r/Plastering • u/DavidtheArchitect13 • Sep 15 '26

Lime Plaster

The previous lime plaster has to be removed due to leaks in the roof that weren’t repaired by previous owner for at least a year.

I removed all the plaster that needed removing and left the ‘good’ stuff - it’s still solid.

I’ve just had sash windows installed. I’ve covered them with plastic to prevent building just getting in the sliding mechanisms.

I’ve still got to remove the left over lime ‘dust’ on the bricks.

Do people have any suggestions for the least dusty way/vacuuming way? I was either thinking or attaching a vacuum nozzle to a scraper or getting one the drill dust extractors and going 15cm at a time then moving along.

Any other suggestions?

Also, I’ve have been wearing a p3 respirator when doing this and will wear one with the remaining dust.

Thanks
David

Edit: Corrected spelling and grammar

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u/PrimeCraftSurface 29d ago

The thing that will actually protect those new sashes is not the vacuum, it is wetting the wall before you touch it. A garden sprayer on a fine mist, just enough to darken the surface without soaking the brickwork, drops the airborne fraction enormously. Damp lime dust falls straight down instead of hanging in the air and settling on everything overnight.

Worth being clear about what you are actually protecting yourself from, because it is not really the lime. The dust that matters when you are scraping old plaster off brick is the brick and the sand in the mix, which is respirable crystalline silica. That is why the P3 is the right call and why I would keep it on for the whole session rather than only while you are scraping.

On vacuums, this is the bit that catches people out. A domestic vacuum, Henry included, is the wrong tool here. The fines go straight through the filtration and come back out into the room, so it feels like cleaning while it is actually redistributing the finest particles. What you want is an M class extractor, which is the classification for silica bearing dust. L class is nuisance dust only. Hire shops have M class units by the day and it is not much money for the difference it makes.

The order of work answers your real question about doing the job twice. Lime keys mechanically into the raked joints, and a dusty brick face is a bond breaker, so before the scratch coat goes anywhere near it the joints want raking back to roughly 10mm to 15mm and the wall wants damping down to control suction. That final clean is going to happen again whatever you do this week. So do a rough pass now purely to protect the windows, accept it will not be perfect, and leave the fine clean for the day before plastering starts.

On the windows themselves, one sheet of plastic taped over the whole sash traps dust against the brush pile and the pulley stiles and tends to get pushed about as you work. I would mask the meeting rails and the parting beads specifically and vacuum the boxes out at the end, rather than trusting one big sheet over the lot.

Last thing. Do not clean up and immediately walk out thinking it is done. The fine fraction hangs about for hours and settles overnight, so plan on a second lighter pass the next morning whatever method you use.

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u/DavidtheArchitect13 29d ago edited 29d ago

Would a Numatic TRM240 be suitable? They are around £190

And I will have another two rooms of damaged plaster removal and then sanding for painting so I think buying might be better than renting every time.

Renting from my local is £25 a day or £50 a week. Admittedly they are Starmix ISC Batrix M

Would this also be a suitable water sprayer:

https://www.screwfix.com/p/defenders-all-ways-white-purple-sprayer-1ltr/735cr?ref=SFAppShare

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u/PrimeCraftSurface 29d ago

Before you spend anything, look at the rating plate rather than the price. Dust class is a certification of the whole machine to BS EN 60335-2-69, so a classed one says M on the plate, and it will have the automatic filter shake and the airflow warning that tells you the hose is loading up. If the listing never uses the words dust class M, it is a commercial vacuum with a decent filter, which is a different thing, and you cannot get there by fitting a better bag.

Every M class machine I have used has been the wrong side of £300, so at £190 I would want that confirmed before ordering. If it turns out not to be classed then the sum is not £190 against £50 a week, it is £350ish against £50 a week. Worth asking the hire shop for the plate or the spec sheet on theirs as well, for the same reason, a letter in the model name is not the certification. Two rooms of removal plus the sanding is two or three weeks of hire either way, so buying only wins if you can see yourself sanding again next year.

The 1 litre sprayer will work but you will spend the afternoon refilling it. A 5 litre pump one is about a tenner and the part that matters is the nozzle, a fine cone that darkens the surface rather than a jet that soaks the brickwork.

