Flexible Moldings

Greetings, Several companies offer flexible ornamental moldings - wreaths, urns, rosettes, etc - which can be cut; twisted; sanded; glued; painted; stained; and with patience, possibly taught to speak. I suppose they are of some type of filled urethane; if so, could someone recommend a resin which could be used for such a project?

Much Obliged, Ethan Gross

Ethan, I've experimented with all the urethane+filler combinations that I can find, (Both rigid & flexible urethanes). Nothing seems suitable for a truly flexible product, like the 'flexmold' that I see out on the jobsites. That material is a filled polyester resin. I have never tried it, because my shop is not set up to work with what I believe to be a WAY more toxic product. (If I open up a can of Bondo we can smell it all over the shop. I can't imagine the styrenes emmitted from pouring polyester into open molds!)

Kevin, Thanks indeed for the quite thorough reply; having always associated polyesters with hardness, I had no idea that they could take a flexible form. (Just recall polyester suits, for example.) Is it the particular filler used which gives them flexibility, or the formulation of the resin itself? Also, what glue/fasteners do you use when you attach your moldings to a work?

Regards, Ethan Gross

Polytek and SmoothOn and I think SynAir sell such urethanes. Filler has to be something with round-ish granules, not plate or rod-shaped granules. At least one comes blond-wood colored. Do your homework.

Hey Kevin,

The health risks of styrene emissions of polyester resin are vastly over exagerrated. Your regulatory body is the U.S. is OSHA. They are currently 'toughening up' styrene regs, they are an easy target. What they want for workers is face masks for over 15 minutes of 40 parts per million (ppm) or over 8 hours at 20 parts per million. To put this in perspective, if you put your head into a bucket of freshly mixed resin (it offgases styrene to cure) you would be breathing 50 ppm. To achieve 20 ppm or lower is fairly easy - but anyone coming in the shop would still think the place reeked. The problem with styrene is that it is detectable to humans as low as 1 ppm! There is a huge variety of polyester resins available today, most people may be familiar with the dirt cheap orthophalic resins of the 1970's, no one I know uses them these days. The fiber glass or 'composite' industry is booming at the present time. If you really have a problem with polyester, switch to epoxy, it is twice the price but much stronger and still the same price as urethane resins

The peeyou resins attack you from behind your back - you can't smell what's bad for you. You must trust the manufacturers. The flexible moldings use the cheapest industrial urethane rubber they can find, cheaper resins are the most dangerous -so be careful.

Learning to make curved moldings in plaster or styrofoam is a much more rewarding endeavour. There is a lot of math involved but I enjoy that too.You can also use the 'reverse' of plaster or foam moldings to make cast concrete, or resin moldings.

The products in question are indeed filled polyester resin. They are made flexible thru the addition of 'plasticizers'- chemicals that will cause them to become rubbery- the filler actually acts to limit the amount of rubberyness you get.

Contact a polyester resin formulator and ask for additives that will add flexibitlity to the resin- but be aware that Kevin is correct that these flexible items are not as dimensionally stable as rigid poly-resin castings.

Gary is correct is pointing out that Urethanes are generally more hazardous to your health than polyester- although some people have a sensitivity to the smell, the only real hazard is from the MEK Peroxide used to catalyze the resin. It vents from the resin for hours or days after curing, but is most hazardous in direct skin contact. Take the precautions that Gary advises and wear long sleeves and gloves.

Kevin is also correct in that Urethanes are far more flexible than many people realize. Most urethane resin castings can be heated in (or with) boiling water to a very rubbery state, bent into a new position, and 'frozen' in that position by cooling them with cold water. This can be done ( without modifying the mold as Kevin suggests ) with demolded parts, even very old and 'cold' parts.

Oderless White urethane resin, from Vagabond Plastics in Warner Springs CA is one of the best for this application- first, its truely oderless, second, It cures a solid white color, third, it has no fillers and is extremely elastic when hot.

As with the polyester resin, the larger the percentage of filler you add, the more brittle the resulting part will be. Unfilled Urethanes are a little harder to paint, tho...

Christopher

I should add that you use boiling water to make urethane resins rubbery because this limits them to 214 degrees F.

Do not use a heat gun or microwave.

You do not want to exceed 300 degrees F. at any cost as beyond this temperature urethanes 'pyrolyze' and vent cyanide gas. Although in small amounts, cyanide is a cumulative poison- it is best to keep exposure to zero whenever possible.

(this is why fires on planes are so deadly- all that urethane foam seat cushion...)

Christopher

Ethan, I'm sure Christopher is right about some kind of plasticizer being added, and the filler toning down the rubberyness. I add filler to the rigid urethanes for three main reasons: 1) To extend the resin. 2) The part will accept paint better. 3) It gives the part a 'porosity', so it can be shot with a nail gun without splitting. This also helps the mechanical bond of adhesives. (The back of every part must be sanded to open up the pores, but that seems to be standard practice anyway.)

Epoxies are no doubt the best adhesives for bonding two dissimilar materials. I like Smooth-on's 'super instant' if the part is to delicate for the nail gun. Otherwise I tell the trim carpenters to use construction adhesive or yellow carpenters glue. The latter might not be the very best, but I have had to remove some parts that were glued with yellow glue, and I was amazed at the bond.

Gary, I'll admit my knowledge of polyester is not first hand. My opinion stemmed from the resin suppliers in Dallas telling me how awful it was to work with. I also did some research for a large consumer products company, as I was trying to get a huge contract for urethane lamp bases. They had tried polyester, and their testing showed it 'offgassed' after it was cured at an unacceptable level for them. I've no idea what that level was, nor could I prove or disprove it, I just tried to convince them that the urethane did not do the same thing. It was all to no avail however, as they went back to wood instead.

Thanks for the reply, very interesting, and good to hear a point of view that's different from what I've heard.

Also might add that I am definately aware of the perils of working with urethanes and isocyanates, and realize that there is some hazard associated with most everything.

that's different from what

A view that is completely different is that maybe we have to stop making crappy artwork, crappy plasterwork - if people can't afford the real thing - to hell with them. I am just taking another load of deco-junk (some of it my own) and electro-gadgets to the dump and neighbourhood yard sale. I sometimes wonder how our 'space/time continuum' can handle much more of this. The Neil Young song 'Piece of Crap' comes to mind - we throw away a piece of crap so we have more room for a new piece of crap.

The more I study ancient cultures and how they were able to incorporate natural materials into natural 'decoration' (art), the more I realize how we have strayed. Watching a T.V. show like 'Antiques Roadshow' where craftsmanship and artisanship of up to the early 1900's also illustrates what has been lost. This level of work has been lost forever?

This, of course, is not aimed at you or anyone on this forum - just a mini-rant! Back to making my wall fountains.

What sad times indeed, when artists sit and talk about which plastic will cause them cancer first!

Just about! I still have a steady flow of hand carved woodwork, but the majority of multimillionaires are building houses on a tighter budget these days.

One does have to wonder what the museums of 100 yrs. hence will have to show for our era!!