Plastering and patching advice please - novice

[yamin]

Hi and a happy new year! The cold has let up just enough in our very cold house to allow me to consider the work in our playroom, where I have some replastering to do. Photos below. I am assuming it is largely a 'skim' hats needed. Very glad to have discovered its lime plaster, so it will be replastered in lime. First thing to know is that I am a complete novice and I have NEVER attempted plastering of any type before - closest I've ever come is decorating the christmas cake with royal icing
Anyway, rightly or wrongly, and NOT taking it lightly as we don't want to ruin the house, I am nevertheless going to attempt the work myself. The room is a 'back' one, little seen. this simly means that we feel more tolerant of imperfections. A course is not practical - time issues/money issues/geography issues. So far so idiotic you may say! But thats as it is, so if anyone is happy to offer me any tips on that basis I would be very grateful.

So, my questions, other than general advice are

1. How to best make it stick. Someone suggested squeeze of washing up liquid in plaster, is this acceptable with lime? Thinking I don't want to pre wash wall with PVA,it being lime
2. I have a box of horse hair, kindly donated and sent to me by DaveBriggs (thanks!) - whats the best proportions?
3. The mix - sloppy or more coarse for the best workability?

As for the photos, you'll see that the bottom od the wall has wholes in int. I expect these to become worse when i remove the skirting board. this is because on this wall there has been 2-3 courses of bricks removed to accommodate a steel lintel for a kitchen extension below (before our time). therefore there is a 'void'. Apparently I can buy a kind of 'mesh' that I can fix to the wall in order to provide a base on which to plaster. Any other advice of how to tackle the problem?

P.s. This is one of the only two warm rooms in the house, with storage heater, so I expect optimal drying conditions.

Many many thaks for ay advice

Abi

 

[Lime]

I'm going to jump in while the wise stay out, I wouldn't skim the wall if the problem is just the crack.
In fact I don't think skimming would cure it.
If the wall is relatively flat, except for the crack, the crack needs to be stabilised.
I would rake it out the whole depth of the plaster to the laths or bricks and then fill with simple polyfilla (the granules mix the best).
Ensure the raked out crack is dust free and very wet then fill as deeply as you can pressing the polyfilla in beyond the plaster depth.
Don't overfill on the surface, scrape the polyfilla completely flush or slightly sunken then leave to dry.
The finish can be anything you wish to use.

 

[Cloudscape]

I have walls that are not as well plastered (or not in as good condition) as yours, and I'll be trying to repair and keep, rather than replaster those. I agree with 'having a go' - a lot of the things that give my house character are the bits that look as though the people who did the work didn't have a clue. :wink: But a lot could be done to your wall with judicious filling and some coats of limewash. If you have loose areas, washer repairs (or "glueing") are possible.

I would not put washing up liquid in anything (apart from the washing up). I know builders use it in c*m*nt, sometimes lots of it. I think it contributed to unstoppable salting on a wall I had built at my last house.

 

[Schoolmarm]

Also the room needs to be cool and damp. The drying out you mention has to be avoided like the plague. Oherwise it will dry up before it carbonates. Bad result.

 

[yamin]

Thanks for advice so far. So I've got

1. No washing up liquid!
2. Turn off the heating for the drying process
3. Possibly don't skim at all. How do I repair the major holes at base of wall though? Happy to avoid the rest!

Cheers

Abi

 

[MdB]

Very much not an expert - haven't lime plastered myself yet, this is what I've learnt from a lime course and what I've read here.

If you are skimming with lime then a 3:2 silver sand to putty is used with no hair. Use lime wash (1:1 putty to water) to damp the surface and help the new layer stick. Rake crack and fill sounds like a good idea. Laths would be the traditional way to fill your hole. What is the rest stuck on to?

 

[DaveBrigg]

if the stick in view behind the skirting board is holding up that part of the wall I would be tempted to put a couple of bricks in the gap, assuming that there is something solid for them to rest on. They wouldn't need to be special bricks, just keep them damp when applying the mortar. This could be a good place to play, since you would afterwards need to hide the evidence behind lime mortar, in which you could drop a small sprinkle of hair. A little seems to go a long way.
I'd agree that it is better to fill the crack than skim, since getting a good finish is not easy (speaking personally of course). The gap at the bottom might be big enough to need lime plaster, mixed as suggested above.
As well as the tips so far:
Wear gloves - lime has a tendency to take the skin off your fingertips, only noticed when you pick up a hot cup of tea afterwards.
When filling a deep hole, use lime mortar but finish it slightly below the wall surface. On some of our walls the hole was filled flush with mortar because it is easier, but then the skim left the repair proud of the surface.
Have a piece of furniture ready to move in front of the repair in case it goes wrong :lol:

 

[Moo]

Have a piece of furniture ready to move in front of the repair in case it goes wrong

That should be copied to Graham's Top Tips.

