I have two different MR books addressing backdrop finishing work at the joints of hardboard. One mentions using spackle, the other: the full drywall application with tape. Pros and cons for each please. I get the impression the drywall mud with tape is more resistant to cracking? I’ve done plenty of spackling in my day but never done any drywall work.
Both are susceptible to shrinkage cracking if applied too thick.
I’d go with the dry wall mud and tape, because I’ve done it many times before, and that’s what I used to prepare the wall for my back drop, but, I used drywall and not hardboard.
I would think the drywall method would hide the seams better.
When I think of spackle, I think of filling small nail holes, and divets, and misc imperfections before painting, and not hiding or covering a joint in a wall system.
I have only ever used ‘exterior’ spackle, but only to clean up weathered and badly pitted door trim or sills, or the ends of large beams that have suffered under the weather for a few years. Spackle designed for exterior repairs dries very hard, and it’s difficult to sand. So, troweling/smoothing well is important at the outset.
Taping and mudding takes longer, but you might find it more easily handled and shaped.
If you have installed the hardboard already, ignore this post.
If you haven’t, you might want to look at using .060 or .080 styrene sheets. In more populated areas they can be found in 4’X8’ sheets. That’s what I use. I cut them to height the long way, and have something just like a hardboard backdrop. At joints I add a 2-3" doubler in the back, glued on with Testor’s gooey type model cement (stays wet long enough to work with on the larger pieces). After dry I fill the crack on the front with Squadron putty and sand smooth. I run a sanding sponge over the entire surface to add some tooth for the paint, wipe down with a damp cloth to remove the dust, then paint. Presto! Long smooth backdrop, (relatively) easily bent to even 5-6" corners if needed.
I suggest making up a little test panel and try both to see what works best for you. Embedding tape on the flat surface will make it more difficult to feather the edges. Drywall has tapered edges to compensate for that.
Something else to consider, since you are only doing small joints would be the Durham’s Rock Hard water putty.
Yes, one of the Kalmbach books suggests covering the joint with mud without tape. So that’s what I did and it cracked within weeks. I redid it 5 years ago with tape and mud and it hasn’t cracked.
The thing to remember is that neither ‘spackle’ nor the better kind of ‘joint mud’ are plaster. They have been loaded with agents like the ‘acrylic’ additives used as bonding agents in concrete patching, and, in some cases, with composite filling material, to be able to bridge gaps with some elastic capability and better strength even when ‘feathered out’.
The tape or mesh is there to further bridge the joint between large panels, so that mutual motion of one panel against the other isn’t magnified into more shear or stress than the material can accommodate.
I personally think it’s a really good idea to use some kind of tape between boards in a backdrop. The problem is that, unlike drywall sheets, the edges aren’t tapered so that the taped joint can be ‘full thickness’ but the outer surface flat when prepared. Expect that even using something like Mylar as the ‘tape’ (which I don’t recommend because mud generally won’t stick to it well without careful compatible priming) you will see the joint as a slightly raised area even if you ‘feather’ carefully, and perhaps you’ll see where the edges of the dutched section are.
I would also recommend that you think about adding a little separate binding agent to the ‘spackle’ you use, whatever it is, if you want a little more strength, or adding one of the available strengthening composites if you have the need, if you find problems with joints reappearing.
In the old days, an ‘answer’ to the joint issues (with ceilings) was to adhere a layer of material like fine canvas over the whole plaster and lath structure to form the final ‘surface’ for painting. In a sense, good wallpapering does the same thing. It might be desirable to dutch the seams of a flat backdrop, say of Masonite or Homasote, with thin paper soaked in a good spackle or mud, then put a whole backdrop painted on paper or oth
After priming and painting all 4 sides of my masonite backdrop panels, I install them with a 1/16th inch gap to allow for any expansion and then use drywall tape and mud, feathering the joint of course. I have not had any problems with cracking or appearence.
