plastering: first attempts

[Fred]

Hello,

I had a go at plastering a plasterboard wall for the first time today and it went quite well. I'm going to try to skim a wall tomorrow. I understand this is harder, so wish me luck!

I've got a few questions based on my experiences so far:

I read that you should add the plaster to the water, not the other way round, yet with mortar I mix the sand and cement and add the water to that. Is it critical to add plaster to water? If done the other way round would it cause the plaster to clump like wall paper paste does?

The problem for a novice like me, is knowing how much water to put in the bucket. I read you should trowel the plaster in but that took me ages so I gave up and just poured from the bag. What is the right way of doing this?

I underestimated how much mix I would need. I mixed a batch then cleaned everything and was cross to find I had to go back and make some more and dirty everything again!

I see you can buy plasterers buckets which have tall walls. Is this so you can make a very big batch to avoid this happening, or is it just to stop if spraying everywhere if you use a paddle on the end of a drill to mix it?

Is there a rule of thumb that you need so much plaster and so much water to cover x square metres? I doubt there is as I suppose coverage depends on what you are plastering on to?

I bought a cheap aluminium hawk. Are aluminium ones better or worse than plastic? I suppose neither rust. I can see how an expensive trowel might be better than a cheap one but with hawks is there any advantage to buying an expensive one?

When should you clean the hawk? Before you start polishing? The second plasterboard wall I did was larger and by the time I got to one end, the first end was beginning to dry so I did not stop. I've cleaned the hawk as best I can but there is some "staining". Does this mean I have not removed all the plaster or is it some chemical reaction between the plaster and aluminium? Need I worry?

What is the trick for long walls? How do you make sure you finish covering the wall before the first bit dries?

Any tips for skimming an old wall? I realise I will have to PVA first.

TIA

[sm_jamieson]

Good luck. I have resolutely given up skimming. I will never get the finish a time-served plasterer does. I always thought those folks who can mime being in a box (you know what I mean) could make good plasterers. Gotta know where flat is. Folks always say just slap on the first coat, then level it when its reached plasticine stage. But that is nonsense. You can only push it around so much. The first application has to be pretty flat - it's localised peaks and ridges that don't matter. A fairly fast sweeping movement helps to get it flat - going to slow gives undulations. Simon.

[<me9]

There is the odd occasion that old plaster is useful. You don't have to wait long for it to go off. Handy for a small job.

The most useful is old bonding compound used for dot&dab. goes off as you hold the dot in alignment.

[john]

I'd quite gotten into the plaster stuff and started 'running' mouldings. First moulding mix I ever did, used two (supposedly fresh) bags of Plaster of Paris. It went off about 30 seconds into the mixing. Stirrer locked into the solid mass and the bathfull of mix started steaming. I could feel the heat from feet away. An overactive imagination deduced it was somehow going 'critical' ,so rapidly exited stage left. (I lived and learnt :)

[John Rumm]

Good luck!

Yup easier to mix without lumps if you add plaster to water. Stick a paddle in the end of a drill (with speed control or low speed!), big floppy bucket. Chuck say 4L in the bottom and the top of a bag. Get mixing, and trowel in some more plaster to get the mix consistency you want.

A bit of both in my experience - you can gustimate the right amount to tip in, and then fine tune by troweling in extra as you mix.

It always take more than you expect!

The big floppy buckets with two handles I quite like. You can mix a whole bag in one go in one if you need to.

You can get a rough idea by working out the volume you plan to apply. Also the British gypsum site has some expected coverage details in their spec sheets. See the PDF on this page for example:

I bought a cheap aluminium hawk. Are aluminium ones better or worse

I prefer the ali - but there is not much in it.

Not really...

Dip in big bucket of water and wipe off with your hand - usually does it for me!

If in doubt, stick a batten up the middle, and plaster up to that (when doing base coat it also gives you something to level against). Once done you can take it off before its completely set and then use the stiff edge of the plaster as you starting level for the next bit.

(you can get metal level guides that are designed to be left in the plaster that achieve the same)

Pump up gardern sprayer. Soak it first all over, then slap on your dilute PVA, then plaster onto that.

[Andrew Gabriel]

[Dave Liquorice]

had been given, make a mould with clay and pour in the plaster of paris...

Also seems a bit odd that no one could get the PoP off, doesn't the school woodworking shop have a hammer and chisel? Getting the lump free from the bucket might be hard once out would be a lot easier to deal with. Wouldn't be nice for the people wielding the hammer/chisel or the student but then niether are the burns... Serious situations call for drastic measures.

[Andrew Gabriel]

You want low gear. If you haven't got a gearbox, you'll need to select low speed, but this is a very good way to burn out a drill, as it's quite a load with not enough cooling. If the drill does start to get hot or smell, take the paddle off and spin the drill at top speed with no load to cool it down.

I use a firm plastic bucket. You must find one with a flat bottom inside, no ridges or indentations, as that will stop you mixing it completely.

