Electricians Tips from a professional electrician

[littlespark]

Electricians Tips from a professional electrician in the UK Electrical Forum

Sometimes you need to work in an old house, and there’s a number of threads on here about how to, say, fit downlights in a lathe ceiling.....

Here’s a start... on lathe and plaster walls without making a huge mess....

Mark where you want the socket to go. Height wise, measure an existing one from either the floor or the top of the skirting.


Next, use a pad saw to find a gap between the lathes. Hit and miss jabbing with the saw until it breaks through.

I will be using a regular dry lining box, so you don’t want to be too close to a vertical joist. Use the pad saw to feel to the left and right. If you can feel a joist, just adjust your planned position.

Once you have the final position, you can draw around a regular metal back box to give your cutout size.

Using a multi tool on a fairly slow speed, you can chip away at the plaster, but not the lathe quite yet.
yet.

Now, with the multi tool on a high speed and a fine toothed wood blade, you can cut neatly through the lathe without much problem. A small wood screw screwed into the middle of the lathe and held tight in pliers will help as the lathe will want to push into the hollow wall.

Now for the biggest tip I can give. Very very important whenever you are doing anything like this;



Always remember to charge your phone fully, or it will die when you’re in the middle of trying to make a hints and tips thread???

 

[snowhead]

Top tip #2, when #1 didn't quite work out,

How To Fix a Hole in Lath and Plaster Walls
Here are two ways approach your lath and plaster repair whether you have a damaged wall or if you need to patch a hole.

Estimated Time
1 to 2 hours, not including drying time
If you’re dealing with damaged lath and plaster walls—for example gaping holes in the wall because of electrical work—here are techniques you can use to repair them. First, you’ll repair the lath and then patch the hole.

How Do You Repair a Hole in Lath and Plaster Walls?
For lath and plaster repair, it’s important to use good techniques and the right materials. It’s better to use a softer, slower-setting lime-based plaster, like the one developed for Big Wally’s line of plaster-repair products, takes about an hour to set, isn’t prone to cracking or delaminating, and needs no sanding, which keeps dust to a minimum. Don’t use so-called patching plaster sold at home centers, it’s much harder than the wall’s original plaster, and it sets in the blink of an eye.

If the lath is in good condition and you need to repair holes, patching is a matter of troweling on layers of mud. Into the 20th century, plaster was applied over wood lath spaced half an inch or so apart over the studs or ceiling joists. Several coats were applied, the first keying into the spaces between the lath to make a stable base. Finish coats came after the base had dried. It’s a common practice to replace missing plaster with a piece of blue board (a wall board made to be coated with plaster), but troweling on base coat is faster.

How to Repair Lath and Plaster in 6 Steps
1. Fix the Lath

Photo by Ben Stechschulte
Replace any missing lengths of lath, and refasten all loose pieces. Use drywall screws, and always drill pilot holes to avoid splitting the wood. If there’s no stud to anchor a lath end, slip a piece of lath into the cavity and screw it to the back of the existing ones, parallel with the studs. Then you can screw new or loose lath to it, as if it were a stud.

2. Stabilize the Wall’s Edge

Photo by Ben Stechschulte
Using a 3/16-inch masonry bit, drill holes every 3 inches around the damaged area, about 1 inch from the edge. Drill until the bit hits the lath. If it misses, pencil a mark by that hole. Vacuum the holes and spray them with plaster conditioner. Wait 15 minutes, then fill all unmarked holes with a squirt of plaster adhesive. Wipe off the excess with a damp rag.

3. Wet the Substrate

Photo by Ben Stechschulte
Dry lath and the exposed plaster edge will suck water out of wet plaster before it has a chance to harden. To prevent this, saturate those surfaces with conditioner. Wipe up any drips or overspray with a damp rag. Wait until the conditioner dries—about 20 minutes—before going to Step 4.

4. Apply the Scratch Coat

Photo by Ben Stechschulte
In a clean bucket with cool tap water, mix Plaster Magic patching plaster to the consistency of natural peanut butter. Using a margin trowel, smear the mix against the old plaster edge, as shown, and over the lath. Keep this layer recessed by half the thickness of the original plaster. Rough up the patch by scratching it with a scarifier, then scrape any blobs off the wall.