This is just an idea, and it may present obvious drawbacks to those more experienced in such things than I, but could you lightly hammer some wire mesh into either side of the gaps? If you can embed it, you’ll only have a smear of compound to cover the gap and fill it, and the wire may act something like the tape. Or, use a surform file and file your own tapers, and then use mudded tape. Could work…?
Not that I’ve seen. I found them at a plastics company in Philadelphia that used to be called Arch Street Plastics. Now they’re named Everything Plastic, and are a part of Total Plastics International. Here’s a link to their locations page: http://www.totalplastics.com/about_us/contact.
They’re farthest west location is Chicago, and farthest south is Tampa, FL (next farthest south is Knoxville TN). I’m sure they are other places west of the Mississippi that carry those sheets, but you’ll have to do a Google search to find them.
if you sand through to it, the spots will not only rust but bloom;
any loose tags of wire will be sharp
Note that the open-weave tape sold for joints can be thought of as essentially the plastic version of metal mesh.
I think you’d be forever trying to cut a consistent taper with a Surform, and the surface you raise on Masonite or Homasote will be rough (and I think relatively water-absorbent). You might get better results with something like an angle grinder equipped with an open disc pad. Be careful not to cut the taper so wide that what you use to sand the joint level ‘dips’ into the tapered section…
I would recommend using Plastic Wood, by DAP. Stronger than most other suggestions. Easy to use, with a putty knife. Been using the product, since the late 50’s, when a similar chemical consistency came in tubes.
I’m going to be another voice against using masonite at all.
My choices:
Styrene as suggested above.
Aluminum coil stock.
or drywall.
Yes you can build a curved backdrop with drywall, we build curved walls all the time…well they end up curved, but it takes some skill with the drywall mud.
For which we would use Durabond, not premixed drywall mud.
Despite whatever success people have had, drywall mud is not designed to stick to the smooth hard surface of masonite.
I’m in construction, and we don’t use masonite for anything…
To clarify, I already have the hardboard in place. Approx 1/8" to 1/4" gaps between sheets.
I do have DAP plastic wood already; I had not considered using that. I read about styrene and considered that. Same with vinyl flooring. Decided on hardboard. I have also wondered about the slight “bump” that is inevitable with using drywall mud, but I’m guessing that can be sanded down like spackle or any other material.
I also have Elmer’s Probond wood filler but I’m not sure how that would perform over time. I don’t know how “elastic” it is. I’ve used it to fill gouges and smaller holes before but not a 4’ tall gap.
Raises another question. Both books I’ve referred to at home (as well as some videos) talk about priming the hardboard with at least one if not two coats of latex primer. I wonder: if that is done before the gaps are sealed would the primer help the drywall mud (or spackle or wood filler) to better adhere to the previously smooth surface? Or would this make no difference in the long run?
Thanks Sheldon, I kinda figured that would be the case. Based on your info I’m at the point where I need to put latex primer on, so I will do that first and then come back to see if anyone else has shared anything on the mud vs spackle issue. Thanks to all above.
I’m assuming any latex-based primer will work fine.
For 4’X8’ sheet styrene, look for “plastics suppliers”. They’ll roll it into a tube and tape it, so it will easily fit into the trunk or back seat of even a small car, or you could carry it under your arm while riding a bus or even a bicycle. I’ve gone through at least five or six sheets for doing the unseen backs of structures, and the support panels for background structure “flats”.
While it may work for a backdrop, as mentioned earlier, I’ve made my layout room walls the backdrop for most of the layout, installing the drywall vertically, as the tapered edges are much easier to finish than the non-tapered ends which result when professional drywallers install longer sheets horizontally. Some of them can do a decent finishing job, but I’ve seen many instances where the work looks like it had been done by an amateur like me.
Taking advantage of the tapered edges makes drywall finishing easy for amateurs, even though it it means more joints, which is the main reason the professionals use 16’ sheets applied horizontally.
However, I used 1/8" Masonite for coving all of the oddly-shaped layout room’s 10 corners…