Wood hardener, wood filler and undercoat?

[Patrizia]

Hello,
My back door was installed only last year but I have noticed that a few cracks have started to appear.
I sanded the door down and was told to apply wood hardener all over the door, which I did.
I am planning to fill the cracks with a wood filler. Am I right in thinking that my next steps should be to use a good undercoat and then some good paint?

 

[JohnD]

Is it made of wood?

 

[Patrizia]

Yes, it is a wooden door

 

[JohnD]

I can't see any benefit in the wood hardener. It is used on rotten wood.

The cracking does seem severe. I wonder if it has had a big change in moisture content.

I'd sand it well to remove the cracked paint. Expose the timber and see if that is cracked or just the paint.

Thick, hard paint will crack on wood. Wood naturally expands when moist and shrinks when dry. Filler will crack.

Look for a breathing external paint system advertised for external woodwork.

Is your door exposed to rain and sun?

 

[Patrizia]

Yes, the door is exposed to rain and sun. I have already applied the wood hardener. After sanding it down, more cracks have appeared.
I think I still need to use a filler to cover the cracks.

Is there any good undercoat which you would recommend?
Replacing the door would be very expensive, as I bought this door only last year and I paid for a workman to install and paint it plus a locksmith for added security.
Thank you!

 

[JohnD]

Filler will crack.

If it is exposed to bad weather, sand it back to the wood. The most durable wood primer is IMO "Oil Based Aluminium Wood Primer" (it dries grey, not silver), preferably with an oil based undercoat and gloss on top. You may need to order it, or go to a proper paint shop. Dulux Trade paint is good but other have their own preferences. DIY paints are formulated to be easy for an amateur to apply, which is not the same as formulated for durability.

When painting indoors, it is not so important, but a front door is most exposed and most on show.

Water based paints are much harder to sand and I am not yet convinced they are as durable. You may find a cheap electric sander helpful to get the cracked paint off.

Thick layers of paint, especially in joints, crack worse than thin ones. Wooden doors have a lot of joints. Paint it in dry weather, when it will be fully shrunk, after the morning sun has warmed it.

 

[opps]

As mentioned above, simply filling the cracked paint is unlikely to work.

The door looks like it is hardwood so I think it unlikely that the cracked paint will have resulted in significant water damage. If that is the case then I do not understand why you were told to apply wood hardener. From your post it sounds like you have applied the wood hardener over the paint which is a waste of time and money.

I can't tell how the door was originally prepared and painted. I too would suggest sanding the whole door back to the timber and starting from scratch otherwise you will refilling the cracks every few months and may end up with water damage.