Basic painting advice

I would undercoat. I've found that with water based undercoats that I have purchased in the past few years have more pigment and covers blemishes whereas the gloss top coat gloss is semi-transparent with a lot less pigment material.

I used a solvent based paint from the sheds a few months ago. It took "forever" to touch dry and still very soft 3 or 4 days later. This weekend I used some old solvent based paint purchased 10+ years ago and this touch dried a lot faster despite the ambient temperature being lower.

No. The purpose of undercoat is to build up reflectivity, and colour. It you are repainting its not necessary.

All you actually need to do is ensure a good adherence to the existing paint.

I'd question the need for even sugar soap.

The water based stuff is OK but it takes a long time to go really hard

I applied some F&B water based satin over some 16 year old F&B oil eggshell. I sanded a bit first. It seems to have stuck OK.

How many different variants would you like?

I'd agree with TNP that you don't need to undercoat, but I do like sugar soap, it does seem to remove decades of grime of all types and gives you a surface that new paint keys to well.

I've more or less gone over to water based gloss in spite of my theoretical objections. But do go for Leyland or another good quality trade paint.

Depends how good the prepared surface is -

Are you sure that you want brilliant dazzling glossy white? I'm more inclined to use a satin off-white for woodwork these days. Oil-based always seemed to adhere better and dry tougher, but who knows how the environmentalists and elfin safety have messed it up recently?

if you want to save time, scraping before a brief sand is quicker.

alkyd doesn't care, you can skip that unless it's manky

if it's discoloured you probably will need it. Try a bit without & see. Und ercoat has high opacity, topcoat generally not.

alkyd every time, it beats the whatsits off water. (People tend to call it oil paint though it's not.)

They have. My recent use of wilko & Leyland taught me it will no longer cov er the slightest of hairline cracks. OTOH it stuck to glass like nothing el se ever has, so maybe it will last better. But it does need much better pre paration than previous paint, generally a complete strip back & fill of eve ry microscopic crack.

NT

But you have to sand anyway to get a decent key. The grime comes off with the paint surface.

Well thanks to all for advice, I think I'll try a good quality water based gloss first in an inconspicuous location, on top of a good sanding and a wipe down and decide from there if I need an undercoat.

I was worried that an undercoat may be needed for the gloss to stick to, but all of the comments seems to be about depth of colour given by undercoat rather than increased adhesion.

I agree. If anyone has ever used silicone "polish" that *must* be got off. Silicone is used as a mould release agent for a reason :)

And modern formulations of household cleaners lack the components they once may have had to do this effectively.

The other option is a quick rub over with sandpaper, or a wet and dry paper or block used wet, if dust is a concern. Just enough to cut the surface and give a key.

I have cunningly avoided the problem by using nothing but bare wood for skirtings and frames and architrave - and coating with Treatex "oil" (oil and wax blend really).

It cannot chip, the wood looks natural and it can be recoated without fuss if it ever gets worn.

On larger surfaces, perhaps spraying would work better.

On Fri, 9 Nov 2018 10:43:31 +0000 Chris B wrote: > I was worried that an undercoat may be needed for the gloss to stick

Also has more build, so will cover small scratches or cracks in the prepared surface.

But that can just spread particularly pernicious contamination around a bit, rather than remove it all.

some tips