Skim coating a difficult wall

Discussion in 'Builders' Talk' started by ajohn, Oct 30, 2018.

  1. ajohn

    ajohn Active Member

    I took some paper of a wall recently and had a bit of a shock. At some point a door and electrics had been added and several other areas patched very badly. No chance at all of something like wallrock hiding the ups and downs. There are actually ridges around the patches. No idea why who ever did it didn't rule them off as they were done.

    The only solution I can see is replastering via a skim coat and ruling it off to get a decent surface. Trouble is that the thickness of that will be pretty variable and it looks like it would be easiest to do the first coat this way and then maybe even let it dry and then apply a 2nd. I'm not sure how the plaster will behave if used like this - more like using a filler. Could do that but would need a rather big bag of filler.

    Any thoughts? It's so bad that if we weren't past the messy stage I'd chisel the lot off and plasterbord it. Can't realistically do it that way now.

    John
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  2. Jord86

    Jord86 Well-Known Member

    Easifill do a 25kg bag if you're not too clever at plastering, very easy to rub down.
     
  3. ajohn

    ajohn Active Member

    That's what I usually use as a filler once I found out about it. Plenty used elsewhere. I just think plaster would be better for this problem and also wonder if a plasterer who just went around skim coating would cope.

    Yes - my plastering isn't too clever. If I do it as I mentioned some areas will probably finish up at zero thickness initially anyway. I have managed to plaster to a depth of 20mm or so using a derby over a much smaller area around 1x1 1/2 m. ;) Finish not too good but ok for papering and another thinish coat would have allowed me to polish it a bit after it had firmed up using a different plaster. ;) I took that off 3 times before I got it more or less right using wickes patching plaster - it dries incredibly slowly. They don't sell it any more not that I would want to use it.

    I have several feather edges I use for other things and as I'm tempted to do it bought a 1200mm speedskim as the derby has seen better days. Feather edges go up to 8ft - use them as guides with a circular saw. LOL so you might say I have the gear that l would need and of course have watched a number of videos that I wish I had seen when I did the small area.

    John
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  4. 14th edition

    14th edition Well-Known Member

    I wouldn't use easifill, sure it goes on well but then you spend hours rubbing down and refilling bits. PVA x 2 and skim. Not sure how big the wall but a plasterer would probably do it in a morning!
     
  5. DIY womble

    DIY womble Well-Known Member

    PVA , PVA , bonding , straight edge , retouch scraped surface with PVA , 3 mm coat bonding and multi 1:1 all over , 2 mm multi, timing is the answer
     
  6. DIY womble

    DIY womble Well-Known Member

    Never add water to the plaster when trowelling up, timing , timing , timing ,
     
  7. DIY womble

    DIY womble Well-Known Member

    And then polyfillll
     
  8. ajohn

    ajohn Active Member

    I wont be doing the entire wall with easyfill. It's great stuff for filling even though it's really a jointing compound. I think it's too sticky to trowel over larger areas. Good for patching as well but it takes some time to dry completely if more than a few mm deep and shrinkage does show when it's deeper. What might be expected from a jointing compound.

    Unlike the plastering I did some years ago I have seen some decent videos that mention time and it looks like multifinish is much easier to use than the wicks patching plaster I used for that, it dried far too slowly - several hours and still soft,

    I've got some areas to do that I can simply rule off the existing wall so will see what happens when I do those. I can't understand why the patching that has been done on the problem wall wasn't done like that. A bit of shrinkage would be better than leaving it proud with trowel marks in places. I've been looking at this wall and wondering what to do about it so started this thread. It will be some days before I get to it. :( Plenty still to do elsewhere.

    True a plasterer would probably do the 2 areas that need this sort of work, there is just a door between them but I suspect some one who just went around skinning basically flat walls may have a problem with it. I can give it a go somehow and if it isn't working out it's not difficult to scrape it off before it becomes more of a problem. It took me 3 goes on the other piece I did but a lot of the problem was getting the mix right even though it still took hours to firm up at all.

    John
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  9. ajohn

    ajohn Active Member

    I just tried mixing easyfill as they reckomend. ;) Works out at 70ml or grams of water to 100g of the filler powder. Come out a lot runnier than I have used for filling but is no where near as sticky to trowel. Mixing by hand was a bit of a pain so if I did it again 1/2 the water first, mix till smooth maybe adding a bit more then the rest. With the lot in it was difficult to mix out little clumps. It comes out like whipped cream only slacker much like plaster. ;) So could plaster with it and then sand. It sands ever so well. 150 grit or finer and it more or less shines.

    One way I could do that fairly well, done it before but this time using thin skin stop beads. Fasten them to the wall bit under 4ft apart, trowel it on and then knife it level with a feather edge using the stop beads as a guide. One would get removed. Then fill in the edge left using the surface that's done once it's dried. The other I did like this is framed in timber and had to build up 25mm in 2 goes. Worked out well done this way using 1/2" timber as a guide. ;) The only reason the join could seen is down to me - finally getting the mix right when I filled in.

