oil base paint dosen't breathe so any moisture will lift the paint. latex
does so some moisture will come through without any issues. I have used
floetrol (sp) available at DD Lowes, and sherwin williams to thin it and
extend drying time (on Latex) which lets it penetrate more and although some
paints do not reccomend it I have not had a problem. Penetrol is for oil
based paints but not as easy to find
"Ether Jones" wrote in message
oups.com...

Is it OK to aggressively thin latex paint with distilled water? My
aim in doing so is NOT to increase coverage, but rather to improve the
penetration into splits and cracks and rough areas. My intent would
be to allow this first thinned coat to soak in and dry thoroughly, then
apply two more coats of the same product, unthinned.

If the answer is "no", could you please give some technical explanation
why it is not a good idea.

I already tried this on some old treated pine deck boards I used to
repair portions of an exterior porch stairs. I washed and rinsed the
boards, then let them dry thoroughly. Then I painted them with an
exterior acrylic latex porch paint thinned 50/50 with distilled water.
This first coat had remarkable penetration. After it dried
thoroughly (a couple of days in 85 degree weather in the garage) I put
2 more coats of the same product, unthinned, allowing thorough drying
between coats. I used these boards to replace some worn exterior
porch stair treads, but they've only been in place for a couple of
weeks so far so I won't know the results for a couple of years.

In the past, I've used an oil primer, followed by 2 coats of latex
topcoat, but haven't had very good results. The latex bonded
tenaciously to the primer, but the primer blistered and peeled away
from the wood. This exterior application sees lots of sun, rain,
snow, and foot traffic.