5. Trowel on the Second Coat

Photo by Ben Stechschulte
Wait until the scratch coat is firm to the touch—about an hour—then mix up a new batch of plaster to a slightly thinner consistency—closer to that of buttercream frosting. Use a plastering trowel to smooth the mix flush with the wall surface; scrape any excess off the wall. Wait another hour for that coat to set.

6. Smooth the Top Coat

Photo by Ben Stechschulte
Using a 6-inch taping knife, scrape the patch area smooth, and cover the patch with a thin layer of ready-mix joint compound. Let dry overnight. Gently scrape it smooth and apply a second coat. On the third day, spread another coat, and after it dries, smooth it gently with a damp sponge. The patch is now ready to prime and paint.

How to Patch Plaster Walls if the Lath is in Good Condition
If the lath behind the old plaster is sound, patching is a matter of troweling on layers of mud. In this video, This Old House host Kevin O’Conner shows you how to patch holes in plaster walls.


Patch Holes in Plaster in 7 Steps
Force base coat into the lath. With all the loose old plaster removed, use a flat trowel to coat the exposed lath with plaster base coat, being sure to work the material into the spaces between the lath. The plaster that goes between the lath is called “keys”, and it locks the material in place. Use a stiff mix so that it won’t sag before it sets. Nylon fibers added in while mixing the base coat add strength.
Fill the area so it’s flush. Once the base coat keyed to the lath, use the flat trowel to fill the area with more base coat. Once the base coat is flush with the surface of the remaining old plaster, smooth it well with the trowel to minimize the need for sanding.
Paint on a bonding agent. When the base coat is dry, brush a plaster bonding agent over it and the surrounding old plaster. Essentially a water-based glue, the bonding agent ensures good adhesion between the old work and the new.
Tape the joints. Go over the joint between the new base coat and the old plaster with nylon mesh tape. This step will reduce the chances of any cracking that happens in the base layers from telegraphing through to the finished surface.
Coat the tape. Using a setting-type veneer plaster, use a taping knife to trowel a thin layer over the mesh tape and surrounding wall. Setting plaster hardens quickly, allowing for the next steps to happen in short order.
Finish with joint compound. After the veneer plaster sets, knock down any high spots with sandpaper, being careful not to sand through to the mesh. Finish the patch with two coats of joint compound, allowing the first to dry before smoothing on the second. The idea is to build up a large enough area to allow it to be blended to the existing wall without creating a noticeable high spot.
Sand smooth. After the second coat of joint compound has dried, blend to the old plaster using 220 grit sandpaper. Focus on blending the edges to the existing wall first, then smooth out the center of the patch.
As you could see, patching missing plaster follows a similar path as the original installation. A base coat is followed by several finish coats and a quick sanding to make old walls look new.

How To Fix a Hole in Lath and Plaster Walls

Follow this step by step guide to help with your lath and plaster repair. We share how to fix a damaged wall. Or, if the lath behind the old plaster is in good condition then how to patch a hole plaster walls by troweling on layers of mud.

www.thisoldhouse.com

 

[Lister1987]

Sometimes you need to work in an old house, and there’s a number of threads on here about how to, say, fit downlights in a lathe ceiling.....

Here’s a start... on lathe and plaster walls without making a huge mess....

Mark where you want the socket to go. Height wise, measure an existing one from either the floor or the top of the skirting.
View attachment 86407

Next, use a pad saw to find a gap between the lathes. Hit and miss jabbing with the saw until it breaks through.
View attachment 86408

I will be using a regular dry lining box, so you don’t want to be too close to a vertical joist. Use the pad saw to feel to the left and right. If you can feel a joist, just adjust your planned position.

View attachment 86409

Once you have the final position, you can draw around a regular metal back box to give your cutout size.

View attachment 86410

Using a multi tool on a fairly slow speed, you can chip away at the plaster, but not the lathe quite yet.
yet.

View attachment 86411

Now, with the multi tool on a high speed and a fine toothed wood blade, you can cut neatly through the lathe without much problem. A small wood screw screwed into the middle of the lathe and held tight in pliers will help as the lathe will want to push into the hollow wall.
View attachment 86412

Now for the biggest tip I can give. Very very important whenever you are doing anything like this;



Always remember to charge your phone fully, or it will die when you’re in the middle of trying to make a hints and tips thread???