    I'd rather use plaster though and have a bag of the ever popular multi finish. The wall is 3m tall and who ever did it has left it a lot thinner at the top. So while most of the plaster will finish up around 3mm thick the top part might taper up to 6 over the last 450mm or so. I can easily set the stop beads vertical with easifill. Is multi finish ok at this thickness?

    John
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  10. CGN

    CGN Well-Known Member

    Bonding plaster is the thing to use to true up the wall before skimming.
     
    Heat likes this.
  11. ajohn

    ajohn Active Member

    I suppose I could use 1 coat - it is available in smaller bags. Skim coats over old walls are usually bonded with pva, I'd guess it would be wise to do the same what ever is used.

    John
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  12. ajohn

    ajohn Active Member

    Thought I would dig this thread up again.
    I'd spent some time filling a wall that wasn't too bad to a level where it would look ok with wallrock on it. It was proving difficult though as the wall had loads of ripples in it. The old 1911 plaster was ok but a huge chimney breast had been removed lots of ripples and ridges where that had been replastered and it was proving difficult to get filler to blend in. Xmas coming so I wanted to gets some of the new kitchen units in, just one run. That allowed me to get rid of some old stuff leavings space for our new table. So decided to get a plasterer in.

    Tried to contact one I used for a wall we had built. Mixed feelings due to a smile on his face when he ran his trowel over a narrow strip of plasterboarding I had done - about 180mm wide with corner reinforcing tape rather than bead on each edge. He mentioned that each time he used it paper lifted up and sure enough he trowelled it until it did. I wasn't too bothered as I stuck the stuff down with water proof pva so it will and did remain in place. Not so keen on him showing me that it could happen.

    I did do a bit of ruled off plastering myself in one area. Went off to quickly as it was a very thing coat in places. Literally minutes. Should have used a wetter mix but no chance of doing a wall so found another plasterer that some one else had use and also had good reviews.

    Ist problem - didn't turn up when he said he would. He did eventually. First thing he did was lay a lot of that sticky plastic film where he would be working and where he would need to walk in and out. Great. I'd agreed to PVA the area he was doing and just as he should he pva's it again. He then made a pretty wet mix far wetter than I could even get on the trowel reliably commenting that he needed to gain some time on a wall like this. On another wall that I could have finished off myself he even used it to build up to something like 6mm thick. Anyway nice clean tidy job but I cut a length of work surface on the 24th due to the delay.

    Ist problem came when I cleared out back boxes. I had removed the sockets and the wires were disconnects. We are fitting new ones. Usually the sockets would be pulled out off the wall. Some were and no problem there. The others were 1/2 full of plaster so some chipping which I filled after getting it out. There was 3mm skim beading about 25mm above these - the plaster was 3mm deep their but had dropped to 1/2 that mid way down the back boxes. This was over plasterboad. The guy could clearly trowel well. Suppose it stretches a mix out to cover more wall. Anyway apart from filling no other problems with this wall.

    After it had all dried as suggested I emulsioned it all. Even the deep stuff had dried which took 2 days longer than he reckoned. Fair enough really. Turns out that some patches of the wall I had him in to fix have about 1/2mm of plaster on them so the pva underneath got damp and the plaster lifted off. Some small areas ballooned up and a sort of crack appear and lengthened over time. I used bare plaster paint. If I tap some areas I can tell that the plaster isn't attached. Odd thing is one area jutted out and he said I can either skim to it or build out around that. It was more of a long gentle ridge, just a more extreme example of other areas - why I had him in. What I should have said is well you are going to coat again aren't you? He left it barely visible. Oddly in the 2 areas where this happened no problem at all.

    So emailed him no reply. I know he had read it as he mentioned back boxes when I phoned him. He did answer the phone 2nd time I tried - fair enough. I told him what had happened - impossible he says as I couldn't give 2 coats that thin. He did go over it all twice but the 2nd time clearly didn't really add any more. He spent quite a while doing it as well. Said he would come and have a look but hasn't.

    Back to the wall that has turned out ok. One of the reasons I had it done was ancient dot and dab. They appeared to have used plaster and then used that to stick plasterboard to it around a larger window that had been fitted. No corner beads at all so the corners were chipped a bit in places so thought may as well have this wall done too. He fitted 3mm skim angle - yep it is 3mm deep at the bead but I'm gob smacked by how quickly it gets thinner.

    I'm reminded of a comment a very elderly plasterer I used years ago made off the cuff as well. I mix the plaster outside, shook his head and said the kids today do it in peoples houses and don't even put the plaster on well and will do anything to get the job done quickly and anything to make a few extra quid. Taking the first plaster I used on the kitchen I got the plaster he happened to have in the bag - very probably not what the wall needed. The latest guy probably saved himself making 2 mixes.

    John
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