We recently completed framing a conical roof with a 24 foot eave radius. The raftertails are notched to accept a two part facia. The top piece of facia is four inches wide and tilted out so as to mimic crown, because of the curve and the tilt the facia must bend two ways, on the flat as well as on the edge. We are using Azec and must heat it to achieve the bend. We have talked to the rep. and plan to heat the Azek in a piece of culvert pipe with a torpedo heater. I was wondering if any of you folks have any experience with thermoforming Azek or similar PVC product and would be willing to offer any advice. Working with a hot piece of plastic is not my idea of a good time and I thought I would see if anyone could help me flatten out the learning curve so to speak. This is also my first time using Azek and I was wondering what folks use to fill nail holes with and to caulk with if the product is not to be painted. I appreciate any thoughts or advice that anyone might have. Jay
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This is a class I want to audit. HGope to learn looking over your shoulder, so to speak.
Excellence is its own reward!
With the way Azek expands and contracts with heat I wouldn't want this job. You are streatching the top edge while compressing the bottom at an abnormal temp. God knows what it'll look like when it cools down or through 4 season changes. Hope you got enough in it to do it again.
The rep claims that it will hold its shape if heated to 325 before installation. She is coming to the site on Wednesday to consult. It will be nailed securely on less than 16'' centers. The piece that is bent two ways is also substantially supported by the piece below it. This stuff also glues up very strong to itself with regular clear pvc glue. The risk of problems now or down the road has been disscused at length between me, the GC, the HO and the Arch. and this is the path that we have chosen. I was kind of rooting for steam bent cypress but the Architect thinks Azec is a great product for this application. We have used solid blocking behind all of the other Azec cornice on the house to prevent distortion but it is not feasible on the circular cornice. This is the first time I have used Azek and was wondering how much it would move with temp change. To be safe I have been gluing all joints and nailing more than I would wood. Jay
325º huh? Buy two long sleeve welders vests and some hotwork gloves. Better get some sunburn spray, ice, and a good burn kit too.
About your oven:You're going to want it's internal temp to be around 600º to 700º, because you will want fast soak time for production. Regulate the temp by moving the propane powered torpedo in and out of the mouth of the drain pipe. Point the torpedo slightly off-axis to provide a swirl and diffuse heat better. Leave about 4' between the mouth of the oven and the near end of the work piece in order to prevent burning the end. Suspend the work in the center of the oven by cutting #4 rebar and sticking them thru the sides. Because you are dealing with a long and flexible piece, you will need a table about 6" wide on top of the rebar for it to slide on. I would use stucco mesh and just make sure the "ridges" are set to prevent the workpiece from catching as it slides into the oven.You will also have to insulate the oven because you will need both ends at near the same temp. The best solution is to bury it in dry sand, however two layers of 2" foil backed wool will do for a while (foil to the outside.) The oven must also be another foot longer than the workpiece because the outlet will chill. This can be allieviated by hanging a stucco mesh screen over the outlet. You can cut 2' off the mouth of the oven by setting 4 stucco mesh diffusers 1"-2" apart 2' inside the mouth (rotate the alignment of the little "vents" in the mesh.) Because you need a venturi effect at the mouth to regulate temp, the mouth dia should be 16". You can use a 16" pipe or use a 4' by 16" galv sheet metal cone to neck down to 10" or 12", maybe even 8" if you use a sandbox oven. But if you make a permanent oven the best would be a double walled (8" inside a 12".) You may want to provide an outfeed table.
About working time:You need more information from the manufacturers Rep. What is the woking temp range? (the hotter you can safely get it, the longer work time.)If the working range is greater than (i'm guessing,) 100º, this crude oven should work OK.What is the destruction temp? Is it the same as or higher than safe working temp.Is it ok to heat and reheat a piece? You will need to sacrifice some pieces to see how long a soak time you need and how long before damage occurs and while you tune the temp settings. (More on that if you need it.)
About working and clamping time:You will be real lucky to get 10mins working time. I doubt that it is possible to hot install. I think you will need a jig on the ground and a lot of spring clamps. If you use 10' pieces you can scribe each piece to fit at 9'4". See how much springback there is before you build your jig.
Good luck, this sounds like a really fun project. I wonder if the Arch thought about how much setup was going to cost him? anyway, you are assured of a reputation.
SamT
Edited 6/17/2003 4:08:31 AM ET by SamT
SamT, Thanks for the detailed reply. I've got to go to work but really appreciate your thoughts. Apparently several manufacturers use Azek as a component of their product and the rep said that she would try to provide us with some technical info from their experiences in thermoforming Azek on a regular basis. I am actually starting to look forward to this project. Jay
Jay- Azek expands IMO alot. I put 1 x 8 trim board 40' long under soffit in april. In August it pulled nails in one section about 6' long and bowed off the house about 5". Temp in april was about 70 degrees august was about 100 thats alot for a 30 degree difference in my book.
________________________________________________If you were arrested for being a quality builder would there be enough evidence to convict you?
expansion.
One of the worst problems early single ply roofs had was the PVC sheets would expand so much in heat of day and summer sun that great big bubbles ( up to three feet tall) would erupt in the surfacce membrane Don't know if anybody uses PVC roofing anymore..
Excellence is its own reward!
Look into the different types of things electricians use for bending PVC conduit. I have seen at least two different kinds, one of which is like a heating blanket that wraps around the conduit (or board, in this case). I would think that this would be a lot easier to control and manage than other ways. Slower, maybe.