Greetings All: Working on the old house I had spoken about some months ago.

Lots of paster & lath walls, most with cracks. Starting with one B/R room and closet.

Have scraped and cleaned out most cracks preparing for taping w/fiberglass mesh and then finishing.

Has had a few [!] coats of paint over the past 60 years and some areas have just paint peeling/cracking, not cracks, but still there are areas that once the flaking paint is gone there are "low areas".

Is there a "secret sauce" for filling these in such as a primer or something that may be just a step or two below that of skim coating the entire room?

Some of the old walls built with wood lath with a thin coat of plaster placed over it contain Asbestos mixed in with the plaster, and the paint may also contain Lead.

Before working on the cracks, you should have a Lead test conducted on the layers of paint and a test done on the plaster itself.

With some of my property's that continue to have cracks in the thin plaster, I have installed 1/4 inch drywall over all of the walls and ceilings. Then after the tape muddling I've had an orange peal texture put over the surface, then primed and painted.

I grew up here and we loved to use the old school oil based paints especially on trim.

Not old enough for horsehair but I am sure that there are worm cans through out the place that we turn a blind eye to.

there is not enough $ or energy to strip off all trim, & pad out the walls. Repairs is what I can expect to do.

I had 3/8'' drywall screwed in over all existing old walls then finished with new inexpensive trim. No more lead paint and cracks to deal with ever. It worked out really well for me as opposed to completely gutting. I learned to finish one room at a time to not get overwhelmed.

Typically, I cut all of the cracks into a 'V' shape, making sure all of the loose plaster is removed...yup...no matter how big the area becomes...after everything loose or crumbly is removed, prime the brown coat (exposed part) with a concrete bonding adhesive. (any box store) This will harden the brown coat. After the bonding adhesive is dry (very fast) use the quick dry "hot" mud to fill the cracks. Fill the cracks to just above the surface and then use the woven fiberglass type tape and cover all cracks. Two overlapping pieces side by side is acceptable for large cracks. For large areas (water damage on ceiling) I often use a cut off piece of fiberglass screen.

Now for the overly anal...I personally no longer do these next steps. Prime the concrete adhesive/bonder w a shellac based primer (spray can)...side note...Shellac primer is a miracle...covers soot, crayons...etc It's the go-to primer of restoration companies. First coat of "setting type" mud...I can't remember the exact brand but one of the powder type "hot" muds has an above average strength. It is a "setting type", and dries as hard as a rock. You would use this to fill the cracks and then use a lightweight mud to skim the tape. (Personally I have gone to using the H. Depot brand dry mix mud, 45min, exclusively for all steps) Your skill will dictate which "speed" to buy. Start w 90min, if you don't know. Easy enough, there is a certain acquired skill to sheetrock work. Best of luck.

I am certain many will ask "Why not just use plaster?" You can, but it's even trickier than sheetrock mud and not something that I carry on my truck. I always have a partial bag of dry mix "hot mud" in my truck. I've used my way for a dozen or more years and never had a problem.

Trust me when I say that the bonding adhesive is the trick. ;)

Oh yeah.... I forgot my warnings.... Listen to Robert. Asbestos. Also, Shellac based primers have been known to cause some "neurological" problems in certain people. It can be some bad stuff. Lots of ventilation, but honestly, the brand name latex primer called Gripper (H. Depot) is my go to primer. They used to market it as a primer for priming tile. Not kidding. In a pinch I have used it as a transitional paint on top of oil base. (Talked to a paint manufacturer, about that one) It sticks to everything, but again, I now skip the prime the concrete adhesive step and go directly to mudding the crack.

Even better - find a guy who knows how to do it and hire him.

Yup durabond is my go to filler. It is extremely difficult to sand. I apply what I need and then using the sharp blade of plastering knife, knock off the high spots of durabond and put a very thin layer of sandable drywall compound over top.

Thank you all for the help. I truly do apprciate it.

Durabond it is.

I did have a retired carpenter help us out with our rental which has an early 50's type wallboard/cementatious sheetrock which has a skim coat of plaster.

I had tried filling and not taping the very thin & myriad cracks to little long term effect.

On a subsequent go 'round of turnover I found this retired carpenter who used the Durabond with the fiberglass mesh.

This method has just about all the rentals issues fixed...long-term.

1GR81- you had me wondering about that fill part...thanks for the correction.

Many thanks to all that took the time to respond.

Oil base primer and paint has such an odor that it not good to use it. Yes some of the better brands of water base paint has an odor however they are safer to use.

Kilz Max is a great primer and acts like the old shellac base oil primers. Go to Kilz website and check it out.

I use Durabond Easy Sand. Much easier to sand.