 

[yamin]

Will a large lego creation constructed by one of my 5 year olds do? (probably more reliable than my handiwork!)

 

[Pford75]

To aid with the filling of the large gap, you could consider putting a piece of cardboard into the gap, with a length of string knotted through the middle of the cardboard. You can then pull this back against the gap as you plaster (hope this makes sense, I can see its not a great description.)

I've used this successfully to repair a couple of holes in the ceiling.

 

[yamin]

That does make sense, thanks, and is a more attractive thought than the 'chicken wire' (don't know what its actually called) plan that I had - I worry that attaching said wire to existing plaster could elicit more breakage! By the way, I was asked earlier and have checked - it appears to be plaster straight onto brick, is that a usual method?

 

[ljn]

After reading SPAB pamphlets on repairing plaster, I have bought my first tub of lime putty (from Jewsons).

I did my first test. a small repair job. A small hole left from removing a big nail. I hoovered out any dust, squirted some watery lime into the hole, waited an hour or so for the water to absorb, then filled the hole with a 50 /50 mix of lime putty and plaster.

I noted two things about the test:

1) I removed the top of the lime putty tub, scooped out a spoonful of putty from under the water and replaced the top. The water seemed to have increased in volume and was overflowing the tub. I is that a chemical reaction, or wasthe tub just full to the brim and I hadn't noticed?

2) In the finished job, the plaster surrounding the repair had. This had not happened in repairs with Layland filler.

 

[Andrew Bodenham]

Try to retain the original plaster on most of the wall unless it really is falling off onto your shoes.

That crack has probably formed as a result of settlement following the installation of the steel beam at the base of the wall. Suggests rather poor methodology by the builder involved, but nothing you can do about that now. What you will need to do is rake out any loose plaster to either side of the crack, back to the brick.

If the resulting crack is less than about 12mm wide then I'd fill it with Polyfilla or similar, in one thick layer followed by one thin layer to finish.

If it's bigger than that then it's worth making up a bit of lime mortar. Go to the builder's merchant and buy a bag of hydrated lime and some sharp sand (aka grit sand). Mix 1 volume lime with 3 volumes sand in a bucket, add enough water to get it looking like cake mix and mix it really well. You can use this straightaway, but in an airtight container it will keep for weeks, even months, and remain useable.

When you're ready to start wet the brick and surrounding plaster well (garden sprayer) and mix a bit of hair into your plaster if your feeling really authentic. Trowel the plaster into the crack, pushing it well onto the brick and surrounding plaster. Aim to build up to within 3mm of the finished surface - you may have to do this in two layers if the existing stuff is very thick.

Let the work dry for a few days, then mix up a bit of lime and fine sand in equal measures and use this to fill the remainder of the depth, trowelling off to a smooth, flush finish as the mix firms up.

There are lots of online guides about lime plastering which you can read to gain more understanding of the process - the one on Mike Wye's site is good. The materials you'll have used cost relatively little, so if it all goes wrong you can just strip it all off and start with fresh. Have a go - it's not rocket science.

That big hole at the bottom is into the web of the RSJ I presume. I'd bridge that with some plasterboard or a bit of expanded metal mesh before proceeding as above. If you use mesh then you really should put a bit of hair in the backing mix.

Fine crazing in the rest of the wall(s) can be filled (not skimmed) with polyfilla or similar, or if you want a smoother decorating surface then simply cover with heavy gauge lining paper and paint. That way you get a nice sound surface whilst preserving the historic fabric of the building for lime plaster enthusiasts to uncover and enjoy in the future. I love lining paper - it's so good at covering scabby surfaces quickly.

Finally, avoid at all costs the thought that you can sand plaster or filler flat if you slap too much on. That way madness lies. Not to mention white dust on every surface in the house. The trick is to avoid putting too much on in the first place.

 

[MdB]

... then filled the hole with a 50 /50 mix of lime putty and plaster.

?!? - when you say plaster, what do you mean? Not heard of anybody mixing putty and any sort of plaster before. You normally make lime plaster from putty and sand. SPAB may well be recommending something I haven't come across though (and they know more than me). Please explain more.

1) I removed the top of the lime putty tub, scooped out a spoonful of putty from under the water and replaced the top. The water seemed to have increased in volume and was overflowing the tub. I is that a chemical reaction, or wasthe tub just full to the brim and I hadn't noticed?

