How to prepare sill for painting

[vincenzo78]

Hi all,

I'd appreciate some advice on painting a masonry sill. The existing paint was pretty flaky to I started scraping and in parts managed to get right down to the bare masonry.

I'm wondering now if I should try to strip the complete sill back but that will be pain as a lot is sound. If not, do I need to use filler to bring parts up level again? Looking at the pictures, how would you proceed? Also, what paint system would be best? Oil based with primer on the exposed parts? Since the previous was oil based it has to be same right?

 

[opps]

If you want a smooth finish, buy some 2 pack filler (upol etc) to fill the low spots and then sand flush. You won't need primer, undercoat and gloss will be fine, I use the Dulux Trade Weathershield oil based system.

Provided that you key the sill sufficiently you don't have to stick with oil based, you could use water based masonry paint if you prefer.

2 pack filler is quite hard to sand, if you want a softer filler look at Toupret Touprelith F. It is more granular though. Prime it with diluted water based masonry paint. I have glossed it in the past but it took about 4 coats of masonry paint and lot of sanding with 180 grit before undercoating and glossing.

 

[vincenzo78]

Thanks for the reply oops. So I think that's what I'm trying to understand, if I have stripped some parts back a couple of layers and left sound paint in other parts is it recommended to use filler or is it ok just to paint over with undercoat and gloss?

 

[Mr Chibs]

I've just redone all the cills on my house (6 x 1.1M), they were worse than yours, they were very very scabby.

I burnt & scraped the paint off, back to stone

I then used this:
https://www.toolstation.com/shop/p7...MIgdDPzv_F1gIVSYGyCh240gixEAQYASABEgKr5vD_BwE

It's made a cracking job, it's easy to sand... it's a bit like plaster of paris.

Then I applied 3 coats of masonry paint. I've used water based.

PS, think my cills looked like cast concrete.

 

[opps]

Toupret Murex, as recommended by Mr Chibs is another top quality exterior filler. It sands to a smoother finish than Touprelith F. Just be warned that it goes rock hard once it gets wet (ie rained on).

I'd recommend filling rather than just painting, you don't want the water to pool in the areas where you removed the paint.

 

[vincenzo78]

Good point about the water pooling oops. I wasn't sure whether filler was overkill since there isn't any actual holes or pits just a difference of 2 layers of paint in places but I know that just painting over will not bring it up level. I'm guessing most diyers would just paint over.

Last question.. should stabilising solution or a primer be used in the stripped back areas before filling?

 

[opps]

stabilising solution

Normally I would say no but it looks like someone else has used ye old powder filler previously (eg Tetrion etc). In my experience they always remain potential points of failure unless removed (with an old chisel).

If you can remove the old traces of white filler then you shouldn't need to seal the sill. If you do need to, consider SBR (don't use PVA), unfortunately I have only ever seen it in 5L containers.

Something else that you may have over looked is the silicone seal on the windows. Your filler and paint won't adhere to it. Personally, I would cut it away and use one of the MS polymers such as CT1, Puraflex 40 (after the painting).

It is one of my many pet hates; the unabandoned use of silicone by people fitting uPVC. I guess that they use it because it is cheap. They want to get paid and shoot off, and seemingly have no regard for the poor sucket that has to paint the silicone infected areas after the event.

Plumbers are often guilty of the same offence...