I vote for idea #1 for a few reasons. I would however go with "2" strapping for a few reasons.

With 2" I would spray with closed cell isostyrene I believe you will get much greater R value than iso panels or trying to foam through 3" or 4" holes top and bottom. Even tough the thickness of the spray vs. panels may be close in R value spraying will save some bucks.

Tried spraying trough top and bottom holes and a combination of top, bottom and middle as a test to see what coverage we would get and then ripped out the plaster and lath and found it only penetrated a few feet up and down. Loose cellulose settles over time and never found it effective in any applications other than attic spaces where at least "12 was used. Also depending on the W5, who, what, when, where, why, the plaster and lath was done never found much of a void if any unless double brick or brick and block construction. Sometime no void to speak of at all.

The second advantage of more being better than less over plaster and lath is I have experienced drywall coming loose over time as the screws didn't have enough penetration into the plaster and lath through strait plaster as in idea number 2. That drywall came loose and started cracking after the first season change. Screwing as well as glueing might have helped. We glued as well and screwed the second time just to be sure.

The other advantage to leaving a larger void back there is that I would run all my wiring through "1.5 ABS to create a raceway. If need be it will be so easy to run more wire/cable in the future. There was no such thing as surround sound back then. Just remember to run it all at the same height above the floor so we don't drive a few picture hooks into our wiring raceway. Might cost a few bucks now and I'm sure if you think about it will come up with a raceway for less $$$ than ABS.

Sorry can't edit this post anymore, I've memorized it.

90 yr old plaster should be repairable, However, if the plaster is in that bad shape, then why not remove it down to the studs and then install drywall? Putting 1.5" strips and drywall will significantly reduce room area, and seems like a bandaid rather than a solution.

Geller the studs may not be the same across so I'd have to spend a lot of time leveling out with strips.

If you pull the plaster down it is faster to sister new 2x to the sides of the old studs high enough to make a new plane for the drywall.

I would still think long and hard before removing plaster.

Drywall is a much lower quality wall.

Unless the plaster keys holding the plaster to the lathe have separated in large areas, repair is not all that hard.

This post was edited by brickeyee on Fri, Jan 11, 13 at 17:22

The walls and ceilings look like a desert. Cracks everywhere through the house and some are 1/2" gaps.

We just had the plaster repaired in a room - tons of cracks and the repairs included replacing chunks that were missing. it was a painless job and the plaster is good as news. I am another vote for repairing.

Remember though I'm having to rewire the entire house.

Yet another vote to repair it and do it right. Drywall
Over the plaster is a remuddle

You only need a couple small holes to fish wire for new circuits...I'd rather keep room space than furring out for drywall. Plaster has better soundproofing and insulating qualities than drywall--blow cellulose in the stud bays for insulation instead of costly foam products which won't work unless you strip everything down to the studs.

Here is a thought: if you aren't moving fixtures, you can attach new wiring to the old and pull it from point to point--maybe brickeyee can tell you if that would work?

This post was edited by columbusguy1 on Sat, Jan 12, 13 at 1:51

First, what is the nature of the present electrical? Is it origional knob and wire or has it been replaced with cloth wire at some time. do you have a breaker panel or old type fuses.
Regarding pulling wire, this simply is not an option if the wire is connected by knobs or properly nailed inside the walls. A total rewire is not a job for an amature.

It is not all that hard to rewire without excessive plaster damage, especially if you learn how to do it yourself.

If you have an unfinished basement under or attic above it is VERY easy to drop line into the stud bays as needed from the unfinished space.

There are even flex bits that allow you to drill sideways from a device box (think receptacle size about 2 in x 4 in)

You do not have to remove the old wring, just disconnect it.

I typically use the old receptacle and switch locations as starting points.
Minimal damage is used to remove the old box completely, then pull new cables and drop in new boxes.

either tear out the plaster or repair it. one room in my house has drywall over plaster and i hate it. that extra 2 inches drives me crazy...i don't think the door openings or windows look right; it is hard to find a stud.

i'd rather have one or the other; not both.

i just spent a while repairing plaster. for the amateur like me it can be very time consuming. but it is rewarding. i would probably pay someone to repair it. pros are incredibly fast.

