Sanding before decorating - how far do you need to go?

ThisIsWeird

Vinyl silk emulsion paints are quite 'plasticky', and many don't sand that well - it will often tear rather than sand. Matt emulsions, on the other hand, tend to sand off to a fine powder.

I guess a lower speed, less pressure, would reduce the 'melting'. Yes, it's darned annoying - I usually resort to wire-brushing the worse off. Partly works.

mi-key

ashe said:

FreeBear said:

ashe said: the surface still has a strong orange peel feel to it which I was hoping to sand away. Is it easier to scrape some easyfill over the bumps with a trowel and then sand smooth & mist coat? Or am I going too far?

I've been using Knaul Fill & Finish to patch up some walls here. Once dry, going over with a moist sponge float helps to feather in the edges and take out any small humps & hollows - A lot less mess than sanding.

Wickes do a 5Kg tub for around £17, but if you shop around, a 20Kg tub shouldn't cost much more than £30.

I've ordered a tub of this so will see how I get on!

ThisIsWeird said:

You have probably done enough work, Ashe. One way to find out...

Here is hoping! We had some minor bubbles in our bedroom, but weirdly only at the top of the walls and they weren't huge or noticeable but thin you would see them if it happened here so trying to do everything possible. We have a small part in the hall where the radiator is that we need to paint so the plumber can come and rehang the radiator (you can see between the fins so needed doing), so we'll give that a go this week and see how the paint takes to it. 

one other query - is it a specific kind of paint that is causing this to happen, or sanding too fast? Pads don't cost the earth but it is happening quite quickly and usually I'd get a lot of life out of a pad on my orbital but it's like it's melting the paint and then it's a hugger to pick it all off 

You can get sanding pad cleaners, they are like a block made out of a rubbery material and work pretty well. I always use them on my belt sander as the belts are pretty expensive for it :

https://www.screwfix.com/p/silverline-sanding-belt-cleaning-block-75mm/127tj

Mistral001

Orbital sanders are likely to create more uneveness than make the wall smooth.   A light sanding by hand with sandpaper is all that is needed usually.  If there are lots of discolorations, then after the light sanding, I would give the wall a coat of white emulsion paint. This will cover up any discolorations and only the blemishes that need filling will be noticeable.  After filling these and sanding them smooth by hand,  paint with a couple of coats of your chosen colour.

ashe

ThisIsWeird said:

Vinyl silk emulsion paints are quite 'plasticky', and many don't sand that well - it will often tear rather than sand. Matt emulsions, on the other hand, tend to sand off to a fine powder.

I guess a lower speed, less pressure, would reduce the 'melting'. Yes, it's darned annoying - I usually resort to wire-brushing the worse off. Partly works.

I think this explains why we had some small bubbles in places in the bedroom as looked like a similar paint. I've googled it and says it's because the silk lifts away and settles as it contracts again, they were only small though and mostly high up, so could be where we missed it with the peel stop. 

The suggested solution seems to be zinsser Gardz, with a few sites saying use peel stop, we already have peel stop, so would that suffice before we do a thin coat of white to undercoat it and then apply the Matt emulsion? Or is Gardz more recommended? 

ThisIsWeird

Not sure, but I think Gardz is an all round sealer/primer, and should effectively separate the old from the new.

'Peel stop' is, I understand, more to hold down loose flaking paint, which isn't really your issue.

Not sure, tho' - hopefully others will know better.

Phil4432

Painting woodwork also?

ashe

Phil4432 said:

Painting woodwork also?

We'll be sanding it, priming and glossing with water based gloss

ashe

So, got some Gardz. I was going to give a quick mist coat but guessing that could cause the issues with bubbling prior to using the Gardz? So just Gardz then emulsion? 

ThisIsWeird

If you are going to use Gardz, then use it first.

ashe

FreeBear said:

ashe said: the surface still has a strong orange peel feel to it which I was hoping to sand away. Is it easier to scrape some easyfill over the bumps with a trowel and then sand smooth & mist coat? Or am I going too far?

I've been using Knaul Fill & Finish to patch up some walls here. Once dry, going over with a moist sponge float helps to feather in the edges and take out any small humps & hollows - A lot less mess than sanding.

Wickes do a 5Kg tub for around £17, but if you shop around, a 20Kg tub shouldn't cost much more than £30.

Got this because quicker than mixing some easyfill, I've used it on a couple of holes where I've taken plugs out of, looks like I'll need a second coat as where the hole is it's shrunk back into the hole but still quick to work with. 

Do you prime it first or can you just paint straight over it once happy with the finish?