Lime, Gypsum or Cement . . . and how to tell the difference

How to tell the difference between traditional lime based mortar and plaster and modern non-breathable gypsum or cement based mixes. Including the vinegar fizz test will lots of examples.

[@bobbysbits2575]

That glass bowl's days are surely numbered...

[@oldhousediy]

😂

[@snips73]

Very useful, I also have an old property (18th century) with many various coverings. Some extremely hard renders

[@oldhousediy]

Thanks. The harder the coverings the more likely they are cement based (unfortunately).

[@snips73]

@@oldhousediy yeah it seems that way, can do more damage taking it off than leaving it on, I’ve got a very hard cement render with a thin skim of gypsum over the top. Difficult to know what’s the best thing to do, I have chipped off a few areas where the gypsum looks damp, but the brick behind under the cement are dry, thinking I might remove the gypsum skim and when lime plastering skim over with lime. It’s an basement, biggest issue seems to be the flag stones under self levelling compound and concrete skim up to the outer walls. Since removing the floor covering and revealing the edge of the stone floor seems to be drying out nicely. Think the damp couldn’t escape so going up the brick wall

[@oldhousediy]

@@snips73 a slow step by step approach is definitely best, you don’t need to hack everything off straight away.

[@LibertypopUK]

great video

[@oldhousediy]

Thanks!

[@peterwalton1502]

Great tip 👏👏👏

[@oldhousediy]

Thanks.

[@lizziemcbizzierobin]

This is fantastic. In my recently Edwardian property (early 1900s) there is lime plaster that very soft and crumbly and coming off the walls. It looks dry but very old and I think it needs redoing. It was probably last done in 1970s by the previous owners. Also, the previous owner put wall paper directly over the lime plaster and when I pull the wallpaper, some of the lime plaster comes off on it too. Interestingly, when I scratched at the lime, it came off very easily (crumbling) but behind it was what look like a dark/black wall. I don't think it's mould or anything like that, and the wall is not wet or damp at all. Do you know what this black/dark wall is? I'm not sure if it was used as a layer before applying the lime plaster. Any thoughts? Thank you

[@oldhousediy]

The black sounds like tanking. Bitumen paint is often used behind gypsum to act as waterproofing. (But it then traps the water.)

[@Pavlo_S.V.]

Hello wanted to ask, in your opinion is possible to use cement (for better setting) with hydrated lime and sand (0,5:1:5 ratio) for rendering a brick wall layed with lime mortar, as it is quite difficult to find hydraulic lime in our region? Or even small amounts of cement will trap moisture, make wall unbreathable and ruin the bricks? Kind regards

[@oldhousediy]

Cement is not good. Naturally Hydraulic Lime (NHL) is probably the compromise you need as this does set. Alternatively you could get some pozzolan and add to a putty or hot lime mix.

[@pmlm1571]

Thanks for showing how to test for lime. You say that NHL is "controversial." I wish you would speak to the difference between Natural Hydraulic Lime and Hydrated Lime. I think NHL is the pure (lime) powder not yet given any water and it has a very hot chemical reaction to water; I think Hydrated Lime (what we have here in the States, "Type S"), which looks just as powdery, is actually already partly re-hydrated (is less reactive to work with). Is this right as far as it goes? Thanks again!

[@oldhousediy]

NHL is hydrated lime but it is impurities in it so that it sets (not carbonates) quicker and even under water. It is similar to Pozzolanic additives. It has been partly slaked (water added) and it does not have the hot reaction when you mix it up. There are arguments that NHL gets harder than putty / hot based over time and can lead to brick stone damage and so is becoming controversial. This is a very good book on lime, really worth a read and I am sure. www.blackdogpress.co.uk/product/lime-in-building-a-practical-guide-by-jane-schofield

[@pmlm1571]

@@oldhousediy Thank You!

[@luckystrike656]

@@oldhousediy didn't the Roman use "Pozzolana"? I heard that lime and pozzolana are the best for plaster/render walls Or is it?

[@sergeiok8499]

@@oldhousediy NHL is actually hydraulic lime, not hydrated. NHL is essentially quicklime, with natural impurities that make it set much faster, much like Portland cement.

[@oldhousediy]

@@sergeiok8499 correct , I think the impurities are present pre-firing so the end result “sets”. NHL = Naturally Hydraulic Lime. I mainly use putty made from hydrated lime these days but the NHL here I had left over from a floor repair when I needed a quicker set. Here’s how I make my putty. Making Lime putty kzbin.info/www/bejne/goW4ioSni550nqc