" i would probably pay someone to repair it. pros are incredibly fast."

On new work they are.

On repairs, not so much.

You stil have to fix every crack and defect before you can skim a new finish layer, and you may not even need to skim the while area.

Good repairs should already be flush with the existing surface.

Very thin cracks (hair cracks) that are not open may not need anything but a coat of paint to cover them.

Brickeyee --

aren't you an example of an 'incredibly fast' pro?

"Have issues with window sills and doors" - Uh, yes, that you will! Understatement of the year.

OK, so there's cracks. What about the plaster itself? Is it firmly adhered to the lathe or is it loose and bowed out all over and falling down in chunks? Cracks do not necessarily mean much of anything. What is typical is that there might be some walls or ceilings that are very loose but most of house reasonably intact. You can use drywall patches on large areas. Ceilings because of gravity are generally the worst - those are the one area where replacing entirely with drywall might make sense bc you wouldnt have the trim/windows/doors to contend with.

Do you really want to be milling thousands of dollars worth of custom trim and futzing with fitting it? Or are you thinking you'd go the remuddle route buying cheap-n-cheesy stock trim from Menards - if you have original trim and other features really think twice about removing those bc that could seriously affect the value of your historic house (vs. doing a well done, careful restoration of original features).

"aren't you an example of an 'incredibly fast' pro?"

Not at fixing lots of large cracks.

Every crack more than about 1/16 inch wide needs to be brushed clean, then vacuumed clean (crevice tool along the crack), then bonding painted into the crack, then your choice of material used to fill the crack while the bonding material is tacky but not dry.

I use Durabond many times.

If the crack sides are still in plane you can use a narrow drywall knife to force the Durabond into the crack and then strike it level.

Durabond does NOT sand easily, so make sure any excess is removed.

Easysand is better for the inexperienced.
At least you can come back and scrape it dry or sand it lightly.

Plaster is not all that useful without a LOT of retarder added.
It sets WAY to fast.

Even narrower cracks can have Durabond forced into them, but running a vacuum is still a good idea.

If a narrow crack is in an area that shows badly, widen it with a Rotozip (buy a lot of bits, plaster eats the edges off in a very few inches) through the finish layer(about 1/8 to 1/4 inch deep) and then treat as a wider crack.

Larger areas that are solid can be patched using bonding agent, but if the lathe is exposed you should try to clean it enough to allow new keys to form to hold the patch in place.

Hi,
We have just done some experimental work with epoxy for filling plaster cracks.This is on a local house museum. We will definitely hear back from them if the cracks return. For a controlled experiment, we have also done some repairs with bonding agent and durabond/mesh, and some traditional lime & horsehair plaster over brick walls.
Casey

If the new wiring is within 1 1/4" of the face of the stud you will probably need to protect it with metal plates.

It is usually best to remove the baseboard and add the wring through the studs or if you intend to put a layer of drywall over all of the plaster, cut out a horizontal strip of plaster at receptacle height and run the wiring through the center of the studs.

Time will tell, but epoxy is not likely to match the thermal ad moisture expansion and contraction of plaster leading to further cracking.

It is liable to be a 'stronger than' inclusion in the repaired surface that leads to further cracking over repeated heating, cooling, and humidity cycles.

This post was edited by brickeyee on Fri, Jan 18, 13 at 11:45

Brickeyee -- you are a heck of resource. The kind of info you give out regularly on here is VERY HARD to come by!

I have been renovating an restoring houses for 35+ years, from pre-revolutionary historic houses (Old Town Alexandria, Virginia) to a few from the 1970s.

I have many feet of bookcase space with project notes from the whole time.

Hi,
The main reason we are experimenting with epoxy (it's flexible gel BTW) is that a repair can be effected in one session with no sanding, no moisture added to the room; we'll see what happens. So far, it definitely has my attention for small stress cracks.
Casey

"flexible gel"

What else have they added to it?

It is not straight epoxy.

That stuff polymerizes into a solid in a one way reaction.