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Lime with perlite instead of sand?

Discussion in 'General Lime Plastering Discussions' started by tta2, Feb 9, 2017.

  1. tta2

    tta2 New Member

    Does anyone have any experience, positive or negative, with using perlite in a lime plaster instead of sand? I'm in the US, and hydraulic lime is almost unheard of - available imported, but outrageously expensive. Likewise with lime putty; available from one or two suppliers in the US, at about 10x the price you pay in the UK (plus shipping!) ($120 for a 5 gallon tub)

    My hope is to be able to use a dry hydrate lime (what's called "Type S" in the US; calcium with a good deal of magnesium) with perlite. Are there any downsides to using the perlite instead of sand; it's what I've always used in gypsum plasters. I'll ultimately be finishing with a smooth trowel finish.

    Thanks in advance for any help!
  2. 3kids1dog

    3kids1dog Member

    Using perlite alone with lime doesn't really work that well because you end up with a mono granular mix which cracks however I use it in a insulation mix with two different grades of perlite and hemp shiv this works really well. Hope that helps
    • Like Like x 1
  3. tta2

    tta2 New Member

    Ah, that helps a lot. I hadn't considered that aspect. There's a local perlite mill that sells what they call their "plaster mix", but I'm not sure if they have a range of sizes in the mix - the guy I talked to said it's used mostly for exterior cement applications. They also form it (burn it? mill it?) in other sizes for other uses, everything from ultra-fine to nugget size. If I were to get a wider range of sizes of perlite aggregate and mixed them together do you think that would do the trick?

    When I was taught to plaster with perlite/gypsum, we always put a shovel of sand into each mix; the story was it would make the mix harder, so the brittle lime/gauging topcoat wouldn't move and crack. I don't know if that was just an old wives tale, since I always followed the rule (didn't want to find out the hard way that they were right!). If I'm using a straight lime/sand finish coat, do you think I'd run into trouble with the softer perlite/lime scratch and brown coats, or are they all flexible enough that they'd get along OK?

    Do you think a lime/perlite fines topcoat would trowel out to a good surface?
  4. Dropsalot

    Dropsalot Private Member

    On this side of the pond we try to make each subsequent coat weaker than the first.
  5. 3kids1dog

    3kids1dog Member

    I think it will maybe crack unless it's mixed for a long time and the water has saturated the perlite giving it more time to shrink if you know what I mean though I've never used multi granular perlite so it might be fine suck it and see I guess
  6. Emmet BARRY

    Emmet BARRY New Member

    I have actually done a lime/perlite mix last week for the 2 external walls of a loft room. Currently working with the stuff the last month. Let me explain the situation.

    I bought a 100 YO, red brick, lime based house next to the sea. Lots of salt and lots of unsuitable material used on the house over the period of over 50 years. Cement render outside. Poor roofing with leaking flashing on chimney and leaking guttering. Inside - gypsum plaster over lime. Poor plastering (Actually plastered around a small dresser instead of moving it. Front windows replaced but back not. Panal walls on some of the external walls to cover the damp caused by the cement render on the outside. Cement flooring on ground floor causing florescence and damp up the adjutant walls.

    So I started with the small loft room. Took months pealing back layer after layer to try and save some original plaster. It was all shot. The mortar in some of the top bricks was shot too. Ended up taking back to brick and the ceiling down. Only thing I was able to save was some of the original lats. So started up with the normal lime/sand mix for the harl and scratch coat as I couldn't find an insulation I liked. Once I had the first coat done I did a little more research and found that they mix perlite with plaster for ovens. Looked into the composition of perlite and it is very similar to sand in 78% of its makeup. I bought a few bags and tested it. The results are good. A 30 minute mix time. I put in 50/50 sand/perlite. If you get the water right it is lovely to work with. Light and creamy. NOT 1 CRACK on the wall. I did water the wall well after but it is looking good so far. It does shift a bit when using a straight edge but just reflect. On a 1m section of the wall I over wet and over worked and still no cracking and no problems. I wish I had discovered it earlier. I will be putting a 2/5/1 mix together for the ceiling onto lath to increase insulation and reduce weight on the ceiling. I did a small patch on the ceiling with leftover wall stuff and had some cracking but I did mistreat that section badly. It was too dry going up and I over wet it then. And there is a big draft in that room so I should have wet it more often. I would suggest using NHL 3.5 on the scratch coat and 2 on the float if going this route. And wet every couple of hours for the first few days followed by a reduced wetting for the following week. I will only use this mix on the external facing walls and regular mix on the internal facing walls. Will skim with putty after a few months after I have the new windows, sills and other wood in.

