Painting onto lime plaster or ecomortar

[Pennyviz]

Hi

Have stripped woodchip off walls and filled any holes with ecomortar R50 - good stuff sticks well but very rough finish, bit like sandpaper.

I gather from Earthborn website that for normal lime plaster you should allow 1 week per 1 mm for plaster to cure before painting with claypaint, and from what I can gather from Ecomortar suppliers this is more like 1 day per 1mm for Ecomortar.

What happens if you don't allow this time? I understand it doesn't carbonate but what does this mean in practical terms - does it simply fall off the walls? Is there a website that explains the process that anyone can recommend?

For future reference, If I was to put a finishing lime topcoat on top of the ecomortar to get a smoother finish, would this work?

Thanks

 

[MDE]

I've put a lime top coat on lime green's ultra ( which I guess is similar) and it works very well. I've used the clay paint as well and the main thing is to ensure that the plaster is hard. This will be quicker for hydraulic lime. Clay paint is breathable so full carbonation ( which takes ages ) can continue.

 

[Pennyviz]

Hmm that is what I initially thought but not so according to Earthborn's page:

http://earthbornpaints.co.uk/all/what-is-the-best-paint-for-lime-plastered-walls/

I think there may be a difference in what 'breathable' means. May be water permeable but not gas permeable? I would have thought it was the other way round but still..

Other sites have mentioned that curing is not the same as drying out.

Just confused!

 

[MDE]

The advice in that link seems odd to me. Lime wash is frequently applied before the plaster is fully cured and works very well. In fact I have used it in a bedroom with no problems and I would say that it is very easy to apply (but protect all surroundings!) and also gives a good low maintenance finish. I used clay paint for a multi-surface finish and that works too. I really can't remember how long I left the lime to cure but I'm sure it wasn't 1 week per mm.

 

[Pennyviz]

Just spoken to Earthborn and Ty Mawr to satisfy my curiosity more than anything. Hopefully if anyone else searches on the subject they might find this thread. St Astier don't even have a contact number and don't respond to email technical queries. Earthborn say that carbonation and drying are different processes. Can put claypaint onto damp gypsum and it will dry out but if you put the paint onto lime it will stop/slow the carbonation process. They say allow 4-5weeks for 5mm lime but couldn't comment on the ecomortar. If you go earlier run risk of paint failing or plaster taking forever to set. He did say he wasn't an expert on lime but known people get into problems especially externally when they want to get on with things because of scaffolding costs. Ty Mawr say to wait 5 weeks for both but said paint would continue to allow carbonation process to continue albeit slowly. Dependent on humidity temperature etc though

On a couple of websites I've seen they say that in the old days they would wait a year before painting.

Be interested to hear of any else's experiences or knowledge.

Penny

 

[MDE]

CO2 is a bigger molecule than H2O so I guess what they are saying is that the clay paint will allow H2O through easily, but CO2 less so. Not a problem with limewash, though.

 

[Pennyviz]

Thanks MDE

 

[Kearn]

I've had a similar situation lately, using Earthborn clay paint over areas of patched skim lime plaster repairs and original c.400 year plaster. My repaired plaster was 3-4 weeks old, so close to carbonated, but not fully. What was eveident was that the fresh plaster sucked moisture from the paint resulting in a lighter shade in these areas, requiring additional coat(s). Ideally these are best left as long as possible before reapplying. I needed to get a bath plumbed in so was happy to do an initial coat, then touch up later. The super flat finish means retouches aren't noticeable. Also, over recent lime plaster, the advice is to put an initial coat of paint mixed with 10-15% water on first then paint as normal.

 

[malcolm]

I've put a lime top coat on lime green's ultra ( which I guess is similar) and it works very well. I've used the clay paint as well and the main thing is to ensure that the plaster is hard. This will be quicker for hydraulic lime. Clay paint is breathable so full carbonation ( which takes ages ) can continue.

Having just looked at the price of earthborn paint I'm tempted to limewash my kitchen. The external walls will be plastered in lime, but the internal walls and ceiling are plasterboard skimmed with gypsom plaster.

The internet doesn't seem to like the idea of limewash on gypsom but is not coherent about why not. Has anyone tried it?

 

[MDE]

I've used the following approach successfully onto a gypsum-plastered plasterboard wall. (Why? - so that the finish would match other walls which are solid with lime plaster finish)
Coat the wall with DG27 (from Mike Wye) first. Then put on a skim coat of fine lime plaster (I used 3:2 with silver sand). Then finish with limewash.

 

[malcolm]

My builder won't like me for that - the plasterboarded walls are new and unpainted. The reason I am thinking about limewash is also to have the same finish on all of the walls. Builder was talking about sanding the plaster before the first coat of paint and maybe that would be enough for a 'key'. I might experiment with a little area.

For other walls I had been thinking about lining paper on top of the lime plaster to make is easier to repair the wall later once future occupants have put layers of non-breathable coatings on. We are going for white throughout as natural light is poor and I like the look of limewash.

 

[paulc]

The internet doesn't seem to like the idea of limewash on gypsom but is not coherent about why not. Has anyone tried it?

Yes, with a lime plaster (1:1 mix of lime putty and marble powder). Without a primer, it flakes off very easily on gypsum plaster (Thistle Multifinish in my case).

Coat the wall with DG27 (from Mike Wye) first. Then put on a skim coat of fine lime plaster (I used 3:2 with silver sand). Then finish with limewash.

I've done a couple of areas, one coated with Febond Blue Grit, and another with an acrylic primer with a handful of silver sand mixed in. Both seem to be standing up well, and no sign of the lime plaster flaking off.

Kreidezeit do a couple of lime based products that they claim can be used straight on to gypsum plaster and plasterboard. Smooth lime Wall Finish and their Brush & Roll-on plasters - Expensive, and they recommend a casein or GekkkoSOL primer first (more expense) - The Brush & Roll-on plaster isn't recommended for damp areas like bathrooms.

There is one more method that you could try - When the gypsum plaster is applied to the wall do a skim with lime plaster while the gypsum is still soft. Not tried this, so can't vouch for it in the long term. It is just one "trick" that I came across on the web.

 

[steveb]

The claypaint is relatively expensive, however it covers very well, dries quickly and 2 coats and you will be done.

I have never used limewash but I think the amount of labour involved is closer to a labour of love rather than a sensible choice - I wouldn't use it on Plasterboard and gypsum.

-Steve

 

[malcolm]

Probably the clay paint is sensible should I ever manage to buy any. Ordering a sample pot on the internet is frustrating - I might be better riding a horse to the supplier.

I guess clay paint will work on the lime and the gypsum and I'll get the same colour on all of the walls so it is probably is the way to go. I'll not be ready to paint for a couple of weeks as the lime base coat is taking forever to dry despite heating and dehumidifiers.

 

[a twig]

The internet doesn't seem to like the idea of limewash on gypsom but is not coherent about why not. Has anyone tried it?

Tried it, limewash didn't stick to the gypsum in my case.

I've got a room that is two walls hydraulic lime, two walls gypsum. After a bit of experimenting, I've just gone for claypaint over the whole lot Yes it will be about £150 worth of paint, but much less faff, so worth it in my book

 

[malcolm]

I'm sold on the clay paint having played with the sample pot. The finish seems very flat (though a little rough to the touch) and the coverage is very good - the little sample pot would probably have covered half a wall and almost doesn't need a second coat.

The final coat of plaster went on last week, and the paint should arrive this week following the normal just in time schedule.