What is this wall made of, and how can I plaster over it?

Hi. I've removed all the plaster from a bedroom and my external walls are brick, along with the dividing wall (end of terrace) and chimney breast. The internal walls are... well, I don't know what we call it. There are some pictures below, of various points in the room. You'll see the white stuff I'm referring to. Joints are a kind of "cement" distinct from the plaster I removed from the surface:















Questions:

1) Out of interest, how do I refer to the white wall material?

2) How can I plaster onto it - would dot & dab work for plasterboard? Can I use wet backing plaster (there was previously some kind of sandy, hairy backing plaster on it)? What preparation would be required?

3) May I PVA the brick walls to seal off all the dust that's still being produced? It's been such a messy job so far and I want to keep it neater. Though I hear that PVA isn't required for dot & dab, is it acceptable and not an issue?

4) Apparently dot & dab is not acceptable on external walls of certain kinds. How can I determine whether my walls are OK for it?

I want to start plastering this room in the next week or so. I may well end up using a mixture of boards and wet plaster. Battening isn't really an option as I don't want to lose all that depth on the walls, and also I'd have to do some serious rearrangement of the door and window frames, especially the PVC one.



Thanks for any advice.

The white walls are thermalite blocks.
You can use PVA solution to seal the dust in.
The original plaster would have been a browning coat, followed by a skim (if its really old, then horse hair could have been added to the browning mix).
Dot and dab is ok - as far as it goes - for plasterboard.
Thats a hell of an area to plaster yourself....have you considered getting a plastering team in? Expert guys will have that done perfectly in no time and the results will be superb.
John

Are your external walls cavity? If they are solid D&D is not a good idea. As for battening taking up loads of room, the tightest dab youll get on them brick walls is gonna be 10mm plus plasterboard, batten is only 25mm plus plasterboard, you can fix your skirtings nice, leave a ventilation gap, have no cold bridges and the skim will dry out quicker.

Burnerman said:

The white walls are thermalite blocks.
You can use PVA solution to seal the dust in.
The original plaster would have been a browning coat, followed by a skim (if its really old, then horse hair could have been added to the browning mix).
Dot and dab is ok - as far as it goes - for plasterboard.
Thats a hell of an area to plaster yourself....have you considered getting a plastering team in? Expert guys will have that done perfectly in no time and the results will be superb.
John

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I had trouble finding a suitable plasterer - the one who came round to quote gave me an outrageous price (£600 just to skim) and the only other one I could interest quoted me a more reasonable £700 for backing + skim (or boards + skim, alternatively) but he hadn't actually seen the room and I wasn't confident in his "decision".

I might as well have a go at it myself, I suppose. What's the worst that can happen?...

1john said:

Are your external walls cavity? If they are solid D&D is not a good idea. As for battening taking up loads of room, the tightest dab youll get on them brick walls is gonna be 10mm plus plasterboard, batten is only 25mm plus plasterboard, you can fix your skirtings nice, leave a ventilation gap, have no cold bridges and the skim will dry out quicker.

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I don't know how we describe the wall construction, I'm afraid - I don't know enough about that sort of thing to be able to look at it and tell.

That's a fair point about battening vs d&d, then. I suppose it's not a huge difference. I'm actually leaning towards trying to apply Hardwall as the base coat. From what I can gather it's no more difficult than skimming (which in itself may be quite difficult, I'm sure) and though I may get a worse finish it's not going to be a disaster.

smp50 said:

I might as well have a go at it myself, I suppose. What's the worst that can happen?...

That's a fair point about battening vs d&d, then. I suppose it's not a huge difference. I'm actually leaning towards trying to apply Hardwall as the base coat. From what I can gather it's no more difficult than skimming (which in itself may be quite difficult, I'm sure) and though I may get a worse finish it's not going to be a disaster.

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The battening will be much easier for a novice and use of boards will give a good surface to skim (assuming you get the boards plumb, butted well etc). This will cost much less than both and would give a good result.

The Hardwall option is a lot lot harder - so not really sure how you get that impression. 'What's the worst that can happen?' It can dry out too fast and crack/fall off, getting it smooth and plumb is not easy. Don't underestimate the volume you'll need to mix either.
If it does go wrong, then getting the stuff off could be horrible or if you then need to go over the top of it, the thickness will then be much greater and approaching battening anyway. It could be a real disaster. You have nicely stripped back walls at the moment. A pro will be happy with this as a start. You half-cover it with Hardwall in a mess, and I suspect your price would go up.

I'd encourage you to research a bit more.
Finding out more about your wall construction would be useful. Try to work out how thick the walls are, that may help indicate if there's a cavity. D&D is not as tough either as floating Hardwall, and if you have a cavity, D&D should be ok.

DIYnewbee99 said:

smp50 said:

I might as well have a go at it myself, I suppose. What's the worst that can happen?...

That's a fair point about battening vs d&d, then. I suppose it's not a huge difference. I'm actually leaning towards trying to apply Hardwall as the base coat. From what I can gather it's no more difficult than skimming (which in itself may be quite difficult, I'm sure) and though I may get a worse finish it's not going to be a disaster.

Click to expand...

