Interior rendering

[regsmyth]

Having read the earlier post about float and set, which I dont quite grasp, could someone advise on the best way to finish the interior walls of my extension.
Most of the walls are thermal block, some are conc block, and some will be stud/plasterboard. There is also the previously painted, ex-external wall to deal with.
My plastering is fine on plasterboard walls and ceilings, but I've never actually done any rendering.
I had assumed to slap on a 6:1 sand/cement render onto all the thermal and concrete blocks, followed by a thin skim. Or am I missing something?

From what I remember seeing in my younger days, the render just gets slapped on, till a little firm, then scraped back with a feather edge to a flat surface, which can be skimmed the following day, or several days later.

There are lots of different walls to work on, so I can try my skills on a small section first. The biggest wall is 6m wide x 4.5m high. Think I'll leave that one till last!

Any advice or guidance much appreciated thanks.

 

[Richard C]

Having read the earlier post about float and set, which I dont quite grasp, could someone advise on the best way to finish the interior walls of my extension.

Which bits did you not understand?

From what I remember seeing in my younger days, the render just gets slapped on, till a little firm, then scraped back with a feather edge to a flat surface, which can be skimmed the following day, or several days later.

More or less , the trick is getting it to stay up there & getting it flat; hence the previous descriptions of float & set several of us posted on. A render base coat was commonly used some years ago, I still use it for repair work but it’ not particularly easy to get it to stay on the wall if your inexperienced; you’d do better using one of the base plasters; Browning, Hardwall or Bonding, depending on the background & what condition it’s in. Preparation is also all important & surfaces painted with gloss or vinyl emulsion need particular attention as they will have virtually no suction if left as as they are & the plaster will either craze & fall off or slide onto the floor as your trying to put it on.

Skimming a wall of 27 sq/m would be a big challenge for an experienced plasterer working on their own but at that height, I would say almost impossible to do in one hit; I would certainly baulk at it! You seem to have had some experienced but plastering isn’t easy, even for the best & most dedicated DIYers. You can pick up a lot of info & guidance by reading through the archive posts, it can get a bit monotonous to keep repeating it all but come back with specific questions as you need.

 

[roughcaster]

Oh Reg, you are definitely missing something as you say. Rendering/floating is a totally different kettle of fish to plastering onto plasterboard...... Slapped on??,, yep,,, can be, but it will never be right. To do it right, it must be put on more or less as described in the "Float and Set" post. Rendering is the kind of job that is worth trying on one small wall first as you said, and if you can't get the hang of it, then take it off. Having someone on hand who can help out would be a bonus too.

Roughcaster.

 

[regsmyth]

Hmmmm.
Well I hadn't thought about it enough to realise getting a flat base coat onto a flat wall wouldn't be as easy as getting flat plaster onto flat plasterboard.
So... specific questions.
The walls are beautifully straight and plumb,insulated cavity walls, so shouldn't be getting damp, so would I be better off using browning, bonding or render?

However, one of the rooms will be a kitchen, which some might say constitutes a potentially damp wall.
Is browning or bonding easier/cheaper than render?

If I use render, presumably plasticiser is a must?

I gather bonding is for low suction backgrounds (eg conc block, p/b) and browning is for moderate suction backgrounds. What is thermal block classed as?

Might there be an issue with browning/bonding going off too quick for me?

So.. battens on the wall. The bit I didn't get was in RC's description of a couple of days ago - I've re-read it several times now and think I understand. He fixes a full length batten horizontally just above the floor, and some short ones fixed vertically along the wall at around head height, then plasters the bit between the high battens until he has a horizontal plastered band around head height, removes short battens, and fills in the gaps left. Then plasters the big bit underneath, then the last bit at the top. (Sorry if I'm re writing what he wrote!).
It might be easier for novice me to use full height vertical battens as per the Wickes link I guess.

Next question - should I use the devils float on all basecoats (ie bonding, browning or render)?
How far should the nails protrude? I can see me ripping all the stuff off the walls in my eagerness.

Am I going to be able to do the job just using my skimming trowel and 8ft feather edge, or should I buy a sponge float, darby, wooden float and devil float.

When to skim - presumably render will need at least a day, what about bonding or browning?

As far as the big wall goes, no worries there, I'll just put my underpants on over my trousers.

Hope this lot of questions doesn't annoy you too much, I'm just trying to be clear on the right way to go. Thanks all.

 

[marshman]

( What is thermal block classed as? ) high suction.
use a waterproofer as your plastersizer, for you, use full length battens, do a thin scratch coat on the whole wall around your battens, then do your float
coat, you need a 6 x 14 inch plastic float ( http://www.tooled-up.com/Product.asp?PID=3231 ) rub the square edges off on your concrete floor so it has
a chamfer all round, then knock in 3 panel pins at one end just so you can see the points, you now have a devil float. you can use this on all backings.

( Am I going to be able to do the job just using my skimming trowel and 8ft feather edge )
yes and no you will need a hawk and a spot board as well

( As far as the big wall goes, no worries there, I'll just put my underpants on over my trousers. ) you might need to.