M12 CMT? If it is a 12v, do you rate it? I know 18v will have more punch but I've got a bucket load of M12 batteries, thinking just basic jobs like drywall, breaking the tongue between floorboards etc

 

[littlespark]

M12 CMT? If it is a 12v, do you rate it? I know 18v will have more punch but I've got a bucket load of M12 batteries, thinking just basic jobs like drywall, breaking the tongue between floorboards etc

The multi tool? M12 Free gift from Howdens for opening an account.

Good enough for what I need it for

 

[Dave OCD]

Sometimes you come across very thick old plaster and can fit a metal box flush directly on the laths, can be a little bit bouncy though and you need to be careful not to split the laths.

 

[HappyHippyDad]

I try to position them actually on the vertical joists in a metal box. Even if the 25mm sits a little proud you can take a small bit out of the joist.
You lose a little in the choice of area you can have it, but it's a much easier and stronger fit.

 

[Dave OCD]

Yes I've done that as well HHD, although the majority these days seem to just whack a surface box straight above the skirting. ?

 

[telectrix]

another tip. totally unrelated but...... when you remove a redundant accessory, before binning it, save the terminal screws ( aslong as undamaged). the number of times i've taken ,say, a new cooker switch out of the van stock to find that 1 or 2 screws have worked loose in transit and disappeared for ever is ridiculous.

 

[nicebutdim]

Don't you keep a range of screws for accessories? Old houses were supplied screws need to be replaced with anything from 30mm - 75mm...

 

[telectrix]

i'm referring to terminal screws, not 3.5mm pins.

 

[littlespark]

I’m now imagining tel with a poly bag full of used terminal screws.

 

[Lister1987]

i'm referring to terminal screws, not 3.5mm pins.

And yet can you buy a pack of say 100 (brand specific) from a wholesaler? Can you hell, you think they would knowing this sort of thing happens.... Maybe they ship them out backed off and held in by a to test bit of thread, look at it wrong and poof there goes the screw

 

[Mike Johnson]

For what its worth: Vertical support members in a wall are studs, joists are horizontal support members normally in a floor or ceiling.

 

[brianmoooore]

Fitted many hundreds of sockets into lath and plaster walls over the years, have tried the methods detailed in this thread, but have found that any that leaves a cut end of laths unsupported will eventually cause problems.
The method I eventually settled on was to cut a rectangle of lath and plaster away, making the vertical cuts in the centre of the adjacent studs, down to the skirting board (especially pre part M) and horizontally just above the top of the proposed socket, and also removing the plaster from the next lath up.
At this stage, you could get a drill inside the wall, and drill a nice central hole down to the space below the floorboards to bring the cables through, then fit a good solid noggin between the studs to screw a metal socket box to. Finally comes two layers of plasterboard, either 9.5mm, 12.5mm, or one of each, depending on the surrounding plaster thickness, with the outer one overlapping the lath left at the top, to reinforce the join when it's skimmed over.

 

[Pretty Mouth]

but have found that any that leaves a cut end of laths unsupported will eventually cause problems.

Exactly this. The plaster to the sides of the cut out is not supported, so very weak. It can be reinforced though, using timber battens, without too much trouble:

• Cut the hole out of the lath and plaster for the backbox with multitool (we're gonna use a steel BB).
• Cut a couple of timber battens, something about 2" X 1" should do. They're going to go inside the wall, vertically, to either side of the hole, and need to be long enough to extend beyond a couple of un-cut laths, both top and bottom. About 150 - 200mm long is about right.
• Reach inside the hole, and carefully pull away the plaster 'keys' from either side of the hole where the battens are to go. We want the battens to press right up against the back of the laths without being fouled by any bits of plaster.
• Now the fiddly bit.
• Liberally coat the face of one batten with PVA, water based gripfill, or similar. Maneuver the batten through the hole and into position vertically to the side of the hole, glue side pressed up against the back of the laths. Hold in place, and drive a screw through the plaster, through an un-cut lath, and into the top of the batten. Repeat for the bottom of the batten. You can put screws through the cut laths into the batten too if you like.
• That side is now reinforced, and will be about as strong as you can hope for in a lath and plaster wall. Do the same for the other side of the hole with the other batten. You can now fix the backbox in place by screwing through the sides into the battens.
• Filler over the screw holes and you're done.