How to repair & maintain asbestos cement siding.

This article explains the maintenance, repair, or replacement of cement asbestos shingle siding on buildings. We describe how to remove and replace individual cement asbestos siding sections while keeping the total job small by avoiding breaking the surrounding shingles. We also describe installing new siding materials such as vinyl siding atop or over asbestos-cement shingle siding - a common practice.

This article series includes a photo guide and text that can help in identification of asbestos-containing wall siding products like asphalt shingles & asbestos-cement siding shingles.

Maintenance & Repair Tips for Asbestos Cement Wall Siding Shingles

We consider asbestos cement wall shingles a durable and fire-resistant roof and an asset to the building provided that the siding is in good condition.

But because the material is easily damaged by a heavy-handed worker unfamiliar with the materials involved, asbestos cement siding has to be repaired and maintained with care.

Replacement cementious wall shingle materials are now available that look almost exactly like the original materials, but that do not contain asbestos.

That's the product we have used to repair the building shown in the photographs in this article.

Small temporary wall siding repairs to individual shingles can be made using copper or aluminum flashing material -- it can be painted color that looks a lot like the remaining cement asbestos shingles, and this approach minimizes the chances of breaking more shingles during the repair.

Watch out: the siding removal procedures discussed in this article pertain to asbestos-cement shingles or fiber cement shingles, not to lap siding or "boards" made of fiber cement. For fiber cement lap siding removal

see SIDING, FIBER CEMENT REMOVAL.

How to Remove and Replace Broken Asbestos Cement Wall Shingles

What about replacing the siding?  Can you side over the existing asbestos cement siding or does it need to be removed? First let's discuss replacing individual broken sections of fiber cement siding:

It is very difficult to remove individual broken asbestos-cement wall shingles, but working carefully it can be done.

Work by an inexperienced contractor can ruin a cement asbestos shingle wall siding and lead to complete replacement that could have been avoidable.

• Pull out exposed nails:
  
  Use vise-grips or end-cutting pliers (illustrated in our FAQs below) or a pair of horse-shoe nail clips or similar tool to carefully pull out the nails from the intact, un-damaged cement-asbestos shingles above and around the damaged shingles. Pull nails carefully so as not to break the intact shingles. Do not try to pry up asbestos cement shingles - they are brittle and will break.
• Slide down the shingle:
  
  Slide out the damaged asbestos cement wall shingles
• Inspect the wall sheathing for leak or water or insect damage that may need repair
• Install a house-wrap or roofing felt over any exposed wall sheathing, sliding its upper edge under the older materials so that any water that penetrates the wall will be directed out not into the wall cavity.
• Carefully slide the new fiber cement shingles into place.
  
  If cement-shingles have to be cut, use the manufacturer's recommended cutting tool, not a power saw that will make a lot of dust.
• Line up the nail holes between the old (upper layer) cement asbestos shingles and the new fiber cement shingles to be secured underneath.
  
  They wont' line up, right? OK so use a tiny masonry bit and drill through the existing hole in the old asbestos cement (intact) shingle and through the new fiber cement shingle below.
• Nail the new shingles in place, carefully - don't let your final hammer strokes drive the nail so hard against the fiber cement shingle or asbestos-cement shingle that you break it.

Guide to Siding over asbestos cement siding:

A common remodeling practice is to install new vinyl or aluminum siding over cement asbestos shingle siding as well as over many other older siding materials when the old siding has become damaged, leaky, or cosmetically ugly. A typical procedure is to install furring strips on the existing wall, avoiding breaking the existing siding. The new siding is then secured to the furring strips so that the new wall siding will be smooth and flat.

Additional steps may be needed to build out window and door trim for aesthetic reasons - so that the windows and doors do not appear to "recede" into the walls of the structure.

How to Remove Damaged Asbestos Cement or Fiber Cement Siding Shingles

Reader Question: Is there a tool for removing nails in cement asbestos shingle siding?

Is there a specific pry or cutting tool to grab and cut the nails On broken shingles you want to replace? - Catfishlynd 9/20/11

Reply: how to remove individual fiber cement or asbestos cement siding or roof shingles

Catfish

When we had to remove broken fiber cement shingle siding we found that indeed it is difficult to remove one shingle without breaking others - making the job grow horribly.

Tools like a slate hook and most types of wire cutters whose jaws required us to place the tool handle parallel to and flush with the shingle surface to get a bite on the nail head did not work because the thickness of the tool or the need to lift and pry the tool against the shingle surface broke fiber cement siding shingles when we tried sliding it between them.

See (SLATE ROOF SOURCES & TOOLS

A hacksaw blade can be used to cut the shingle nails and is so thin it won't break the shingles if you work carefully but it has two serious disadvantages:

• This is a very tedious approach not suitable for removing many fiber cement of cement asbestos shingles
• The cut nail end remains in place in the nail hole of the under-shingle, making it difficult to get a new supporting nail in place.

