Superdec problems - blistering

[thehouse]

My first post here so hello everyone

I've been having some issuse with Sadolin Superdec on existing gloss. Usually this is the trouble-free paint everyone swears by, so I'm a bit puzzled what's gone wrong.

I'm repainting a neglected front porch in Superdec Black Gloss. The old paint was flaking but I prepped the living daylights out of it to be extra sure of no problems. Rubbed down, washed, degreased with meths.

Two days after applying the Superdec, it had huge blisters. Strangely, when I cut into them, the blister went right back to the timber. In other words, the superdec is firmly bonded to the existing paint but has somehow caused that paint to blister.

I rang Sadolin for advice and they said redo the blistered sections, but today, before I got round to it, many more blisters have appeared. They appear to be brought on by the hot sunshine.

Superdec is supposed to be fine applied on top of existing paint. Has anyone got any ideas what might have gone wrong?

 

[Pigeon85]

Sounds to me like the previous paint was not bonded properly to the timber, I would advise to prime the bare wood prior to any painting. After priming you could fill the areas to blend them back in.

 

[thehouse]

The paint seemed pretty well bonded until the superdec went on top. Almost like the superdec is inadventently stripping it.

 

[sparkwright]

How dry was the wood before you started?

Could this be trapped moisture?

Had a similar problem only once with Superdec. Where bare wood was present, and I feathered it, it did blister here fairly quickly - which I've not experienced. It had three coats. Eventually I re-did, just by repeating the process, and it was ok. Odd, but there ypu go.

 

[sparkwright]

You said black. Black paint can blister more frequently, in my opinion.

 

[thehouse]

The wood seemed pretty dry. I washed it down thoroughly but left a decent time in warm weather to dry.

sparkwright, you say it blistered where bare wood was present but did it blister over the bare wood or over the existing paint? For me it is stuck firmly to to the bare wood but causing the existing to blister.

I have been wondering about the black issue. My current working theory is that the shiny blackness of the new coat combined with the blistering sunshine (pun intended) conspired to cause the problem. Black gloss gets very hot in direct sun. The existing coat was black but faded. I'm imagining that any of the old paint that couldn't handle the sun had already fallen off and that the remainder could handle the amount it absorbed when faded but not the extra amount once wrapped in a bright new glossy layer.

Or am I just trying to justify sticking with Superdec when I should really switch to Bedec barn paint or something else less sensitive?

 

[sparkwright]

I remember black was always said to attract heat, and black window sils always seemed to blister quite quickly.

How long did the surface have to dry before you started painting? Mind you, you say the paint below this blistered...

 

[thehouse]

I can't swear to it (memory like a seive) but I think I left it overnight to dry. Even if I didn't it would have been 3 or 4 hours in warm weather

 

[Bosswhite]

Dosent mean the moisture content within the Timber was dry,

You say the Timber was neglected, did you test it with a Moisture Meter ?

They are cheap enough, less than £10 for DIY model

 

[thehouse]

I was under the impression those things were little better than divining rods - vary the force with which you push them against the timber to get pretty much any reading you like.

But if they've worked for you I might pick up a cheapo on ebay.

 

[jaqsax]

I too have had problems with Sadolin Superdek blistering. We painted the front door with this a few weeks ago. We sanded down the wood and gave it 2 coats as we were instructed by the shop. Within days the paint had bubbled in several areas when exposed to the sun. Some were quite large blisters and some smaller. These just peeled off like a plastic skin.I rang the store who had mixed the paint who said I should contact Crown direst. I did this and they passed me back to the store, The guy came out and said we had not prepared the surface correctly. Not true. He then gave us some PVA undercoat primer and told us to remove the paint and sand it all down, apply the primer and re-coat. We did this thoroughly which took us several days. Result OK for a couple of days and then the same thing occurred.
On-going!!!!

 

[ic1927]

Had this problem once with superdec. Did a garden bench that had previously been painted with Leyland uc and gloss. The paintwork was sound, I sanded it, dusted it, wiped it down with meths, when the superdec went on it blistered lifting the old paint off right back to bare wood, ended up stripping it all back, priming with Zinsser 123 and two coats of superdec and it was fine. Strange how superdec can lift uc and gloss like that.