Mortar Type For Fieldstone Foundation Repair

chelsea

I've got a 100 y.o. house with a fieldstone foundation. The outside appears ok. The mortar on the inside is dry and crumbling. You can pretty much go around and scoop it out with your hand,very powdery and dry. What is the correct type of mortar to use to repair it? Type S mortar mix ok?

atmasonry

Hi Chelsea, I have seen this many times. Type "S" will do fine but I recommend adding a shovel of portland per halve bag mix. It will become more impervious and will be much stronger. It also will hold up to packing in the joints better. Use a grout bag and tuck pointer to fill then after it sets a bit seal it by jointing with the tuck pointer or large round jointer.

Have fun.

Tscarborough

Be very careful about which type of mortar you use to repair that with. It sounds like a lime mortar was used, and if you use a portland mortar to tuck it you will most likely have serious issues in a short amount of time.

The portland mortar will trap moisture in the wall and cause all of the lime mortar to disintegrate. A lime mortar is your best bet.

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chelsea

thanks guys. Any way to tell if its lime mortar? Its all kind of sandy and crumbly. Got most of the loose stuff out in a section of the wall and its just a pile of rocks at this point. All the mortar pretty much fell apart. Also,the outside is holding up a lot better than inside.A few cracks at the corners ,not much deterioration like on the inside.

Tscarborough

You can pour some vinegar on it and see if there is a good reaction, but from your description and the age of the house, it is almost certainly lime mortar. The exterior may have already been repaired with portland cement, which would help explain why it has deteriorated on the inside. If so, you may as well replace it all with portland mortar, but doing small areas at a time.

Type S is fine, but Type N would be even better.

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It ain't Rocket Science unless you are building rockets.

chelsea

Thanks for the info.