Hi, I have a question about some horse hair plaster repair that I need to repair again.
I had to repair a number of cracks in my horse hair plastered hallway – 1920s house. I used a system that I used before – Big Wally’s Plaster Magic (drill a hole to the lath, squirt in glue, screw in disks with drywall screws to pull it against the laths, wait 24 hours and can joint compound over it). I used this method in my bedroom and it was successful (didn’t recrack).
So I used the same method on the hallway, with one change: after the glue dried, I dug out the crack with a utility knife and went over it with joint compound. Well about 9 months later it cracked along the same lines as the original crack!
So my questions: any opinions why it recracked along the SAME crack lines? How to repair so that it won’t crack again? Someone suggested I used durabond with mess tape.
Any thoughts will be greated apprecited!
Replies
Joe
Time of year is important in plaster crack repair-next to the whether or not the structure is sound behind it.
Your mention of 9 mos. since repair to re-crack suggests seasonal change as a possible culprit. Heating season shrinks the frame, warmer humid weather expands it. At even just a small bit of change, cracks reappear.
I find the best repairs I've done (longest lasting) were done during the heating season. I do use Durabond (original) and tapes-sometimes paper, sometimes mesh. That should be a given whenever repairing either a patch or just cracks-especially those that aren't just superficial but probably are contributed by frame or complete backer break.
The use of plasterweld on some repairs adds addtional insurance on skim coats.
When you dug out the crack, you exposed loose dust of the old plaster mix.
Then you tried to get premix drywal mud to stick to that loose dust.
It didn't happen
You have to seal / prime that area. There are plaster weld products specially formulated, but anything with white PVA glue works. Weldbond, Acryl60, Elmers....
and mix some into the mud too
Personally I do not like bucket mud for laster repairs. Durabond or real plaster.
Plaster repair
Do you mean seal/prime the area ONLY if I am using joint compound?
If I use Durabond, I don't have to seal/prime the area?
Thanks!
Always seal the crack and dusty surfaces with a PVA glue or sealer/bonding agent
Joe
If doing a repair on old plaster I am a firm believer in Plasterweld. Of course, you can use thinned PVA glue or take the easy out and buy a gallon of plaster weld. Pretty much the applicators should be considered throwaway (the glue sets and you may think you can clean it out............................)
My experience on many plaster repairs, if I don't use the bonding agent, I might get either paint or skimcoat peel.
If I do use the bonding agent, never had a failure or non-structural crack reappear.
There's something in the chemical makeup of some plasters (or some areas of plaster) that just doesn't mate up with compound, whether Durabond , Lightweight, nor with bucket muds. Remember there is more adhesive in Durabond, Less in Allpurpose bucket and even less in Topping bucket. Best to use the best.
Joe
Yes, I've learned the hard way that after you open up a crack it's vital to either vacuum or use compressed air to rid the area of loose dust. It's good to prime the adjacent area to help ensure adhesion and it's good to prime the edges of the crack itself. The layer of primer seals the crack and this stops the dry existing plaster from sucking too much water too quickly from the new plaster you apply. Too much suction, pulling too much water out of the new plaster too quickly causes shrinkage and that causes crack in and of itself. However, some amount of suction is good for adhesion but once the edges are primed there may be very little ability for that to occur... so it becomes very important to apply some plasterweld. The repair becomes more bulletproof if you continue on with paper tape which is bedded with setting compound. And from that point on you can texture with a mix of setting compound and regular joint compound. That's about all that's humanly possible.
Often plaster gets a bad rep as a crack prone material but I've found that this is usually the result of a lousy initial installation. Wood lath is an 'iffy' proposition to begin with and then the scratch and brown coats were simply not thick enough and probably not rich enough in the plaster to sand ratio to stand up to time, seasonal movement, and settling.
Plaster Repair
Thanks for your comment.
What do you use to "prime" the edges - paint or some other substance?
The bonding agent in latex primer is PVA so we are saying the same thing, except that it is thinned down more in the paint
Piffin,
Yes. Some plastering crews will prep their brown coats with a layer of PVA to cut down on suction, and that gives them added working time for the finish coat. Other plastering people (my own camp in my plastering escapades) will soak the brown coat with water, which works toward the same end without the unintended consequence of reduced adhesion. But in crack repair, I've found that simply soaking the edge with water won't kill the suction enough and there will be visible shrinkage sppearing as a hairline crack... The real insurance, though, is the use of tape that is bedded in setting compound. That's a very strong repair and if a crack re-appears through that then it's likely something structural is going on.