What we found worked best was to use a pair of end-cutting pliers, called by some folks nippers or a "nail biter" - sold at hardware stores in various sizes.

Buy a tool whose handle and cutting face will be at right angles to the work surface and whose cutting face is flush (with the cutting angle filed just on the inside of the cutting edges.

Working CAREFULLY we found we could usually grab the nail head protruding just proud of the fiber cement shingle and pull it straight out.

We use two sizes of end-cutting pliers made by Channellock, like the Channelock 358 8-inch End Cutting Plier tool shown in our photo just above. "Grab the nail head and yank" straight out seemed to work best.

Watch out: don't pry against the cement asbestos shingle with the nail puller nor other tools or you'll risk breaking the shingle below.

The nail extractor made by Jefferson Tools (shown at left) might also work provided that you do not pry directly against the cement asbestos shingle, OR you are prying only against a siding section that is already damaged and going to be replaced.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-07-01 by inspectapedia.com.moderator (mod) - Context Information to Guess at Fiber Cement or Asbestos Cement Shingle Age

@Bill Garland Tx,

I suspect, from the presence of those crisply-inked lot or production code numbers stamped on the back of your siding, that it's a modern fiber cement shingle product. Older asbestos cement shingle siding (or roofing shingles) don't commonly have that crisp inked identification data stamped on their inner surface.

Context Information Useful to Guess at Fiber Cement or Asbestos Cement Shingle Age includes at least the following items:

• Building country, city (or other geographic locator),
• Building age
• Building history of renovations or repairs to the exterior including any records of siding work or repairs
• Siding stamps or identification codes: manufacturer's stampings on the siding inner surface - there are roughly twenty manufacturers who produced asbestos-cement or later, fiber-cement shingle siding products. You've provided an example of this data stamping on an AC or FC shingle

Watch out: on an older, pre 1980s building that sports cementious shingle siding or roofing it is possible to find a mix of both old asbestos-cement shingles and newere non-asbestos fiber cement shingles. To the naked eye, they may look almost exactly the same.

So don't assume that post 1986 FC shingles are the only kind on your building unless you have other information confirming that fact.

I'd like to see a photo of the other side of these FC shingles.

Other types of fiber cement siding - clapboard-style - can be identified, as we discuss

at SIDING, FIBER CEMENT IDENTIFICATION

But I don't have the same telltales for FC shingles.

On 2021-07-01 by Bill Garland Tx

Can you tell by the numbers on the back of the exterior wall tile if these are asbestos/cement tiles?

On 2021-06-23 by inspectapedia.com.moderator (mod) - options for roofing over fiber cement or asbestos cement shingle roofs

@David,

Answering the easiest question first, home inspection standards and where there are laws, laws, in most US states require that the inspector include the roof in the home inspection and that the minimum reporting standard would include the roofing material and the condition of the roof.

If the inspector for some reason found a roof both inaccessible and not visible inspector would be obligated to explain that to the client and also to explain the implications of that limitation such as the possibility of leaks, water damage, and potential significant expense for roofing repair. But it would be unusual to have no view at all of any of a building roof.

It is important that in choosing a home inspecto, home buyers find someone and whom they have complete trust and confidence in both the person's competence and in the complete absence of any conflicting interests such as, in my opinion, depending on referrals from real estate agents or any other parties to the transaction which may force them to have conflicting interests.

Before assuming that we have to have a very costly roof removal or cover over of the entire roof on the home it would make more sense to have a more careful and complete understanding of what leaks are present, what is their cause, and what repairs are actually necessary.

It is perfectly possible to repair a cement asbestos shingle roof if the damage involves broken or missing shingles and possibly if the damage to the roofs flashings.

Repair work is done by a roofer who has familiarity with that material and it essentially uses the same methods as slate roof repairs.

In addition there are fiber cement products on the market that look exactly like their older sister's asbestos Cement Products.

And they work similarly well and have similarly good long life.

Of course I know nothing about the condition of this specific building's roof nor the extent of its damage, leaks, or needs.

And the roofer who called for replacement may be a great contractor. Or not.

I caution that we sometimes find a contractor who condemns a building system, product or material when the truth is that the particular contractor is simply not familiar with that product.

I regret to report that I have seen buildings at which a slate roof, covered using slates that typically have a 300-year life expectancy, and that needed only minor localized repair, suffer from a contractor who was unfamiliar with the material and who convinced the building owner that the slate product was not a good one and that it should be completely removed and replaced with asphalt shingles that had a 20-year life.

That sad disaster could have been avoided had the building owner simply contacted a roofing company who specialized in slate.

