A parge coat is a thin masonry coating that is applied over interior and exterior masonry block and stone walls. Kind of like frosting on a cake. It is most often seen on above grade foundation walls and the interior of basement walls. I’ve inspected hundreds of homes where the parge coating was not properly applied and loose and cracking and falling off in chunks, sometimes as soon as the same year it was applied.
The purpose of a masonry parge coat is to protect the materials making up the wall, the stone, brick or masonry block and the mortar in the joints that hold the wall together. The parge coat forms a water resistant, protective barrier that helps prevent water penetration into the building materials that can cause moisture damage or spalling deterioration.
As in many things good preparation, using the proper materials and the correct technique make a world of difference. A good parge coat job will be practically maintenance free and last for many decades. A poorly applied parge coat could last less than a year, looking worse than before you started and need almost constant maintenance and repair some cases.
Parge coating being applied on a stone foundation wall with a rough trowel pattern.
For a quality parging mix its best to use a mix of about about 3 parts sand to at least 1 part portland cement. You can add 1/4 to 1/2 part lime powder to make it a little easier to spread or apply. This is mixed with enough water to get a nice consistency, not too runny. If your not experience be careful to not add too much water, you can add a little at a time. I like to use a little bit of liquid adhesive or acrylic admix, along with the water, using about 10% – 15% as much as water.
Adding the adhesive or acrylic admix will help it to be a longer lasting repair. The admix looks like milk or thinned out Elmer’s glue, and it is sticky. It’s also a little expensive, but worth the extra investment. It helps the parge mixture to get a better bond or stick better to the wall and makes the finished parge coat a lot more water resistant almost water proof.
Before you mix your parge mix you want to clean up the wall, power washing or a hose and brush is good to clean off dirt and loose particles and chunks. After your parge mix is ready to go, mist a section of wall with water to get it damp – usually changes the color. As soon as the wall was surface soaks up the water, no drips apply your parge coating. Usually wetting a section of wall ahead of where you are working has it just about ready when you get there.
For some more information, found a pretty good webpage on this subject with pictures and detailed info at the: New York Renovator
Parging was used on the open ends of the natural stone riser used to support the tread stone of our stoop, as you step into the house. Is that usual and is it a good idea?
I would say that is not a normal application, as for if it was a good idea, I’m not sure, it depends on why they did it and if it was properly applied.
A 30-year-old 15’x15′ detached storage building in our yard has a 1″ crack in the poured concrete foundation that is visible on the outside wall. It was there when we bought the house 10 years ago and is stable. The visible portion of the foundation wall is about 12″ – 16″ high from the ground up to where it is covered by the Hardie plank siding. I’m sprucing up the shed and am considering parging the foundation wall just for aesthetic purposes. I’d appreciate your thoughts on whether parging would be a good use of our time and money. The other alternative of affixing a faux stone veneer would be a lot more expensive.
Parge would probably work ok if the crack is stable. Probably a good idea to back fill the crack with some backer-rod (closed cell foam that comes in different diameters) push it into the crack about an inch deep then fill the crack with masonry caulking flush with the wall. Then when applying the parge coat, tape the crack seam with fiberglass mesh tape, similar to how sheet rock joints are taped and mudded. Let that crack patch dry, then parge coat over top. If the crack is not stable you may get a small hairline crack at the patch. If there is any continued movement at the crack even if you covered with stone, it might crack through the stone veneer.
Hey Tom,
Just bought a 100+ y/o home with a stone and mortar foundation. Most of the house has a crawlspace underneath with a portion having been dug out as a basement. I am looking for a waterproofing or water control solution, as the old stone foundation gets wet when there is a heavy rain. This moisture leads to mold and seeps up into the floor joists. Waterproofing from the outside is not an option, given the urban setting.
Several waterproofing contractors have recommended a drain system to be installed just inside the stone foundation wall in the crawlspace. I’m concerned about the structural integrity of the foundation and digging too close to the wall. One contractor said the solution is to first do a parge coat on the stone foundation to secure and protect it when digging near the foundation wall. Also to install a footer ledge at the base of the foundation wall to support the sub-wall soil (since there is no footer)
Does this use of a parge coat seem to make sense? Any other thoughts?
Should you be careful with how you parging is completed on old homes? Like point tucking should be carefully completed to not damage the old brick. Is there a special way to parge old homes?
It all depends on the condition of the stone or brick or masonry materials. If they are in a deteriorated condition special attention is required for repairs and maintenance. Deteriorated materials may not be suitable for the parge coating to properly bond to. If you are not sure it would be best to consult with an experienced mason for recommendations.
Installing a footer ledge at the base sounds like a good idea for the conditions you described. I would be hesitant at excavating soil next to a support wall that has no footer. Parge coating can be beneficial for both inside and outside of foundation walls.
Hi. We had our house parged on a hot day with a colour added. It has several cracks and the colour is not uniform. Also they finished it with swirls. How would you fix this situation? I would prefer no colour, swirls or cracks next time. Your advice would be very appreciated.
Check referenced for the quality of the installer or company doing the work. Be sure to communicate fully with them what you expect and get a detailed quote including warranty of work performed, from them in writing.
What is the purpose of adding lime? It was recommended to me to use a mix with lime in it due to the age of the house/foundation (100 years old this year). Would like to know the significance… Thanks in advance.
“Limestone” is a cement or portland ingredient or additive and acts as a seed crystal for the cement, better distributing the reaction products and increasing the reactivity of the cement.
How do you calculate how much Portland and sand you need for parging?
Hi we hired a masonry to tuckpoint (repair mortar) and then to skim coat the interior and exterior walls of our 200 year old field stone basement house. He only skim coated and did not remove any of the deteriorated mortar from walls nor was the stone cavities filled in. We wanted the work done because our basement had a lot of sand on the floor from the walls and their was a draft coming in. He used type S mortar to do this. Could you please tell me what I can expect from not having all the deteriorated mortar be taken out first. Thank you very much.
I saw the pictures you emailed me. It looks like from what I can see that the parge coat for the most part has sealed the joints. That is helpful. It is hard to say how much deteriorated mortal has fallen out of the joints, so I can’t give a definitive answer, but it is a lot better than it was. Tucking pointing would have been better but may have cost a lot more and may not have been needed. A good parge coat should keep the wall from getting any worse which would usually be a good thing if the wall did not have loose or missing rocks.
I don’t do enough of that kind of work. Check with a good mason, or search online.