Metal backed paper tape or even expanded metal mesh if you have enough wall thickness to bed it in. I would probbaly cut away a lot of the drywall surface to gain bedding depth. Durabond can be as thick as you want. I have used it to replace plaster grounds occasionally, and those are a full 3/4 inch thick. Mix it with minimal water to about peanut butter consistency and the shrinkage is very small (unlike pre-mix that shrinks like crazy as it hardens by drying). Not having to repeatedly hit screw head dimples is reason enough to use Easysand. Plaster and setting joint compound harden by chemical reaction, not water evaporation.

Zenpotter, I would never try to discourage you from repairing your bathroom walls with authentic lime putty, reinforced with horsehair, and smoothed out with a wooden float. My understanding is that 100 per cent lime putty takes about one year to fully cure. Regardless of what type of finish is applied, it will be necessary to fasten some sort of lath, such as wood lath, or wire lath, or rocklath, to the structure of the house. This is generally done with nails. You might have to actually remove more of the original plaster, in some places, to get good access to a wooden beam or stud, in order to securely attach the lath as needed. If you decide to use sheetrock as your backing for finish plaster, then it will be necessary to coat the sheetrock with an adhesive, after it is installed, but before the finish coat plaster is applied. However, if wood lath or wire lath is chosen, then you can apply a modern base coat plaster, pre-mixed. The pre-mix base coat will very likely contain chopped fiberglass to improve its strength, instead of horsehair. Since chopped fiberglass is not so good to breath, you should use come care when mixing this with water, to avoid raising a cloud of dust. Base coat plaster will set up in less than an hour, and can be coated with finish plaster the same day, if necessary. There is no great skill involved in application of base coat plaster. You have to mix it with reasonable care, and press it in place with sufficient force that it penetrates the lath, and binds firmly to the wall or ceiling. It needs to be troweled reasonably flat, and should be slightly below the intended surface plane, so there is some allowance for finish coat plaster. Base-coat does not have to be perfectly flat, or free of tool marks. Finish coat plaster is made from slaked lime and gauging plaster(aka plaster of paris). High quality type S finish lime, made from dolomite limestone, is easy to work with and gives good results. Finish coat plaster application is a learned skill, and not easy to describe in detail. As soon as the plaster is mixed, it begins to set up, and will harden in less than 30 minutes. You have to work fast, and there is a limit to the size, in square feet, that can be done in one mix. If the base-coat plaster is fresh, and still damp, then no misting will be required. If the base-coat has thoroughly dried out, it will rob moisture from the finish coat plaster, and interfere with both application and cure. Misting the base coat with water, before troweling on finish coat, will prevent this problem. If you decide to teach yourself how to apply finish coat plaster, my suggestion is to start with an area around one square foot, for your first trial. With initial success, you will gain confidence, and can begin make larger mixes, and plaster larger areas. The wall doesn't care if it gets plastered in small increments or in one fell swoop.

Any butt joint without reinforcing tape of some kind installed prior to a skim coat will fail, usually pretty quickly. Masonite is especially unstable so it's somewhat surprising that more seams have not opened up. If you really want to try gluing, I'd opt for cyanoacrylate - aka super glue in the gel form so that it does not run excessively. Non-water containing and sets up fast enough so that a simple brace or even hand pressure would be all that's needed. Not that it makes a great deal of difference, but are you sure the skim coat is actual plaster and not joint compound? I also hate to be pessimistic, but you'll likely have continuing problems with these joints.

Hi, I've patched just a few plaster walls. My goal was to cover the hole and make it look good. 3x7 is a small patch. This is how I would do it. Cut a piece of sheetrock 5x9 (thickness isn't important). Score the back of the 9x5 piece 1 inch all around then break the 1 inch piece off the back then peel the 1 inch piece off the front paper. You should now have a piece that is 3x7 on the back and 9x5 on the front. Fit the patch to the hole . It may take some scraping you don't want it too tight. Spread some mud on the edge of the hole and patch and the paper on the patch. Set it in the hole a use a 4 inch blade to set the patch. Let it dry. Most times the patch will be a little lower than the original surface let the patch dry finish as needed. Good Luck Woodbutcher