If storing putty for an extended time, you want a layer of water on the top. However, when I come to use it, I normally pour it off as otherwise the mix can end up to wet. If the tub is left a while, a little more always seems to appear though.

2) In the finished job, the plaster surrounding the repair had. This had not happened in repairs with Layland filler.

?? - Not sure what you are on about there.

 

[Carol]

Go for it Yamin! I am definitely not an expert but have done lots of patching tiny bits and one big patch with several coats. The first bit is always the worst, but lime is much easier than the pink stuff to patch up. I wonder if you are missing a lath or two under the hole, if so and you can replace them it will be easier. Do consider a couple of coats of a limewash or distemper on the rest as it looks (from the photo) to be not too bad overall. Lime does something incredible (and chemical) with smallish cracks and covers them all up beautifully, so you may only need to patch the large crack and the hole by the skirting. I used lime putty and sand in various mixes and made quite small very amateur quantities (a builder would snigger!) in a small bucket until I was more confident, then I just used a bigger bucket.

It's a bit like icing a cake, the consistency resembles soft royal icing, but the rest of them will laugh at me for saying that!

Wait for Gervase to reply, he is a mine of information

 

[Nigel Watts]

I too would fix laths to the studs before repairing the hole, even if it means cutting a bit more out to get to the next stud. I would also advise cutting the edges of the old plaster back at an angle so that the the new plaster holds it all in, wedge fashion. Make sure you wet the lath well before plastering and you must use hair in the coarse stuff.

Plaster (of Paris) and lime putty mixes were routinely used by 19th and early 20th century lime plasterers, mainly for running cornices in situ. It is also effective as a filler for making small repairs (much cheaper than polyfilla and the like if you have a tub of putty to hand, and more workable). It needs to be worked in well as it can shrink significantly while it dries, and surfaces need to be wetted first to reduce suction. It goes off quite quickly so only make it in small batches.

 

[yamin]

Loads of information and advice, which I need to make noted on in the morning I think. Thank you all so much, its been really helpful. My initial thoughts are that i'm going to avoid a skim, gouging out and repairing the crack in the wall, and properly replastering the holes at the bottom, using either cardboard or wire grid to anchor the plaster. I need to go through all the notes to sort out my lime plaster from lime mortar from putty from etc etc! That'll keep me busy! Want to at least get the basics right though, even if my total job not that professional.

Thanks for giving me the confidence to try it!

more questions no doubt, as they occur!

Cheers

Abi

 

[ljn]

Sorry for the shoddy post. An essential part must have got lost during a copy and paste action...

The surface of the wall I was attempting to repair is lime.
I had read that lime putty tends to shrink when setting, while "plaster of paris" tends to expand?
And that for small repairs, you can mix the two.

I have repaired cracks grooves, nail holes etc in another wall using Layland SDM flexible filler. Similar to Polyfiller.
The result was pretty neat to perfect.

My 50/50 lime plaster of paris experiment resulted in a swelling of the lime around the repair. I thing I noticed in repairs done previously by others. I presume this is due to the wetting of the old lime.
The repairs done with the Layland SDM flexible filler left the wall completely flat.

I did the test on a small hole, about 1 cm in diameter. I did it as a test in view of repairing larger areas. I wonder if the swelling of the original lime is permanent and if it is avoidable.

 

[Andrew Bodenham]

Interesting observations re: expansion - I'd be surprised if the effect was permanant, but it's not something I've encountered in my own repair work.

Decorators fillers (polyfilla, etc) are formulated to be easy to mix, easy to apply, non-shrinking, easy to sand, and with an appropriate pot-life for typical applications. They work so well for minor repairs that I can't see any point in messing around with home-brew fillers that probably don't work so well.

 

[yamin]

OK guys, so first phase is complete! Worked with

1. Wetting with spray of limewash 1:1 lime putty:water
2. Mixed mortar hydraulic lime: sharp sand 1:3
3. Bit of horse hair

Used to fill the cleaned up crack, which turned into 3 inch wide gap by time removed all falling plaster! Went on ok - horse hair only thing that bit of challenge as tendency to clump and 'roll'. However, quite pleased with the result. Not as hard as I thought. Have filled to approx 3mm below surface as advised and will make up a skim mix, a little thinner and without horse hair, to finish off. Suspect this may be the hardest part - achieving smoothish finish. Still, I rather enjoyed it! have yet to tackle holes at bottom of wall which will need expanding grif stuff to provide backing to plaster onto, but one step at a time!

Thanks again for help!

Abi