Lime plastering (again)

[plasticpigeon]

Hello all. I live in an early Edwardian terrace from 1904. Certainly a lot of walls need replastering as the plaster is either crumbling away or has come unstuck from the wall, especially around door frames and window frames. there are also places where the skim falls off with the wallpaper but the render behind is ok. I am convinced that the render although a kind of brick brown colour is lime as it fizzes in vinegar. However the skim (which is original) is much harder and more pink and I wonder if it may be gypsum.

I tried my hand at lime plastering in a small area where I am putting pipes as I know it will be hard to plaster behind the pipes. I used Nhl 3.5 with sharp sand (2.5:1) for render to about 12mm. Then NHL 2 with fine sand (around 1to 1.5:1), for the skim. However, try as I might I couldn't get a smooth finish. It is flat and level but close up looks a bit grainy . I would like to get a smooth finish on the walls. What do people think of using gypsum over lime, or is there a finer aggregate that can be used in the top coat, like talc or something> Any advice would be very gratefully recieved.

Thanks

Jerome

 

[plasticpigeon]

I must add I'm a beginner diy plasterer so may have just gone too slowly or maybe not added enough pressure. The small area has turned out quite smooth as I put 2 skim coats on. The large area just had 1 skim which required more straightening than I thought as the original lime base was very crooked., so maybe a 2nd skim would make the finish better. Anyway here are some pics.

 

[MatthewC]

...there are also places where the skim falls off with the wallpaper but the render behind is ok. I am convinced that the render although a kind of brick brown colour is lime as it fizzes in vinegar. However the skim (which is original) is much harder and more pink and I wonder if it may be gypsum.

...What do people think of using gypsum over lime?...

So many questions in reply:
How do you know the skim is original? It certainly sounds like a more recent gypsum addition, especially if it comes off the render easily (because of damp?). Do you have any damp issues? What is on the external walls? Brick and lime mortar? Why use NHL for the render? (I don't think that's usual but can't think why not...)

Gypsum over lime? Pointless if you are expecting the house to breathe. For a fine finish check out lime plaster on line, e.g. Mike Wye do a "Regency" plaster for a second skim which is VERY smooth.

I'm sure others will add more from their greater experience...

Matthew

 

[rebeccac]

How about a clay plaster/paint?You can buy pure clay that you mix with pigment and even lime putty if you want.There are many recipies online and its very easy.

www.myabruzzohome.blogspot.com

 

[plasticpigeon]

I'm pretty sure the skim is original as it is the same through the house, and 4 other houses on the street have the same. Also the skim is very thin, maybe 2 to 3 mm and there is only rough render underrneath. Perhaps it could be lime gauged with gypsum. It is certainly harder than lime on it's own but seems to have fine sand in it. i think it may have come loose in places due to structural movement. The base being soft seems to cope better with movement where as the skim comes loose in places. It is a terraced house and the construction is brick. The house isn't particularly damp, in fact it is surprisingly damp free for an old house that hasn't been looked after. on the plus side there is no chemical injection damp course or cement render anywhere! i used NHL as it is more freely available than putty and can be stored as powder. It also sets reasonably hard reasonably quickly. St Astier and Roundtower lime have info on plastering with NHL so i thought it was a good compromise. My girlfriend has told me she thinks the finish is good enough and that I should get on with the heating so it looks like i will have to leave it!! However I will have lots to do in the coming months and i would prefer to stick with lime, so I will investigate this regency plaster.

 

[Zebra]

No expert, but I did go on a lime plastering course at Ty Mawr in October, and all I really know is from that. I seem to remember them saying that the sand used for top coat is called silver sand, or kiln dried, I think! Very smooth and free running and makes a very fine plaster. Anyway, I think your plastering looks pretty good.