Sanding Moulding Profiles

Tips and tricks for sanding the profiles surface of trim moldings without overly softening the sharp edges. August 21, 2006

I have about 2,400 linear ft of trim and base that I am staining/clearcoating. I need to find a way to easily sand between coats. Do any of you know how to make a sanding block that fits the shape of trim? I have heard of using Bondo to get the shape and then gluing sandpaper to it. Is there a better way - maybe a little stronger - like fiberglass or something like that??

Forum Responses
(Architectural Woodworking Forum)
From contributor A :
In the past I've used a section of moulding wrapped loosely in cling film, made up of a 4-sided carton with an opening at the bottom on each side to pass the moulding through then just sprayed in expanding urethane foam. Itís not pretty, but it works. If you wax the moulding really heavily that works too, but it's then a problem getting the sandpaper to stick.

From contributor B:
Put some coarse sticky back sandpaper on the profile and rub a piece of foamboard (blueboard - extruded polystyrene insulating foam) against it until you have a counter profile. Now put some fine grit sticky back paper on your sanding block and you are good to go. If the grain raise is not too bad, scotchbrite will knock it down well enough, although the sandpaper may clog and need replacement more often than is convenient.

From contributor C:
Bondo is what I have most often seen, however you could do the same thing making the sanding block out of epoxy and micro balloon additive or with fiber glass. This should pretty much give you a very long-lasting block.

From contributor D:
When I have a lot of molding to sand I use a profile sander. It is a wheel with flaps of cloth sand paper on it that you can mount to a drill motor.

From contributor A:
I've used the slashed abrasive wheels in the past and found that they can only handle a limited range of shapes. They have a tendency to knock the edges off finer angles on the moulding and not be able to get into the little corners you sometimes get in fancy cornices (crown mouldings).

For longer runs I use a Volpato LBK oscillating edge sander which has an additional profile sanding head on it (non-oscillating). This allows me to use a friable abrasive wheel which I set-up by back feeding a square-cut piece of the moulding into the wheel while it's turning to form the profile sanding shape. I then feed normally to sand the profile - a bit like using a spindle moulder as the machine has two cast-iron fences and we have a power feeder on our unit, too. But itís a bit of an expensive solution for 2400 ft of trim. Worth looking at if you do a lot more, though.

From contributor E:
Take a look at a sanding head from Klingspor called a Mac Mop. It works great on mouldings without killing the profile edges.

From contributor A:
To contributor E: What speed do they run at?

From contributor E:
3400 rpm is the listed max. I have heard that they work better at lower speeds like 1725.