stiles. Then hold the joint in alignment and drive a screw through the hole and into the end of the rail.

5. Check the fit in the window
Make sure the gap is the size you are expecting and will work with your weatherstripping.
Write the window number on the frame, and label the bottom of the frame so it can always be returned to this particular window opening and oriented the same. This is important because in a later step the film will be shrunk to fit each opening. If a completed frame is installed in another window the film may be stressed and show wrinkles or come loose at the edges.

6. Apply the film and weather stripping

Stick the film to the edge of the wood frame with double-stick tape.

Apply double stick tape to the edge of the wood frame.
Lay the film out on a clean table. Lay the wood frame on the film. Pull the backer off of the tape, revealing the sticky tape. Working along one end of the frame, lift the edge of the film up and press it into the tape. Work along the opposite end of the frame, stretch the film to work out any wrinkles and lift the film, pressing it into the sticky tape. Then do the same on both sides of the frame. Trim off the loose edges of extra film.
Do the same to apply the film on the other surface of the frame.
Apply 2" wide clear tape to the edges of the frame, wrapping the edges of the tape onto the faces of the frame, sticking it to the face surfaces of the film on both sides. Press the tape down with a wallpaper seam roller.

Apply the weatherstripping or gasket to the edge of the frame.

7. Install the frame in the window


It's easy to do. Just wiggle it into place.

8. Shrink the film with a hair dryer
Be cautious to not over-shrink the film. If it is too tight it can pull the tape off. I try to get out most of the wrinkles in the film but not all, which might make it too tight. Over the years the film continues to shrink as it ages, sometimes up to a full inch, which pulls the tape loose, or twists the wood rails.

9. Fasten the frame in the opening


I have been driving a screw into each corner of the window frame, leaving the screw stick out past the frame about 1/2" blocking the frame from blowing out. Each year I am careful to reuse the same hole, and to not strip out the threads in the hole. Eventually the hole could wear out. There are various spring pin, and slot lever hardware fasteners that could be used to hold the frame in place, but they all involve drilling holes or cutting slots in the window trim.

10. Sit back and enjoy the cozy comfort of your new air panels


Go ahead, have a seat...

Maintenance of Air Panels

The plastic film can be damaged since it is so thin, but small holes and rips can be neatly taped with 2" clear tape, and not look too shabby if there are only one or two behind the curtains. When the tape fails at the edges of the plastic film I usually re-tape it, or put on new plastic film. (the old plastic film could be reused on a smaller window if it is less that five years old.)

Alternatives

This article is about making your own air panels, but if you cannot, I often recommend these pre-made panels:


WindowDressers is a volunteer-driven non-profit organization dedicated to helping Maine residents reduce heating costs, fossil fuel consumption, and CO-2 emissions by lowering the amount of heat loss through windows. http://windowdressers.org

Downeast Interior Storms
Rendon Sabina
47 Chase Farm Rd.
Newcastle, Maine 04553
207.380.7680
rendon at downeastinteriorstorms dot com
http://www.downeastinteriorstorms.com/

Eugene Mueller
Energy Wise Mfg
563.542.2134
http://www.energywisemfg.com/insiders.html

Advance Energy Panels (AEP)
James Levine
(800) 819-9463
http://www.windotherm.com
AEP now has kits to make panels.

R-Plus Window Insulators
http://www.proactiveenergyconcepts.com/proof.html

Indow Windows
Sam Pardue
http://www.indowwindows.com/

[johnleeke]

Materials Update:

Pile & fin: Durable, expected long life (decades),the plastic fin will cause some abrasion on the window trim surface, perhaps not suitable for delicate important paint and fragile aged patinated wood surfaces. Source: ART www.advancedrepair.com

Backer rod: Sof-Rod brand product proven life is 8-10 years, expected life 20+, no other brands or products tested or in use. Source: http://www.demandproducts.com/backrod.html

[VermontGal]

Hello John,

Thanks for your excellent how-to on the air panels. I used to live in Portland myself (Congress St just over the top of Munjoy Hill) but I finally settled down and bought an old 1850s house in Montpelier VT where I am spending a *happening* Saturday evening in November making air panels!

