Home>Discussions>INTERIORS>Molding & Carpentry>Finding Studs in Old Plaster Walls with a Twist
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Just Deb
Finding Studs in Old Plaster Walls with a Twist

Wondering if anyone has advice for finding studs on old plaster walls. Our house was built in 1946. The builders used a method of hanging drywall and then coating it with a substantial layer of plaster over the drywall. We do not have the traditional wood or metal lathe as a scaffold for the plaster. We have been told that this is referred to as plaster reinforced drywall. The walls appear to be almost two inches thick.

Our problem comes when trying to hang anything heavy. Rather than using anchors we would like to hang some heavier shelves directly into the studs. We have tried three different types of modern stud finders to accurately locate the studs with very little luck. This usually ends in drilling holes in the general vicinity until we get lucky enough to find wood. I've additionally tried a strong magnet in the hopes of locating nails behind the studs with little luck as well.

Maybe we need something even more powerful. Has anyone ever run into a similar problem? Any suggestions on better products or other methods would be greatly appreciated.

Thank you.

Clarence
Re: Finding Studs in Old Plaster Walls with a Twist

The correct term for the type of plaster system is called gypsum board base ( ROCK LATH )with a 3/4 inch plaster brown coat and a finish coat total thickness normaly would not exceed 1" MAX.
You should be able to measure out from a corner 16 inches and find the center of the first stud out from the corner.
Than 16" OC

dj1
Re: Finding Studs in Old Plaster Walls with a Twist
Clarence wrote:

The correct term for the type of plaster system is called gypsum board base ( ROCK LATH )with a 3/4 inch plaster brown coat and a finish coat total thickness normaly would not exceed 1" MAX.
You should be able to measure out from a corner 16 inches and find the center of the first stud out from the corner.
Than 16" OC

Good answer, except that too often you find walls where the studs are not 16 o.c exactly. Better to drill narrow holes, in a low and not so visible area, and locate the studs this wqy, then just fill the holes.

Just Deb
Re: Finding Studs in Old Plaster Walls with a Twist

Thanks for the quick replies to both of you. We have tried the method of measuring 16" OC from the corner with some luck, but not all of the studs are not that predictable. Often the first stud will be about 12" out, followed by another that might be 16" out, and then another at 12". Sadly, this old house doesn't follow too many of the expected protocols!! I guess we'll just have to keep at it. Sad thing about it is that a project that should normally take about 20 minutes always ends up taking hours! Guess we'll trade off the character of our old house for a few inconveniences any day.

Thanks again for the prompt responses!!

t_manero
Re: Finding Studs in Old Plaster Walls with a Twist

I am also exasperated by my plaster board walls. I hear you, a hour to find the studs, and twenty minutes for the actual work.

I just ordered a Diamond Resource 10129-ST Stud Thud Magnetic Stud Finder -- it's a specialized use of rare-earth magnet ($10 plus shipping) from Amazon.com but haven't received it.

Check back in about 2 weeks.

Other advice received included knowing that a stud is left or right of an outlet, and from there, try 16" OC, testing with dj1's drilling hole method. Also, try a rare-earth magnet along the baseboard looking for nails; it assumes the carpenter was nailing to studs.

bostonmoose
Re: Finding Studs in Old Plaster Walls with a Twist

I just tried the earth magnet last night. It located very few studs....2 to be exact. What I did then was use an electronic stud finder on "Deep stud" scan to find the stud and see if it matched up with the ones the magnetic one found. I was paranoid so I wanted a double check. Also, our studs were 24" apart. Our place was built in 1908.

Fencepost
Re: Finding Studs in Old Plaster Walls with a Twist

A couple more options:

Try a thermal imaging (infrared) camera. With it you may be able to identify a temperature difference between where the studs are and where they aren't. The best thermal imaging cameras can detect very minute variations in temperature. However, they are expensive -- maybe you can rent one.

If you have tall baseboards, remove them. Then cut into the wall behind the baseboard to identify the locations of the studs. Map them out for future reference, and replace the baseboards.

HoustonRemodeler
Re: Finding Studs in Old Plaster Walls with a Twist

If there is attic access, look for the top plates then the nails holding the wall studs in place OR holes drilled for plumbing / electric. If need be, use a piece of wire coat hanger as a very thin, long drill bit and drill through the ceiling near the wall. This will give you a reference point to measure to. Normally the ceiling joists set atop the wall joists, but that may not be the case.

t_manero
Re: Finding Studs in Old Plaster Walls
bostonmoose wrote:

I just tried the earth magnet last night. It located very few studs....2 to be exact. What I did then was use an electronic stud finder on "Deep stud" scan to find the stud and see if it matched up with the ones the magnetic one found. I was paranoid so I wanted a double check. Also, our studs were 24" apart. Our place was built in 1908.

My house is 1964 Plaster Board (1" thick) with 16" OC studs.

(1) The magnet method was mostly useless, and for me, only for finding nails in baseboard (which may or may not actually hit studs). The magnet never found metal in walls, even to the left or right of an outlet. If it found metal, I still had to small drill to actually locate the stud, and then use the 16" OC method to approximate the next stud.
(2) The 16" OC method, for me, is also very iffy - it seems 16" OC really means 12-17" OC, especially along a wall between cutouts like windows & doors.
(3) While dotting the lower half of a wall with small holes looking for 2 studs is the most exact method, finding the first stud is often exasberating.
I just bought the Franklin ProSensor 710 ($50 from Amazon) - - I haven't actually used it (i.e., confirming location of studs), but the reviews seem to indicate it is excellent for drywall, and serviceable for plaster. I get readings that look consistent when $20 electronic finders and magnets gave no readings; it easily found a known HVAC vertical duct and gave "positive" readings that seem to be consistent (for example, same readings at different heights to discount detecting a horizontal fire stop).
I believe the sensor comes with a 30-day money back arrangement (unconfirmed, do your own research), so for me, it is promising; I intend to keep just as being very good for dry wall.

Why is this a big deal ? avoids hours of effort on a 20 minute job, and minimize plaster damage since repair/repaint seems way harder/longer to me.

Fencepost
Re: Finding Studs in Old Plaster Walls with a Twist

Funny thing is, when I go to cut a hole to install a new electrical box, 9 times out of ten I manage to hit a stud with the first hole I drill... if I don't or can't check for the locations of the studs first. Which means not only do I have to move the location for the box left or right, but now I have to patch the wall.

Mastercarpentry
Re: Finding Studs in Old Plaster Walls with a Twist

When the house was built, the trim carpenter had to hit the studs to nail in the baseboards, so that's where you look for stud locations. If the painters did a perfect job with the putty so that you can't see the nails (kudos to the painters) then get a magnet or better yet, a magnetic 'wiggle' type of stud-finder made for finding metal studs in commercial walls. Find one and 16" centers should work- if they don't then it's not hard to find them all this way one at a time. If you need the exact center, use a small finish nail (or drill for plaster) and probe into the wall where the top of the baseboard meets the wall downward. A dab of caulk (almost always white) will hide those holes well till the next time you paint.

Just another of my 'idiot-proof' methods for those of us like me who tend to forget that things don't always work as they are supposed to

Phil

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