Seams in hardboard backdrop question

[jacon12]

I've completed the masonite hardboard backdrop except for filling in the cracks between boards and covering over the screw heads. My question is, is it necessary to tape over the seams, the area between two boards, as you would on drywall, then 'mud' over that, or is it ok to use caulk (the type that doesn't dry out and can be painted over) to fill and smooth over these areas? How did you do yours?
Jarrell

[selector]

I have not done it yet, but I intend to use powdered 'wood' putty. Mix, spatula in and flatten, and sand when it is dry. Repeat if necessary.

[rrinker]

If you use drywall mud, you almost certainly have to tape, otherwise it will surely crack. I hadn;t thought of caulk before, but the problem I see with that is it shrinks as it cures, so if you fill up and make the crack nice and perfectly smooth, a day or so later, it will be depressed below the surrounding surface. A second application might be enough to keep it perfectly level. - or use a bit too much, and then once cured shave it off with a blade, even with the surrounding hardboard.

--Randy

[jacon12]

Thanks Randy and Crandell. I found my misplaced MR book on building benches etc. It suggests tape and drywall mud. I know the tape usually goes in that very slight depression between two sections of drywall, then the mud evens things out. The masonite has no depression and there isn't even much of a crack between two sections to force anything into, such a caulk.
Hmmm...
Oh well, I'll let you know how it comes out in a few days.
Jarrell

[leighant]

I taped and floated with drywall compound. Had no problems for two years, then moved out of this house, and had to remove layout to rent it.

http://www.railimages.com/albums/kennethanthony/aad.jpg
The cufved corner is right over the turret tower of the courthouse.

[wp8thsub]

I have had excellent results using elastomeric vinyl patching compound on Masonite backdrops, combined with fiberglass tape over the seams. Depending on how much movement you'll be dealing with due to temperature/humidity changes, plain paper tape and drywall mud can crack and/or separate from the Masonite surface. The elastomeric compound can't be sanded, so it has to be applied very carefully. Imperfections in its surface can then be filled with a coat or two of regular mud. Once the mud is sanded smooth, there isn't a continuous layer of it to crack. I use the same procedure on fascia, where it has also proven very durable.

[selector]

I used the wood putty as a sealant base on my river and lake, using the technique I describe above. It did not shrink, was easily sanded smooth, and held the epoxy very well.

What you could do is mate the two masonite edges close, but slightly pointed outward as opposed to trying to get a smooth curve. Use the tape and fill technique with which you are familiar to fill in and round that inner curve. Once it is thoroughly dried (leave it for a few days, ensuring the room humidity doesn't exceed 60%), you will notice if it needs extra work. If not, paint away.

[cmrproducts]

I have looked at all of the suggested ways of using joint compound, Squadron putty, etc. They all work but I was worried about the joint cracking after many years. Also I did not like to spend all of that time trying to smooth out the joint when using joint compound, as it seemed that the joint never looked smooth.

I finally tried using the paper tape for drywall joints but instead of using the joint compound to attach it to the backdrop I just painted it to the backdrop! I don’t use primer as a first coat on the Masonite. I had a lot of cans of mis-matched paint that I had picked up at the big-box stores over the years and used it to seal the Masonite. Yes, I had to paint a number of coats on the Masonite but I have had better luck using this method than I have with primer ( you may have had better experiences with the primer) and besides with the mis-matched paint it was only $5.00 a gallon compared with the price of new primer.

I would roll on a coat of paint on the Masonite and then let it dry for several weeks (this is the key)! I have a lot of backdrop that I did (a 25 x 75 ft layout room) so I could be working on another part of the layout while the first section would dry.

I used the screws and countersink method with a 1 x 2 backer at each joint. Once the first or second coat of paint was dry I would begin the paper tape install. I would cut the tape to length and then I would put a heavy coat of paint at the joint. By heavy coat I mean that it would be just about to the point of running. I would paint the back of the paper tape and then put the tape on the joint and work it into the paint.

Next I would paint the exposed side of the paper tape with paint and let it dry. Once it was real dry (3 to 4 days) I would then use the joint compound to fill in the edges and smooth out the joint area. So far it has worked very well and most of the joints are now over 3 years old and look as good as the day they were first painted and finished.

BOB H – Clarion, PA

[jacon12]

QUOTE: Originally posted by leighant

I taped and floated with drywall compound. Had no problems for two years, then moved out of this house, and had to remove layout to rent it.

http://www.railimages.com/albums/kennethanthony/aad.jpg
The cufved corner is right over the turret tower of the courthouse.

Leighant, those are some good looking trees on your layout. What method did you use to make them?
BTW, thanks for your help!
Jarrell

[jacon12]

Wow, there are certainly a lot of methods to do this job. I appreciate the help guys. I'll just have to make up my mind which way I want to go.
Thanks for the help!
Jarrell

[grandeman]

I started with joint compound and tape and it works well. I also tried a couple of seams with, gasp, regular old masking tape! It was easy, clean and, so far, looks good. Latex paint covers it right up.