In my house (England) there are multiple holes from old pipes in the walls. The walls are made of red bricks and the house is approximately 70 years old. I want to fill in those gaps - also in some of them there are still pipes, but they are loose, so the space around the pipes also needs filling in.

Now, I understand that because my bricks are old, a modern, strong mortar might not be suitable as it might crack the bricks - is that so?

I was thinking of filling in the holes with expanding foam and only finish off with mortar on the outer surface, like 1/2" deep only. Is that a good idea? Is the expanding foam safe for old bricks?


1 Answer 1


You have the right idea about the expanding foam, it will do any harm to the brick. A word of caution, if the surrounding areas are not protected with masking tape and paper, the probability of the foam making a mess that will be VERY difficult to clean.

Use the foam springly, giving it about 15 minutes to a half hour to expand before adding more to fill the cavity, only to find out it is now overflowing uncontrollably.

You also heard right about mortar and old brick. In the States and perhaps in the UK, there are different kinds of mortar. I am a bit rusty on this, but the types are Type I, Type N and type S.

Type S is for use only with new brick that are rated for extreme weather conditions. This type will damage older or softer brick during the freeze/thaw cycles of winter. Type N is a softer mortar that is more compatible with older brick. Type I may be as well, but do some reading up on the types to learn first hand the differences.

When mixing the mortar, no need to get it too wet like peanut butter, it will smear and be messy when applied on vertical walls. Mix it a bit stiffer so it barely holds a ball when formed in your hand, as in if it were dryer, it would fall apart. This will aid in keeping the mess to a minimum. A lot will drop, but it will not smear the wall.

  • Nite that expanding foam doesn't handle sunlight well over the long run. You can protect it somewhat by painting the outside surface -- which can also make it less obvious as a patch.
    – keshlam
    Aug 7, 2023 at 14:36
  • @keshlam , his plan was to use that as a backer and finish off the outside with mortar. You are spot on about the sunlight, expanding foam doesn't do to well over the years exposed.
    – Jack
    Aug 8, 2023 at 2:51
  • Sigh. Apologies for not reading carefully.
    – keshlam
    Aug 8, 2023 at 5:27
  • @keshlamI do the same thing to many times.....
    – Jack
    Aug 8, 2023 at 13:10

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