We are finishing the wattleing of our timber frame walls and are about ready to start making the Daub/cob to press onto the wattle. My research has provided the recipes for the daub and lime plaster, but unfortunately not the exact sequence for applying each…
Can anyone tell me specifically how long to let the daub/cob dry before plastering?
Do we need to mist the daub walls before applying?
How long does the plaster then need to dry before lime washing?
How long do finished panels need to be protected from rain and other weather after finished?
I started by posting under COB, then someone told me to try here under plaster/finishes…only echoes…i don't understand? This is a forum with lots of people doing cob buildings no? Perhaps they are all busy?Or no one every renders their cob…which is also hard to believe…maybe its not my day
Hey there I can't speak with any authority on your question, but I recently (8 months ago) managed to put up lime plaster walls in my bathroom just over lath, and have since experimented pretty extensively with cob and with clay and lime plasters. In general I find that you want your underlying layer to dry reasonably quickly, but not so quickly that it starts to contract and crack away. Adding more layers of plaster or wash prematurely to the first coat slows that drying process and simultaneously creates a situation in which the plaster you're applying is adhering to a still-malleable surface. No idea where you are, but if the cob you're applying is only a few inches thick you shouldn't have to wait more than a week or so to start applying your plaster. You always want to mist the wall to be plastered before applying the plaster (except maybe drywall? which I'm currently experimenting with... seems like you want that relatively dry) so that the underlayment doesn't soak up the moisture in the plaster too quickly and cause poor adherence.
Same general rules go go for the lime wash. Let the previous coat dry decently for a week or so (maybe more maybe less again this is all just my own personal EXTREMELY LIMITED experience) depending on your particular conditions and then splash on the limewash.
Can't say exactly how long everything should be protected from the weather. Ideally they'd be protected by your overhangs forever, but in the short terms I'd put up some kind of rainscreen if any horizontally blowing precipitation is expected.
Some precise types might consider this blasphemy but in general I find earthen plasters to be exceedingly forgiving. Mess up? Get the area wet and spread it out. Apply the next coat too soon? It usually dries and bonds just fine anyways. Cracks? Patch them with more plaster and knit it into the surrounding area.
I'm interested in hearing more about the wattle and daub. I have a decent understanding of the system, but I'm curious to know how you insulated/added mass? I would guess you have some kind of loft/insulation inside the walls, and the wattle is forming the exterior encasement? Sounds cool, best of luck.
Thanks for the advice, we will try to follow as we can. As to your question, we don't have any added insulation, just traditional wattle and daub, (saplings or lathing woven in betwixt vertical pieces filling every timber frame panel then daubed and plastered on both sides keying the daub together through the cracks in wattle)
We are curious how these walls will work, such as insulation, condensation and so forth...its an experiment but an OLD way of building, so a gamble. In retrospect light clay would have been an easier and more efficient method of infill but I learned of that too late for this build, perhaps our next.
What Lime did you use for your plaster? How did you mix it?
This is the thread I made way back when I was trying to actually have a bathroom in my house in the middle of a cold February. I believe I touch on several aspects of mixing and applying lime plaster though m picture-taking was limited... Bill Bradbury is the man when it comes to plaster knowledge (and loads of other stuff, read any and all of his commentary throughout the site). He's really committed to finding a way to make walls breathe well, even in conjunction with our modern materials. I believe he is suffering from a bad internet connection at the moment given a fire he recently at his place in Utah but hopefully he will show up in time to congratulate you on a job well done.
I mixed my lime putty with a high-powered corded drill and a paddle mixer. I let that slake for a week or so before mixing it into sand in a large tub with a hoe. 3:1 lime putty to sand ratio BUT, I would say make a couple of test swatches on the wall, with a little more or a little less sand, and with a little more or a little less water. When it's right, you'll really know. I did not make more than one or two trials and felt pretty unsure when I finally started doing it. My mix was too thick and chunky, I was pushing a ton of it straight through the lath. But by the end of the first coat I had added a bit more putty and a bit more water and was getting a really nice buttery, creamy spread, smoothing it out over the wall.