The windows DO have more than 1/16" difference along the sash stops. Nothing in my house is square - it's an old tenement house that was moved from one foundation to another in the early 1900s. Your instructions suggest to select the weatherstrip based on this fact, but don't make a recommend for which weatherstrip.

I have been wanting to go for durability and best airsealing with the 5/8" foam backer -- but I know that closed cell foam is also fairly rigid.

Two questions:
- Is there a different weather strip that I should consider that is more flexible with this variation in distance?
- If you think I should proceed with the foam backer, any tips for cutting the foam backer accurately to "sculpt" to the sash stops?

Thanks for any advice!

I much appreciate the benefit of your years of experience.

Thanks also for the encouragement to keep the old windows. I have "newer" but still leaky 2-pane wood sashes in most of the house, but on a couple of windows I have 12x12 left -- reused by a previous owner so that now they are the storm windows.

I had an energy audit done (blower door, infrared camera), and they recommended doing a good job of weatherstripping as preferable to replacing the windows. I need to tell them about air panels!

Thanks,
Becka

[johnleeke]

[andy.corvallis]

I make interior and exterior storm windows out of regular screen frame material. I take thicker clear plastic on the roll by yard that you can buy at most hardware or fabric stores. This is note sheet plastic you use to cover stuff up with. I clamp the frame down so when the plastic is strech the screen does not pull to a hour glass shape I clamp it down over the frame and roll the round spline into the four corners first. Then proceed around all side rolling in the spline in to pull the plastic tight. If you get the right plastic this will last at least 10 year. I know of people that have gotten 30 years without replacing the plastic. The plastic look old and yellow but was still keep the weather out. I put layers of foam tape on the frame to build it out to be flush with the trim and then use small metal turn jobbes that swivel and hold in the strom with just a little tension. We have doing this for over thirty years. i figure they pay for themselfs in a couple of years depending on how much air years windows leak. We have starting putting them on both the inside and outside of our windows.

andy

[johnleeke]

Andy:

This sounds good. The use of standard screen stock would be good for those who cannot cut their own wood strips, though perhaps a bit more costly.

I'm always looking for a better plastic material. Can you let us know exactly what plastic you are using? Product name & number, manufacturer, etc? How much does it cost?

Also, what is the little metal turn jobbe that holds with compression? Have you got a maker and part number? Or, can you attach a picture here?

[andy.corvallis]

The glazing is called Glassine, manufactured by PVC Tech Corp in Japan, comes in 12 gauge and one thickness heaver, about 52 yards per roll, comes in 36î, 48î, 54î and 63í widerolls. Cost is .50 a square foot retail Aluminum screen from cost at .40 a foot, corners .25 each, foam about 4.00 per screen and die cast.30 (jobbe)each with screw (need four +)

I have tried to attach pictures of some windows I have done and the die cast screen clip but it did not work.

andy

[Laura]

Do any experienced interior storm builders have helpful hints on cutting the backer rod evenly?

I built my first prototype last weekend. In spite of very limited woodworking skills, the frame came out much better than expected. I cut the backer rod with scissors and it is noticeably wavy with small gaps visible along the window stops. I have three decades of sewing experience, so I'm used to handling scissors but this turned out to be an unexpected challenge. My prototype storm is good, but if I could improve the weatherstripping just a bit it would be perfect.

I have 24 more windows to practice on, but I'd love to benefit from the experience of others, too. Has anyone used something other than scissors? Did it help?

[johnleeke]

Are you using the Sof-Rod brand backer rod? This particular backer rod product is relatively soft and easy to cut with scissors. Other backer rod products are stiffer and more dense and may be harder to cut with scissors.

Dispite our mommies' teaching us to use our best fabric scissors ONLY on fabric; use your best and sharpest fabric scissors on the backer rod.

Have you been to the live online video conferences? I can demonstrate backer rod cutting at the next conference. Learn how to join us at a conference here:

http://historichomeworks.com/hhw/conf/vidconf.htm

[Laura]

Thanks for the quick reply, John. I didn't use the Sof-Rod for my prototype, but planned to order it for the rest if I was able to complete one successfully. (Didn't want to be stuck with 540' that I couldn't use.) Sounds like it may solve my problem. I'll order it today.

