Primer or Undercoat for Exterior Timber?

Hi

I am confused about the way to prepare exterior timber prior to applying the top coat of paint. I ask these questions in relation to the construction of outdoor items such as car ports and fences.

Should I treat the cut ends of CCA treated timber with a primer or an oil-based undercoat?

What about non-treated timber?

I have been told by a carpenter to use a slightly diluted oil-based undercoat followed by an acrylic topcoat because this gives good protection to the timber by having the undercoat penetrate the timber and the acrylic providing a flexible outer skin.

I have also received advice from Solver paints that acryilic paint should not be applied over oil-based undercoat.

Advice on paint cans invariably mentions the use of a primer.

I am confused and need advice.
Thanks

I'll leave the question of what primer/sealer to others better qualified.

What I would recommend is that you paint the cut ends of CCA with the green, liquid CCA generally available in Bunblies etc.

As I undersatnd it, CCA timber is vacuum treated to instill the poison (used to be Copper, Chromate, Arsenic). Generally the poison only seeps into the surface a bit. Hence when you cut, you leave large areas of lightly treated/untreated timber bare. Hence the touch up with the preservative.

If the cut ends are to be on/in the ground I stand them in the CCA solution, to soak overnight. Or if you're a bit shonky (like myself) sump oil and diesel mix works too. No termite gonna enjoy that feed.

I'd go with the builder, the oil undercoat provides plenty of protection. You can put acrylic over oil but not the other way around. Using a self priming paint like solarguard etc should by definition work with the oil undercoat. In my experience using the paints like solarguard without the oil based undercoat greatly shortens the life of the top coat. By the way this topic has been covered a few times you might try a search and see what you turn up.

John

John

The liquid that Bodgy mentioned is called Re-seal by Protim Solignum, and is sold in a plastic container of granules, usually in your hardware store near timber preservatives and sealers.

Bodgy's (Bodgies ?) advice is spot on with cut ends, most people don't bother but the granules are cheap and it is worthwhile.

Oil based undercoat under acrylic topcoat seems to be the accepted wisdom, if the Solver advice is otherwise and you are keen on their paint, try making a call to their head office and try to get to talk to a chemist or someone else with technical knowledge and get to the bottom of it.


Good luck.............cheers...............Sean, naked undercoat :D

Haven't used CCA prefer northern N.S.W. hardwood as it doesn't twist warp as much

As for untreated timber I agree with John , but two coats of undercoat if possible. The Solarguard he mentions I have used and no complaints other than the price, still you only get what you pay for.

As my old dad use to say put plenty of paint on , you can paint a house with a gallon of paint if you put it on thin enough , but you'll need to re-paint it next week.

Rgds


Ashore