is this lime plaster? and can I lime plaster over it?

[thetyreman]

does this look like lime plaster to you?

the top layer looks sort of white with what looks like bits of gray ish aggregate inside, the yellow colour might be pigment or the original wall colour,

I recently wanted to remove old artex from a wall, and have come to the conclusion it's way less work just plastering over it, how would I know that the plaster is lime or not? it doesn't have the typical pink ish look that you normally see and could very well be the original late 1930s plaster, it's also weird that there's no plasterboard underneath, which is what made me suspect it could be lime...

The actual artex layer is much much thinner than I realised, in parts 1-2mm, so I recon it wouldn't need a thick layer, and I was thinking of doing it with traditional lime plaster instead of modern gypsum based stuff,

thoughts?

regards,

Ben.

 

[Droogs]

if you look at it and it is whiter rather than grey or pinkish, that is usually an indicator that it is lime and you can spray a little white vinegar and it starts to fizz a bit then it is lime

hth

 

[MikeG.]

Plasterboard didn't exist in 1930.

What's the substrate, Ben? Is it a stone wall? How hard is the plaster (can you mark it with a thumbnail, for instance)? Can you see any hair or other fibre in it? I can't, and that immediately makes me suspect it may not be lime. Also, I'd expect lime plaster to be thicker than that, as it is usually built up in at least 3 coats. Finally, I don't think Artex sticks very well to lime plaster, so unless the vinegar test reveals obvious bubbles/ fizzing, I suspect that we're dealing with something else.

 

[thetyreman]

it's a brick wall, internal wall, the plaster is quite hard but feels very smooth, I tried the test with white wine vinegar and there's no fizzing, I was just surprised that it's a sort of white/grey colour.

 

[Droogs]

Probably put on in the 70s judging by the paint on top of it. Probably a portland based mix

 

[MikeG.]

Quite hard........or very hard? Is it at all shiny (if you can find a piece without paint or other covering)? Plaster of Paris was sometimes used as or with a plaster, and that was nightmare-hard, slightly shiny, and very smooth. Lime plaster doesn't generally feel smooth.

Not all gypsum plasters are pink. I use one (called Universal One Coat) which is white. This could be an early gypsum plaster before pink became the standard colour, or it could be a PoP plaster. It could also be some sort of render-and-set, with a cement-based undercoat using a light coloured sand.

 

[Doug B]

It looks similar to what was on the walls of my 1940 house basically a weakish sandy cement render with a plaster skim on top, that skim was hard but the render was bone dry & perished in large patches, on the plus side it was easy to remove from the engineering bricks the walls are built from.

 

[MikeJhn]

Lime plaster will re emulsify if submerged in water, chop a bit off and put it in a bowl of water.

 

[squib]

Be careful removing artex as it has asbestos in it.

 

[KimG]

Looks more like Skimming to me which is Gypsum based, is it hard and somewhat brittle? If so it is most likely standard Gypsum skimming, if it's not brittle and white and sort of tough, then it's more likely Lime.

Lime will be white, but you can get white skimming too so colour isn't a reliable test.

Regardless of which it is though, you should just clean any loose off and paint etc, then you will be fine to replaster using Lime, you'll need a bit of skill to get a good finish though. I have been in the trade for 40 years, so I do have a little background.

 

[novocaine]

Sorry but its not lime. Its very very dry gypsum. Same as on the walls of my house. Its fragile as anything in that state and can be knocked off the wall with a scrapper. Its not worth going over with lime.

 

[MikeG.]

......Lime will be white......

More often off-white/ ivory/ cream, depending on what it's been mixed with (chalk or sand).

-

It's well established now that this isn't lime, and therefore plastering over it with lime wouldn't be a good idea.

 

[MikeG.]

....... Its very very dry gypsum. Same as on the walls of my house. Its fragile as anything......

But he said it was hard. One of the reasons why I suggested that plaster of Paris might be involved.

 

[sammy.se]

Be careful removing artex as it has asbestos in it.

Only before a certain year... I think after the early 80s there was no more asbestos in it, but check online for the precise year.

 

[novocaine]

Possible Mike. But could also be a high silica content. Stays rock hard on the suface but crumbles beneath.

 

[MikeG.]

Yep. One of these things that could really only be decided by holding a lump of it in your fingers and seeing it for yourself.

 

[thetyreman]

Be careful removing artex as it has asbestos in it.

I had it tested by bradley enviro, sent a couple of samples to a lab and it's asbestos free, thanks.