Advice on Painting Concrete

BrensBenz

First time here so be gentle.

I'm just a simple wood mechanic, bamboozled by anything to do with concrete. My window sills, the caps on my gate pillars and the concrete floor in my shed will not stay painted! Paint seems to flake off in months. Other concrete surfaces around the exterior of the house are fine - two or three coats of Sandtex, or similar, stays on for years but the same paint flakes off the sills and caps.

Three coats of (very expensive) International floor paint flaked off my shed floor in less than a year. I could hoover the floor back to bare concrete! The local wise man told me to apply PVA(?) / EPA(?) / EVA(?) first so, next time, I did that. Can't remember the mixing ratio but it was as advised. More coats of floor paint and....IT FLAKED OFF AGAIN! And not just from traffic areas, the paint flaked off under benches and tool trolleys too.

If it matters, the shed is clad steel, about 12 years old and used for woodwork, boat storage, etc. It's insulated, dry and quite cosy. I wanted a quality, durable floor so, when it was being laid, they told me it was "rich".

The wise man blames the salty air in NCD but why does it only affect concrete sills, caps and shed floors?

cardwizzard

Apply couple coats of stabiliser prior to paint. Excellent at adhering to smooth concrete. The paint will stick to this.

BrensBenz

cardwizzard wrote: »

Apply couple coats of stabiliser prior to paint. Excellent at adhering to smooth concrete. The paint will stick to this.

Many thanks, cardwizzard. Sounds exactly what I need.
However, I know nothing about this stuff. Any brand? Any DIY shop? Is it similar to PVA / EPA / EVA? (Sorry, can't remember what it was called......but it didn't work!)

cardwizzard

BrensBenz wrote: »

Many thanks, cardwizzard. Sounds exactly what I need.
However, I know nothing about this stuff. Any brand? Any DIY shop? Is it similar to PVA / EPA / EVA? (Sorry, can't remember what it was called......but it didn't work!)

We use the crown stuff but only because the shop is handy. Never had a problem with it. Get the slow drying over night stuff, better imo.

Off course rest of the major brands carry it to and have used them with no bother also, so whatever is closest to you.

Safehands

BrensBenz wrote: »

First time here so be gentle.

I'm just a simple wood mechanic, bamboozled by anything to do with concrete. My window sills, the caps on my gate pillars and the concrete floor in my shed will not stay painted! Paint seems to flake off in months. Other concrete surfaces around the exterior of the house are fine - two or three coats of Sandtex, or similar, stays on for years but the same paint flakes off the sills and caps.

Three coats of (very expensive) International floor paint flaked off my shed floor in less than a year. I could hoover the floor back to bare concrete! The local wise man told me to apply PVA(?) / EPA(?) / EVA(?) first so, next time, I did that. Can't remember the mixing ratio but it was as advised. More coats of floor paint and....IT FLAKED OFF AGAIN! And not just from traffic areas, the paint flaked off under benches and tool trolleys too.

If it matters, the shed is clad steel, about 12 years old and used for woodwork, boat storage, etc. It's insulated, dry and quite cosy. I wanted a quality, durable floor so, when it was being laid, they told me it was "rich".

The wise man blames the salty air in NCD but why does it only affect concrete sills, caps and shed floors?

The first thing to examine is the flakes of paint when they come off. Is there concrete still adhering to the back of the paint? Unlikely with the cappings or cills, but very possible with the floor. If the paint is coming off clean, then you have no adhesion. With precast units like cappings, this could be due to some residual mould oil left on the concrete, so simply degreasing may work. If they are very dense then paint a little brick cleaning acid on prior to painting and wash off with water. This will open the pores and promote adhesion. I wouldn't bother wth PVA's. Make sure everything is dry before painting. In the shed is it possible you have some contaminant on the floor, oil or silicone spray or some other material? Did you do any preparation prior to painting, any grinding or sanding. Could the floor be wet? Is there a dpm?
These are all the questions which need to be answetred before deciding how to proceed any further.

BrensBenz

cardwizzard wrote: »

We use the crown stuff but only because the shop is handy. Never had a problem with it. Get the slow drying over night stuff, better imo.

Safehands wrote: »

Is there concrete still adhering to the back of the paint?
Last attempt to paint the floor was a couple of years ago so I can't answer that. Also, the flakes were very small.
In the shed is it possible you have some contaminant on the floor, oil or silicone spray or some other material?
No. First attempt to apply paint was about a month after laying the concrete. At that time, I worked away from home so the shed was empty and unvisited for about a month while the concrete cured. And I have the biggest locks you've ever seen on the shed door!
Did you do any preparation prior to painting, any grinding or sanding.
The only "pre" work before the first floor paint was a quick hoovering, just in case. When that paint flaked off, I tried again but with PVA(?) first.
Could the floor be wet?
No, it's bone dry. I've insulated the roof and walls with aeroboard and ply but with a dark colour cladding, it still gets quite cosy inside. The floor acts as a huge storage heater. My main stock of "good" carving and boat wood is in there and it doesn't show any signs of damp. Also, dozens of spiders.
Is there a dpm?
Yes. Approx 6 inch concrete slab on hard core went down first and was covered with a tarp. A couple of weeks later, the shed frame was bolted to the slab, a membrane went down and another 3 inches of concrete (the "rich" mix) went over that.

Gentlemen, I'm most grateful for your advice.

Safehands, I've added answers to your questions above.
The boat should be launched by early Summer so I'll have room to have another go with paint then. I'll try a few coats of stabiliser first this time.

And yes, I know it's only a shed but WE know how important a shed is!

Safehands

BrensBenz wrote: »

Gentlemen, I'm most grateful for your advice.

Safehands, I've added answers to your questions above.
The boat should be launched by early Summer so I'll have room to have another go with paint then. I'll try a few coats of stabiliser first this time.

And yes, I know it's only a shed but WE know how important a shed is!

OK, the most likely cause is residual moisture in the "rich mix". Anything over 5% can cause paint to debond, and a month may not have been long enough, especially if it was laid outside summer months and if the paint was not water based or at least moisture tolerant. I'd go with a waterbased epoxy if you are doing it again. I don't think the stabiliser is necessary. Have a look at "Resin Surfaces" products on Google. They are based in the UK. They will surely have one that suits.

BrensBenz

Safehands wrote: »

OK, the most likely cause is residual moisture in the "rich mix". Anything over 5% can cause paint to debond, and a month may not have been long enough, especially if it was laid outside summer months and if the paint was not water based or at least moisture tolerant. I'd go with a waterbased epoxy if you are doing it again. I don't think the stabiliser is necessary. Have a look at "Resin Surfaces" products on Google. They are based in the UK. They will surely have one that suits.

Sounds fierce technical!
The floor was laid round about this time of year - Spring. Both attempts were with International Floor Paint and I'm open to correction but I don't think the paint was water based.
I'm actually familiar with Resin Surfaces Ltd (long story) but I might try paintshop.ie first - they're local and they stock water-based epoxies.

And I'll try the stabiliser on the caps and sills. If it works, the Leader of the Opposition might give me permission to go sailing.

Thanks Again.