how to prevent wicking of water that causes wood rot

[jihhwood]

I discovered rot in the 1x8 trim at the base of two columns on either side of a small portico by the front for to my home. The trim covers a load-bearing pressure-treated 4x4. The rot was caused by moisture, since the 4x4 column (not rotted) and the trim sit on a concrete floor. It’s really just a cosmetic job: I’ve cut away the rotted wood and plan to make a “collar” at the base of the columns. I want to avoid having the trim touch the concrete since the problem will only recur as water is wicked up by the wood. I had planned to simply leave a space of about ¼ inch between the concrete floor and the bottom of the “collar”. But I wondered if there’s a neater way to prevent wicking. One fellow who posted a video dealing with this kind of problem used an asphalt shingle that he placed at the bottom of the post. Looked OK, but I wonder how useful that would be. I’d appreciate your thoughts about alternative fixes, if there are any. Thanks.

[jteneyck]

I would use AZEK composite instead of wood, or a similar product. Works just like wood, paints well, and will never rot.

John

[museumguy]

jteneyck said:

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I would use AZEK composite instead of wood, or a similar product. Works just like wood, paints well, and will never rot.


this, we use it at work all of the time. I used it as trim on my house. You can sand and seal the edges that are exposed for a better visual appearance. We used to sand them to 400 grit and wipe on MEK, it gave us a nice looking edge. This was done on non painted pieces to keep the dirt out.
John

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[dlorenz]

Composite material would definitely solve the issue.

One typical problem is that in the initial install, there is no priming of the trim end, making it easier for wicking to occur.

If you wanted to use wood, you could use treated material.

If you do use wood, keep the bottom at least 1/4" off the concrete and back-cut the wood so that moisture will tend to drip off the outside edge instead of flowing underneath the end of the wood. And prime the end of the wood with an oil-base primer.

Hope this helps.

[Curlycherry]

I've got a little plastic post block that is under my posts. They can be trimmed around it one wants or they can be left exposed like mine is without much detriment.

[SkyGlider]

jihhwood said:

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But I wondered if there’s a neater way to prevent wicking. ..... I’d appreciate your thoughts about alternative fixes, if there are any.

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Two ways to reduce/prevent wicking:

- 1. Reduce wicking (maybe even prevents wicking) by painting ends with wood hardener. I do that on all exterior bare wood horizontal surfaces and bottom end grain before I paint the house. Let the wood hardener wick into the joint between the horizontal and vertical surfaces. Even when re-painting after scraping down to bare wood. Wood hardener has the consistency of water so it absorbs into the wood and wicks into joints very well.

- 2. Prevent wicking like in your case. Coat the bottom edges with finishing fiberglass resin. With good coats, guaranteed not to allow wicking at the bottom edge where the resin is. Can coat up about 1/4" - 1/2" from the bottom on the vertical surfaces but the finished paint will show a different texture. IMO, no one will notice. If multiple coats to be used, use laminating resin (dries tacky) on the initial coats. Important to use finishing resin as the last coat to harden all lower coats. Do not use finishing resin for multiple coats since finishing resin dries hard by wax going to the surface, and wax prevents a good bond for a next coat. Fiber glass resin is expensive.

Skyglider

[daveferg]

Similarly, I have an oak garden bench. I coat the bottoms of the legs (which sit on concrete) with epoxy and it's worked well for 15 years.

A couple other tips----

---if it won't affect the looks---a slight bevel cut in the bottom will help to let water drain off and not let the end grain sit in water.

---Design your trim so that you have a base molding with horizontal grain in contact with the concrete----it won't wick up water that way

---But, it's still best to isolate wood from any masonry with a nonabsorbent material---sheet metal, rubber, etc.

BTW---don't forget to back prime all trim before you put it up---with this and proper precautions already mentioned, you likely won't have to replace that trim again in your lifetime.

[jihhwood]

Terrific advice and suggestions. Having the confidence to do the job -- knowing I'm going to do it correctly -- makes me look forward to getting to work. Thanks to each of you for your thoughts and guidance!

[Foggy]

When they built my house they used a thin sheet of closed cell plastic/risen/foam? between the cement and the wood plate. It came in a roll 6 or 8 in. wide.