Sandstone does not make good chimney material in areas where it can rain a lot. I know that, as the more-or-less proud owner of what probably once was a quite impressive chimney. Sandstone is porous, and if exposed to years of rain, it can and does flake. A couple years ago when I bought the place, I did some patching of the mortar and waterproofed with a water-based silicone solution from DAP. I used that because it specifically said it worked on stone, which some other common treatments did not, and it was fairly inexpensive. Didn't last too long however. So....anyone got any suggestions for a better treatment? The stone still looks pretty good, at least from a distance, so I want a clear coating of some kind. Is there something specifically made for this application?
Good question, but the bottom line is that the chimney either must be waterproofed or otherwise completely protected from the rain. My son-in-law happens to do sheet metal work, and I've considered having him build me a cap for the entire chimney, with some overhang. The chimney is about eight feet long and three wide, so we're not talking a trivial cap. And this would still not protect the exposed faces of the stones. So, it seems to me my best route is to waterproof. Maybe I need the Gore-Tex of waterproofing!
This all came up yesterday, after a full night of rain....naturally. Who discovers leaks when it's not raining? Anyway, I was having my breakfast and planning a fun day of oil changes for the vehicles and inspecting the crawl spaces under the new additions for signs of water and such, when I noticed a wet spot on the fireplace facing, which is also sandstone. Since we had a new roof put on last year during the additions (BIG $$$), and also had copper flashing installed around the chimney (at a cost of several hundred $), I was unhappy. Fortunately, I was alone in the house at the time and only peeled the paint from the walls with my lamentations. I went into the chimney to see what I could see and found water seeping down the bricks, but not on any of the decking. Up on the roof, the flashing looked OK to me, but I had my SIL look at it to give me his professional opinion. He didn't do the job last year because he had other commitments when it basically had to get done quickly. Though he would have done things a little differently, he said the flashing was properly installed and unlikely to account for the water we were seeing. That left the mass of stone and quite a few less than perfect mortar joints. It was forecast to rain again yesterday afternoon, but I had the DAP waterproofing I mentioned, and since it is water based, I figured I'd spray it on the still damp stone and hope the rain held off for a few hours. It rained two hours after I sprayed, and continued to rain about an inch during the night. This morning the wet spot inside is dry, so either the waterproofing did the job or the rain has to fall in a particular way to get in. I'm going to wait until it's as dry as possible, patch some more of the mortar joints, and treat the whole thing again. Since I've already used this silicone spray, I guess I'm comitted to it this year. However, if anyone knows of a better, longer lasting treatment, I might use it next year.
If you're seeing water inside, its most likely due to poor pointing, not porosity. You may want to have a mason take a look at the chimney and give you some recommendations for repair. Also, take a look at your entire roof.
Oftentimes the point where water is entering the roof is far from where it ultimately gets into the house. A case in point is my Dad's home. He has a older house with a slate roof on the main house and a copper roof over a small sunroom. For years he was getting water in the house between the sunroom and main house. After many callbacks, the roofers give up on the sunroom and checked the main roof. They then found a point where water was entering at the ridge cap, going down a rafter and then getting into the sunroom.
The best product I have found is Valspar concrete and masonry waterproofer, which can be found at Lowe's. Here is a link: Lowe's. You can expect it to last 3-4 years between applications. I would recommend applying two coats allowing 24 hours between coats the first time you use it. Then just reapply one coat every 3 to 4 years.
Good point. In fact, I just made some repairs to the cap. I believe cracks in previous repairs were responsible for most if not all of the leaks because I was finding damp spots everywhere I pulled out loose mortar, tar, and at least two different kinds of caulk. I do believe, however, that even if the grout joints were all good, the porosity of the sandstone would be a problem. This stuff is like a sponge. As Egon pointed out, there can also be problems with waterproofing such materials, in that trapped water might cause more damage if it has no where to go. Some of the silicon-based treatments, like the Velspar recommended by in another post, claim to allow some breathing while preventing major water accumulation. I think that might be what I need to try to achieve, after making my repairs.
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