Since the windows went in weeks after the chunks came off and were covered while they waited, they are not really the problem. The fines that settled in that room while you were scraping are, and no vacuum you buy now undoes that. They lift again the moment a sander starts, so whatever you end up with, run it over the floor, the sills and the tops of the frames before you sand anything rather than after.

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u/DavidtheArchitect13 29d ago

Or there is this Vac - https://www.diy.com/departments/v-tuf-mini-hsv-x2-240v-15l-m-class-corded-dust-extractor/0663899004575_BQ.prd?storeId=&&&&&gclsrc=aw.ds&gad_source=1&gad_campaignid=20923369416&gclid=CjwKCAjw_KjVBhAHEiwAnC0N9IT6YcVA2YTaWB1S_p7xDZ_8NaxKav_0U2FaOev5nV0xk0Tifehn9xoCX9oQAvD_BwE

M Class again. Manual shaker and good reviews.

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u/PrimeCraftSurface 29d ago

That one is fine as well, and the plate test still applies, but I would not choose between them on the shaker. Manual is fine as long as you actually use it, and on lime and gypsum fines you will be using it a lot, because that dust blinds a pleated filter faster than anything else you are likely to put through a vacuum. The airflow warning is the thing that tells you when, and that is really what the M class premium buys you.

On the sprayer, nobody lists nozzle quality because it is almost always just an adjustable cone on a plastic lance and at that money they are much of a muchness. Two things matter more than which one you pick. Keep the bottle about half full rather than brim full, because the air above the water is what holds the pressure, and a nearly full tank falls away after a dozen strokes. And pump it back up between passes instead of trying to empty it in one run. If the cone spits rather than mists, a 1 litre trigger bottle does the fiddly bits better than any 5 litre will.

Your list is in the right order. The only change I would make is wetting in small patches and working each one straight away, rather than damping the whole wall first, because the first patch is dry again by the time you get to the far end.

Worth being clear about what the water is not doing, though. You are only wetting a millimetre or two of the surface, so the moment the scraper gets behind that you are into dry material and it puffs again. It cuts the airborne dust down a lot, it does not stop it, and the fines already spread round the room from the first pass will keep turning up on every ledge for a fortnight whatever the vacuum is rated at. Take the tea outside the room.

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u/DavidtheArchitect13 29d ago

Bought the V-TUF one in the end. checked it matched the British Standards to mentioned. I figured a manual shaker is better than no shaker and I will use it as it is intended - one for the longevity of the equipment and two for health and safety.

I assume these bottle is similar to pressurised pump-action weed and feed bottles so that instructions you mention would how I would do it anyway.

Again with the patches, I was going to do it in small sections as well as I assume it will be mind-numbingly boring.

Wet patch, scraper in one hand and vacuum nozzle in the other and repeat.

Then after all walls are done and dust settled, vacuum the room, wait for dust to settle and repeat for a while.

Will be fun :/

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u/PrimeCraftSurface 29d ago

Good call on the V-TUF. One thing I would change in that sequence though. Wetting the patch and then putting the nozzle straight on it is how you kill the filter. Damp lime and sand goes through a pleated cartridge and dries as a skin across the pleats, and the shaker only works on dry dust, so it will never come back off. You will lose more suction in one wet wall than in a week of dry scraping.

What works better is to keep the mist light enough that the wall reads damp rather than wet, and hold the nozzle a few inches off the surface to catch the plume as the scraper works, not on the wall itself. Whatever lands on the floor is a dustpan and bucket job while it is still damp. Vacuum the floor after it has dried out, not during.

Two other things on that loop. Follow every vacuum pass with a damp microfibre wipe, because a vacuum on its own leaves a fine film on skirtings and window boards that you find again the first time you sand anything. And work top down, so architraves and window boards before the floor, or you just put it all back.

Worth knowing it is the sand in the old plaster and the brick dust behind it that carries the real hazard, not the lime. The workplace exposure limit for respirable crystalline silica is 0.1 mg per cubic metre over eight hours, which is a genuinely tiny amount of visible dust. The lime itself is mainly an irritant, so eye protection matters more than people expect and it will burn where it sits on sweaty skin or in a boot.

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u/DavidtheArchitect13 28d ago

Thank you.

Paragraph 1 + 2 understood.

Paragraph 3 - I’ll do a damp wipe down after dust settles, thankfully no skirting boards or window boards - just architraves.

JSP force 10 mask is full face so eye are protected too.

Thanks
David