Three coat lime plaster-PT 2

[Anonymous]

I found that a cross grained float was particularly good. This is a wooden float with the grain of the wood running at right angles to the long axis of the float. It has more "bite" and an ordinary wooden float.

In my three coat work over both lath and brick I had less problem with the lath than the brick, which had much more suction. One section on brick failed to ahere properly at the first attempt, but the second attempt, using a wetter mix, was fine.

Mine is a town house which would have had quite a high standard of finish. For my second coat I used a system of dots and screeds to get the plaster reasonably level.

 

[Anonymous]

You could do with a variety of sizes for the wooden float. If you buy a commercial one it will be big and heavy, but for dealing with the cracks and polishing off the surface a smaller one is good, even a tiny 5"x3" is good, especially for tight corners. You can't buy them so you need to make them. As Nigel says below, the wood (hard wood) needs cutting so the grain runs across the float. Sand off the corners so you don't have any sharp edges, and fit a handle, which can be anything you have to hand really.

As the cracks appear, wet them down and work them with the smaller float, you will find it much easier. My tutor even used those hard plastic floats you can buy, but he cut them up so that the end result was a thin strip rather than a fat hollow shape. They work like wood and don't bring too much lime to the surface.

The plaster you removed, put it back in the mixing bag and rework it. Don't scrap it. Also, I'd avoid reducing the hair. The quantity of hair should not cause a sticking problem. Go back to the full hair load (which will stop a lot of the cracking) and solve the sticking problem in one of the other ways mentioned. I too have thrown the stuff on the wall before I had a bit of training, but its much easier to apply with the float providing the mix is plastic enough. Start in the top right corner of the wall and spread from left to right. This seems to be the wrong way round, but actually is much better for getting an even coat. You are pushing the new plaster into the previous batch and so keep the thickness even. If you go right to left you are feathering it out and can find it undulates.

Sue

 

[Anonymous]

There is a lime plaster available that will fix your problem.
cccCheck this web site http://www.masterofplaster.com
This is a Historical correct material it is slacked lime and premixed ready to use.

 

[Anonymous]

I bought my cross grained float about 3 or 4 years ago from a pretty standard tool merchant in the Holloway Road near where I live. I believe they are still used in the (non-lime) plastering trade, especially for external render work, so can still be bought. Ideally the handle should be fitted into a dovetailed slot on the back, quite a tricky joint to cut by hand (and one of the few where I would resort to my electric router).

 

[Anonymous]

But as you know (as you posted a reply ...) the OP has already posted a message on that site asking if this is a lime product - there is certainly a lack of information regarding what it actually is on the site.

We've all been there with 'miracle products' which are in fact not what is needed for historic buildings.

There is lime and there is lime! What exactly is it?

 

[Anonymous]

The technical data for the 'Master of Plaster' tubs states that it contains:
Calcium Carbonate
Silicon Dioxide
Gypsum
Non Asbestos Talc

Which would seem to indicate that it's not a pure lime plaster and certainly not breathable or flexible.
It sounds more like a specialist guaged plaster and may well be just the ticket for repairing cornices and mouldings (albeit rather expensive as a pre-mixed tub), but would certainly not be the best stuff for general surface plastering, and not as advised on their web-site, which suggests using it as a skim coat, with three coats no thicker than a coat of paint.

 

[Anonymous]

Thanks - I missed that bit! (Doh...)

Bit like Limelite then - which is aptly named!

 

[Anonymous]

Lime is calcium hyroxide. It doent contain lime then.

This stuff is going nowhere near my laboriously cleaned cornices. Pure lime putty for small mends; lime putty plus Plaster of Paris (freshly mixed) for running, for larger mends, and for sticking cast detail back in place; pure Plaster of Paris for casting in moulds.

 

[Anonymous]

In response to Suji's post on the MoP website:


http://www.masterofplaster.com/forum/ShowMessage.asp?ID=103

 

[Anonymous]

A claim like:
"Manufacturers of the only Historically Accurate premixed restoration plaster." on the MoP website
would not be allowed in the UK.