I used two limes, both Type-S hydrated. Basically powered lime is super chemically unstable and is dying to bond with water, so they mix it with a bit of water to form hydrated lime that is slightly more stable, but still able to bond further on its way to reverting to limestone. It's pretty interesting actually and not totally dissimilar to drywall, which is essentially gypsum that has been mixed with just enough water to form a rigid crystalline structure. Hence drywall and lime's fire retardent natures. They have water bound up in them so they actually can't exceed 212 degrees until all of their water is boiled off.
I'd be really curious to see pictures of your progress. I'm terrible at posting my own, and usually even my finished pictures still have tools and trash taking up half the frame but I sure like looking at other people's. How did you affix the wattle panels to the timbers? What style of frame did you build? I'm kind of curious to see how self-builders are putting stuff together naturally on a budget (though maybe you're not on a budget). Condensation-wise I can't imagine you'll have any problems whatsoever, that thing is gonna breathe beautifully, and with the plaster it's definitely not gonna be drafty as long as your flashing and utility stuff is good. I have no idea where you're located, but no insulation around here in Michigan would be killer. I'd be burning a cord a month through the winter. If you do find over time that you're disappointed by the performance, you could obviously always increase the thickness of your walls. And if you didn't want to lose interior space you could look into installing a wall truss of some sort. I'm actually trying to figure out how to build this raised porch on the north side of my house at the moment so that I can beef up my northern wall by a good foot and a half. I haven't decided whether it will be clay-woodchips or straw bales, but I'll keep the forum abreast if and when I manage to get going on that.
Right now I'm digging some drainage trenches to carry runoff to my crater garden in preparation for the eventual extended roof overhang, so I'll get back to it. Gotta finish before I harvest this evening.
Take this into consideration: I AM NO EXPERT PLASTERER! I have worked with lime and done small projects and done lots of reading on the subject.
My advice is to wait at the bare minimum two months before applying a lime plaster otherwise you may run the risk of the plaster cracking heavily because your wattle cob is still drying.
Even in the hot dry climate of Yemen I believe they wait a year to lime plaster after the last brick is laid. These walls are substantially thicker than yours but it also looks like you're in a decently humid area?
ONCE PROPER DRYING of you walls has taken place here are the steps I would take to plaster your walls.
1. Make sure your lime has been slaked for a proper amount of time per the type of lime you use. I've only used type S lime that you get from big home improvement (oxy moron?) stores, and while the longer it slakes the better it is, after 24 hours it is sufficient for use.
2. Make a key on your cob walls no more than a 1/4" deep on your walls. This can be done with anything that will gauge into the wall to that depth.
3. Make a lime wash primer about 12 parts water to 1 part lime. Paint this mix onto your cob walls applying 3 coats waiting 24 hours in between each and misting with clean water before each application. This will provide a stronger substrate to plaster onto.
4. Now you can start plastering your walls with lime. Mist your walls down with water the night before you plan to plaster, and mist right before applying plaster and mist anything that starts to look "dry" before applying plaster to it.
5. I would do 2-3 layers of plaster. The first would be 3 parts sand to 1 part lime, the second 2.5 parts sand to 1 part lime if you do a third I would make this the weakest at 1.5-2 parts sand to one part lime.
Now after the first coat is leather hard, meaning it is hard to press finger into but can scratch with finger nail I would key the whole plaster to a depth of 1/8". Cover the wall with berlap sacks and keep them moist or cover with plastic and keep the wall moist for at least 4 days. Then apply your second layer in the same process omitting the key after it is leather hard. Make sure to keep your final layer moist for the prescribed 4 day minimum. I would apply a lime wash at any time after the four days or do a fresco the day after your final plaster layer is applied. The asthetics of your plaster will depend on the trowel and technique you use which would probably take up a whole thread on its own. And this post barely gleans the surface of lime plaster mixes, techniques, types of lime, curing time, application, troweling ect, ect, ect......... ect ect ect...... ect.
With that being said, IF YOU HAVE 0 PLASTERING EXPEIRIENCE DO LOTS OF TEST PANELS! Practice, practice, practice.
Also make sure that while your plaster is curing, to keep sun, wind and rain from contacting the curing plaster.
And practice more.
And post more vids/pics.
Stay where you are, work with what you have, do what you can
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