    Give me a shout if you have any questions. Anyone in the south of Ireland who wants to see it in action I am happy to show you.
    • Like Like x 2
  7. Lastlaff

    Lastlaff Well-Known Member

    Welcome onboard mate.
    What perlite did you use and was it mixed sized granuals? Post any pics you have.
  8. jamesthefirst

    jamesthefirst Private Member

    Did you add any hair to the mix for the ceiling Emmet?
  9. Emmet BARRY

    Emmet BARRY New Member

    Hi Lastlaff,

    It was a generic perlite with grain sizes from dust to 2-3mm. It is not graded well enough for me so I add a bit of sand to reduce the chance of cracking. This weekend I will be doing a perlite rich mix for the ceiling so I will try to get back to you in a few weeks to tell you the results. As this will be on a draughty lath ceiling I assume the scratch coat will crack as the moisture is being drawn off at a massive rate. Not really bothered as I can heal it with some lime wash. Photo on 29-03-2017 at 13.44.jpg Photo on 29-03-2017 at 13.44 #2.jpg Photo on 29-03-2017 at 13.44 #3.jpg Photo on 29-03-2017 at 13.44 #4.jpg Photo on 29-03-2017 at 13.44 #5.jpg Photo on 29-03-2017 at 13.45.jpg Photo on 29-03-2017 at 13.45 #2.jpg Photo on 29-03-2017 at 13.45 #3.jpg Photo on 29-03-2017 at 13.44.jpg Photo on 29-03-2017 at 13.44 #2.jpg Photo on 29-03-2017 at 13.44 #3.jpg Photo on 29-03-2017 at 13.44 #4.jpg Photo on 29-03-2017 at 13.44 #5.jpg Photo on 29-03-2017 at 13.45.jpg Photo on 29-03-2017 at 13.45 #2.jpg Photo on 29-03-2017 at 13.45 #3.jpg Photo on 29-03-2017 at 13.44.jpg Photo on 29-03-2017 at 13.44 #2.jpg Photo on 29-03-2017 at 13.44 #3.jpg Photo on 29-03-2017 at 13.44 #4.jpg Photo on 29-03-2017 at 13.44 #5.jpg Photo on 29-03-2017 at 13.45.jpg Photo on 29-03-2017 at 13.45 #2.jpg Photo on 29-03-2017 at 13.45 #3.jpg Photo on 29-03-2017 at 13.44.jpg Photo on 29-03-2017 at 13.44 #2.jpg Photo on 29-03-2017 at 13.44 #3.jpg Photo on 29-03-2017 at 13.44 #4.jpg Photo on 29-03-2017 at 13.44 #5.jpg Photo on 29-03-2017 at 13.45.jpg Photo on 29-03-2017 at 13.45 #2.jpg Photo on 29-03-2017 at 13.45 #3.jpg
  10. Emmet BARRY

    Emmet BARRY New Member

    Sorry about the repeat pics. Don't know what happened
  11. Emmet BARRY

    Emmet BARRY New Member

    James - The mix I used for the patch I did was lightly haired. I should not have used it as it was not haired enough and was not made up for ceiling work, it was leftover from the wall. I will be heavily hearing the mix at the weekend. I will add synthetic fibres.

    I have read a few posts of people putting gypsum over lime. DON'T do it. I have proof that they don't mix. The gypsum has salts in it which draw moisture and the lime is supposed to hold the moisture. If you mix them the lime moisture will be drawn to the gypsum and destroy it.

