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Oil-base paints are best protection against the transfer of moisture

Question - I would like to find more information on vapor retarding paint.

- D.H., West Chicago, Ill.

Answer - Most major manufacturers of paint have vapor retarding paints. An oil-base paint will provide the best protection against moisture transfer. the ability of a material to resist moisture movement is called is permeability, of "perm rating."

To be a moisture barrier a material should have a perm rating of 1 or less. For instance air has a rating of 160 perms while glass is rated at 0.001 perms. The larger the perm number the more easily moisture can pass through the object. Latex paint on drywall is rated at 3 to 5 perms, whereas oil-based paint on drywall is rated at o.5 to 1 perm.

The interesting thing about a vapor retarding latex paint is that it works well when there is no moisture, but as the moisture levels rise the mermeability of the latex also rises. When it's dry, a low perm latex paint works, but when it's wet it doesn't.

Question - I have a damp spot that is marring the wall near my chimney. Should I line the flue or seal the chimney somehow or go ahead and have someone check the cap? Another person quoted in your column said they had tried this but to no avail. I don't want to waste my time with it if it is not necessary. I don't think I have a "decorative top" on my chimney, either, which you mentioned could cause trouble sometimes. Am I going to have to have somebody dig nto the wall/ceiling in the bedroom to see what is going here?

- Cathy in Nashville, Tenn.

Answer - What you need to do, and this will pinpoint the problem with little or no expenditure, is cover the chimney to see if this stops the pesky dampness and leak.

It is extremely important, however, that you not cover a chimney that is part of a working furnace or water heater flue system. Once the chimney is covered, it stops being a chimney and any gas- or oil-fired appliance connected to the chimney could cause carbon monoxide to build up inside the home. Carbon monoxied is an odorless, colorless, poisonous gas that can cause death or serious disabilities.

With all this in mind, you can now proceed to cover the entire chimney top down to the third or fourth row of bricks or stone with a weather proof cover. Clear plastic visqueen or a rain tarp can be sued.

After a few heavy rains you will be able to determine if the top portion of the chimney is the problem area and you can proceed from there.