The battening will be much easier for a novice and use of boards will give a good surface to skim (assuming you get the boards plumb, butted well etc). This will cost much less than both and would give a good result.

The Hardwall option is a lot lot harder - so not really sure how you get that impression. 'What's the worst that can happen?' It can dry out too fast and crack/fall off, getting it smooth and plumb is not easy. Don't underestimate the volume you'll need to mix either.
If it does go wrong, then getting the stuff off could be horrible or if you then need to go over the top of it, the thickness will then be much greater and approaching battening anyway. It could be a real disaster. You have nicely stripped back walls at the moment. A pro will be happy with this as a start. You half-cover it with Hardwall in a mess, and I suspect your price would go up.

I'd encourage you to research a bit more.
Finding out more about your wall construction would be useful. Try to work out how thick the walls are, that may help indicate if there's a cavity. D&D is not as tough either as floating Hardwall, and if you have a cavity, D&D should be ok.

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I just measured my walls and they're ~280mm thick. The pictures of the windows above show you a bit of their structure. Does this tell us whether they're cavity or not? The old plaster was <15mm thick in total, around the windows, and <20mm elsewhere - so I'd like to keep it around this mark if possible so that I don't have to really change the window and door frame trim (which I can't actually remove currently, in fact).

I know that using a wet backing plaster could go wrong, but I'm tempted to try it. I know of other DIYers who've managed and surely so long as I don't make some huge error in judgement then it should completely fail? I mean, what would I have to do wrong to completely ruin the wall, mix it incorrectly or something? I don't know.

I'd encourage you to research a bit more.

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Do you have any particular resources you think I should read? I've been looking at this job literally for months now and not getting anywhere with it because I just haven't comitted to a course of action and gone for it. I'm not sure what else I should research, what more do I need to learn before just having a go one way or another?

I will let the pros comment on wall thickness etc, as I'm not a building expert.

On the plastering, if you want to limit the thickness in the window alcove, then you could D&D plasterboard on the reveals regardless if you did go for the battening on the main walls.
From looking at your pic around the turquoise door, it looks like you have enough of the architrave (trim) off already.

You're right other DIYers have tried it - myself included. I have floated entire rooms but only did it after I'd been on a course to teach me the basics, and had skimmed most of my previous house as well as patched up a lot of areas of backing plaster with Bonding and even floated some small areas. I would still not call myself an expert.
For floating completely blank walls you need to setup screeds to work off and is hard getting it all level and mixing the large volumes of plaster. Suction is tricky and if you don't manage it correctly, you're in trouble. You have at least two different backgrounds in the room, which may well behave differently to each other. D&D or battening would remove this from the equation for you.

Don't get me wrong, I'm all in favour of us DIYers having a go - I just think you need to build up to things and there is no substitute for hands-on practice but building up slowly. To float this job at your first attempt in my opinion is a bridge too far.
If you can batten or D&D then I think you can do most of the work yourself and achieve a good result in taking your time. Then you only need a pro to skim for you. I'm sure you can keep shopping round to get a more reasonable skim quote. As is the way though - don't just go on price. See some work examples first. There are a few chancers out there.

One concern is hanging the radiator back up. Would I just have to make sure there's a good bit of adhesive where the hole's going to be drilled? Or, do I cut the plasterboard out and put the brackets straight into the brick?

And the clearance between the brickwork and the window/door frames or trim is very narrow, 5-15mm I guess I'd have to adjust them somewhat if I do use plasterboard.

I also have no idea how I'll get plasterboard home (I'd have to pay to get it delivered, I suppose) and I can't just get a few to "try" one wall first and see if I'm happy with it.

I just have a really bad feeling about it in general, I think I'd almost rather get a plasterer in than DIY with plasterboard. I don't like the stuff.

Is there any harm in really going to town with the adhesive, like half a bag per board (8' x 4') so that when pressed on there are hardly any hollow spots at all? I'd be much happier with that, I think.

It looks like I can get 12 boards and 5 x 25kg of Wickes adhesive for under £100.

i would say you have solid walls looks like you have 9 in bricks turned the other way, if your old plaster had hair in it then they would have been done with lime what part of the country are you in?

stevethespreader said:

i would say you have solid walls looks like you have 9 in bricks turned the other way, if your old plaster had hair in it then they would have been done with lime what part of the country are you in?

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Norfolk.

smp50 said:

Norfolk.

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to bad if you was near me i would have helped you out

stevethespreader said:

i would say you have solid walls looks like you have 9 in bricks turned the other way, if your old plaster had hair in it then they would have been done with lime what part of the country are you in?

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And I can't dot & dab solid walls, right? For some reason that I don't quite understand, it will be too susceptible to moisture or cold, right?

So, I basically have to batten the external walls? That's a real pain because it will come out further than the glass in some of the windows, haha...

you can dot and dab solid walls its just that the adhesive can be comprimised if the wall becomes damp

Yes there can he massive problems if the wall gets damp with D&D. Also these walls are cold in winter. You could even batten and board over with insulated plasterboard, i know it's nearly another inch of space but if an inch or two is making things tight then perhaps the billiards table should do in another room.