Friday, March 10, 2017

Regret for my Past Self: Correcting Caulk

When I built my tiny house by myself I used a Snapper Shear to cut the fiber cement siding. I love this tool because it's quiet and feels relatively safe compared to a circular saw with a fiber cement blade. But most production carpenters don't use this kind of tool because it costs over $300 and it's what Alton Brown would call a uni-tasker.

The video talks about the advantages of the tool, but leaves out the main problem. A saw leaves a sort of burnished edge. The shear basically works by pulverizing the product. It leaves the cut end very dusty. I did not realize at the time this was going to be a problem in the future, but I should have. Caulk can't stick to dust. Where the factory ends butt up against the corner boards the caulked joint looks perfect. But the ends I cut, the caulk didn't stick. Little cracks appeared. I should have washed the ends of the siding in a bucket of water and then let them dry before caulking.
Crack between caulk and cut end of siding
The weather has been pretty good for working outside so I decided it was time to take care of this problem. I worked up a special tool for cutting the caulk at the corner board so I wouldn't go too deep and cut into the house wrap. I used my straight mat cutter with a 3" scraper blade modified to fit it. This turned out to not work any better than my regular utility knife so I'm not even going to put up photos.

The most useful tool was a dental spatula I got as part of a $5 set from PJ Tool and Supply, the same place I got some hemostats, also useful.
Here's the useful dental spatula

I really wore down the end of this little tool
After I cut the caulk where it was very strongly bonded to the corner boards I got all the old caulk out of the joint.
Caulk didn't fail, just the bond to the siding
I hoped the caulk would take most of the dust with it, but it sort of didn't. I could make dust come billowing out of the crack with a little brush I got at the grocery store by the dental floss. I washed the whole house down with a scrub brush and a hose after I opened up all the cracks. Then I scrubbed out each little crack again with the brush until I could not make any more dust come out.
I cleaned the ends of the siding with tiny brushes for cleaning braces
I used Dap Dynaflex 230 caulk when I built my house. I like it. It was my fault I had to redo it, no fault of the product. But for the sake of curiosity I wanted to use a different caulk for the replacement. I did some research and found some people on the Fine Homebuilding forums like this stuff called Big Stretch by Sashco. I made a special trip to Lowes to get some Big Stretch since they don't carry it at Home Depot.

I actually don't like it as much as the Dap. It feels kind of gritty. And it didn't fill the gaps as well. Some places it shrank so much I had to caulk again after I painted to make it look consistent. Time will tell how it does in the long run.

Tiny house benefits. All the caulk I had to replace only comes to 115 grams
Because I'm a woman who has eyes I put down a drop cloth while I dug out the old caulk. I dropped the pieces into the same apron I use to pick blueberries. Any stuff that fell on the cloth, I scooped it up before I moved to the next corner. At the end of the job I had about 115 grams of wasted caulk. This is a data point without a purpose.

I was able to recaulk all these joints with less than one tube of caulk. I bought one gallon of paint and repainted the lap siding on three sides of the house. I still have over a quart of paint left. Tiny houses rule!

I repainted the siding on the front porch when I built the porch and turned the door around to swing out. That was 2013. I changed from flat to satin paint on the front porch then. So this time I made all the lap siding satin. I left the flat paint on the shingle siding and overhangs. The caulk seems fully adhered to all the joints of the shingle siding even though I cut the top edge of that with the shear to fit the angle of the gable. I would say it was due to not being in direct sun, but on the north side of the house the lap siding caulk joints failed and they are in the shade all the time. Perhaps larger joints don't exert as much pulling force against the bonded edges. My corner joints are pretty tight, but they are within the specifications of the product. I left bigger gaps for the shingle siding.

Oh, I just figured it out sitting here typing this. The expansion and contraction of a long siding run changes the size of the end gap more than what would happen next to a narrow shingle. Even the short pieces of lap siding between windows are longer than the widest shingle. Expansion and contraction is cumulative.

Next blog: The rabbit hole I went down to pretty up the lines to my minisplit and a new use for the siding shear.

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