New to plastering - some advice needed

[EdTurtle]

Hi, I am currently renovating a whole house, and the walls aren't great.



In some rooms we have taken the paint off with a scraper, filled holes/gouges etc. then new mist coat followed by paint. The walls look OK, but you can see the filled areas unfortunately. Also, where we have filled, once sanded the mist coat didn't take the first time around the areas we had filled and sanded (I now know this is because as we have sanded we have polished the wall too much for the paint to adhere). The mist coat did go on with the second coat, but the walls still have sunken areas where the paint is thinner.



Basically for the other rooms I want to skim the walls instead (scraping paint takes ages, filling again takes ages! and after all that work they don't look great - soul destroying!)



Just after a bit of advice really, sorry if it is obvious



Firstly - trowels. I am looking at a lot of advice, regarding the size and make of trowel, have probably settled on a 13inch marshaltown trowel, but when I actually get the trowel, what should I look for? Difference between stainless and gold stainless for example, should the trowel be curved or dished, and if so which way? I have a small ragni trowel, but it has a rough corner that leaves lines everywhere! So I know I have to look out for one that doesn't have rough corners, but anything else?



Secondly - I will skim over the walls that have been painted already - so I assume just water down PVA and skim with multifinish. Do I need to do two coats, or is one OK because the walls have already been plastered once?



Thirdly - the small areas I have done already seem to go off very quickly, I was told to put on the wall, wait for a bit to firm up then trowel over but they go very hard very quickly. Someone told me the plaster was too old and 'off', this makes sense but could there be another reason as well? How long should it take to go firm - half an hour, two hours?



Finally - I will practice on some old plasterboard offcuts I have - fundamentally is this the same as skimming over the walls I have now (thermalite - concrete render and then plaster). Also, any other advice you think I need to know!?



Thanks in advance

 

[Doggit]

A 13" Marshaltown is a good starting point, and a stainless bedded in (sharp corners have been filed off for you) should work well, and you wouldn't appreciate anything better.

you'll need to do a 3:1 pva coat on the walls, and the edges of the surrounding walls, and let it dry. Some people recommend a second coat, and the got to work as it's drying, but one coat of pva should suffice.

You want a fresh bag of plaster, and a couple of spare bags just in case. You'll put your first coat on, wait about half an hour or so (but keep checking it) for it to start to get a little harder, and then put a second coat on. Then as the second coat starts to harden, you'll then start to flatten in, and work from there.

 

[EdTurtle]

Ok, that's very helpful, thanks. Just curiosity though, why two coats? why not one, surely the underneath plaster that's already there would be the equivalent of the first coat or am I missing something?

Also, forgot to ask earlier, but as practice I was also going to skim my garage walls... They are just plain thermalite blocks at the moment. Can i literally just skim them twice in the same way (PVA and then two coats as you mention above) without the render underneath first. I appreciate that the finished surface will be much thinner this way, but its only a garage so not a problem for doorframes etc?

Thanks

 

[Doggit]

I'll honestly admit that I have no idea why you put two coats of fresh plaster on in one go, but I can say that it works. I taught myself to plaster, and I used to do just one coat, and it was hard work. Somehow (and hopefully one of the real experts will tell us both why) 2 coats seem to be more manageable, and easier to get flat, and it doesn't seem to go off so quickly - and it's what's recommended on the pack.

As long as you pva the thermalite blocks first, you can then skim straight on to them.

 

[EdTurtle]

Having tried a small area, yes it does seem to be easier to put it on in two coats! My only problem with doing this on the walls is that the finished surface is already about 5mm past the edge of the door lining, which makes the architrave sit very wonky, didnt want to add too much more thickness to the walls!

Having looked at the trowels on screwfix (nowhere else local i can use) i see they have two 13" trowels, anyone know what the difference is :
http://www.screwfix.com/p/marshalltown-duraflex-plaster-s-finishing-trowel-13-x-5/1163h
http://www.screwfix.com/p/marshalltown-permashape-finishing-trowel-13/57284

Also, you mention that i should get a bedded in one,

http://www.screwfix.com/p/marshalltown-mpb165d-permashape-broken-in-finishing-trowel-16/22048 would this be better than the above two (they dont say bedded in) or is too big for a beginner?!

Thanks

 

[Doggit]

Oddly enough, they are all finishing trowels so in theory, should all be the bedded in type. 16" is a bit big for a beginner, so I'd go for option 2.

If you've got to 5mm, then you're putting it on just a little too thick. Even with 2 coats you'd be able to get to about 2-3mm, so press a little harder as you spread it on, so it goes on a bit thinner.

 

[EdTurtle]

Ok, ill go in and have a feel of all the trowels and go from there thanks

Sorry, what i mean is the original builders rendered the house, then plastered it well beyond the door linings (about 5mm). They fitted the architraves flush with the door linings, so they stick out at the back. I have replaced the architrave, and fitted them flush with the wall, leaving a large gap between the architrave and door lining (which i have then filled with gripfill). This isnt ideal, but looks better than the way they had done it, at lease i have dont it so the architrave is flat on the wall. Ideally, if i could go back, i would replace the door linings with wider ones, but this is a learning curve after all!

So what I meant is, with the gap already at 5mm, then me skimming 2-3mm on top of that, it leaves a very large gap. Does that make sense?! I suppose, i could take off some of the old render/plaster before i skim, but thats quite a big job then, or could i fit the architraves etc and then skim around them, making sure theres not much additional thickness where the woodwork is? I did have a guy come to have a look at the wall (plasterer) and he said he would work around the architraves etc... i must admit that didnt seem right.

Thanks

 

[Doggit]

If I've understood you correctly, then you need to add a thin piece of wood (about 8mm) to the door frame, skim up to that height, and then add the architrave back on. If you sent the thin piece of wood back in from the front of the door frame, but slightly out from where the architrave would go, then you can make it out as an extension of the architrave.

 

[EdTurtle]

Yes, i think you have understood correctly, as what you describe would work as a fix, the only problem being how to blend the wood in to the new architrave/door frame, wouldnt you see the joins, ie it would crack over time?

Thanks for all your help

 

[Doggit]

That's what I was trying to explain. Think of it as also being added on to the architrave so that you create a more decorative moulding, but you're fixing it on to the frame first.

 

[EdTurtle]

Ok, i see now, that makes sense.

I'll give it a go, getting trowel tomorrow hopefully!

Thanks again