Finishing Polyurethane Mouldings

      Tips on finishing plastic trim material to match wood trim, using commonly available products. November 27, 2007

I have a job coming up in a few months that's going to require about 350 feet of crown and 350 feet of base moulding. The customer is requesting a polyurethane material. I don't know why, it's just what they want. The concern for me is that the designer wants all the moulding to match the cabinetry, which I'm doing in clear alder, Euro beech and birch. The color is a dark brown, sort of an aged mahogany look. It's actually a simple finish, BLO based wiping stain with water based CV for topcoats.

How do you finish this poly moulding? I've learned that you can paint it and then use gel stains to mimic the look of wood and then topcoat. A painter buddy says that on some of the synthetic mouldings, you can even use the same stains as on wood with close results. I have a few months to play with this stuff and if it gets too annoying, I have someone who will finish it for me, so that helps.

Forum Responses
(Finishing Forum)
From contributor C:
Your buddy is right. I have been asked to do this and also to blend in multiple woods of different colors many times to match a different bulk wood used to build cabinetry. My method is to seal in the molding with acrylic sealer - Delta Labs 525 sealer - until it is smooth enough to glaze over. I then apply a glaze mix that exemplifies the lightest background color of the sealed primary cabinet wood. I then seal that glaze in and mix another glaze to apply over the first that gives me the color I need to match the primary wood as close as possible. When that glaze is again sealed in, the color should be very close. If not, you can apply a color corrected third glaze to match it exactly. After sealing the last glaze in, it is best to apply two or more coats of acrylic sealer, then sand smooth and topcoat. All this should be accomplished with the moldings in place and shaped as necessary so there is no chance of cracking the finish, as would be the case if bent after finishing. If there is not going to be any bending, then this is not necessary to concern yourself with. But try to apply within a few days when the finish is still pliable.

From contributor B:
That sure is a lot of work for 700 ft. of trim.

From contributor C:
Yep, but it will give you the desired results for your client. There are no quick fixes for great results.

From the original questioner:
I won't be able to install it within a few days. More like a few weeks, as the job is out of state and I can't go in until all the other trades are finished. So all of our stuff will sit in a storage container onsite. I think I'm going to have to end up having someone else finish this stuff.

From contributor C:
Are the pieces going to be bent at all? If not, and you can install them without bending, you'll be okay. But of course this is totally up to you.

From the original questioner:
I can't think of any bending involved. We don't even have to cope or miter corners on the crown, as we're using blocks. The base is almost all straight runs with only a few corners. How does this stuff cut after being finished? My other concern was having to touch up ends. Does it flake at all? I was planning on making scarf cuts before finishing, but I can't practically make end cuts offsite.

From contributor C:
On wood there is no problem, but on this stuff there could be some chipping. It should be minor and easy to touch up by a qualified touchup person.

From contributor R:
I know that these poly mouldings are less expensive than wood, but I can't help but wonder if there is any financial advantage to spending a whole lot more money finishing a product that will almost look like wood. Seems like they might be saving pennies on the material only to be spending dollars on the labor.

From contributor C:
You're right. The only advantage is when you have a fancy hand-carved look that would cost you big bucks to duplicate in real wood, or when tight curves are needed that would be very expensive. It is used in Florida for these reasons mainly on so-called high end pieces. I do a lot of faux finishing so I am used to copying all wood grains onto such surfaces and others as well. But no matter how good you are, it still does not look like natural wood would look. All you're really doing is copying the basic wood and color affect at best.

From the original questioner:
It was specified by the end customer. The designer didn't really want to use it, but this was one of their inflexible wants. It's not really any cheaper than wood, it's just a simple profile. I don't really care one way or the other. It'll get figured out and then that will be something else I can add to my ever decreasing brain space. As for the cost? Well, they're willing to pay the extra.

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