Sand/de-nib between coats of on exterior woodwork?

[Krome10]

Hi all

I am currently doing up my external wooden windows. I have used Zinsser Bullseye 123 as the primer and will be using Eico Alterior Eggshell for the topcoats:

http://eico.co.uk/products/eico-alterior-eggshell-1l/

Should I lightly sand / de-nib the primer before painting the first topcoat? And should I sand/de-nib between topcoats?

Aside form general advise on that, what would be very helpful to know is what purpose the sanding/de-nibbing serves? Is it purely to get a better and smoother finish? Or does it make for a longer lasting job? In other words, is it purely aesthetics or does it serve practical purposes too?

Many thanks

Max

 

[RobinBHM]

De-nibbing is generally done after the first coat. Applying any finish to bare timber dries with any fluffy grain, wood dust and raised grain leaving the surface rough.

A bit of rubbing back may be needed if required between subsequents coats if the surface is still rough.

Any sanding back between coats doesnt improve adhesion

 

[morturn]

The trick with painting is the get paint on, not sand it off. All your main rubbing down should be done before any panting so the surface should be clean, smooth and free from lose or flaking material.

Then apply a coat of primer to any bare wood and to the rebaits before re-puttying. Priming will raise the grain and set upright any wood fibres, so a light run down just to de-nib the surface of the primer.

Re-putty and fill the cracks and holes and apply a coat of undercoat. I often used to hear people say that “it just undercoat”, but a good solid undercoat is key. It should leave the surface free form any defects, clack, shakes or holes and it should look solid and covered. If it’s not, then undercoat again.

I do not share the view that “any sanding back between coats doesn’t improve adhesion”, in my opinion it does, and most importantly it removed any bits of dirt, debris or flies that have settled onto the wet surface before it dries. Again, a light rub over, mind the corners and edges, don’t break the surface of the paint.

The product you are interested in look like an eggshell finish, so it may be a question of applying two coats of the same.

 

[Krome10]

Thanks for the replies - much appreciated.

I'm not so worried about a smooth finish, I just want the paint job to last as long as possible. If I can get away without a de-nib without affecting the performance then that's what I'll do. If the de-nib helps with adhesion - even with eggshell paint - then I guess I'll bite the bullet. Hmmmmm, decisions decisions!

Cheers

 

[Phil Pascoe]

Make sure you don't over sand the timber, it can be counter productive as paint will peel off it more easily. Also make sure you knock off the arrises, for the same reason. A good lagging with a good preservative is worthwhile.

 

[ED65]

Re-putty and fill the cracks and holes and apply a coat of undercoat. I often used to hear people say that “it just undercoat”, but a good solid undercoat is key. It should leave the surface free form any defects, clack, shakes or holes and it should look solid and covered. If it’s not, then undercoat again.

Completely agree. Doing this half-heartedly is what leads to many premature failures of the topcoat.

I do not share the view that “any sanding back between coats doesn’t improve adhesion”, in my opinion it does,

It does or it doesn't depending on the paint/coating and one or two variables.

Any finish than can meld with itself (shellac or solvent-borne lacquers) doesn't require any sanding at all, although you can do it to help achieve a smoother final surface naturally. Those finishes which react chemically to provide a bond, this actually covers nearly all other finishes, the roughness of the surface does nothing to improve adhesion as long as the next coat is applied in good time: within the 'recoat window'.

Where you absolutely must sand or scuff is applying to dissimilar materials with a very smooth or glossy surface or when the previous coating of the same finish has had a chance to cure, i.e. you're beyond the recoat window and therefore the dried paint/whatever can no longer be reacted with.