 

[Richard C]

So... specific questions.
The walls are beautifully straight and plumb, insulated cavity walls, so shouldn't be getting damp, so would I be better off using browning, bonding or render?

I’m no render expert but I would steer you away from render & towards using base plaster; render will give you more time but unless you’re used to rendering, I think you you’ll find it much more difficult to work with. If it’s new Thermalite blocks you could use Browning or Hardwall; probably Hardwall as it may be a little more forgiving but you must damp down well before starting or it’ll all end up on the floor, concrete blocks, use Bonding. You can use Bonding on Thermalite blocks but you would have to seal it first & there is a different technique or you’ll never get it on there.

However, one of the rooms will be a kitchen, which some might say constitutes a potentially damp wall.

Just because it’s a kitchen doesn’t mean the wall will be prone to damp, condensation yes but they are 2 completely different things, it won’t matter. Not sure what you’re doing exactly but are you aware of the Building Regs covering new/renovated kitchens?

Is browning or bonding easier/cheaper than render?

Don’t really know how it would compare but I don’t think there would be much in it; depends where you get your materials from but mixing render requires a rather more effort than stirring “mud” in a flexi-bucket!

If I use render, presumably plasticiser is a must?

Yes; but render mix will also vary depending on what your doing.

I gather bonding is for low suction backgrounds (eg conc block, p/b) and browning is for moderate suction backgrounds. What is thermal block classed as?

Correct; Theramalite blocks are high suction & I would go with Hardwall but Browning can be used if you take extra effort to control the suction.

Might there be an issue with browning/bonding going off too quick for me?

Possibly, as I said above.

So.. battens on the wall. The bit I didn't get was in RC's description of a couple of days ago - I've re-read it several times now and think I understand. He fixes a full length batten horizontally just above the floor, and some short ones fixed vertically along the wall at around head height, then plasters the bit between the high battens until he has a horizontal plastered band around head height, removes short battens, and fills in the gaps left. Then plasters the big bit underneath, then the last bit at the top. (Sorry if I'm re writing what he wrote!). It might be easier for novice me to use full height vertical battens as per the Wickes link I guess.

;
I think you’ve got RC description but everyone has their individual methods. These will mostly be how you were taught or develop over a period of time to suit individual comfort zone needs; doesn’t mean to say one is any better or worse than another as long as the end result is the same. For you, I would say go with full height battens if that’s what you feel comfortable with.

Next question - should I use the devils float on all basecoats (ie bonding, browning or render)?

Yes you should scratch but it could be a Devils float or any other improvised implement to achive the same effect.

How far should the nails protrude? I can see me ripping all the stuff off the walls in my eagerness.

Only just through, the idea is to provide a “scratch” as a key for the next coat, you don’t want deep scores all over the wall.

Am I going to be able to do the job just using my skimming trowel and 8ft feather edge, or should I buy a sponge float, darby, wooden float and devil float.

Yes, I would say so; if you were going to do more work it’s worth kitting yourself out but you can get by with the minimum if it’s limited to self indulgence.

When to skim - presumably render will need at least a day, what about bonding or browning?

Bonding/Browning finish as soon as it’s set, if you let it dry out you will have to seal beforehand or it’ll suck the life out of the finishing plaster & it’ll go lumpy & craze.

As far as the big wall goes, no worries there, I'll just put my underpants on over my trousers.

Good luck with that one then; in fact good luck with it all. You’ve certainly got some balls even attempting it but you may be a natural, who knows; just start small & take your time to learn as you go.

 

[NickB_99]

are you aware of the Building Regs covering new/renovated kitchens?

Not aware of kitchen specific - Richard, please can you elaborate?

For you, I would say go with full height battens if that’s what you feel comfortable with.

I think I would be with you on the full height battens to start with. Understood RC's description - but feel I would need the 'stabilisers' to start with!

Bonding/Browning finish as soon as it’s set, if you let it dry out you will have to seal beforehand or it’ll suck the life out of the finishing plaster & it’ll go lumpy & craze.

Thoroughly agree. Fallen foul of this once already (only wet with water lots just before doing the mix) and it really didn't slow it down once the multi-finish went on. In fact it sucked it so quick that as soon as each stroke of multi went on, it dried giving no chance to smoothe
Fortunately the second coat of multi seemed to just about be ok as the first coat had taken the sting out of it. Will try not to make that mistake again.

As far as the big wall goes, no worries there, I'll just put my underpants on over my trousers.

I would be with you there. Terrifying.
There are some good posts I've seen so far about large walls though with blending in with a step etc.

Good luck

 

[regsmyth]

Hmm. Now you've got me worried.
(Thanks for all replies - you all deserve a merit mark - your comments are invaluable).
I'm particularly concerned that if I use bonding or hardwall, I'll be too slow to get the multi finish on before it gets extra absorbent. Hence I might try the render option as per Marshmans reply. At least I might get a break for a cup of tea or a sleep before I start slapping the multi finish around.
Marshman, why should I use waterproofer as the plasticiser? Seems like an odd suggestion. And do you mean I should do a thin render scratch coat, then maybe later in the day, build it up with more render to the thickness of the battens? This is probably what I'll try anyway.

