Joints, Paying attention to the detail
Paying attention to detail with joints.
There is a big difference between a professional job and a DIY one. Sharp lines v wobbly ones. Smooth surfaces v lumps and bits. I try to take a good professional job another level higher, by paying more attention to detail than the last decorator.
Hairline cracks in joints
See a hairline crack. when the room heats up in the summer and cools down in the winter the plaster and the board beneath the plaster expand and contract at different rates This results in a crack at the weakest point.
To deal with these movement cracks, decorators use a flexible acrylic “caulk”.
This product fills the joint and moves more than the materials it is bridging. It isn’t fool proof in this day and age of hot houses. However, it is the recognised decorating trade solution to the hair crack problem.
Caulk is ideal for an invisible quick repair. But it is tricky to apply because it skins over quickly. It is OK if you get a perfect result first or second time, but if you keep fiddling with it with a dry finger, it beads up and you end up with snots on the ceiling and walls which you cannot sand down easily. If, at all. Paying attention to detail, you should keep a wet rag or a wet wipe with you at all times to clean up.
Also, if you rely on your finger to get into corners, you lose the sharp 90 degree angle. A simple solution is to use a screw driver and damp rag to form the sharp right
Hairline crazing on joints
Sometimes, acrylic caulk solves the issue of cracking – only to create another issue on joints. Hairline crazing! You may even have seen it, if you take a really close look at where the ceiling and wall lines meet. When you apply flexible acrylic caulk and then paint over it with vinyl (matt) emulsion, they dry out at different rates. And, the difference in surface tension can create a subtle crazing effect in the paint along the line of the joint.
I was covering my bases by using high quality vinyl matt emulsion and mid-range rather than cheapo trade caulk. I also tried to let caulk harden overnight (even though 2-4 hours is the recommended time). And, for belt and braces, I painted a coat of oil based undercoat on top of the acrylic caulk before emulsioning it.
This arcane approach seemed to cut out that particular crazing problem. Most of the time. But, only most of the time! I got let down occasionally, even bending over backwards to get it right, and there seemed to be no rhyme or reason to it.
I believe I was barking up the wrong tree with the rant below. Basically I now think the issue is not about the caulk, but standard vinyl emulsio. It is low in acrylic resin, high in vinyl polymer content and is therefore not compatible with acrylic caulk.
Conversely, the high acrylic content premium matt paints I use exclusively now, don’t cause any crazing whatsoever. And, the Dulux Tech support advice, finally, was to use Diamond eggshell as a sealercoat over acrylic caulk.
It pretty much worked. Guess what, Diamond eggshell is a premium product. Probably high in acrylic resin content, and low in vinyl content, so it tends not to react with acrylic caulk.
Could Joints be that simple?
The bottom line, if you don’t want to bend over backwards and still risk failure with caulk, use high quality acrylic emulsion. Do not use cheapo vinyl matt with any half decent caulk from one of the paltry 3 manufacturers supplying our dec centres these days.
The acrylic caulk scandal!
If I used cheap DIY emulsion, which contains a high proportion of filler (chalk, for want of a better word) and DIY caulk which is possibly a bit short on acrylic, I would understand why caulk can craze. But I use good trade (vinyl matt) emulsion. And, I spend a bit more than the average on good trade caulk. Yet, I still, and loads of other decorators doing everything by the book, cannot guarantee the final result.
All I can say is that there must be more to compatibility between caulk and emulsion than “good” ingredients, but who knows?
The manufacturers are no help. While they all insist that we use theircompany undercoat with their company gloss to ensure perfect results, they won’t commit to which emulsion X will work with caulk Y.
Personally, I don’t think the likes of Dulux are interested in committing. Unlike unlike their paint which they control like hawks, they don’t have a guaranteed consistent high quality supply of caulk that they will stand by.
Caulk is a generic commodity, a bit like White Spirit, that anyone can buy in bulk. From, various 3rd party manufacturers. And, re-brand as your own. So who knows what rubbish they will use if they can make a few extra euros profit.
So, either I buy 5000 tubes of caulk from a supplier who will guarantee the
formula works with the emulsion I use. Or, I rely on the undercoat trick
to try overcome a problem of the manufacturer’s making.
Realistically, acrylic caulk is not the weakpoint in the crazing debate, vinyl matt probably is.
And that is why they have probably kept quiet, because in truth, their “premium” emulsions aren’t that high quality compared to the “posh” companies favouring high acrylic resin content.