Plastering

dahamsta

Appreciate a little help with a plastering job. Photo here, plastered blocks in an old (~40 years), damp caused some of it to go soggy. I've chipped off the loose stuff and I'm happy doing the skirt and paint, but I've never done any plastering and my polyfilla repairs have always been average at best. YouTube only turns up yanks doing outside plastering, or repairs to plasterboard. There'd be very little wall on display when the rad is back up, so I'm disinclined to get a plasterer in unless I really will make a hames of it.

Any tips for me, or links to relevant vids?

policarp

If the wall is still damp, that problem will have to be fixed first before re-plastering. Also that job looks to be a little too big for a Polyfilla repair.

dahamsta

The source of the damp was a rad, I mentioned this would be put back on the wall; obviously this has been fixed. I wasn't considering using polyfilla, it was mentioned in passing. So, plastering?

policarp

Firstly I would suggest applying 1 or 2 coats of Polybond at a ratio of 5 or 6 parts water to 1 part Polybond. This should be dry enough for plastering after about 1 or 2 hours. Then mix your plaster in a clean bucket by adding the plaster to clean water, a little at a time, until you reach a creamy consistency.
Then apply this to the wall with a steel plastering (I would suggest a 10") trowel to the same thickness as the existing plaster, getting it smooth at this stage is not that important, but just make sure you no big humps or hollows.
Then depending on the plaster and drying conditions you will have to wait until the plaster sets a little. Rule of thumb here is that if your thumb nail goes into the plaster but your thumb doesn't.
You should still have a little plaster left at this stage and now you will need a small quantity of water in a separate bucket and a 4" or so brush (paint brush type will do). Now wet the plaster lightly and smooth it out using a small bit of the leftover plaster and repeat this until the plaster has a shine on it.
Also I don't see your rad brackets, maybe you might fit these and plaster around them or just put the screws in their holes to make refitting the rad easier.
This will be a pretty messy job and I would suggest covering the rad valves
with a plastic bag or taping them up.

red sean

Hi policarp, not hijacking the thread but I've seen ready mixed stuff being used for taping joints, would this do? I may have a similar job to do after the plumber has been and gone.

dahamsta

Great comprehensive answer policarp, thanks very much for that. The rad was moved slightly as part of the repair, so I'll drill new holes for that when I'm done.

I've a few follow up questions:

1) Should I apply the plaster in layers and build up to the original thickness, or bring it up to that depth in one go?

2) I realise it's not an exact science, but roughly how long will it take to dry before I smooth?

3) How long should I leave the finished product before painting?

policarp

red sean wrote: »

Hi policarp, not hijacking the thread but I've seen ready mixed stuff being used for taping joints, would this do? I may have a similar job to do after the plumber has been and gone.

That stuff you're talking about is for filling joints in plaster boards but can be used for small patch plastering, only it doesn't give as good a finish.

policarp

dahamsta wrote: »

Great comprehensive answer policarp, thanks very much for that. The rad was moved slightly as part of the repair, so I'll drill new holes for that when I'm done.

I've a few follow up questions:

1) Should I apply the plaster in layers and build up to the original thickness, or bring it up to that depth in one go?

2) I realise it's not an exact science, but roughly how long will it take to dry before I smooth?

3) How long should I leave the finished product before painting?

1) You can apply it in layers if you like, probably be easier for you.

2) That depends on the drying conditions and the plaster you use.
New or fresh plaster dries slower than old plaster. Really old plaster sets almost instantly.A rough guide would be the thumb nail test. Stick your thumb nail into the plaster and when your nail goes into the plaster but your thumb doesn't then start rubbing up.

3) You will see the plaster drying as it gets lighter. When the dark or damp spots are gone then you can paint.

red sean

policarp wrote: »

That stuff you're talking about is for filling joints in plaster boards but can be used for small patch plastering, only it doesn't give as good a finish.

Thanks for the reply, policarp. Any idea the name of that stuff as I only have a small bit but might touch up a few places in the garage as well. Can use them to practice!

milehip1

get a pail of ready mixed joint compound(it'll store for a couple of years if kept properly)
apply, smooth over with a wide paint brush when still wet, sand down when dry.

policarp

red sean wrote: »

Thanks for the reply, policarp. Any idea the name of that stuff as I only have a small bit but might touch up a few places in the garage as well. Can use them to practice!

For small patches milehip1 is spot on.
Fill all deep holes first and leave about 3 or 4 mm deep for final filling coat.

Scimcoat is used plastering jobs.

red sean

Thanks for the help lads.

dahamsta

Thanks again policarp. This would be new plaster. Are we talking 30 minutes or 10 hours territory? This is the mother's house, if it'll take some time, I'll feck off and do something else.

milehip1

if your mixing skim it normally takes about 2hrs iirc,
if you want to slow it down use a few drops of vinegar in the mix,
if you want to speed it up(rapidlly) throw in a handful of cement dust,

ready mixed compound takes a bit longer, but as you sand it down after it's dry you can walk away for as long as you like

policarp

dahamsta wrote: »

Thanks again policarp. This would be new plaster. Are we talking 30 minutes or 10 hours territory? This is the mother's house, if it'll take some time, I'll feck off and do something else.

It's impossible to say for certain but could be up to an hour.
If you leave it for 10 hours you'll need a Kango, not a trowel.

dahamsta

That's all the guideline I need, thanks again for all your help.