On 2021-06-23 by David

A relative bought their first rental property which shortly had a leak in the roof. Roofer came in and advised it was a cement asbestos roof material and an abatement company would have to be used to remove it.

The home inspector failed to find that along with other minor items.

The seller stated unknown to that question but there were previous roof repairs. Not sure about legal repurcussions to get them to cover the cost of replacing.
Is there a cost effective way to remediate.

Are there roof that can be laid over top of this one?

Saw a post about a metal roof. Wondering how it could be done safely or if there are other better materials.

On 2021-02-13 by (mod) - use non-asbestos fiber cement shingles to replace broken asbestos cement shingle siding

Roy

With apology, I can't assess the risk of damage to your home from a brief text inquiry, but in general, if the home's exterior siding is damaged or lost so that water can leak into the home's walls, that risk mold contamination, water damage to electrical components, and over a longer period, it invites insect and rot damage.

You will want the broken asbestos-cement shingles removed and replaced with sound fiber-cement shingles that look exactly the same as their older asbestos-containing brothers and sisters.

If there has been wind-blown rain towards those damaged walls you might want some inspection for water damage.

On 2021-02-13 by Roy

I have asbestos cement siding on my home. After Hurricane Delta I noticed strips of black felt paper sticking out from behind the shingles. Will this cause problems with my home?

On 2021-01-03 - by (mod) -

Matt:

To remove F siding shingles nailed as you describe, try working from below the intact shingle, sliding up a hacksaw blade to find and cut the nails that hold the top of the broken shingle in place beneath the intact one.

You'll still need to pre-drill or punch nail holes in the replacement shingle.

On 2021-01-03 by Matt

How do you replace Fiber-Cement siding shingles that are nailed the normal way with the nails hidden under the row above?
All the videos I find online show exposed nails at the bottom of each shingle, which is an obvious no brainer.
The only instruction I can find are only for wood shingles, nailing upward as close to the upper row as possible.
For that method I would have to predrill holes in each one.

On 2018-07-29 by Steve

I have to cut in a single gang electrical box for an outlet how do you cut the recy
tangle without breaking the shingles

On 2018-05-02 - by (mod) -

I would use the techniques and the article above to remove a few fiber cement or asbestos cement siding shingles in the area of worst separation damage and order to investigate the underlying cause. There's no point in trying to research cure a siding before we know why it's coming off. For example you could just be nailing to riding sheathing.

On 2018-05-02 by Eric

I'm working on a project that requires work to some fiber cement or cement asbestos siding that is not cracked but rather is separating from the surface behind and I'm wondering what is the best strategy to reserve the siding without breaking it

On 2017-07-10 by Homeowner

Thanks for the article. When I tried to replace some broken shingles with cf ones, the new CF ones were literally half the thickness so I had to rip some shim board to get them to angle out correctly. Of course, literally a week later the replacement paper-thin ones were broken as well .

so I think step 1 would really be "measure the thickness of your shingles and spend several weeks trying to find replacement CF ones that match the size, shape, texture and thickness".

On 2017-04-05 by Garland

Gotcha. That all seems doable.
I really appreciate the article and the response.

On 2017-04-05 - by (mod) - is there any reason to replace the asbestos shingles when siding over with vinyl?

Garland

Good question.

If the damage area is small - say a foot - then your vinyl siding will span that with no visible effect.

If the damage area is larger or if there is more than abut 3/16" of wall surface depth variation across the repair area such that the vinyl might be wavy on re-installation, I'd suggest just shimming out the wall in the nail locations for hanging the siding back in place across that space.

Be sure that your housewrap laps under the window sill and under (by a neat cut) the existing house wrap (probably felt paper) that remains in place above the work area, and that it laps over the remaining house wrap below the work area - so that any wind-blown rain into the wall (getting behind the siding) will flow out and down the wall rather than into it.

On 2017-04-05 by Garland

HI,
Handy article. I've got vinyl siding over asbestos shingles, and have a small rot problem caused by water not from outside, but from a window in a shower.

I would like to repair the rot to the 1 x 6 sheathing.

If I were to remove my vinyl, and then the asbestos shingles to repair the sheathing and waterproof around my new window, is there any reason to replace the asbestos? Could I just build back out to level with OSB, housewrap and reinstall my vinyl?

Question: Is it possible (and legal) to install a metal roof over the existing asbestos cement shingles?

(Oct 3, 2014) Tina said:
I am looking at an old house that has a cement-asbestos shingled roof. Is it possible (and legal) to install a metal roof over the existing shingles?
Thanks!

Reply:

Tina

Yes, metal roofing is installed over many existing roofs, usually with a felt underlayment.

But there may be some trouble (uneven surface created by broken-up cement asbestos roofing or siding) or mess nailing through the existing roof or even working on it unless steps are taken to avoid breaking up the original material.

...

Continue reading at FIBER CEMENT SIDING - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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