I am about to start finish work on a porch located in Canada (cold, snowy winters and muggy summers).
I’m going to use Mirtec boards (an exterior grade wood composite) which calles for 1/8″ gaps at joints.
My question is: What is the best caulking to use? I want to be able to shape the caulking to be flush with the boards and then to paint it. I’m thinking polyurethane but am not an expert on the subject.
Thanks
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Replies
Urethane is what I would use in that situation. It will last years longer than any other caulk I have ever encountered, and stay flexible until long after you and I are gone. But be forwarned, it's a PITA to work with. especially if you're not familiar with it. On the other hand, if you're painting everything, you probably won't have any problems at all.
My favorite brand is NP-1 made by sonneborn. Just make sure it's nice and warm out when you're using it, this stuff is not very friendly to work with in cold weather
Thanks. Any tips on how to shape it? Specifically, I will want to make it nice a flush with the trim.
I've heard that for silicone, good 'ol spit is will keep a scraper from sticking when shaping it. Will that work for urethane too or will the stuff stick like honey just like my urethane glue!?
I also use NP1 and I like it. It tools differently than urethane glue ... it doesn't run or drip ... think of sticky peanut butter ... really nasty stuff ... but a great product. Don't use you finger, with or without spit ... use a cloth dampened in paint thinner or lacquer thinner or similar. Use a metal putty knife and tool it slowly, and clean the tool with the damp cloth. The caulking store where I buy my NP1 also sells a wide variet of caulk guns and tooling knives. Buy a decent gun. I have two knives, they look just like the Wilton cake decorating knives, but one has a tapered blade.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
I use my finger with it Ed. And then I wait 2 weeks till it wears off!!! I also use plastic spoons to tool it. They work well and you can't beat the price. (And there's the extra pleasure of stumping my wife when she can't figure out why there are more forks and knives than spoons.)
A rag soaked in Laquer thinner has always been my prefered method. Mostly because you're also gonna need that rag for cleanup. They make a product called "Reducer-990" which is designed to cut it, but laquer thinner works just as well and cost a lot less. I like the plastic spoon suggestion, I have used that for silicone before with some success.
Also, remember- you're dealing with highly toxic chemicals here, take steps to try to keep it off of your hands as much as possible. Skin is not made of rubber, it's actually quite permeable. Any time you get something on your fingers, some of it will be absorbed into your system. While once in a while probably won't hurt anyone, we as proffessionals use stuff like this pretty regularly. Think about what a 20 year accumulation might do to your kidneys.
Edited 7/18/2004 6:22 pm ET by Mark "If I were a carpenter"
Thanks. Your caution reminds me of a guy I worked with one summer (summer job for me). We were roofing a commercial building (flat roof) and used some PT lumber in spots. This guy was dunking cut ends of the PT lumber into a bath of CCA with his bare hands. By the end of the day his hands were bright green. Ugh.
Yeah, but he didn't have worms. or lice.
Good points about toxicity and so forth. I glued a lot of furniture several years ago and used polyurethane for the first time. Since it didn't have a strong smell, I didn't worry much about ventilation. Then I got like asthma--wheezing every night and a cough that wouldn't go away. Still have trouble now and then and I think it was because I breathed those glue vapors. Has gotten better (been maybe three years), but not gone away entirely. It's easy to do yourself permanent damage and almost as easy to take precautions that keep you safe.
I use a spray bottle filled with paint thinner. A spoon or a concrete trowel used to strike brick mortar joints, works well.
Sonneborn (sp?) and Silka-Flex perform well.
MES
A little off topic, but with Miritec (sp?) I think it is extremly important to seal the cut ends with primer or paint before installin the "boards"...
Good point. Thanks.