I took the liberty of adding some begginner's suggestions (and an variation on Phil's method) to the Wiki.
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's_GuideSlight tweak to formatting to help set the two apart and a couple of other minor bits.
Whilst my method (wot I learnt from Ron the Builder):
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's_Guide#How_to_skim_-_variationseems to work for me, I have not the experience to know if there are any stupid or wrong bits in there.
Anyone with plastering knowledge, please comment!
It's basically the same as Phil's method, but includes a flattening in stage after the first coat rather than the second. And more detail for beginners from a beginner.
It's actually only talking about skimming, which is only part of plastering. Would make more sense to name it something with skimming in it, unless you intend it to cover plasting eventually. It may make sense to cover scratch coat plastering in a separate article anyway -- they're reasonably different.
PVA isn't used when applying plaster to a surface which is still wet from itself being plastered or sand+cemented. (This means still initially wet, and not as a result of you wetting it, which doesn't count.) Sand+cement must be left for 24 hours before being plastered, but plaster should be recoated same day if possible. If you miss this deadline, you may need to leave it to dry and then use PVA.
I don't agree with not properly flattening the first finish coat. If you slap a second coat on too soon, and without doing this, you're really just working with one thick coat, which is going to be harder to keep flat and even.
Could do with a description of what the various coats are for...
Scratch coat (under coat) is to give you a flat, vertical (horizontal for ceiling) surface, regardless of the undulations of the underlying wall.
The finish coat is to give you a smooth finish over the scratch coat. Two coats are required. The first gives you a smooth surface by bringing the level of the whole wall up to the level of the highest peaks on the scratch coat. This should be leveled more than you suggest, but it can't be polished because the high points of the scratch coat will be on the surface of it. The second finish coat gives you headroom over all of the scratch coat peaks, which means you can polish it without hitting hard bits.
In Mixing, it's important not to go OTT with a power mixer. In particular, you mustn't wisk air into the mix, and over- mixing will also make it go off quickly. A proper power mixer is much slower than most drills, and has low gearing. The risk with using a drill is that you need to run it slowly, and unless it has a good low gear, it won't blow enough air through the motor to cool it given the high load imposed, and it may overheat. You can mitigate this somewhat by taking off the stirrer/chuck, and running the drill at top speed with no load, which will cool it down. Do this as a matter of urgency if you start smelling hot motor (don't just turn it off and leave it to cool on its own). Do remember to take the stirrer off first though!
In Cleanliness, the other important thing is that bits of plaster from you last mix, if allowed to contaminate the next mix, will make it go off more quickly and less controllably. So it's important to thoroughly clean all the tools between mixings (particularly if you're a beginner). As you say, plaster washings can go on the garden (I chuck it over the lawn), but mustn't be poured into the drains. If you don't have a garden area, pour it into a large tank or drum so the plaster sinks and sets at the bottom, before pouring off the water.
Andrew Gabriel coughed up some electrons that declared:
OK - Perhaps it could be renamed. I was thinking about adding something about undercoat plastering on various surfaces as I encounter them.
OK - thanks, I can certainly add that in.
I should mention that I'm only responsible for the second method that does flatten the first coat off, before applying the second. I didn't feel qualified to pass judgement on the first method which was already there.
Ah - OK. If I can just nick that verbatim more or less, I can add it.
Would you use a derby (or long bit of wood) on the undercoat to achieve flatness?
I'll stress again, I'm probably the wrong person to write a plastering wiki bacause I'm basically clueless - I just though it might be useful to add a true beginner's perspective.
:->>>
But I can copy n paste!
Yes - I did get a bit of this. But the air bubbles smoothed out fairly easily. It's this or 100+ quid for a real mixer :( I'll try the SDS on a slower setting next time.
Hmm - I might have seen that. One mix did seem to be setting faster than the others - I had a fight to get it on the wall before it started going.
Sound advice. I think my 8kg Aldi has such an high thermal mass that it doesn't care. But if using a more normally sized drill it could be a problem...
That would be bad (TM)
OK.
Thanks for the comments Andrew - I'll work them in...
I have posted a few detailed articles on scratch coat plastering which you can probably find with google. The technique I describe is called dots and screed (which you can probably search on).
I've also done some detailed articles on finish coat plastering.
's_Guide#How_to_skim_-_variation>> seems to work for me, I have not the experience to know if there are any
When skimming the pva should be allowed to go tacky, not dry. Any hairline cracks shoud be taped over with scrim , this can be stuck on by using a small mix of plaster trowelled along the crack and the scrim tape pressed onto this. Self adhesive scrim is no good on its own as the surface area for the adhesive is next to nothing. Scrim tape should be used where there is a change in the substrate material.
Hello Tim. In regards to Ron vs Phils methods. Ron is a highly skilled plasterer who has simply tailored Phils method, or if you like fine tuned Phils method to suit himself. Most plasterers have little quirks and minor variations. If you follow Ron's instructions as a novice you will quickly come unstuck, for he can lay on 4 m2 a minute, very evenly due to 30 odd years practise, therefore has the time to drink tea. This I can say with some authority for I am Ron the Builder. I must say I never expected anyone to even watch the vid but am delighted you found use of it. Good luck with your projects.
snipped-for-privacy@googlemail.com coughed up some electrons that declared:
No sh*t?!
Well, I have to extend a large measure of thanks to you Ron.
If it hadn't been for your video, I wouldn't have bothered even trying. I can only learn this sort of thing by watching, not reading...
OK - fair enough - you don't cover polishing in much detail and this is where I have problems. The neighbour next door complimented my efforts (he's a builder), even though I'm sure he was being nice because the polish is rather crappy, in the wrong light. But your video did at least help me get the stuff on flat, to the point a quick run over with a sander will probably tart it up well enough. And it didn't cost me £25/m2 ;->>>
BTW - are you a professional instructor? If not you should be, you've got the presentation skills :)
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