Richard C, thanks too. You are worth a million. Just to put you in the picture, this is a full extension I've built, with planning and regs and all that. It's just taking a long time. A long, long.... long long long time.

Ref the big wall, my clever idea was that if I put my underpants on over my trousers, I might be blessed with superman like strength, speed and the ability to float around in the air.
In hindsight, I think this is unlikely, but as yet, I don't have a plan B.

Actually, Plan A was to get the old bloke in who rendered the outside single handedly. Except (apologies if I start ranting), he used a numpty to put the angle beads on, and my carefully calculated drip under each window cill had to be buried under as much as 25mm of render!! Just don't get me started....
(And his and most peoples response would be "so what's the problem?")
So I daren't get him back in case I go off on one.

 

[Alastairreid]

Great step by step concise instructions their from richard c!!
well worded and easy to understand for the diyer

ever thought about college lecturing richard

 

[NickB_99]

Hmm. Now you've got me worried.
......
I'm particularly concerned that if I use bonding or hardwall, I'll be too slow to get the multi finish on before it gets extra absorbent.

Was not my intention to worry you.
I'm only a DIYer, but have tried to gain experience whilst just thinking small initially. My thinking that if it didn't work quite as expected, it would be not too difficult to put right.
By only doing a little at a time, I've not had a problem with Bonding or Multi going off. I'm not very quick and so not tried to overstretch!
E.g. if I've skimmed a wall (biggest so far about 3.5m x 2.4m), I did first coat with one mix and then did a fresh one for coat #2. I'm sure the pros here would dwarf it, but it meant it was workable throughout and not put me under too much time pressure.
On top of patched Bonding which has dried out, or on painted walls - PVA has been invaluable. I'd like to try Browning or Hardwall next to expand my basic repertoire. But again only small initially!!
I guess I'm trying to say don't worry!

Richard C, thanks too. You are worth a million.

Agreed - hats off to you. Not just Richard, but also RC, Roy C, Noseall, Alastairreid & co. A lot to mention - there is a wealth of experience on this forum & you are always willing to share and explain slowly! Big thank you

Ref the big wall, my clever idea was that if I put my underpants on over my trousers, I might be blessed with superman like strength, speed and the ability to float around in the air.
In hindsight, I think this is unlikely, but as yet, I don't have a plan B.

I'm sure the experienced guys here can advise on the best course of action for your big wall. Try not to be daunted and just build up to it getting confidence on the smaller jobs.

 

[marshman]

( Marshman, why should I use waterproofer as the plasticiser? Seems like an odd suggestion. And do you mean I should do a thin render scratch coat, then maybe later in the day, build it up with more render to the thickness of the battens? )

yes, the waterproofer for a scratch coat on thermalite blocks will cut down the suction, will give you time to rule off your float coat, keep your render
fresh / workable, and let your float coat cure set and not quick dry to dust and will give you more time to work your skim coat.

 

[Richard C]

Just to put you in the picture, this is a full extension I've built, with planning and regs and all that.

OK, it’s just that many plough on into new/renovation work in kitchens & bathrooms without realising it must comply with current regs on forced ventilation &, as it’s a special location, the electrical work must comply with Part P & be certified as such. This sort of puts restrictions on who can do the work but if in any doubt, have a look at the sticky in the Electrical Forum which will explain.

Ref the big wall, my clever idea was that if I put my underpants on over my trousers, I might be blessed with superman like strength, speed and the ability to float around in the air. In hindsight, I think this is unlikely, but as yet, I don't have a plan B.

Hears’ a Plan B for you: Just divide the wall up into manageable chunks!
Plastering what was the external house wall in some conservatories, particularly Edwardian, can be a challenge, presenting a gable around 3.5m high; even higher in some cases! Shouldn’t be a problem with the float coat as you can work between the battens but for the finish skim, a dodge I’ve used is to fix a thin coat plaster stop bead (you can get these up to 3m long) & work up to that, removed the bead & then skim the other half up to & blending in with the raw edge. Get it right & you should need very little if any making good with filler; obviously skim up to the stop side of the bead & not over the heel as you would normally!

 

[Richard C]

Great step by step concise instructions their from richard c!!
well worded and easy to understand for the diyer
ever thought about college lecturing richard

Well thank you for your kind words ; never done any lecturing as such but my previous life involved both writing & interpretation of technical specifications/publications & the preparation & delivery of training. Not plastering I would add & I'm just a mere beginner to some of the other regular contributors on here.

 

[Alastairreid]

Great step by step concise instructions their from richard c!!
well worded and easy to understand for the diyer
ever thought about college lecturing richard

Well thank you for your kind words ; never done any lecturing as such but my previous life involved both writing & interpretation of technical specifications/publications & the preparation & delivery of training. Not plastering I would add & I'm just a mere beginner to some of the other regular contributors on here.

ah, so thats where you get your descriptive talents from richard
personally i sometimes find it difficult putting into words the best way to tackle jobs from a diyers perspective . i have a habit of wrongly presuming they know more than they do.
and then you have the problem of getting overly technical and getting into a long drawn out post, like i am now

 

[regsmyth]

Thanks all again. 1 tonne of sand on it's way!