I'm glad to hear that the Sof-Rod is softer, too. Because the product I was using was very stiff, I had to make the outer dimensions of my frame smaller. Something more compressable should be forgiving for an amateur like me.

***Gasp!*** Use my best scissors! That's going to be tough. I'll try, but it so goes against my training that I may burst into tears on the first cut. (laugh)

I haven't been to the live seminars, but have been catching up on the replays. I'll try to remember to join you on Tuesday.

Thanks again for your help.

Laura

[johnleeke]

[Laura]

Whew, that's a relief! (Actually, I would never use my best scissors, but I promise I will use the second best. LOL)

Laura

[johnleeke]

Jeff reports:

[johnleeke]

Rosemary writes in, and I reply:
Rosemay wrote:
> John,
> my elderly carpenter, Neil, is trying to make the interior storms by ripping down a sheet of 3/4" plywood to 1 1/2 strips - he has a very caring concern for my budget and plain wood strips cost more. He has tried framing strips for material, but figure they will warp terribly and they are very rough.
> with the plywood, The screws unscrew with the movement of the frame as he handles it, so now he wants to use metal back plates, etc., etc., etc.....
>
> Is it possible to do this project with plywood? do we need backplates? will the plastic film help keep the frame less flexible?
>
> what is supposed to be a simple, inexpensive solution to leaky cold windows is rapidly getting out of hand - Help!



Rosemary:

I'm currently repairing, installing and making a few more interior storms here at my place.

> with the plywood, The screws unscrew with the movement of the frame as he handles it, so now he wants to use metal back plates, etc., etc., etc.....
>
> Is it possible to do this project with plywood? do we need backplates? will the plastic film help keep the frame less flexible?

Technical:
I have not used 3/4" plywood, but I can imagine how this is going. The plywood is much heavier than pine so there is more stress on the joints during handling. If he is trying to use butt joints & sheetrock screws (as in my online article) then the plywood will tend to split out and not hold the screws well, additional reinforcement hardware or braces might well be needed at the joints.
Clear straight-grain Eastern White Pine, as I have used, is lighter in weight and less likely to split at the corners. A simple butt-joint and one single sheetrock screw have proven easy to make and durable over the past 11 years I have been making these. The first round make in 1996 are still holding up with no wood or joint failures. Other species of wood could also be good, such as clear poplar (sometimes costs less than clear pine). Others have used hardwoods to match the interior finish woodwork.
In general plywood is made and best used in large sheets. Solid wood is best used in long narrow stick-like forms, much like it grows in the trees.

The very thin film I use should not be counted on to hold the wood frame in shape.

Economic:
It looks as though the plywood approach could cost more than the solid wood approach considering additional corner parts, and additional labor, depending on the labor rate and how many windows.

Recommendation:
Consider saving the plywood for another project and going with solid wood, as per instructions. This is what we know actually works.

If solid wood is not a possibility and plywood a must, I would use 1/4" thick plywood, perhaps maple or birch veneer, ripped to a minimum of 2" wide, with full lap at the corners, clamped and glued, full glue-cure time. It would take a lot of time to sand all those edges to prevent splinters, and might require varnishing all edges and surfaces to keep the splinters in check over the long term. These would need something more continuous than just screws in the corners to hold them in place in the window.


yer pal in preservation,

John

[jefinch]

[quote="Laura"]Do any experienced interior storm builders have helpful hints on cutting the backer rod evenly?

This is probably too late for Laura but I do have a solution to produce the half-round backer rod from round. I took a piece of scrap 5/4x6 board and drilled a hole in it near one end. I think the hole was 5/8". I then fashioned a slot centered on the hole. I made another piece of wood with, as I recall, an 11/16" hole and a slot. The slot is for a utility knife blade that needs to be secured at a bias between the 2 pieces of wood, which are screwed together (if the blade is parallel with the board surface it won't cut well). Clamp the board in a vice, cut a slot in the end of your backer rod and insert the rod through the smaller hole of the cutter. Now simply feed and pull the rod through the hole and you will be creating D-rod from round.