Start off by 1/4 filling the bucket with water, and keep troweling in plaster as you mix it smooth. Try not to entrain air into the mix or to mix it much more than is necessary; you aren't making a cake. Finish coat should be slightly more runny that scratch coat. When you load up the trowel face, if you swivel it round vertical, finish coat should slide off, whereas scratch coat should stay put just, but slide off if you give the trowel a small vertical movement to get the plaster to break grip.

Once you get more familiar with mixing, you can adjust the quantities appropriately.

That's completely normal. You have to clean everything between each new mix anyway, as contamination by the previous mix will cause the new mix to set faster.

When I've mixed up, I pour it out onto a board (damped first time), and then go and clean up the bucket and paddle. The new plaster will wait a few minutes, but trying to clean up the implements after you've put the plaster up is harder. Don't let the plaster washings go down a drain. I chuck them over the lawn.

As a novice, you'll only get through half of it before it's set though. I tend to use the black 3 gallon/14 litre buckets. One of those full is what I can comfortably get on the wall in time (less so for finish coat). If you're pouring out onto a board (which is probably easier for a beginner than loading the plaster from the bucket), then you need a large enough board to hold the amount you mix up.

Cheap plastic ones can suffer fatigue after a lot of use and the handle breaks off.

Talking of which, buy a tube of barrier cream (Savlon and Boots do them). Chemists often have it, or you can order it from CPC. Plaster can do quite nasty things to your skin otherwise. Also, avoid repeatedly washing with soap during the job - just wash plaster off with water if you need to, until you've finished.

If you end up with cracked hands through not using barrier cream, then an after treatment is to rub in vasalene. However, as someone here said before, it's much easier to get a skin problem than it is to get rid of one, so do use barrier cream.

You don't need to. You just need to apply the next area before the previous one sets.

I did a long post some time back describing how to make the scratch coat flat using a technique known as "dots and screeds".

extend this to a long wall, you use several screeds, and you can level them by using a string streched across the screed fronts.

[John Rumm]

Yup agreed, should have mentioned that.

BTW - Makro have some cheap mixer drills at about £30 currently...

off cut of plasterboard on a workmate seems to do it ok - but wet it well first...

For finish coat, that's true. For bonding, it depends on what you are plastering, and how thick IME. I was redoing the inside of the dwarf walls of an old conservatory once - various lumps and bits missing meant that the base coat needed to be quite thick to come out level all over. It was quite easy to get through a bag at a time in that case. Onto a nice new built wall it would be a different story though.

I usually wear latex gloves for this sort of job....

[John Rumm]

copping so much of the blame as it seems they gave the correct instructions. Perhaps they did not spell out the dangers of P of P adequately.

Shame no one had a SDS to hand!

[Phil L]

When skiming old plaster, make sure there are no nails, tacks, blue-tack, clumps of wallpaper or any other 'bits' on the wall, if there are, remove them prior to applying PVA.

Apply PVA generously, don't skimp and give it two coats if possible, the second after the first has dried....it doesn't matter whether you skim over the pva dry or wet, but any patches not treated with pva will dry almost immediately and make a bollocks of the trowelling-up process.

To do a long wall, start at one end (point 1) with stepladders and apply a band across the top of the wall about 2 -3 feet down from the ceiling, all the way from one end to the other. Get down, remove steps out of area and apply another band the same width in the middle of the wall, then, apply the last band whilst you are kneeling down, don't be tempted to drop back onto what's already covered. Once the full wall is covered in plaster, start again where you started originally (point 1) and apply a thin 2nd coat, taking out most of the imperfetions, don't be too picky, this is still only an initial phase. Follow the same route over the wall as you did with the 1st coat, until it's had a 2nd coat and is looking fairly flattish. Wash implements, hawk, trowels, mixers and buckets. Start again at point 1 and go over the entire wall with a light splash of water over about a square metre at a time and take out any imperfections, repeat this process until you are happy with the finish.

If at any time you are putting more marks in than you are taking out, stop and wait for 5 minutes to allow the plaster to go off slightly then have another go, starting from point 1 again.

[Phil L]

This should have read, 'a 2-3 foot band, from the ceiling down', that is to say, the top 2-3 ft of the wall

[Fred]

I'm not sure that I will ever get that finish either but if you are going to paper over it, it doesn't matter if it is not 100% perfect, or at least that was my line of thinking. I've had two different plasterers do work for me before and neither of them have a perfect finish; there were odd swirls here and there, so I'm not sure even a pro gets it 100% right, or perhaps my plasterers weren't good ones!

One thing I have not understood is how you know that the thickness is uniform. I have managed to smooth the surface but how do I know I don't have 4mm on one side, sloping to 2mm on the other? OTOH the walls weren't straight or smooth in the first place; if they had been, I wouldn't have needed to plaster them, so things can't get any worse than they already were, can they?

[Fred]

I had heard this about this accident when, IIRC, they were talking about it on the Jeremy Vine show on Radio 2 a few months ago.

I was surprised to hear it set so fast and so hot.

