Which wall plaster to use

jsmoke

jsmoke

jsmoke

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I have a large hole in a plaster wall next to the outside of the front door frame I need to fill. From my quick research it's probably lime plaster. The flat was probably build in the 60's or so yence not modern plaster etc.

So how would I identify a suitable plaster filler, it's a sizable hole so the plaster will need to he exactly the right type. I'd really need a pro's advice, hoping there is one on here.
 
Well from searching it seems some plasters are specific with regard to the size, depth and current plaster in the hole. It's a big hole up to 20cm deep. Also needs to bond well with the current plaster etc. I am new to all this.

I don't want to fill it up to find it all starts breaking up and falling out after a few weeks.

Can you tell any thing from this?

IMG-20181118-164129646.jpg
 
Plaster has a number of grades.. and you build up from the base bonding, skimming etc through to the fine finishing.

When you do plaster into the hole - PVA the hole to stop things being crumbly and it helps stabilise the plaster along the joins. However if there's any loose plaster - it comes out.

British Gypsum Thistle - Bonding Plaster - this is what I use at the back, it's got some fine grit and bonds hard at the back. There's also Hardwall Plaster that will take a block or brick wall as a base and is even stronger but I have managed to get away with straight bonding plaster - if the block behind needs attention then it normally gets repointed with concrete.

Into the Bonding layer I have used fibreglass mess or even metal mesh (when backing into a plasterboard hole to act like reinforcement.

Then "key" the bonding plaster, so the next layer has something to adhere to.

British Gypsum Thistle - Finishing plaster - this is fine plaster and will give you a good final finish to sand down and then base coat on to. I use Pollyfiller 3-in-1.

I have racked out seven cracks in our interior of the house - initially one looked like a simple hairline crack.. ripped it out back to the block and the block had fractured. So it pays to understand why the plaster has cracked too.
You will need a good wall sander with a bowl type thing that collects the dust into the vacuum. It will make mess. The minimum you will need is a respirator mask for the dust and safety glasses, something to put plaster into the crack (metal blade plaster knife). Get a paint tin to mix the plaster.

Lime is old school and specialist, for example: http://www.limestuff.co.uk/pages/products.html
 
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It's outside the main door but still inside a block of flats. So how much bonding plaster do I use, do I say fill the hole to maybe an inch depth left then use the finishing plaster. And how many layers. Say the hole is 0.5m x 0.3m x 0.2m, how many layers would I need and how long to dry between layers and would I use PVA between layers. I'm assuming ofc as it's a big hole I will need to do it in layers.

Any chance of a fairly detailed timeline, just so I get it right - such as,

1. Paint all plaster surface with PVA
2. Leave PVA to dry then add a second coat
3. Plaster 2 inch thick bonding plaster
4. Leave to dry for 2 days?
5. Another 2 inch layer of BP
6. Dry and PVA
7. Keep layering till an inch depth left
8. Finish with FP
9. Sand and paint

Sort of thing?
 
Finishing plaster has a maximum depth of about 1-2cm.

1. Rack out - tap around the crack to hear any hollowing, I normally pull it out as the plaster has busted away from the backing (cracks travel in 3 dimensions).
2. vacuum out to get a debris clear area

20cm is a deep hole to fill.

2. Wet crack (oo-err) this helps the new plaster dry slower.
3. Let it get to damp then PVA but use 4:1 with water then you will need to start plastering while it's tacky. Really work the PVA into the edges.
4. Then layers - I would probably be tempted to use a hardwall plaster as it will be able to hold itself better. Then Bonding and then finishing.

I would definitely recommend putting a mesh in there - it will help reinforce the plaster further. You can get couple of fibreglass mesh patches and simply paste them in. The fibre ones are easier to cut with scissors the metal mesh work too but cutting with pliers is a pain and I've stuck my finger with a sharp end before..

How long? Well it depends on the layer under and how quick the water is sucked from the layer ("suction") - this can cause cracks if the plaster dries too fast. You may need to add water as you go along with a brush so that the cracks close. The deeper the plaster layer the longer it takes to dry overall. Lime plaster is has a high suction

What you don't want is to go too fast, ignore that the plaster layers are drying too fast and then find the layers crack. I've had hairline cracks - but use water and simply work the plaster a bit until it closes. Normally then it dries without cracking.

If you do let the layer dry out completely, then water+PVA mix and have the layers not smooth to allow the next layer to key.

For that size hole I would get a Hawk and plastering trowel - it will help and then at the top layer you can then smooth off easily enough.

I use plastic paint tin and a paint mixer on a drill (in screwdriver mode) to mix the plaster - fast, effective but just remember to wash the plaster off the mixer.
 
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Making it harder than you need to. While there is nothing wrong with the above approach people are telling you to buy, PVA, Bonding, Hardwall and Multi-Finish.

Just get some Easi-fill and fill it in a few layers.
Clean it out, damp it with plain water a little. Then fill.
Easi-fill is suitable for sanding as well so you will get a perfect finish.
It dries in hours as well so will be ready to paint the same day.
 
20cm is a crazy deep hole
Do you think there was always a gap in there or something, missing half brick or something

Personally that deep I would be filling with part of a brick/block and cement, and then plastering a couple of inches or so.

How big is the hole? Are we talking fist size, foot size, bigger?
 
Mercenary Keyboard Warrior said:
20cm is a crazy deep hole
Do you think there was always a gap in there or something, missing half brick or something

Personally that deep I would be filling with part of a brick/block and cement, and then plastering a couple of inches or so.

How big is the hole? Are we talking fist size, foot size, bigger?
Click to expand...

20cm was too much more like 10cm.
 
Thats still pretty deep, for most walls thats still a structural depth. Is it along side a frame or something, could be they just decided to let the plaster fill the hole.
problem is when it fails it will more then likely come out as one, if you were to fill with cement to say 3cm deep then that should stay in place even if the plaster fails again.
 
Yeh I thought it may all come out it not done correct, the pva and mesh should help. Still undecided on bonding vs hardwall.
 
jsmoke said:
Yeh I thought it may all come out it not done correct, the pva and mesh should help. Still undecided on bonding vs hardwall.
Click to expand...
Hardwall is the better option if it's going onto masonry.
Don't try and do too much in one go or it will take ages to dry think 2cm at a time is about the limit with Hardwall.
 
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