Thread: House Painting - Undercoat or not?

Hi Guys,

I know this should be on a home improvements site, but I don't know of or visit any.

I will soon be re-painting my weatherboard house where I will be stripping back all the old paint to bare timber and re-painting.

I know that Dulux Weathershield and Wattyl Solarguard can be painted on without priming, but is it better to prime? If so, oil or water-based?

I emailed Dulux and asked the same question and they said given the age of the timber weatherboards (50 years old) they said to use their oil based one step.

So my options are:
1. 2 coats of Dulux Weathershield direct on the timber
2. 1 coat of water based 1 Step Primer Sealer Undercoat, 2 coats of Weathershield.
3. 1 coat of oil based 1 Step Primer Sealer Undercoat, 2 coats of Weathershield.

What do people think? (I know Dulux has already offered me their advice, but just thought I'd confirm it). Remember the hard part if the sanding/stripping, so one extra coat of sealer is no hassle in the scheme of things if it is considered worthwhile.

Any help is much appreciated.

Thanks,
Pete

The main problem I see with your spec is removing the old paint, this is really not necessary, only paint that is loose and no longer adhering needs to be removed. If it stays on the new coats will prevent it from further UV and water degradation.

If you can remove the existing paint with moderate effort with a scrapper then it should come off. You can also criss cross it with knife cuts at say 4mm apart and try to remove with good quality adhesive tape. Again if it comes off easily then strip otherwise leave.

Leave strippers, thermal guns well alone these are too strong - if you need the adhesive bond is ok. Reaplce weatherboards that are too rotten, otherwise rot treat.

Depending on the amount of existing paint film that needs to be removed you will end up with an uneven surface, about the paint thickness. Get a water based filler, e.g. timber mate and thin down with water until about like a cake mix consistency.

Paint, trowel on lightly using very flexible blade (not putty knife) this over the depressed regions until lightly overfilled. Then sand smooth and remove any gloss from the existing remaining paint (say 180 grit paper), the new paint needs a 'tooth' to adhere to.

With priming use an oil based primer if the timber may bleed, dark timber e.g. WRC, merbau (unlikely for W/ are the worst for this. Baltic pine is a very common timber for W/B and the self priming acrylics paints Solaguard, etc. no priming is required over non bleeding timbers. Oil based primer is required if they may bleed, this is mainly an issue with new timber.

Depending on how well the wall comes up would generally hedge towards low sheen finish as it hides surface imperfections more, and gloss paint tdrops its gloss anyway in a couple of years under the sun.

I hope you can trust me about not removing the old paint as it really is unnecessary and will save you so much work. Make sure you get a good respirator old paint can be very nasty.

I am a qualified among others a NACE coating inspector and have worked in around coatings for a long time.



Clive