How to Repair Fiber Cement Siding - The Complete Guide

 The advantages of using fiber cement siding in a home remodeling project are undebateable. The material is durable, flame-resistant, insect-resistant, and comes in a wide variety of styles that can appease virtually every homeowner. There is one alleged drawback of using fiber cement that is commonly uttered which is that fiber cement is hard to work with. Granted, if you do cut the material with a circular saw (without a dust cover) it will produce a lot of debris in the work area. This can easily be alleviated by using a shear attachment which cuts slower but also eliminates almost all of the waste tossed into the air though.

When working with fiber cement it's also important to support long pieces on the ends and in the middle as you are carrying it from the cut area to the installation spot. The material can 'snap' if allowed to bow but this is no different than the buckling that vinyl or aluminum siding would do under the same circumstances. Siding pieces should always be hung by at least two people so this leads us to examining the final aspect of working with the material – how to repair fiber cement siding.

What Goes Wrong With Fiber Cement?

Some industry publishers dub fiber cement as a '100 year product' so there really should be no need to ever have to repair it right? The truth is there is always variables with any home product that could require repair down the line, mostly having to do with faulty installation (gaps, uneven, loose from poor nailing, lack of backer flashing) but could also include rodents, collisions, extreme weather, or water damage to the underlayment. The damage will have to be analyzed to see if it can be a cosmetic fix or if the boards need to be replaced altogether.

Understanding How Fiber Cement is Installed

Removing fiber cement boards from the exterior of a home is basically installing in reverse. Therefore it's important to know how the product is installed to begin with. Fiber cement lap siding is generally blind-nailed at the top of the plank with the nails being covered by the subsequent row of siding (except in high wind areas where it is also nailed at the bottom of the piece.) Boards are also held into place by waterproof caulk in gaps at the edges and sometimes at butt joints after the fact if the back flashing has failed.

Removing a Damaged Board

Boards that have cracked, have huge holes, or have delaminated and been stripped of painting, should be replaced as it is the best long term fix option. In order to remove the board you'll have to pull out or cut off the nails, which are likely located underneath the overlapping siding on the row above. Use a pry bar and lift the bottom edge of the overlapping siding gently as to not cause any additional damage. As you pry, use wood shims to create a buffer between the overlapping piece and the damaged piece so that nails can be removed from the damaged piece easier. If there isn't enough access to remove the nails, use a hacksaw to cut them (remember to remove the nub before installing the new piece.)

Depending on where the damage is (in the middle, near the end, across the entire board) you can either perform fiber cement siding crack repair by removing the entire board or just the section needing replaced. Use a siding square to draw a straight line and a reciprocating saw to cut away the damaged section if doing a patch job.

Replacing With the New Board

If the reason the damaged board needed to be removed was because of constant water exposure, you'll need to inspect the underlayment and backer board behind the siding to make sure it too hasn't rotted or become vulnerable. There's no sense in making repairs until any problems have been alleviated. If multiple rows of siding had to be removed always work from the bottom up when installing the replacement pieces. Check the 'reveal' or exposed areas on other sections of the home to know how much space to leave when installing replacement boards – using a chalk line if needed to make sure this stays consistent from end to end. When sliding the last board into place underneath an overlapping row of siding, you may have to face nail it into place because the top nailing lip is hard to reach. Use some touch up paint to cover up these face nails and then re-caulk any gaps to completely repair fiber cement lap siding.

Fixing Holes in Fiber Cement

There's no doubt that removing entire sections of board risks damage to corresponding areas but in many ways it's the only tried and true way of how to repair cracked fiber cement siding. If you need to repair fiber cement siding hole because of raccoons, mice, squirrels, birds, etc. there may be a way to fix the sections while they are in place. To repair hole in fiber cement siding there is a special putty that can be used as a patch. This putty should be included in every fiber cement repair kit. The patch is mixed, formed, and spread to match the contours of the board. You then let the patch dry and sand it to blend into the surrounding parts of the plank. Finally, paint the area and although the patch may not be cosmetically perfect it blocks out water and insect access.

What to Do About Flaked Fiber Cement Paint

Fiber cement siding comes either pre-finished or primed for painting in the field. Although it is more expensive, most people opt for the factory finish because it is baked on and more resistant to weather and UV rays but perhaps most importantly covered by a warranty. That being said, there are times when either factory or field paint can fail because the cut ends weren't covered, the wrong paint type was used (acrylic is recommended), the boards were stained, the planks weren't painted within 90-180 days of manufacture, the surface was dirty, there was an unreasonable amount of moisture and so on and so forth on a case by case basis.

The fiber cement siding repair question then is what to do about the damaged areas? The least expensive and simplest option will always be to scrape off the damage, clean and prime the area, then use a 100% acrylic paint to see if it resists further damage. If the repaint doesn't match the factory color or continues to show problems, replacing the 'bad' boards can be a viable solution.

How to Repair Loose Fiber Cement Siding

There are two main reasons that cause fiber cement siding to come loose, both of which stem from faulty installation of either missing a stud or nailing too high on the pieces. A plank that is nailed too high will start to sag because the thin top lip has started to give. This can be diagnosed by a lot of vertical movement in the board. Planks that have been nailed missing the stud will start to pull away from the house. Either way, the simplest fix is to face nail the boards back into place, this time hitting the stud. If there is no stud available (such as near gable trim) and the plank is curling or rattling, it's recommended to 'pin back' the board by face nailing it 3/4” to 1” from the bottom – strictly for aesthetics and not to increase wind load. Caulk can also be used to secure an angled cut or some other section where a backer is not available.

Understanding Dealing With Fiber Cement Gaps

One thing to note about gaps between joints of fiber cement siding is that they are left there on purpose. Although the material expands and contracts less than wood, best installation practices still allow for some movement and to respond to shifts in the home. Edge gaps are filled with caulk to prevent water damage and every siding butt joint should have flashing behind it to do the same. The flashing should be a non-discreet color so that it is barely noticeable. If there are significant gaps that are destroying the aesthetics of the siding (board too small to begin with, too large of expansion gaps) the best practice is to remove and replace, both for cosmetics and moisture prevention.

Fiber cement siding is a highly durable product but anything installed 30-40 years on the exterior of a home is going to be vulnerable to damage at some point. Luckily, another versatile benefit of this product is that fixes are usually easy and generally inexpensive. Just remember to always eliminate the underlying problem (water damage, rodent infestation, delaminated boards, etc.) before making repairs as you'll just be running around in circles.