Homes and History Committee

Taking Care of your Historic Atlanta Home - Repointing Bricks


Pointers for making sure your home has many healthy years ahead.

Repointing Bricks

Check out this Preservation Brief from the National Park Service.

View examples of damage: The Mason You Hire Can Destroy Your House

Most homes built prior to 1930 need softer N, O or K mortar mixes. (Capital letters go from hard to soft in MaSoN wOrK.) The extra lime & sand in these softer mortars allow for a greater amount of expansion & contraction in the damper crawl space (think of it as soft, healthy gums for your teeth)....do not use straight Portland cement (sidewalk cement, quick dry) as mortar - placing a mortar that is too hard between the softer bricks will cause them to crack and crumble as the seasons change.

Your existing mortar will likely differ from a premixed formula. The main priority is to make sure it's softer than the standard Portland Cement mix is  - with a greater lime content to self-heal small cracks. Here's how to visually inspect your mortar.

Type O is NOT sold in Atlanta at Home Depot or Lowe's.
You can get Type O Tuck Pointing Mortar (AMX 420) from it's NewCastle manufacturer at:

georgiamasonrysupply.com
125 Industrial Park Cir, Lawrenceville, GA 30046


How to mix your own Type O from Type N Mortar
Type N is 1-1-6, Type O is 1-2-8. Where second number is lime, third is sand.
So for a 60 lb bag of Type N mortar, each of the 8 parts is 7.5lbs.
So to create Type O, add 1 part hydrated lime (7.5 lbs) and 2 parts sand (15 lbs).

 
60 lbs (8 parts) - Type N Mortar (not cement)
7.5 lbs (1 part) - Lime
15 lbs (2 parts) - Sand

The original mortar in your chimney probably has a slight yellow tinge or a buff color typical of older mortars. You can optionally add a little buff-shaded masonry cement color to tone it out, but not too much since it may look orange.

How to Apply
Clear to 1 inch using chisel or angle grinder.
Wet (drench) the existing bricks so they do not pull moisture out of the drying mortar.

If you want an exact match for the consistancy or color or your mortar, check out the Mortar Analysis and Matching Service at USHeritage.com

This article provides a formula for making Type O mortar from portland cement (not from portland mortar)
1 part Portland Cement Type-N NOT MORTAR (Careful, avoid buying "Mortar" since it already has sand mixed in.)
2 parts Mason's Hydrated Lime Type-S (Amazon) - Also not sold at Home Depot or Lowe's
8 or 9 parts washed building sand (9 for larger grains)

Type S or "Special" hydrated lime products can be used after a short soak period with excellent workability. 

Don't let a mason water seal or treat the bricks (bricks DON'T need it). Avoid applying anything that cannot be reversed.

The original historic mixes ranged from 1:2 to 1:3 lime to sand ratio and tended to be closer to 1:2.
Since we are usign 1 part portland cemend as 1 of 3 parts of the lime side of the equation, a 3:8 ratio puts us between 1:2 and 1:3.
1:3 suits a general building sands, Whereas 1:1½ suits a fine local sand. Source
 

Avoid Over Vapor Barrier-izing

Be weary of over vapor barrier-izing your ground. This can focus "rising damp" into your piers where they touch the ground and create a faster capillary action of ground water concentrated right up into your wood structural members.