On the radio they mentioned there had been a similar accident at a school in Scotland but details were not circulated to other schools; if they had been, perhaps this accident could have been prevented?

A quick google found this:

talks about a Scottish accident "years ago". I don't know if it is the same one. It says that the pupil lost two fingers and that the rescue attempt did "harm", so I'm unsure whether they are implying the chisel did more damage than the plaster.

OTOH how would they know what damage would have been done if they had not got the chisel out? I would like to think that they were right to try to help.

[Fred]

What type of drill are we talking about here? recently I posted about core drilling and I made the mistake of thinking a large hole required a slow speed until John pointed out that an sds on full speed is relatively slow compared to a "traditional" drill.

I wouldn't use an expensive sds drill to mix plaster but I have a £50 Screwfix model I could use. Would you still need a low speed for an sds drill?

I remember Wickes sold a special "high torque" drill for mixing but I think they discontinued it last year. Perhaps people don't buy/need a special drill for mixing any more? Are they any good?

I see Tool station sell different sizes of paddles quite cheaply. Some are hex to fit into a normal drill chuck, others have a thread. Do the cheap hex ones do the job? Do you just buy the biggest one you can or is there a danger that the biggest ones will overload your drill?

Yesterday everything went well. Today less so. I don't know whether this was because I was plastering a wall rather than a plasterboard. Perhaps the PVA was too wet, too dry, too dilute (I used 5:1 as stated on the label)? Perhaps it had nothing to do with the PVA.

I think I may have mixed it too dry and I think this is why I found it harder to spread and why it seemed to dry before I was ready. Yesterday it was quite running and a few dollops fell off and onto the floor. Today I think it would have stayed put if the trowel was upside down, so I think today's problems were too little water.

I think I am probably overmixing too. Being new I suppose I was nervous about it being lumpy so I may have mixed too long. I think there were some air bubbles when I first spread it on the wall. If they are there, I guess I'll find out in a few years if I use a steam stripper to remove the wallpaper!

It's just a bit soul destroying to have to clean the same things over and over again and ity doesn't help if you are cleaning them in the garden but plastering the bedroom furthest away, like I was!

I was caught out by this. I had assumed that you got the plaster straight from the bucket. Fortunately I had some plasterboard off cuts and used those. The problem is they are for one-off use only and then had to be thrown away. What do others use: a scrap of plywood?

I have done half a wall with one batch but then got nervous that by the time I had mixed the second batch the bit I had done would have set. I think the wall looks ok, so it was probably beginner's nerves worrying about nothing but I don't suppose I'll know for sure until I look at it once dry.

Thanks for all your help to everyone who replied.

[Fred]

Thanks. Your post and Andrew's overlapped, so I have tried to reply to you both in one post. Thanks again.

[Jim K]

this:

link at bottom of page1 of that pdf links to a 2005 BBC news report

- so it was publicised but not picked up (enough) what else was occurring in 2004 (assuming the case took the usual min 6months to trial?

cheers Jim K

[Dave Liquorice]

The student hadn't followed the instructions, perhaps if the information had be circulated the instructions may have been reinforced and the dangers pointed out. Hindsight is wonderfull...

with it. 4l of PoP gets to skin damage temperature in less than 30 mins and gets an awful lot hotter in the next 30 mins.

It isn't clear, maybe the removal of the setting PoP also removed the skin? But which is worse removing some already damaged skin and the heat source or letting the whole hand slowly cook...

That is my view. Sometimes seemingly drastic action is required to produce a better overall outcome.

[stuart noble]

I used part of an old kitchen carcass last time. Anything that's non-absorbent basically.

I admire you having a go at a whole wall as a beginner. I'm happy levelling up to to beads, but freehand is a skill I fear I won't have time to acquire in this lifetime. Also, I find plaster THE most frustrating stuff to work with. With most d-i-y jobs you can get a professional result if you take your time but, with plastering, there's only one way to work, and that's fast.

[John Rumm]

Well the ideal is a "mixer" drill. These are usually geared down to 500 rpm or similar, so they turn with high torque, slow speed, but keep the motor running at speed and hence well cooled.

Personally I just use my 18V combi drill in low gear - its small enough to use one handed. Low gear tops out at 600 rpm, and the speed controller is good enough to prevent spraying it all about the place when starting off with mostly water!

I have used my SDS for plaster - with a SDS adaptor chuck. Generally although there is a tendency to reserve ones nicest tools for "best", the reality is the pro tools will tend to stand up to this type of use better anyway.

An accelerator trigger is good unless you can mix the first bit by hand when its particularly sloppy. Once you start getting some thickness in the mix a SDS flat out and a smallish paddle will most probably be ok running flat out.

Well they are used by folks doing lots of mixing - so unless that is your line of work, you won't be doing enough to make it worthwhile buying a dedicated drill.

You can on occasion pick up cheapies that might do the job. Silverline don one, and there is the Makro fairline branded one at £30 at the moment.

For DIY levels of plaster mixing, the smaller paddle with a couple of twisted flutes on the end is usually plenty.

Something like: