Replacing water-damaged hardboard wood siding.

Exterior Repairs:

Replacing A Single Piece Of Hardboard (Masonite) Siding

In This Article:

Nails in the section of siding above the repair are removed. The damaged siding is removed and the Celotex wall sheathing is patched. New fiber cement siding is installed.

Related Articles:
Skill Level: 2-3 (Basic to Intermediate) Time Taken: About 2 Hours

By , Editor


There was one piece of siding on the north side of my house that had started to rot after 45 years.

While repainting the house, I figured it would be a good time to replace the rot-damaged siding.

Masonite siding with rot or water damage.


Metal end caps at corner of house with wood siding. One potential problem:

Before removing any siding, these metal corner caps (end caps) need to be removed.


I pried out the nails in the metal end caps. Pulling nails from metal end caps on wood siding.


Siding end corner caps made from metal, aluminum. The metal siding end caps came out with minimal effort, by simply pulling straight down.


The Siding Above - Removing The Nails:

I drove a pry bar under the lower edge of the siding above the piece being replaced. Then I forced the board outward a fraction of an inch. Prying up siding to remove nails.


Removing nails in siding. I pushed the siding back against the wall, so the nail head protruded. Then I was able to remove the nail with a pry bar.


I repeated this process for every nail above the 12-foot section of siding that was going to be replaced.

I placed a couple of shims (red arrow) between the first and second rows of siding, just beyond the end of the bad section.

Shims used to create gap between siding boards.\


Damaged hardboard siding fell off wall after removing nails. Then I wiggled the section of bad siding and it literally fell off the wall. The wood fibers had rotted around every nail.


Beneath the bottom piece of siding, there was a narrow strip of siding that had been installed as a spacer (to kick out the bottom edge of the first siding panel). Spacer strips behind siding.


This house has Celotex fiberboard sheathing applied directly over the studs, as was common practice in the 1950's through the 70's. Fiberboard sheathing such as Celotex is nothing but JUNK. Even when new, Celotex sheathing has very little structural strength and provides minimal insulation value. But if unprotected, Celotex absorbs water and over time it rots and warps badly.


Patching The Celotex Sheathing:

Removing nails in Celotex fiber board wall sheathing. I snapped a chalk line 3 inches above the foundation.

Then I pulled out all the nails below this line.


I set my circular saw to a cutting depth just slightly greater than the thickness of the Celotex board (which is about 5/8" thick), then I cut along the chalk line. Cutting Celotex sheathing to remove water-damaged area.


House framing behind Celotex board, sill area and rim joist. The Celotex board just fell off the wall, exposing the "mudsill" and rim joist.


By The Way...

If you've ever wondered why there are so many spiders and bugs in your house, here is one of the answers:

Many houses have significant gaps between the foundation and the framing (1 and 2), between adjacent pieces of framing lumber (3), and between the framing and the sheathing.

Once, while working on a foundation, I laid down on the ground and watched several spiders crawl up the foundation and disappear behind the sheathing. I believe that these gaps provide a veritable highway for crawling insects to enter the house.

Gaps in house where framing meets foundation.


Pressure-treated 1x4 fastened to wall to patch bad section of Celotex board. I fastened a pressure-treated 1x4 to the sill plate and rim joist.

This 3/4" thick filler strip was thicker than the original 5/8" thick Celotex board, but that shouldn't be a problem because the bottom edge of the siding needs to stick out farther than the top edge.


To create the proper angle for the first piece of siding, I fastened a 1-inch wide strip of thin plywood to the lower edge of the wall.

I happened to need a 3/16" thick spacer, so I used a couple of strips of Lauan plywood.

Strip of wood nailed to lower edge of wall, to kick out bottom of first siding row.


New Siding:

New fiber cement siding panels, one pre-painted. Earlier I bought a couple of 12-foot long pieces of 12-inch wide fiber cement siding.

This siding has a wood-grain textured face, which I didn't want. So I primed and painted the back side of one siding panel.


Cutting Fiber Cement Siding:

Cutting fiber cement siding isn't as simple as cutting wood siding. A regular steel blade will become dull and useless within seconds. A carbide-tipped blade is necessary, but even that may become dull sooner than normal.

The other problem is dust. Fiber cement siding creates lots of nasty abrasive dust when cut with a blade, so it's best to do the cutting outdoors... and make sure the dust doesn't cover any cars in the area.

This special dust-collecting saw from Makita has a tungsten-carbide blade that is specially made for cutting fiber cement siding and backerboard. Makita dust-collecting circular saw for cutting fiber cement siding.


Tungsten-carbide coated jig saw blade for cutting cement board or fiber cement siding. This inexpensive tungsten-carbide-coated jig saw blade is an excellent choice if you only need to make a few cuts.

But, this blade cuts kinda slow, and it can be difficult to obtain straight cuts.

The third choice for cutting fiber cement siding is a pair of siding shears. Shears are like power scissors that cut out a narrow strip of material from the siding. I'm told that power shears are the tool of choice for most professional siding installers.


I laid out the nail hole locations. Then I hammered the tip of a narrow nail set through the siding to pre-punch the nail holes. I did this because nails often bend when being driven through fiber-cement siding. Pre-punching nail holes with a fine nail set.


Nail used as spacer between adjacent pieces of siding. I used a nail for a spacer between adjacent siding boards.


While my helper held the siding in place, I nailed the new siding to the wall.

I used 2-inch galvanized box nails to fasten the siding at the bottom.

Nailing fiber cement siding to wall.


Nailing wood siding above repair patch. Then I re-nailed the piece above my repair.

Since I discarded the original nails, I used 2 inch galvanized framing nails for this. I needed the extra length to reach the studs (because the Celotex board has no ability to hold nails).


I replaced the metal corner caps.

I just slid the metal under the siding above, and made sure the lower end was tucked under the lower edge of the siding.

Replacing metal corner caps on house with wood siding.


Nailing metal corner caps. Then I nailed the corner caps to the siding with small galvanized box nails.


The new siding after installation.

The back surface of the fiber cement siding has a slight burlap-like texture, but it's nearly impossible to see unless you get really close.

Exterior siding after being repaired with new siding panel.



Caulking end joint between siding panels. I caulked the gap at the end with siliconized acrylic latex caulk. I also caulked any nail heads that had voids or craters around them.

Later I will apply a second coat of paint to the new section of siding.


More Info:

Tools Used:
  • Basic Carpentry Tools
  • Pry Bar
  • Chalk Line
  • Circular Saw
  • Nail Set
Materials Used:
  • 12-inch wide Fiber Cement Siding
  • Nails, 2", 2" Galvanized
  • 1x4 Treated
  • Narrow Strips Of Plywood
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Written October 20, 2009