    My reasoning for the perlite is that the similarity to sand should mean it is compatible. It contains no hydroscopic components that I can make out. It is closed celled (unlike vermiculite) which means it won't 'soak' up water but should have enough pocks and pits to hold a little water so the wall can take being a little damp with out any ill effects. It is light so is ideal for lath ceiling work. Insulating qualities are great as well as noise reduction and fire resistance.
  12. jamesthefirst

    jamesthefirst Private Member

    OK sounds good Emmet nice to see you are enjoying having a go. If you see any cracks just lightly spray it with water and gently rub up with a wooden float this should help it blend back in.
  13. Emmet BARRY

    Emmet BARRY New Member

    No cracks after 2 weeks. I prefer to self heal the plaster with a heavy lime wash if still within the time frame. It has worked for me in the past but rubbing it up after with a float works even better. Good tip James.

    I have a friend from a local lime company coming out to see my mix. He is very interested in it and he is a nice chap. I love working with lime anyway and have done a few friends houses in the past. I'll tell you guys what he has to say as he has all the equipment to analyse it and he is a bit of a geek for stuff like this.
    • Like Like x 1
  14. tta2

    tta2 New Member

    I'm wondering how the lime/perlite worked out for you. Was your topcoat lime/perlite or did you go to lime/sand for the top? Did you do a troweled topcoat or sponge/float? How's it holding up?

    For my topcoat I used lime and perlite fines - almost dust-like. It didn't trowel out as well as the lime/gauge topcoat I'm used to using. Shrinkage was a problem, and it almost seemed like the aggregate material compressed under the trowel but then expanded again when I took the pressure off. This is my first time not using any gypsum, so I'm not sure if its a problem with my understanding or the materials.
  15. Emmet BARRY

    Emmet BARRY New Member

    Hi tta2,

    It has worked out very well. As I am living in the house I can care for it more frequently than a contractor so I can wet it every few hours. Perhaps it needs more care than traditional lime/sand, not sure but the layers I applied myself were fine with little or no cracks except for micro cracks which healed well.

    So for the internal facing walls I used a sand lime mix. No perlite as I want them to act as heat retainers.
    I only discovered this perlite mix after doing the scratch coat so only the 2 external float coats and the whole ceiling are lime/perlite but I would have done it all in the perlite mix if I had discovered before I started. The perlite was graded from dust to 2-3mm which is why I added some well graded sand in too.

    I did the ceiling scratch coat in a perlite/sand/lime mix. So about 5/1/3. It was fine and no cracks after 3 weeks. I then decided to get a plasterer to do the ceiling float coat as it is a very low ceiling and I wanted it very straight.
    He said he had worked with lime a lot. I was mixing and he was applying. I came up with the last batch and noticed that the plaster was very wet. He told me he was watering down my mix to make it easier to apply. It was runny. Not happy so told him he would only get the balance once it had cured. Went up that night to float and patches had dropped off and he had not plastered the corners. No way to float it. So I had to scratch it. Left it for a while and it began to crack. I then did a float coat myself a few weeks later. His coat ended up cracking my scratch coat and float coat, badly in some places. Not one crack on the walls that I did. Shame, he lost out on 70% of his payment because he wouldn't invest an extra hour or 2 to do it correctly. I am currently feeding the cracks with a heavy lime wash to get free lime into the cracks. The walls are perfect, only a few micro cracks which I washed once and are healed.

    I floated the float coat, then sponged any shrinkage I could see developing and again floated any cracks followed by a devil float. I will be putting a putty skim once the skirting, windows etc are in.

    I am waiting for windows for the house so I can't finish the room till that's sorted as the window reveals are to be plastered around.

    So I think the ideal method, which I will do next -
    Perlite graded from dust to 3-5mm
    Scratch coat -NHL 3.5. Mix of 4/2/3. perlite/sand/lime
    Float coat. - NHL2. Mix of 5/1/2
    Mix well till creamy (It seems to take a bit longer to plasticise)
    Wet ever 6-12 hours for 2 weeks.

    Attached Files:

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