I need to parge an exterior concrete retaining wall and could use a bit of advice. The wall was poured 3 years ago and I’ve finally ground down the seams from my forms. On top of the wall will sit a single course of antiqued rock face CMUs that I’m making, along with a stone or concrete cap.
Can I apply the parge mixture straight to the wall or is there a bonding agent/additive that should be used first?
How thick a layer of parge can be applied and can I build up successive layers to even out a slightly wavy wall? I assume you start with a scratch coat, then add a finish coat from there?
Can I acid stain the finished results like a concrete floor?
Edited 7/19/2007 9:20 pm by pino
Replies
After three years in your climate, that concrete is pretty well cured.
IMO, the best treatment would be a light sand blast. But you would have to buy another toy. . . er, I meant, tool.
Wewt the wall down good the evening before you start.
Now because you only want to mix up about as much as you can apply in 30 mins, and because the adhesive also has a working time, I would add the adhesive to my mix water at about 4:1. 5 gallons of mixed water will go a long way.
For straightening the waves, figure on using twice as much mud as you first think. This straightening is a two-step process; First, with your float and hawk, slather on enough mud to raise a trougth above the crests, but stay away from the high points a few inches. Then, use the darby in one movement from bottom to top to scree the mud level between the two crests. Don't worry if the edges of the fresh mud doesn't meet the crests. Knock off any that crosses a crest.
Clean the darby and give it another swipe.
Before the work behind you gets much more than an hour old, hang wet burlap on it. You should be able to do a couple of hundred feet in a day. At the end of the day, make sure all the burlap is wet and hang some visqueen over it all to retard evaporation.
The hardest part is learning to use the darby. Start in back and don't be afraid to scrape the just applied mud off and try again. You really don't want to over work it with the darby.
After it's cured overnight or longer, level off the crest areas where the parging didn't reach. Recure. Now you're ready for the final finish coat.
For finishing, just use the hawk and steel float, putting on a thin and well burnished layer.
The finishing trowel technique and movment will effect the final appearance, so you should try to find a repeatable rhythm for your wrist movements.
SamT
Thanks for the detailed info. I've only got about 40' of wall (5' high) to do, but being an DIYer that is challenge enough.Does it matter whether I use a wood or metal darby? I've got an old wooden one in great shape that I picked up from a garage sale that I used when I finished my colored and textured sidewalk. I've got a great masonry & concrete supply house that rents as well, so picking up a metal one is no problem.
You can use a wood one. I used to make my own when I as a finisher. Nowadays they use a straight piece of wedge shaped aluminum called a slick, and then you float it.
>Pino^SamT
what sam said... but... if you can wet the wall and it takes water (ie... absorbs) then bonding will be better....
i had a guy show me this... on your final coat.... use white styrofoam as your finishing tool... scrap blocks maybe 6x6 or 8x8 inches... 1.5-2" thick... and start scrubing/finishing the wall once it had taken a set... (where you are leveling/smoothing Not Moving material) have alot of scrap blocks of foam around... you'll be amazed how flat you can get the wall with these... it works don't know "why" it just does...
p