I need to parge an old poured concrete retaining wall that is part of a below-grade terrace. How thick can I build up the parging without compromising its integrity? The wall is a bit wavy and I’d like to straigthen it out some while parging.
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Replies
If you go much more than 3/4"
If you go much more than 3/4" thick, you need to fasten metal lath to the concrete first. I wouldn't go thicker than 1-1/2" even then.
Thanks
I'll keep it under 3/4" which should take out most of the uneveness. How many coats shoud I use to build up to 1/2"- 3/4"? I assume like skim coating plaster, I need to sneak up on it a little at at time?
Use 1/2" furring strips as
Use 1/2" furring strips as screed rails on your first coat. Use a straight edge when placing them to keep them all in plane. Lay up the parge between the rails and float it level with them. When it has set enough to not be soft or sticky, remove the furring strips and float where the strips were level wit the first coat. The following day trowel on the final 1/4" layer with your preferred finish (spong, trowel, rubber float, etc.)
You might want to think about an acid wash of the old concrete befor adding a parge coat, and definitely use a bonding agent to make sure the first coat sticks to the wall. Keep the whol;e finish as damp as you can to get a slow cure and reduce the amount of mud cracking in both the first and final coats.