Rot Doctor

[Miscellaneous Q&A Index]

Subject: Repairing Rot on Fence Post Tops

Date: Monday, September 10, 2012


I am in the process of overhauling a 20 year old wooden fence and have a number of questions that I’m hoping you can help me with.

I am replacing all of the 8′ fence panels (52 panels total) but am hoping to keep most (if not all) of the 6x6 pressure treated fir posts. So far, of 11 panels torn down, all of the panel posts appear to be structurally sound but several of them have dry rot in the caps of the post and at least two have substantial rot to a depth of 3–5″ into the top of the post. (please see pictures for reference) I’m assuming, based on the tutorial on your web site for Beam and Joist Rot, that a combination treatment of CPES* and Fill-It* (possibly with sawdust added) would be your recommended solution for this type of issue but I am hoping you can confirm that before I head down that path.

Top of post Side of post

CPES* would definitely be the first product to use. The Fill-It* doesn’t need any sawdust. And while some of this product would be useful, you would also likely want the Layup & Laminating Resin* (LLR) which can be used plain for smaller cracks, or mixed with sawdust for larger voids, both of which appear in your images.

I have a couple of other fence project related questions that I’m also hoping you can answer.

1. Will the treatment and fill of the posts give it an equivalent level of structural integrity and as the original wood? And, is “yes”, what is the expected lifetime of this treatment?

Epoxies, ours included, are stronger than the wood itself. Used properly, the structural strength should be significant, at least approaching the original. Possibly exceeding, but difficult to quantify without destructive testing. Basically the lifetime expectancy is indefinite, or at least longer than the wood - keeping in mind that epoxies are not UV stable and sunlight will slowly break them down, paint or UV coatings will protect them.

2. For a total of 52 6x6″ fence posts, all of which will arguably need to at least be sealed and at least 50% that will need some filler, can you make an educated guess as to what quantity of treatment chemicals I would need to purchase from your company to complete this job?

My best educated guess would be one pint of CPES*, and one quart of fillers per post, for the post illustrated in the image given. The fillers would be some combination of the Fill-It* and LLR*/sawdust.

3. Some of the posts also have split cracks down the side. (see second picture for reference) Is there any reason I should consider treating these cracks as well?

Once the ends have been repaired, moisture getting into the cracks on the side will not significantly increase the moisture content of the wood, so there is not a huge need to treat and seal them. I would coat the inside with CPES* an leave it at that.

4. For a job this large I am hoping there are some tools or techniques that would make the job more efficient; e.g., a caulking gun or something similar to dispense both the sealant and filler. What would you recommend?

For the CPES*, I would just brush/pour it on the ends. For the vertical cracks, a pump up garden sprayer works well, but would be glued shut, so that is a one time use applicator.

For the Fill-It*, I would just push it into the cracks on the side near the top with a putty knife, after the CPES* has been applied and cured. Once the Fill-It* cures, it will contain the LLR*, which can be poured in. Initially, un-thickened for for smaller cracks, then thickened with sawdust for the larger, final fills.

5. Lastly, do you have any recommendations on what I should treat the new fir and cedar fence panels with for NW weather related issues? (I typically default to Miller Paint for wood treatment products on my deck)

CPES* applied to critical areas is excellent for extending the life of exterior wood. End grain, fastener holes, and any place where two pieces of wood touch are the critical areas. After that, you can coat the rest with whatever pleases you. Keep in mind, that CPES* applied only in certain areas may cause the subsequent stain to have two different looks. Please test before you commit to anything.

Thanks very much for your time and advice.


* These products are unavailable, we are selling comparable products that will perform these same tasks. Feel free to contact us if you need assistance with which products to use.

[Miscellaneous Q&A Index]

Have questions?

Contact us by phone 206-364-2155 or e-mail (send us your pictures) at and we will gladly answer questions about our products or how to apply them. With 20+ years of experience and many more in the boating and construction industries, not much surprises us. We are here to help our customers solve their issues. Let us help you to not have any surprises in your repair project.

Our business hours are 6:30 AM to 5:30 PM Pacific Time, Monday–Friday.
Tech support is available over weekends and holidays 8:30 AM to 5:30 PM Pacific Time.

The Rot Doctor, Inc.
P.O. Box 30612, Seattle, WA 98113
Voice: 206.364.2155    Fax: 206.364.4744    E-mail:
The Rot Doctor, Inc. ©1997–2021. All rights reserved.